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The toxicologically most relevant mercury (Hg) species for human exposure is methylmercury (MeHg). Thiomersal is a common preservative used in some vaccine formulations. The aim of this study is to get further mechanistic insight into the yet not fully understood neurotoxic modes of action of organic Hg species. Mercury species investigated include MeHgCl and thiomersal. Additionally HgCl2 was studied, since in the brain mercuric Hg can be formed by dealkylation of the organic species. As a cellular system astrocytes were used. In vivo astrocytes provide the environment necessary for neuronal function. In the present study, cytotoxic effects of the respective mercuricals increased with rising alkylation level and correlated with their cellular bioavailability. Further experiments revealed for all species at subcytotoxic concentrations no induction of DNA strand breaks, whereas all species massively increased H2O2-induced DNA strand breaks. This co- genotoxic effect is likely due to a disturbance of the cellular DNA damage response. Thus, at nanomolar, sub-cytotoxic concentrations, all three mercury species strongly disturbed poly(ADP-ribosyl)ation, a signalling reaction induced by DNA strand breaks. Interestingly, the molecular mechanism behind this inhibition seems to be different for the species. Since chronic PARP-1 inhibition is also discussed to sacrifice neurogenesis and learning abilities, further experiments on neurons and in vivo studies could be helpful to clarify whether the inhibition of poly(ADP-ribosyl) ation contributes to organic Hg induced neurotoxicity.
Arsenic-containing hydrocarbons are one group of fat-soluble organic arsenic compounds (arsenolipids) found in marine fish and other seafood. A risk assessment of arsenolipids is urgently needed, but has not been possible because of the total lack of toxicological data. In this study the cellular toxicity of three arsenic-containing hydrocarbons was investigated in cultured human bladder (UROtsa) and liver (HepG2) cells. Cytotoxicity of the arsenic-containing hydrocarbons was comparable to that of arsenite, which was applied as the toxic reference arsenical. A large cellular accumulation of arsenic, as measured by ICP-MS/MS, was observed after incubation of both cell lines with the arsenolipids. Moreover, the toxic mode of action shown by the three arsenic-containing hydrocarbons seemed to differ from that observed for arsenite. Evidence suggests that the high cytotoxic potential of the lipophilic arsenicals results from a decrease in the cellular energy level. This first in vitro based risk assessment cannot exclude a risk to human health related to the presence of arsenolipids in seafood, and indicates the urgent need for further toxicity studies in experimental animals to fully assess this possible risk.
Arsenic-containing hydrocarbons are one group of fat-soluble organic arsenic compounds (arsenolipids) found in marine fish and other seafood. A risk assessment of arsenolipids is urgently needed, but has not been possible because of the total lack of toxicological data. In this study the cellular toxicity of three arsenic-containing hydrocarbons was investigated in cultured human bladder (UROtsa) and liver (HepG2) cells. Cytotoxicity of the arsenic-containing hydrocarbons was comparable to that of arsenite, which was applied as the toxic reference arsenical. A large cellular accumulation of arsenic, as measured by ICP-MS/MS, was observed after incubation of both cell lines with the arsenolipids. Moreover, the toxic mode of action shown by the three arsenic-containing hydrocarbons seemed to differ from that observed for arsenite. Evidence suggests that the high cytotoxic potential of the lipophilic arsenicals results from a decrease in the cellular energy level. This first in vitro based risk assessment cannot exclude a risk to human health related to the presence of arsenolipids in seafood, and indicates the urgent need for further toxicity studies in experimental animals to fully assess this possible risk.
We study the thermal Markovian diffusion of tracer particles in a 2D medium with spatially varying diffusivity D(r), mimicking recently measured, heterogeneous maps of the apparent diffusion coefficient in biological cells. For this heterogeneous diffusion process (HDP) we analyse the mean squared displacement (MSD) of the tracer particles, the time averaged MSD, the spatial probability density function, and the first passage time dynamics from the cell boundary to the nucleus. Moreover we examine the non-ergodic properties of this process which are important for the correct physical interpretation of time averages of observables obtained from single particle tracking experiments. From extensive computer simulations of the 2D stochastic Langevin equation we present an in-depth study of this HDP. In particular, we find that the MSDs along the radial and azimuthal directions in a circular domain obey anomalous and Brownian scaling, respectively. We demonstrate that the time averaged MSD stays linear as a function of the lag time and the system thus reveals a weak ergodicity breaking. Our results will enable one to rationalise the diffusive motion of larger tracer particles such as viruses or submicron beads in biological cells.
On the role of fluoro-substituted nucleosides in DNA radiosensitization for tumor radiation therapy
(2014)
Gemcitabine (2′,2′-difluorocytidine) is a well-known radiosensitizer routinely applied in concomitant chemoradiotherapy. During irradiation of biological media with high-energy radiation secondary low-energy (<10 eV) electrons are produced that can directly induce chemical bond breakage in DNA by dissociative electron attachment (DEA). Here, we investigate and compare DEA to the three molecules 2′-deoxycytidine, 2′-deoxy-5-fluorocytidine, and gemcitabine. Fluorination at specific molecular sites, i.e., nucleobase or sugar moiety, is found to control electron attachment and subsequent dissociation pathways. The presence of two fluorine atoms at the sugar ring results in more efficient electron attachment to the sugar moiety and subsequent bond cleavage. For the formation of the dehydrogenated nucleobase anion, we obtain an enhancement factor of 2.8 upon fluorination of the sugar, whereas the enhancement factor is 5.5 when the nucleobase is fluorinated. The observed fragmentation reactions suggest enhanced DNA strand breakage induced by secondary electrons when gemcitabine is incorporated into DNA.
On the role of fluoro-substituted nucleosides in DNA radiosensitization for tumor radiation therapy
(2014)
Gemcitabine (2′,2′-difluorocytidine) is a well-known radiosensitizer routinely applied in concomitant chemoradiotherapy. During irradiation of biological media with high-energy radiation secondary low-energy (<10 eV) electrons are produced that can directly induce chemical bond breakage in DNA by dissociative electron attachment (DEA). Here, we investigate and compare DEA to the three molecules 2′-deoxycytidine, 2′-deoxy-5-fluorocytidine, and gemcitabine. Fluorination at specific molecular sites, i.e., nucleobase or sugar moiety, is found to control electron attachment and subsequent dissociation pathways. The presence of two fluorine atoms at the sugar ring results in more efficient electron attachment to the sugar moiety and subsequent bond cleavage. For the formation of the dehydrogenated nucleobase anion, we obtain an enhancement factor of 2.8 upon fluorination of the sugar, whereas the enhancement factor is 5.5 when the nucleobase is fluorinated. The observed fragmentation reactions suggest enhanced DNA strand breakage induced by secondary electrons when gemcitabine is incorporated into DNA.
Polypeptoid block coloymers
(2014)
Die vorliegende Arbeit behandelt Untersuchungen zum Einfluss ionischer Flüssigkeiten sowohl auf den Rekombinationsprozess photolytisch generierter Lophylradikale als auch auf die photoinduzierte Polymerisation. Im Fokus standen hierbei pyrrolidiniumbasierte ionische Flüssigkeiten sowie polymerisierbare imidazoliumbasierte ionische Flüssigkeiten. Mittels UV-Vis-Spektroskopie wurde in den ionischen Flüssigkeiten im Vergleich zu ausgewählten organischen Lösungsmitteln die Rekombinationskinetik der aus o-Cl-HABI photolytisch generierten Lophylradikale bei unterschiedlichen Temperaturen verfolgt und die Geschwindigkeitskonstanten der Radikalrekombination bestimmt. Die Charakterisierung des Rekombinationsprozesses erfolgt dabei insbesondere unter Verwendung der mittels Eyring-Gleichung ermittelten Aktivierungsparameter. Hierbei konnte gezeigt werden, dass die Rekombination der Lophylradikale in den ionischen Flüssigkeiten im Gegensatz zu den organischen Lösungsmitteln zu einem großen Anteil innerhalb des Lösungsmittelkäfigs erfolgt. Weiterhin wurden für den Einsatz von o-Cl-HABI als Radikalbildner in den photoinduzierten Polymerisationen mehrere mögliche Co-Initiatoren über photokalorimetrische Messungen untersucht. Hierbei wurde auch ein neuer Aspekt zur Kettenübertragung vom Lophylradikal auf den heterocyclischen Co-Initiator vorgestellt. Darüber hinaus wurden photoinduzierte Polymerisationen unter Einsatz eines Initiatorsystems, bestehend aus o-Cl-HABI als Radikalbildner und einem heterocyclischen Co-Initiator, in den ionischen Flüssigkeiten untersucht. Diese Untersuchungen beinhalten zum einen photokalorimetrische Messungen der photoinduzierten Polymerisation von polymerisierbaren imidazoliumbasierten ionischen Flüssigkeiten. Zum anderen wurden Untersuchungen zur photoinduzierten Polymerisation von Methylmethacrylat in pyrrolidiniumbasierten ionischen Flüssigkeiten durchgeführt. Dabei wurden Einflussparameter wie Zeit, Temperatur, Viskosität, Lösungsmittelkäfigeffekt und die Alkylkettenlänge am Kation der ionischen Flüssigkeiten auf die Ausbeuten und Molmassen sowie Molmassenverteilungen der Polymere hin untersucht.
Ziel der Arbeit war die Entwicklung von farbstoffmarkierten Polymeren, die einen temperaturgetriebenen Knäuel-Kollaps-Phasenübergang in wässriger Lösung ("thermo-responsive Polymere") zeigen und diesen in ein optisches Signal übersetzen können. Solche Polymere unterliegen innerhalb eines kleinen Temperaturintervalls einer massiven Änderung ihres Verhaltens, z B. ihrer Konformation und ihres Quellungsgrads. Diese Änderungen sind mit einem Wechsel der Löseeigenschaften von hydrophil zu hydrophob verbunden. Als Matrixpolymere wurden Poly-N-isopropylacrylamid (polyNIPAm), Poly(oligoethylen-glykolacrylat) (polyOEGA) und Poly(oligoethylenglykolmethacrylat) (polyOEGMA) ein-gesetzt, in die geeignete Farbstoffen durch Copolymerisation eingebaut wurden. Als besonders geeignet, um den Phasenübergang in ein optisches Signal zu übersetzen, erwiesen sich hierfür kompakte, solvatochrome Cumarin- und Naphthalimidderivate. Diese beeinträchtigten weder das Polymerisationsverhalten noch den Phasenübergang, reagierten aber sowohl bezüglich Farbe als auch Fluoreszenz stark auf die Polarität des Lösemittels. Weiterhin wurden Systeme entwickelt, die mittels Energietransfer (FRET) ein an den Phasenübergang gekoppeltes optisches Signal erzeugen. Hierbei wurde ein Cumarin als Donor- und ein Polythiophen als Akzeptorfarbstoff eingesetzt. Es zeigte sich, dass trotz scheinbarer Ähnlichkeit bestimmte Polymere ausgeprägt auf einen Temperaturstimulus mit Änderung ihrer spektralen Eigenschaften reagieren, andere aber nicht. Hierfür wurden die molekularen Ursachen untersucht. Als wahrscheinliche Gründe für das Ausbleiben einer spektralen Änderung in Oligo(ethylenglykol)-basierten Polymeren sind zum einen die fehlende Dehydratationseffektivität infolge des Fehlens eines selbstgenügenden Wasserstoffbrückenbindungsmotivs zu nennen und zum anderen die sterische Abschirmung der Farbstoffe durch die Oligo(ethylenglykol)-Seitenketten. Als Prinzipbeweis für die Nützlichkeit solcher Systeme für die Bioanalytik wurde ein System entwickelt, dass die Löslichkeitseigenschaft eines thermoresponsiven Polymers durch Antikörper-Antigen-Reaktion änderte. Die Bindung selbst kleiner Mengen eines Antikörpers ließ sich so direkt optisch auslesen und war bereits mit dem bloßen Auge zu erkennen.
Ziel dieser Arbeit war die Entwicklung von Methoden zur Synthese von auf Phenol basierenden Naturstoffen. Insbesondere wurde bei der Methodenentwicklung die Nachhaltigkeit in den Vordergrund gerückt. Dies bedeutet, dass durch die Zusammenfassung mehrerer Syntheseschritte zu einem (Tandem-Reaktion) beispielsweise unnötige Reaktionsschritte vermieden werden sollten. Ferner sollten im Sinne der Nachhaltigkeit möglichst ungiftige Reagenzien und Lösungmittel verwendet werden, ebenso wie mehrfach wiederverwertbare Katalysatoren zum Einsatz kommen. Im Rahmen dieser Arbeit wurden Methoden zum Aufbau von Biphenolen mittels Pd/C-katalysierten Suzuki-Miyaura-Kupplungen entwickelt. Diese Methoden sind insofern äußerst effizient, da der ansonsten gebräuchliche Syntheseweg über drei Reaktionsschritte somit auf lediglich eine Reaktionsstufe reduziert wurde. Weiterhin wurden die Reaktionsbedingungen so gestaltet, dass einfaches Wasser als vollkommen ungiftiges Lösungsmittel verwendet werden konnte. Des Weiteren wurde für diese Reaktionen ein Katalysator gewählt, der einfach durch Filtration vom Reaktionsgemisch abgetrennt und für weitere Reaktionen mehrfach wiederverwendet werden konnte. Darüber hinaus konnte durch die Synthese von mehr als 100 Verbindungen die breite Anwendbarkeit der Methoden aufgezeigt werden. Mit den entwickelten Methoden konnten 14 Naturstoffe - z. T. erstmals - synthetisiert werden. Derartige Stoffe werden u. a. von den ökonomisch bedeutenden Kernobstgewächsen (Äpfeln, Birnen) als Abwehrmittel gegenüber Schädlingen erzeugt. Folglich konnte mit Hilfe dieser Methoden ein Syntheseweg für potentielle Pflanzenschutzmittel entwickelt werden. Im zweiten Teil dieser Arbeit wurde ein Zugang zu den sich ebenfalls vom Phenol ableitenden Chromanonen, Chromonen und Cumarinen untersucht. Bei diesen Untersuchungen konnte durch die Entwicklung zweier neuer Tandem-Reaktionen ein nachhaltiger und stufenökonomischer Syntheseweg zur Darstellung substituierter Benzo(dihydro)pyrone aufgezeigt werden. Durch die erstmalige Kombination der Claisen-Umlagerung mit einer Oxa-Michael-Addition bzw. konjugierten-Addition wurden zwei vollkommen atomökonomische Reaktionen miteinander verknüpft und somit eine überaus effiente Synthese von allyl- bzw. prenylsubstituierten Chromanonen und Chromonen ermöglicht. Ferner konnten durch die Anwendung einer Claisen-Umlagerung-Wittig-Laktonisierungs-Reaktion allyl- bzw. prenylsubstituierte Cumarine erhalten werden. Herausragendes Merkmal dieser Methoden war, dass in nur einem Schritt der jeweilige Naturstoffgrundkörper aufgebaut und eine lipophile Seitenkette generiert werden konnte. Die Entwicklung dieser Methoden ist von hohem pharmazeutischem Stellenwert, da auf diesen Wegen Verbindungen synthetisiert werden können, die zum einem über das notwendige pharmakologische Grundgerüst verfügen und zum anderen über eine Seitenkette, welche die Aufnahmefähigkeit und damit die Wirksamkeit im Organismus beträchtlich erhöht. Insgesamt konnten mittels der entwickelten Methoden 15 Chromanon-, Chromon- und Cumarin-Naturstoffe z. T. erstmals synthetisiert werden.
Es ist in dieser Arbeit gelungen, starre Oligospiroketal(OSK)-Stäbe als Grundbausteine für komplexe 2D- und 3D-Systeme zu verwenden. Dazu wurde ein difunktionalisierter starrer Stab synthetisiert, der mit seines Gleichen und anderen verzweigten Funktionalisierungseinheiten in Azid-Alkin-Klickreaktionen eingesetzt wurde. An zwei über Klickreaktion verknüpften OSK-Stäben konnten mittels theoretischer Berechnungen Aussagen über die neuartige Bimodalität der Konformation getroffen werden. Es wurde dafür der Begriff Gelenkstab eingeführt, da die Moleküle um ein Gelenk gedreht sowohl gestreckt als auch geknickt vorliegen können. Aufbauend auf diesen Erkenntnissen konnte gezeigt werden, dass nicht nur gezielt große Polymere aus bis zu vier OSK-Stäben synthetisiert werden können, sondern es auch möglich ist, durch gezielte Änderung von Reaktionsbedingungen der Klickreaktion auch Cyclen aus starren OSK-Stäben herzustellen. Die neu entwickelte Substanzklasse der Gelenkstäbe wurde im Hinblick auf die Steuerung des vorliegenden Gleichgewichts zwischen geknicktem und gestrecktem Gelenkstab hin untersucht. Dafür wurde der Gelenkstab mit Pyrenylresten in terminaler Position versehen. Es wurde durch Fluoreszenzmessungen festgestellt, dass das Gleichgewicht z. B. durch die Temperatur oder die Wahl des Lösungsmittels beeinflussbar ist. Für vielfache Anwendungen wurde eine vereinfachte Synthesestrategie gefunden, mit der eine beliebige Funktionalisierung in nur einem Syntheseschritt erreicht werden konnte. Es konnten photoaktive Gelenkstäbe synthetisiert werden, die gezielt zur intramolekularen Dimerisierung geführt werden konnten. Zusätzlich wurde durch Aminosäuren ein Verknüpfungselement am Ende der Gelenkstäbe gefunden, das eine stereoselektive Synthese von Mehrfachfunktionalisierungen zulässt. Die Synthese der komplexen Gelenkstäbe wurde als ein neuartiges Gebiet aufgezeigt und bietet ein breites Forschungspotential für weitere Anwendungen z. B. in der Biologie (als molekulare Schalter für Ionentransporte) und in der Materialchemie (als Ladungs- oder Energietransporteure).
Biological materials have ever been used by humans because of their remarkable properties. This is surprising since the materials are formed under physiological conditions and with commonplace constituents. Nature thus not only provides us with inspiration for designing new materials but also teaches us how to use soft molecules to tune interparticle and external forces to structure and assemble simple building blocks into functional entities. Magnetotactic bacteria and their chain of magnetosomes represent a striking example of such an accomplishment where a very simple living organism controls the properties of inorganics via organics at the nanometer-scale to form a single magnetic dipole that orients the cell in the Earth magnetic field lines. My group has developed a biological and a bio-inspired research based on these bacteria. My research, at the interface between chemistry, materials science, physics, and biology focuses on how biological systems synthesize, organize and use minerals. We apply the design principles to sustainably form hierarchical materials with controlled properties that can be used e.g. as magnetically directed nanodevices towards applications in sensing, actuating, and transport. In this thesis, I thus first present how magnetotactic bacteria intracellularly form magnetosomes and assemble them in chains. I developed an assay, where cells can be switched from magnetic to non-magnetic states. This enabled to study the dynamics of magnetosome and magnetosome chain formation. We found that the magnetosomes nucleate within minutes whereas chains assembles within hours. Magnetosome formation necessitates iron uptake as ferrous or ferric ions. The transport of the ions within the cell leads to the formation of a ferritin-like intermediate, which subsequently is transported and transformed within the magnetosome organelle in a ferrihydrite-like precursor. Finally, magnetite crystals nucleate and grow toward their mature dimension. In addition, I show that the magnetosome assembly displays hierarchically ordered nano- and microstructures over several levels, enabling the coordinated alignment and motility of entire populations of cells. The magnetosomes are indeed composed of structurally pure magnetite. The organelles are partly composed of proteins, which role is crucial for the properties of the magnetosomes. As an example, we showed how the protein MmsF is involved in the control of magnetosome size and morphology. We have further shown by 2D X-ray diffraction that the magnetosome particles are aligned along the same direction in the magnetosome chain. We then show how magnetic properties of the nascent magnetosome influence the alignment of the particles, and how the proteins MamJ and MamK coordinate this assembly. We propose a theoretical approach, which suggests that biological forces are more important than physical ones for the chain formation. All these studies thus show how magnetosome formation and organization are under strict biological control, which is associated with unprecedented material properties. Finally, we show that the magnetosome chain enables the cells to find their preferred oxygen conditions if the magnetic field is present. The synthetic part of this work shows how the understanding of the design principles of magnetosome formation enabled me to perform biomimetic synthesis of magnetite particles within the highly desired size range of 25 to 100 nm. Nucleation and growth of such particles are based on aggregation of iron colloids termed primary particles as imaged by cryo-high resolution TEM. I show how additives influence magnetite formation and properties. In particular, MamP, a so-called magnetochrome proteins involved in the magnetosome formation in vivo, enables the in vitro formation of magnetite nanoparticles exclusively from ferrous iron by controlling the redox state of the process. Negatively charged additives, such as MamJ, retard magnetite nucleation in vitro, probably by interacting with the iron ions. Other additives such as e.g. polyarginine can be used to control the colloidal stability of stable-single domain sized nanoparticles. Finally, I show how we can “glue” magnetic nanoparticles to form propellers that can be actuated and swim with the help of external magnetic fields. We propose a simple theory to explain the observed movement. We can use the theoretical framework to design experimental conditions to sort out the propellers depending on their size and effectively confirm this prediction experimentally. Thereby, we could image propellers with size down to 290 nm in their longer dimension, much smaller than what perform so far.
Wood is used for many applications because of its excellent mechanical properties, relative abundance and as it is a renewable resource. However, its wider utilization as an engineering material is limited because it swells and shrinks upon moisture changes and is susceptible to degradation by microorganisms and/or insects. Chemical modifications of wood have been shown to improve dimensional stability, water repellence and/or durability, thus increasing potential service-life of wood materials. However current treatments are limited because it is difficult to introduce and fix such modifications deep inside the tissue and cell wall. Within the scope of this thesis, novel chemical modification methods of wood cell walls were developed to improve both dimensional stability and water repellence of wood material. These methods were partly inspired by the heartwood formation in living trees, a process, that for some species results in an insertion of hydrophobic chemical substances into the cell walls of already dead wood cells, In the first part of this thesis a chemistry to modify wood cell walls was used, which was inspired by the natural process of heartwood formation. Commercially available hydrophobic flavonoid molecules were effectively inserted in the cell walls of spruce, a softwood species with low natural durability, after a tosylation treatment to obtain “artificial heartwood”. Flavonoid inserted cell walls show a reduced moisture absorption, resulting in better dimensional stability, water repellency and increased hardness. This approach was quite different compared to established modifications which mainly address hydroxyl groups of cell wall polymers with hydrophilic substances. In the second part of the work in-situ styrene polymerization inside the tosylated cell walls was studied. It is known that there is a weak adhesion between hydrophobic polymers and hydrophilic cell wall components. The hydrophobic styrene monomers were inserted into the tosylated wood cell walls for further polymerization to form polystyrene in the cell walls, which increased the dimensional stability of the bulk wood material and reduced water uptake of the cell walls considerably when compared to controls. In the third part of the work, grafting of another hydrophobic and also biodegradable polymer, poly(ɛ-caprolactone) in the wood cell walls by ring opening polymerization of ɛ-caprolactone was studied at mild temperatures. Results indicated that polycaprolactone attached into the cell walls, caused permanent swelling of the cell walls up to 5%. Dimensional stability of the bulk wood material increased 40% and water absorption reduced more than 35%. A fully biodegradable and hydrophobized wood material was obtained with this method which reduces disposal problem of the modified wood materials and has improved properties to extend the material’s service-life. Starting from a bio-inspired approach which showed great promise as an alternative to standard cell wall modifications we showed the possibility of inserting hydrophobic molecules in the cell walls and supported this fact with in-situ styrene and ɛ-caprolactone polymerization into the cell walls. It was shown in this thesis that despite the extensive knowledge and long history of using wood as a material there is still room for novel chemical modifications which could have a high impact on improving wood properties.
In den vergangenen Jahren wurden stetig wachsende Produktionskapazitäten von Biokunststoffen aus nachwachsenden Rohstoffe nverzeichnet. Trotz großer Produktionskapazitäten und einem geeigneten Eigenschaftsprofil findet Stärke nur als hydrophile, mit Weichmachern verarbeitete thermoplastische Stärke (TPS) in Form von Blends mit z. B. Polyestern Anwendung. Gleiches gilt für Kunststoffe auf Proteinbasis. Die vorliegende Arbeit hat die Entwicklung von Biokunststoffen auf Stärkebasis zum Ziel, welche ohne externe Weichmacher thermoplastisch verarbeitbar und hydrophob sind sowie ein mechanisches Eigenschaftsprofil aufweisen, welches ein Potenzial zur Herstellung von Materialien für eine Anwendung als Verpackungsmittel bietet. Um die Rohstoffbasis für Biokunststoffe zu erweitern, soll das erarbeitete Konzept auf zwei industriell verfügbare Proteintypen, Zein und Molkenproteinisolat (WPI), übertragen werden. Als geeignete Materialklasse wurden Fettsäureester der Stärke herausgearbeitet. Zunächst fand ein Vergleich der Säurechlorid-Veresterung und der Umesterung von Fettsäurevinylestern statt, woraus letztere als geeignetere Methode hervorging. Durch Variation der Reaktionsparameter konnte diese optimiert und auf eine Serie der Fettsäurevinylester von Butanoat bis Stearat für DS-Werte bis zu 2,2-2,6 angewandt werden. Möglich war somit eine systematische Studie unter Variation der veresterten Fettsäure sowie des Substitutionsgrades (DS). Sämtliche Produkte mit einem DS ab 1,5 wiesen eine ausgprägte Löslichkeit in organischen Lösungsmitteln auf wodurch sowohl die Aufnahme von NMR-Spektren als auch Molmassenbestimmung mittels Größenausschlusschromatographie mit gekoppelter Mehrwinkel-Laserlichtstreuung (GPC-MALLS) möglich waren. Durch dynamische Lichtstreuung (DLS) wurde das Löslichkeitsverhalten veranschaulicht. Sämtliche Produkte konnten zu Filmen verarbeitet werden, wobei Materialien mit DS 1,5-1,7 hohe Zugfestigkeiten (bis zu 42 MPa) und Elastizitätsmodule (bis 1390 MPa) aufwiesen. Insbesondere Stärkehexanoat mit DS <2 sowie Stärkebutanoat mit DS >2 hatten ein mechanisches Eigenschaftsprofil, welches insbesondere in Bezug auf die Festigkeit/Steifigkeit vergleichbar mit Verpackungsmaterialien wie Polyethylen war (Zugfestigkeit: 15-32 MPa, E-Modul: 300-1300 MPa). Zugfestigkeit und Elastizitätsmodul nahmen mit steigender Kettenlänge der veresterten Fettsäure ab. Ester längerkettiger Fettsäuren (C16-C18) waren spröde. Über Weitwinkel-Röntgenstreuung (WAXS) und Infrarotspektroskopie (ATR-FTIR) konnte der Verlauf der Festigkeiten mit einer zunehmenden Distanz der Stärke im Material begründet werden. Es konnten von DS und Kettenlänge abhängige Glasübergänge detektiert werden, die kristallinen Strukturen der langkettigen Fettsäuren zeigten einen Schmelzpeak. Die Hydrophobie der Filme wurde anhand von Kontaktwinkeln >95° gegen Wasser dargestellt. Blends mit biobasierten Polyterpenen sowie den in der Arbeit hergestellten Zein-Acylderivaten ermöglichten eine weitere Verbesserung der Zugfestigkeit bzw. des Elastizitätsmoduls hochsubstituierter Produkte. Eine thermoplastische Verarbeitung mittels Spritzgießen war sowohl für Produkte mit hohem als auch mittlerem DS-Wert ohne jeglichen Zusatz von Weichmachern möglich. Es entstanden homogene, transparente Prüfstäbe. Untersuchungen der Härte ergaben auch hier für Stärkehexanoat und –butanoat mit Polyethylen vergleichbare Werte. Ausgewählte Produkte wurden zu Fasern nach dem Schmelzspinnverfahren verarbeitet. Hierbei wurden insbesondere für hochsubstituierte Derivate homogenen Fasern erstellt, welche im Vergleich zur Gießfolie signifikant höhere Zugfestigkeiten aufwiesen. Stärkeester mit mittlerem DS ließen sich ebenfalls verarbeiten. Zunächst wurden für eine Übertragung des Konzeptes auf die Proteine Zein und WPI verschiedene Synthesemethoden verglichen. Die Veresterung mit Säurechloriden ergab hierbei die höchsten Werte. Im Hinblick auf eine gute Löslichkeit in organischen Lösungsmitteln wurde für WPI die Veresterung mit carbonyldiimidazol (CDI)-aktivierten Fettsäuren in DMSO und für Zein die Veresterung mit Säu-rechloriden in Pyridin bevorzugt. Es stellte sich heraus, dass acyliertes WPI zwar hydrophob, jedoch ohne Weichmacher nicht thermoplastisch verarbeitet werden konnte. Die Erstellung von Gießfolien führte zu Sprödbruchverhalten. Unter Zugabe der biobasierten Ölsäure wurde die Anwendung von acyliertem WPI als thermoplastischer Filler z. B. in Blends mit Stärkeestern dargestellt. Im Gegensatz hierzu zeigte acyliertes Zein Glasübergänge <100 °C bei ausreichender Stabilität (150-200 °C). Zeinoleat konnte ohne Weichmacher zu einer transparenten Gießfolie verarbeitet werden. Sämtliche Derivate erwiesen sich als ausgeprägt hydrophob. Zeinoleat konnte über das Schmelzspinnverfahren zu thermoplastischen Fasern verarbeitet werden.
The habilitation thesis covers theoretical investigations on light-induced processes in molecules. The study is focussed on changes of the molecular electronic structure and geometry, caused either by photoexcitation in the event of a spectroscopic analysis, or by a selective control with shaped laser pulses. The applied and developed methods are predominantly based on quantum chemistry as well as on electron and nuclear quantum dynamics, and in parts on molecular dynamics. The studied scientific problems deal with stereoisomerism and the question of how to either switch or distinguish chiral molecules using laser pulses, and with the essentials for the simulation of the spectroscopic response of biochromophores, in order to unravel their photophysics. The accomplished findings not only explain experimental results and extend existing approaches, but also contribute significantly to the basic understanding of the investigated light-driven molecular processes. The main achievements can be divided in three parts: First, a quantum theory for an enantio- and diastereoselective or, in general, stereoselective laser pulse control was developed and successfully applied to influence the chirality of molecular switches. The proposed axially chiral molecules possess different numbers of "switchable" stable chiral conformations, with one particular switch featuring even a true achiral "off"-state which allows to enantioselectively "turn on" its chirality. Furthermore, surface mounted chiral molecular switches with several well-defined orientations were treated, where a newly devised highly flexible stochastic pulse optimization technique provides high stereoselectivity and efficiency at the same time, even for coupled chirality-changing degrees of freedom. Despite the model character of these studies, the proposed types of chiral molecular switches and, all the more, the developed basic concepts are generally applicable to design laser pulse controlled catalysts for asymmetric synthesis, or to achieve selective changes in the chirality of liquid crystals or in chiroptical nanodevices, implementable in information processing or as data storage. Second, laser-driven electron wavepacket dynamics based on ab initio calculations, namely time-dependent configuration interaction, was extended by the explicit inclusion of magnetic field-magnetic dipole interactions for the simulation of the qualitative and quantitative distinction of enantiomers in mass spectrometry by means of circularly polarized ultrashort laser pulses. The developed approach not only allows to explain the origin of the experimentally observed influence of the pulse duration on the detected circular dichroism in the ion yield, but also to predict laser pulse parameters for an optimal distinction of enantiomers by ultrashort shaped laser pulses. Moreover, these investigations in combination with the previous ones provide a fundamental understanding of the relevance of electric and magnetic interactions between linearly or non-linearly polarized laser pulses and (pro-)chiral molecules for either control by enantioselective excitation or distinction by enantiospecific excitation. Third, for selected light-sensitive biological systems of central importance, like e.g. antenna complexes of photosynthesis, simulations of processes which take place during and after photoexcitation of their chromophores were performed, in order to explain experimental (spectroscopic) findings as well as to understand the underlying photophysical and photochemical principles. In particular, aspects of normal mode mixing due to geometrical changes upon photoexcitation and their impact on (time-dependent) vibronic and resonance Raman spectra, as well as on intramolecular energy redistribution were addressed. In order to explain unresolved experimental findings, a simulation program for the calculation of vibronic and resonance Raman spectra, accounting for changes in both vibrational frequencies and normal modes, was created based on a time-dependent formalism. In addition, the influence of the biochemical environment on the electronic structure of the chromophores was studied by electrostatic interactions and mechanical embedding using hybrid quantum-classical methods. Environmental effects were found to be of importance, in particular, for the excitonic coupling of chromophores in light-harvesting complex II. Although the simulations for such highly complex systems are still restricted by various approximations, the improved approaches and obtained results have proven to be important contributions for a better understanding of light-induced processes in biosystems which also adds to efforts of their artificial reproduction.
In this work, the development of temperature- and protein-responsive sensor materials based on biocompatible, inverse hydrogel opals (IHOs) is presented. With these materials, large biomolecules can be specifically recognised and the binding event visualised. The preparation of the IHOs was performed with a template process, for which monodisperse silica particles were vertically deposited onto glass slides as the first step. The obtained colloidal crystals with a thickness of 5 μm displayed opalescent reflections because of the uniform alignment of the colloids. As a second step, the template was embedded in a matrix consisting of biocompatible, thermoresponsive hydrogels. The comonomers were selected from the family of oligo(ethylene glycol)methacrylates. The monomer solution was injected into a polymerisation mould, which contained the colloidal crystals as a template. The space in-between the template particles was filled with the monomer solution and the hydrogel was cured via UV-polymerisation. The particles were chemically etched, which resulted in a porous inner structure. The uniform alignment of the pores and therefore the opalescent reflection were maintained, so these system were denoted as inverse hydrogel opals. A pore diameter of several hundred nanometres as well as interconnections between the pores should facilitate a diffusion of bigger (bio)molecules, which was always a challenge in the presented systems until now. The copolymer composition was chosen to result in a hydrogel collapse over 35 °C. All hydrogels showed pronounced swelling in water below the critical temperature. The incorporation of a reactive monomer with hydroxyl groups ensured a potential coupling group for the introduction of recognition units for analytes, e.g. proteins. As a test system, biotin as a recognition unit for avidin was coupled to the IHO via polymer-analogous Steglich esterification. The amount of accessible biotin was quantified with a colorimetric binding assay. When avidin was added to the biotinylated IHO, the wavelength of the opalescent reflection was significantly shifted and therefore the binding event was visualised. This effect is based on the change in swelling behaviour of the hydrogel after binding of the hydrophilic avidin, which is amplified by the thermoresponsive nature of the hydrogel. A swelling or shrinking of the pores induces a change in distance of the crystal planes, which are responsible for the colour of the reflection. With these findings, the possibility of creating sensor materials or additional biomolecules in the size range of avidin is given.
Wir schlagen einen allgemein anwendbaren Algorithmus vor, der unter Verwendung des Skalarprodukts von Kraft und Weg zum richtigen Vorzeichen in den Gleichungen für die Arbeit und die Potentielle Energie bei reversiblen Prozessen (Druck-Volumen-Änderung, Dehnung, Elektrostatische Wechselwirkung, Hub)führt. Wir zeigen, dass es dabei möglich ist, systemimmanente oder externe Kräfte zu benutzen. Wir zeigen, dass bei Verwendung von systemimmanenten Kräften das Skalarprodukt mit negativem Vorzeichen anzusetzen ist. Zudem ist es sehr wichtig, nötige Vorzeichenwechsel bei den einzelnen Schritten zu beachten. Wir betonen dies, weil gelegentlich übersehen wird, dass ein Vorzeichenwechsel nötig ist, wenn das Wegdifferential ds durch das Höhendifferential dh beziehungsweise durch das Abstandsdifferential dx oder dr ersetzt werden muss.
The supercapacitor is one of the most important energy storage devices as its construction allows for addressing many of the drawbacks related to batteries, but the low energy density of current systems is a major issue. In this doctoral dissertation, with a view to attaining high energy density supercapacitor systems that can be comparable to those for batteries, new heteroatom-containing carbons in the form of particles and three-dimensional films were investigated. A nitrogen-containing material, acrodam, was chosen as the carbon precursor due to the inexpensiveness, high carbonization yield, oligomerizability, etc. The carbon particles were prepared from acrodam together with caesium acetate as a meltable flux agent, and disclosed excellent properties in hydroquinone-loaded sulphuric acid electrolyte with high energy densities (up to 133.0 Wh kg–1) and sufficient cycle stabilities. These properties are already now comparable to those of batteries. Besides, conductive carbon three-dimensional films were fabricated using acrodam oligomer as the precursor by the inexpensive spin coating method. The films were found to be homogeneous, flat, void- and crack-free, and high conductivities (up to 334 S cm–1) could be obtained at the carbonization temperature of 1000 ºC. Furthermore, a porous carbon three-dimensional film could be formed using an organic template at the first attempt. This finding demonstrates the film’s potentiality for various applications such as supercapacitor electrode; the essential absence of contact resistance within the network should contribute to effective transportation of electron within the electrode. The progress made in this dissertation will open a new way to further enhancement of energy density for supercapacitor as well as other applications that exceeds the current properties.
It was the goal of this work to explore two different synthesis pathways using green chemistry. The first part of this thesis is focusing on the use of the urea-glass route towards single phase manganese nitride and manganese nitride/oxide nano-composites embedded in carbon, while the second part of the thesis is focusing on the use of the “saccharide route” (namely cellulose, sucrose, glucose and lignin) towards metal (Ni0), metal alloy (Pd0.9Ni0.1, Pd0.5Ni0.5, Fe0.5Ni0.5, Cu0.5Ni0.5 and W0.15Ni0.85) and ternary carbide (Mn0.75Fe2.25C) nanoparticles embedded in carbon. In the interest of battery application, MnN0.43 nanoparticles surrounded by a graphitic shell and embedded in carbon with a high surface area (79 m^2/g) were synthesized, following a previously set route.The comparison of the material characteristics before and after the discharge showed no remarkable difference in terms of composition and just slight differences in the morphological point of view, meaning the particles are stable but agglomerate. The graphitic shell is contributing to the resistance of the material and leads to a fine cyclic stability over 140 cycles of 230 mAh/g after the first charge/discharge and coulombic efficiencies close to 100%. Due to the low voltage towards Li/Li+ and the low polarization, it might be an attractive anode material for lithium ion batteries. However, the capacity is still noticeably lower than the theoretical value for MnN0.43. A mixture of MnN0.43 and MnO nanoparticles embedded in carbon (surface area 93 m^2/g) was able to improve the cyclic stability to over 160 cycles giving a capacity of 811 mAh/g, which is considerably higher than the capacity of the conventional material graphite (372 mAh/g). This nano-composite seems to agglomerate less during the process of discharge. Interestingly, although the capacity is much higher than of the single phase manganese nitride, the nano-composite seems to only contain MnN0.43 nanoparticles after the process of discharge with no oxide phase to be found. Concerning catalysis application, different metal, metal alloy, and metal carbide nanoparticles were synthesized using the saccharide route. At first, systems that were already investigated before, being Pd0.9Ni0.1, Pd0.5Ni0.5, Fe0.5Ni0.5 and Mn0.75Fe2.25C using cellulose as the carbon source were prepared and tested in an alkylation reaction of toluene with benzylchloride. Unexpectedly, the metal alloys did not show any catalytic activity, but the ternary carbide Mn0.75Fe2.25C showed fine catalytic activity of 98% conversion after 9 hour reaction time (110 °C). In a second step, the saccharide route was modified towards other carbon sources and carbon to metal ratios in order to improve the homogeneity of the samples and accessibility of the particle surfaces. The used carbon sources sucrose and glucose are similar in their basic structure of carbohydrates, but reducing the (polymeric) chain length. Indeed, the cellulose could be successfully replaced by sucrose and glucose. A lower carbon to metal ratio was found to influence the size, homogeneity and accessibility (as evidenced by TEM) of the samples. Since sucrose is an aliment, glucose is the better choice as a carbon source. Using glucose, the synthesis of Cu0.5Ni0.5 and W0.15Ni0.85 nano-composites was also possible, although the later was never obtained as pure phase. These alloy nano-composites were tested, along with nickel0 nanoparticles also prepared with glucose and on their catalytic activity towards the reduction of phenylacetylene. The results obtained let believe that any (poly) saccharide, including lignin, could be used as carbon source. The nickel0 nano-composites prepared with lignin as a carbon source were tested along with those prepared with cellulose and sucrose for their catalytic activity in the transfer hydrogenation of nitrobenzene (results compared with exposed nickel nanoparticles and nickel supported on carbon) leading to very promising results. Based on the urea-glass route and the saccharide route, simple equipment and transition metals, it was possible to have a one-pot synthesize with scale-up possibilities towards new material that can be applied in catalysis and battery systems.
In this work, thermosensitive hydrogels having tunable thermo-mechanical properties were synthesized. Generally the thermal transition of thermosensitive hydrogels is based on either a lower critical solution temperature (LCST) or critical micelle concentration/ temperature (CMC/ CMT). The temperature dependent transition from sol to gel with large volume change may be seen in the former type of thermosensitive hydrogels and is negligible in CMC/ CMT dependent systems. The change in volume leads to exclusion of water molecules, resulting in shrinking and stiffening of system above the transition temperature. The volume change can be undesired when cells are to be incorporated in the system. The gelation in the latter case is mainly driven by micelle formation above the transition temperature and further colloidal packing of micelles around the gelation temperature. As the gelation mainly depends on concentration of polymer, such a system could undergo fast dissolution upon addition of solvent. Here, it was envisioned to realize a thermosensitive gel based on two components, one responsible for a change in mechanical properties by formation of reversible netpoints upon heating without volume change, and second component conferring degradability on demand. As first component, an ABA triblockcopolymer (here: Poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (PEPE) with thermosensitive properties, whose sol-gel transition on the molecular level is based on micellization and colloidal jamming of the formed micelles was chosen, while for the additional macromolecular component crosslinking the formed micelles biopolymers were employed. The synthesis of the hydrogels was performed in two ways, either by physical mixing of compounds showing electrostatic interactions, or by covalent coupling of the components. Biopolymers (here: the polysaccharides hyaluronic acid, chondroitin sulphate, or pectin, as well as the protein gelatin) were employed as additional macromolecular crosslinker to simultaneously incorporate an enzyme responsiveness into the systems. In order to have strong ionic/electrostatic interactions between PEPE and polysaccharides, PEPE was aminated to yield predominantly mono- or di-substituted PEPEs. The systems based on aminated PEPE physically mixed with HA showed an enhancement in the mechanical properties such as, elastic modulus (G′) and viscous modulus (G′′) and a decrease of the gelation temperature (Tgel) compared to the PEPE at same concentration. Furthermore, by varying the amount of aminated PEPE in the composition, the Tgel of the system could be tailored to 27-36 °C. The physical mixtures of HA with di-amino PEPE (HA·di-PEPE) showed higher elastic moduli G′ and stability towards dissolution compared to the physical mixtures of HA with mono-amino PEPE (HA·mono-PEPE). This indicates a strong influence of electrostatic interaction between –COOH groups of HA and –NH2 groups of PEPE. The physical properties of HA with di-amino PEPE (HA·di-PEPE) compare beneficially with the physical properties of the human vitreous body, the systems are highly transparent, and have a comparable refractive index and viscosity. Therefore,this material was tested for a potential biological application and was shown to be non-cytotoxic in eluate and direct contact tests. The materials will in the future be investigated in further studies as vitreous body substitutes. In addition, enzymatic degradation of these hydrogels was performed using hyaluronidase to specifically degrade the HA. During the degradation of these hydrogels, increase in the Tgel was observed along with decrease in the mechanical properties. The aminated PEPE were further utilised in the covalent coupling to Pectin and chondroitin sulphate by using EDC as a coupling agent. Here, it was possible to adjust the Tgel (28-33 °C) by varying the grafting density of PEPE to the biopolymer. The grafting of PEPE to Pectin enhanced the thermal stability of the hydrogel. The Pec-g-PEPE hydrogels were degradable by enzymes with slight increase in Tgel and decrease in G′ during the degradation time. The covalent coupling of aminated PEPE to HA was performed by DMTMM as a coupling agent. This method of coupling was observed to be more efficient compared to EDC mediated coupling. Moreover, the purification of the final product was performed by ultrafiltration technique, which efficiently removed the unreacted PEPE from the final product, which was not sufficiently achieved by dialysis. Interestingly, the final products of these reaction were in a gel state and showed enhancement in the mechanical properties at very low concentrations (2.5 wt%) near body temperature. In these hydrogels the resulting increase in mechanical properties was due to the combined effect of micelle packing (physical interactions) by PEPE and covalent netpoints between PEPE and HA. PEPE alone or the physical mixtures of the same components were not able to show thermosensitive behavior at concentrations below 16 wt%. These thermosensitive hydrogels also showed on demand solubilisation by enzymatic degradation. The concept of thermosensitivity was introduced to 3D architectured porous hydrogels, by covalently grafting the PEPE to gelatin and crosslinking with LDI as a crosslinker. Here, the grafted PEPE resulted in a decrease in the helix formation in gelatin chains and after fixing the gelatin chains by crosslinking, the system showed an enhancement in the mechanical properties upon heating (34-42 °C) which was reversible upon cooling. A possible explanation of the reversible changes in mechanical properties is the strong physical interactions between micelles formed by PEPE being covalently linked to gelatin. Above the transition temperature, the local properties were evaluated by AFM indentation of pore walls in which an increase in elastic modulus (E) at higher temperature (37 °C) was observed. The water uptake of these thermosensitive architectured porous hydrogels was also influenced by PEPE and temperature (25 °C and 37 °C), showing lower water up take at higher temperature and vice versa. In addition, due to the lower water uptake at high temperature, the rate of hydrolytic degradation of these systems was found to be decreased when compared to pure gelatin architectured porous hydrogels. Such temperature sensitive architectured porous hydrogels could be important for e.g. stem cell culturing, cell differentiation and guided cell migration, etc. Altogether, it was possible to demonstrate that the crosslinking of micelles by a macromolecular crosslinker increased the shear moduli, viscosity, and stability towards dissolution of CMC-based gels. This effect could be likewise be realized by covalent or non-covalent mechanisms such as, micelle interactions, physical interactions of gelatin chains and physical interactions between gelatin chains and micelles. Moreover, the covalent grafting of PEPE will create additional net-points which also influence the mechanical properties of thermosensitive architectured porous hydrogels. Overall, the physical and chemical interactions and reversible physical interactions in such thermosensitive architectured porous hydrogels gave a control over the mechanical properties of such complex system. The hydrogels showing change of mechanical properties without a sol-gel transition or volume change are especially interesting for further study with cell proliferation and differentiation.
The sharply rising level of atmospheric carbon dioxide resulting from anthropogenic emissions is one of the greatest environmental concerns facing our civilization today. Metal-organic frameworks (MOFs) are a new class of materials that constructed by metal-containing nodes bonded to organic bridging ligands. MOFs could serve as an ideal platform for the development of next generation CO2 capture materials owing to their large capacity for the adsorption of gases and their structural and chemical tunability. The ability to rationally select the framework components is expected to allow the affinity of the internal pore surface toward CO2 to be precisely controlled, facilitating materials properties that are optimized for the specific type of CO2 capture to be performed (post-combustion capture, precombustion capture, or oxy-fuel combustion) and potentially even for the specific power plant in which the capture system is to be installed. For this reason, significant effort has been made in recent years in improving the gas separation performance of MOFs and some studies evaluating the prospects of deploying these materials in real-world CO2 capture systems have begun to emerge. We have developed six new MOFs, denoted as IFPs (IFP-5, -6, -7, -8, -9, -10, IFP = Imidazolate Framework Potsdam) and two hydrogen-bonded molecular building block (MBB, named as 1 and 2 for Zn and Co based, respectively) have been synthesized, characterized and applied for gas storage. The structure of IFP possesses 1D hexagonal channels. Metal centre and the substituent groups of C2 position of the linker protrude into the open channels and determine their accessible diameter. Interestingly, the channel diameters (range : 0.3 to 5.2 Å) for IFP structures are tuned by the metal centre (Zn, Co and Cd) and substituent of C2 position of the imidazolate linker. Moreover hydrogen bonded MBB of 1 and 2 is formed an in situ functionalization of a ligand under solvothermal condition. Two different types of channels are observed for 1 and 2. Materials contain solvent accessible void space. Solvent could be easily removed by under high vacuum. The porous framework has maintained the crystalline integrity even without solvent molecules. N2, H2, CO2 and CH4 gas sorption isotherms were performed. Gas uptake capacities are comparable with other frameworks. Gas uptake capacity is reduced when the channel diameter is narrow. For example, the channel diameter of IFP-5 (channel diameter: 3.8 Å) is slightly lower than that of IFP-1 (channel diameter: 4.2 Å); hence, the gas uptake capacity and Brunauer-Emmett-Teller (BET) surface area are slightly lower than IFP-1. The selectivity does not depend only on the size of the gas components (kinetic diameter: CO2 3.3 Å, N2 3.6 Å and CH4 3.8 ) but also on the polarizability of the surface and of the gas components. IFP-5 and-6 have the potential applications for the separation of CO2 and CH4 from N2-containing gas mixtures and CO2 and CH4 containing gas mixtures. Gas sorption isotherms of IFP-7, -8, -9, -10 exhibited hysteretic behavior due to flexible alkoxy (e.g., methoxy and ethoxy) substituents. Such phenomenon is a kind of gate effects which is rarely observed in microporous MOFs. IFP-7 (Zn-centred) has a flexible methoxy substituent. This is the first example where a flexible methoxy substituent shows the gate opening behavior in a MOF. Presence of methoxy functional group at the hexagonal channels, IFP-7 acted as molecular gate for N2 gas. Due to polar methoxy group and channel walls, wide hysteretic isotherm was observed during gas uptake. The N2 The estimated BET surface area for 1 is 471 m2 g-1 and the Langmuir surface area is 570 m2 g-1. However, such surface area is slightly higher than azolate-based hydrogen-bonded supramolecular assemblies and also comparable and higher than some hydrogen-bonded porous organic molecules.
In der vorliegenden Arbeit werden verschiedene Spektrometer für die Analyse von Gasen bzw. Gasgemischen vorgestellt und deren Design, Aufbau, Charakterisierung und Optimierung beschrieben. Das Resultat der Optimierung und Weiterentwicklungen ist ein spektral breitbandiges Cavity-Ring-Down-Spektrometer (CRD-Spektrometer). Ausgangspunkt der hier vorgestellten Arbeit ist ein Spektrometer auf Basis klassischer Absorptionsspektroskopie in einer Multireflexionszelle. Für dieses Spektrometer wurde als Strahlquelle ein Superkontinuumlaser verwendet. Der Vorteil dieses Spektrometers liegt in seiner Kompaktheit. Mit diesem Spektrometer wurden Absorptionsspektren von mehreren Reingasen und einem Gasgemisch über einen Wellenlängenbereich von 1500 nm – 1700 nm aufgenommen. Der qualitative Vergleich mit zu erwartenden Spektren, welche auf der HITRAN-Datenbank basieren, zeigte eine gute Übereinstimmung. Die quantitative Interpretierbarkeit der Daten war jedoch stark eingeschränkt aufgrund des hohen zufälligen und systematischen Fehlers der Messungen. Als Konsequenz aus der als nicht zufriedenstellend bewerteten quantitativen Interpretierbarkeit der Daten wurde eine alternative Messmethode gesucht, welche eine höhere Sensitivität und Genauigkeit ermöglicht. Die Wahl fiel auf die Cavity-Ring-Down-Spektroskopie, eine resonatorgestützte Variante der Absorptionsspektroskopie. Wesentliche Vorteile dieser Technik sind a) die Unabhängigkeit von Leistungsschwankungen der Strahlquelle, b) ein effektiver Absorptionsweg von bis zu mehreren Kilometern, welcher sich unmittelbar auf die Sensitivität der Messungen auswirkt, c) die Ermittlung absoluter Absorberkonzentrationen, ohne die Notwendigkeit einer Kalibrierung oder den Vergleich mit einer Referenzzelle und d) die Vernachlässigbarkeit von Absorptionen außerhalb des Resonators. Als notwendiger Zwischenschritt auf dem Weg zu einem breitbandigen CRD-Spektrometer wurde zunächst ein monochromatisches CRD-Spektrometer designt, aufgebaut und charakterisiert. Für die effektive Einkopplung von Strahlungsenergie in einen Resonator ist die Anpassung der Strahlparameter an die Mode des Resonators notwendig. Voraussetzung dieser Anpassung ist die Kenntnis der Strahlparameter, welche experimentell ermittelt wurden. Im Laufe des Aufbaus des Spektrometers ergab sich, dass trotz der Modenanpassung die Einkopplung der Strahlungsenergie in den Resonator gestört wurde. Daraufhin wurden systematisch mögliche Ursachen dieser Störung untersucht und das Spektrometer optimiert. Mit diesem optimierten Spektrometer wurden Spektren gemessen, welche sowohl qualitativ als auch quantitativ gut mit den zu erwartenden Spektren übereinstimmen. Als Nachweisgrenze dieses Spektrometers wurde ein Wert für den Absorptionskoeffizienten alpha von 10^-8 cm-1 bestimmt. Mit dem monochromatischen CRD-Spektrometer war es zudem möglich, isotopenspezifische Messungen durchzuführen. Für das breitbandige Spektrometer wurde als Strahlquelle eine ASE-Diode (amplified spontaneous emission) verwendet. Dabei handelt es sich um eine inkohärente Strahlquelle. Mittels Messungen nach dem Prinzip der Cavity-Enhanced-Absorptionsspektroskopie wurde die generelle Funktionalität des resonatorgestützten Spektrometers überprüft. Anschließend wurden die wellenlängenabhängigen Abklingsignale des leeren und des mit einem CO2-Luft-Gemisch gefüllten Resonators gemessen und ebenfalls mit den zu erwartenden Spektren verglichen. Qualitativ stimmen die experimentellen Spektren gut mit den zu erwartenden Spektren überein. Für die quantitative Interpretation der Daten wurde ein spezieller Algorithmus entwickelt, der die spektrale Auflösung des Systems berücksichtigt. Mit dem vorgestellten Spektrometer ist so die qualitative und quantitative Interpretation der Spektren möglich. Die Nachweisgrenze des breitbandigen Cavity-Ring-Down-Spektrometers wurde zu einem Wert von alpha = 8x10^-7 cm-1 bestimmt. Der systematischen und der zufällige Fehler der Messungen lagen bei Werten von ca. 1%. Bei diesem Spektrometer handelt es sich um einen Prototyp. Mittels Optimierung des Systems lassen sich sowohl der Wert der Nachweisgrenze als auch die Fehler der Messungen verbessern.
Hydrothermal carbonisation
(2013)
The world’s appetite for energy is producing growing quantities of CO2, a pollutant that contributes to the warming of the planet and which currently cannot be removed or stored in any significant way. Other natural reserves are also being devoured at alarming rates and current assessments suggest that we will need to identify alternative sources in the near future. With the aid of materials chemistry it should be possible to create a world in which energy use needs not be limited and where usable energy can be produced and stored wherever it is needed, where we can minimize and remediate emissions as new consumer products are created, whilst healing the planet and preventing further disruptive and harmful depletion of valuable mineral assets. In achieving these aims, the creation of new and very importantly greener industries and new sustainable pathways are crucial. In all of the aforementioned applications, new materials based on carbon, ideally produced via inexpensive, low energy consumption methods, using renewable resources as precursors, with flexible morphologies, pore structures and functionalities, are increasingly viewed as ideal candidates to fulfill these goals. The resulting materials should be a feasible solution for the efficient storage of energy and gases. At the end of life, such materials ideally must act to improve soil quality and to act as potential CO2 storage sinks. This is exactly the subject of this habilitation thesis: an alternative technology to produce carbon materials from biomass in water using low carbonisation temperatures and self-generated pressures. This technology is called hydrothermal carbonisation. It has been developed during the past five years by a group of young and talented researchers working under the supervision of Dr. Titirici at the Max-Planck Institute of Colloids and Interfaces and it is now a well-recognised methodology to produce carbon materials with important application in our daily lives. These applications include electrodes for portable electronic devices, filters for water purification, catalysts for the production of important chemicals as well as drug delivery systems and sensors.
Gegenstand der Dissertation ist die größen- und eigenschaftsoptimierte Synthese und Charakterisierung von anorganischen Nanopartikeln in einer geeigneten Polyelektrolytmodifizierten Mikroemulsion. Das Hauptziel bildet dabei die Auswahl einer geeigneten Mikroemulsion, zur Synthese von kleinen, stabilen, reproduzierbaren Nanopartikeln mit besonderen Eigenschaften. Die vorliegende Arbeit wurde in zwei Haupteile gegliedert. Der erste Teil befasst sich mit der Einmischung von unterschiedlichen Polykationen (lineares Poly (diallyldimethylammoniumchlorid) (PDADMAC) und verzweigtes Poly (ethylenimin) (PEI)) in verschiedene, auf unterschiedlichen Tensiden (CTAB - kationisch, SDS - anionisch, SB - zwitterionisch) basierenden, Mikroemulsionssysteme. Dabei zeigt sich, dass das Einmischen der Polykationen in die Wassertröpfchen der Wasser-in-Öl (W/O) Mikroemulsion prinzipiell möglich ist. Der Einfluss der verschiedenen Polykationen auf das Phasenverhalten der W/O Mikroemulsion ist jedoch sehr unterschiedlich. In Gegenwart des kationischen Tensids führen die repulsiven Wechselwirkungen mit den Polykationen zu einer Destabilisierung des Systems, während die ausgeprägten Wechselwirkungen mit dem anionischen Tensid in einer deutlichen Stabilisierung des Systems resultieren. Für das zwitterionische Tensid führen die moderaten Wechselwirkungen mit den Polykationen zu einer partiellen Stabilisierung. Der zweite Teil der Arbeit beschäftigt sich mit dem Einsatz der unterschiedlichen, Polyelektrolyt- modifizierten Mikroemulsionen als Templatphase für die Herstellung verschiedener, anorganischer Nanopartikel. Die CTAB-basierte Mikroemulsion erweist sich dabei als ungeeignet für die Herstellung von CdS Nanopartikeln, da zum einen nur eine geringe Toleranz gegenüber den Reaktanden vorhanden ist (Destabilisierungseffekt) und zum anderen das Partikelwachstum durch den Polyelektrolyt-Tensid-Film nicht ausreichend begrenzt wird. Zudem zeigt sich, dass eine Abtrennung der Partikel aus der Mikroemulsion nicht möglich ist. Die SDS-basierten Mikroemulsionen, erweisen sich als geeignete Templatphase zur Synthese kleiner anorganischer Nanopartikel (3 – 20 nm). Sowohl CdS Quantum Dots, als auch Gold Nanopartikel konnten erfolgreich in der Mikroemulsion synthetisiert werden, wobei das verzweigte PEI einen interessanten Templat-Effekt in der Mikroemulsion hervorruft. Als deutlicher Nachteil der SDS-basierten Mikroemulsionen offenbaren sich die starken Wechselwirkungen zwischen dem Tensid und den Polyelektrolyten während der Aufarbeitung der Nanopartikel aus der Mikroemulsion. Dabei erweist sich die Polyelektrolyt-Tensid-Komplexbildung als hinderlich für die Redispergierung der CdS Quantum Dots in Wasser, so dass Partikelaggregation einsetzt. Die SB-basierten Mikroemulsionen erweisen sich als günstige Templatphase für die Bildung von größen- und eigenschaftenoptimierten Nanopartikeln (< 4 nm), wobei insbesondere eine Modifizierung mit PEI als ideal betrachtet werden kann. In Gegenwart des verzweigten PEI gelang es erstmals ultrakleine, fluoreszierende Gold Cluster (< 2 nm) in einer SB-basierten Mikroemulsion als Templatphase herzustellen. Als besonderer Vorteil der SB-basierten Mikroemulsion zeigen sich die moderaten Wechselwirkungen zwischen dem zwitterionischen Tensid und den Polyelektrolyten, welche eine anschließende Abtrennung der Partikel aus der Mikroemulsion unter Erhalt der Größe und ihrer optischen Eigenschaften ermöglichen. In der redispergierten wässrigen Lösung gelang somit eine Auftrennung der PEI-modifizierten Partikel mit Hilfe der asymmetrischer Fluss Feldflussfraktionierung (aF FFF). Die gebildeten Nanopartikel zeigen interessante optische Eigenschaften und können zum Beispiel erfolgreich zur Modifizierung von Biosensoren eingesetzt werden.
In dieser Arbeit wurden sphärische Gold Nanopartikel (NP) mit einem Durchmesser größer ~ 2 nm, Gold Quantenpunkte (QDs) mit einem Durchmesser kleiner ~ 2 nm sowie Gold Nanostäbchen (NRs) unterschiedlicher Länge hergestellt und optisch charakterisiert. Zudem wurden zwei neue Synthesevarianten für die Herstellung thermosensitiver Gold QDs entwickelt werden. Sphärische Gold NP zeigen eine Plasmonenbande bei ~ 520 nm, die auf die kollektive Oszillation von Elektronen zurückzuführen ist. Gold NRs weisen aufgrund ihrer anisotropen Form zwei Plasmonenbanden auf, eine transversale Plasmonenbande bei ~ 520 nm und eine longitudinale Plasmonenbande, die vom Länge-zu-Durchmesser-Verhältnis der Gold NRs abhängig ist. Gold QDs besitzen keine Plasmonenbande, da ihre Elektronen Quantenbeschränkungen unterliegen. Gold QDs zeigen jedoch aufgrund diskreter Energieniveaus und einer Bandlücke Photolumineszenz (PL). Die synthetisierten Gold QDs besitzen eine Breitbandlumineszenz im Bereich von ~ 500-800 nm, wobei die Lumineszenz-eigenschaften (Emissionspeak, Quantenausbeute, Lebenszeiten) stark von den Herstellungs-bedingungen und den Oberflächenliganden abhängen. Die PL in Gold QDs ist ein sehr komplexes Phänomen und rührt vermutlich von Singulett- und Triplett-Zuständen her. Gold NRs und Gold QDs konnten in verschiedene Polymere wie bspw. Cellulosetriacetat eingearbeitet werden. Polymernanokomposite mit Gold NRs wurden erstmals unter definierten Bedingungen mechanisch gezogen, um Filme mit optisch anisotropen (richtungsabhängigen) Eigenschaften zu erhalten. Zudem wurde das Temperaturverhalten von Gold NRs und Gold QDs untersucht. Es konnte gezeigt werden, dass eine lokale Variation der Größe und Form von Gold NRs in Polymernanokompositen durch Temperaturerhöhung auf 225-250 °C erzielt werden kann. Es zeigte sich, dass die PL der Gold QDs stark temperaturabhängig ist, wodurch die PL QY der Proben beim Abkühlen (-7 °C) auf knapp 30 % verdoppelt und beim Erhitzen auf 70 °C nahezu vollständig gelöscht werden konnte. Es konnte demonstriert werden, dass die Länge der Alkylkette des Oberflächenliganden einen Einfluss auf die Temperaturstabilität der Gold QDs hat. Zudem wurden verschiedene neuartige und optisch anisotrope Sicherheitslabels mit Gold NRs sowie thermosensitive Sicherheitslabel mit Gold QDs entwickelt. Ebenso scheinen Gold NRs und QDs für die und die Optoelektronik (bspw. Datenspeicherung) und die Medizin (bspw. Krebsdiagnostik bzw. -therapie) von großem Interesse zu sein.
Diese Arbeit befasst sich mit der Synthese und Charakterisierung von organolöslichen Thiophen und Benzodithiophen basierten Materialien und ihrer Anwendung als aktive lochleitende Halbleiterschichten in Feldeffekttransistoren. Im ersten Teil der Arbeit wird durch eine gezielte Modifikation des Thiophengrundgerüstes eine neue Comonomer-Einheit für die Synthese von Thiophen basierten Copolymeren erfolgreich dargestellt. Die hydrophoben Hexylgruppen in der 3-Position des Thiophens werden teilweise durch hydrophile 3,6-Dioxaheptylgruppen ersetzt. Über die Grignard-Metathese nach McCullough werden statistische Copolymere mit unterschiedlichen molaren Anteilen vom hydrophoben Hexyl- und hydrophilem 3,6-Dioxaheptylgruppen 1:1 (P-1), 1:2 (P-2) und 2:1 (P-3) erfolgreich hergestellt. Auch die Synthese eines definierten Blockcopolymers BP-1 durch sequentielle Addition der Comonomere wird realisiert. Optische und elektrochemische Eigenschaften der neuartigen Copolymere sind vergleichbar mit P3HT. Mit allen Copolymeren wird ein charakteristisches Transistorverhalten in einem Top-Gate/Bottom-Kontakt-Aufbau erhalten. Dabei werden mit P-1 als die aktive Halbleiterschicht im Bauteil, PMMA als Dielektrikum und Silber als Gate-Elektrode Mobilitäten von bis zu 10-2 cm2/Vs erzielt. Als Folge der optimierten Grenzfläche zwischen Dielektrikum und Halbleiter wird eine Verbesserung der Luftstabilität der Transistoren über mehrere Monate festgestellt. Im zweiten Teil der Arbeit werden Benzodithiophen basierte organische Materialien hergestellt. Für die Synthese der neuartigen Benzodithiophen-Derivate wird die Schlüsselverbindung TIPS-BDT in guter Ausbeute dargestellt. Die Difunktionalisierung von TIPS-BDT in den 2,6-Positionen über eine elektrophile Substitution liefert die gewünschten Dibrom- und Distannylmonomere. Zunächst werden über die Stille-Reaktion alternierende Copolymere mit alkylierten Fluoren- und Chinoxalin-Einheiten realisiert. Alle Copolymere zeichnen sich durch eine gute Löslichkeit in gängigen organischen Lösungsmitteln, hohe thermische Stabilität und durch gute Filmbildungseigenschaften aus. Des Weiteren sind alle Copolymere mit HOMO Lagen höher als -6.3 eV, verglichen mit den Thiophen basierten Copolymeren (P-1 bis P-3), sehr oxidationsstabil. Diese Copolymere zeigen amorphes Verhalten in den Halbleiterschichten in OFETs auf und es werden Mobilitäten bis zu 10-4 cm2/Vs erreicht. Eine Abhängigkeit der Bauteil-Leistung von dem Zinngehalt-Rest im Polymer wird nachgewiesen. Ein Zinngehalt von über 0.6 % kann enormen Einfluss auf die Mobilität ausüben, da die funktionellen SnMe3-Gruppen als Fallenzustände wirken können. Alternativ wird das alternierende TIPS-BDT/Fluoren-Copolymer P-5-Stille nach der Suzuki-Methode polymerisiert. Mit P-5-Suzuki als die aktive organische Halbleiterschicht im OFET wird die höchste Mobilität von 10-2 cm2/Vs erzielt. Diese Mobilität ist somit um zwei Größenordnungen höher als bei P-5-Stille, da die Fallenzustände in diesem Fall minimiert werden und folglich der Ladungstransport verbessert wird. Sowohl das Homopolymer P-12 als auch das Copolymer mit dem aromatischen Akzeptor Benzothiadiazol P-9 führen zu schwerlöslichen Polymeren. Aus diesem Grund werden einerseits Terpolymere aus TIPS-BDT/Fluoren/BTD-Einheiten P-10 und P-11 aufgebaut und andererseits wird versucht die TIPS-BDT-Einheit in die Seitenkette des Styrols einzubringen. Mit der Einführung von BTD in die Hauptpolymerkette werden insbesondere die Absorptions- und die elektrochemischen Eigenschaften beeinflusst. Im Vergleich zu dem TIPS-BDT/Fluoren-Copolymer reicht die Absorption bis in den sichtbaren Bereich und die LUMO Lage wird zu niederen Werten verschoben. Eine Verbesserung der Leistung in den Bauteilen wird jedoch nicht festgestellt. Die erfolgreiche erstmalige Synthese von TIPS-BDT als Seitenkettenpolymer an Styrol P-13 führt zu einem löslichen und amorphen Polymer mit vergleichbaren Mobilitäten von Styrol basierten Polymeren (µ = 10-5 cm2/Vs) im OFET. Ein weiteres Ziel dieser Arbeit ist die Synthese von niedermolekularen organolöslichen Benzodithiophen-Derivaten. Über Suzuki- und Stille-Reaktionen ist es erstmals möglich, verschiedenartige Aromaten über eine σ-Bindung an TIPS-BDT in den 2,6-Positionen zu knüpfen. Die UV/VIS-Untersuchungen zeigen, dass die Absorption durch die Verlängerung der π-Konjugationslänge zu höheren Wellenlängen verschoben wird. Darüber hinaus ist es möglich, thermisch vernetzbare Gruppen wie Allyloxy in das Molekülgerüst einzubauen. Das Einführen von F-Atomen in das Molekülgerüst resultiert in einer verstärkten Packungsordnung im Fluorbenzen funktionalisiertem TIPS-BDT (SM-4) im Festkörper mit sehr guten elektronischen Eigenschaften im OFET, wobei Mobilitäten bis zu 0.09 cm2/Vs erreicht werden.
Diese Arbeit befasst sich mit der Synthese und der Charakterisierung von thermoresponsiven Polymeren und ihrer Immobilisierung auf festen Oberflächen als nanoskalige dünne Schichten. Dabei wurden thermoresponsive Polymere vom Typ der unteren kritischen Entmischungstemperatur (engl.: lower critical solution temperature, LCST) verwendet. Sie sind bei niedrigeren Temperaturen im Lösungsmittel gut und nach Erwärmen oberhalb einer bestimmten kritischen Temperatur nicht mehr löslich; d. h. sie weisen bei einer bestimmten Temperatur einen Phasenübergang auf. Als Basismaterial wurden verschiedene thermoresponsive und biokompatible Polymere basierend auf Diethylenglykolmethylethermethacrylat (MEO2MA) und Oligo(ethylenglykol)methylethermethacrylat (OEGMA475, Mn = 475 g/ mol) über frei radikalische Copolymerisation synthetisiert. Der thermoresponsive Phasenübergang der Copolymere wurde in wässriger Lösung und in gequollenen vernetzten dünnen Schichten beobachtet. Außerdem wurde untersucht, inwiefern eine selektive Proteinbindung an geeignete funktionalisierte Copolymere die Phasenübergangstemperatur beeinflusst. Die thermoresponsiven Copolymere wurden über photovernetzbare Gruppen auf festen Oberflächen immobilisiert. Die nötigen lichtempfindlichen Vernetzereinheiten wurden mittels des polymerisierbaren Benzophenonderivates 2 (4 Benzoylphenoxy)ethylmethacrylat (BPEM) in das Copolymer integriert. Dünne Filme der Copolymere mit ca. 100 nm Schichtdicke wurden über Rotationsbeschichtung auf Siliziumwafer aufgeschleudert und anschließend durch Bestrahlung mit UV Licht vernetzt und auf der Oberfläche immobilisiert. Die Filme sind stabiler je größer der Vernetzeranteil und je größer die Molmasse der Copolymere ist. Bei einem Waschprozess nach der Vernetzung wird beispielsweise aus einem Film mit moderater Molmasse und geringem Vernetzeranteil mehr unvernetztes Copolymer ausgewaschen als bei einem höhermolekularen Copolymer mit hohem Vernetzeranteil. Die Quellbarkeit der Polymerschichten wurde mit Ellipsometrie untersucht. Sie ist größer je geringer der Vernetzeranteil in den Copolymeren ist. Schichten aus thermoresponsiven OEG Copolymeren zeigen einen Volumenphasenübergang vom Typ der LCST. Der thermoresponsive Kollaps der Schichten ist komplett reversibel, die Kollapstemperatur kann über die Zusammensetzung der Copolymere eingestellt werden. Für einen Vergleich dieser Eigenschaften mit dem gut charakterisierten und derzeit wohl am häufigsten untersuchten thermoresponsiven Polymer Poly(N-isopropylacrylamid) (PNIPAM) wurden zusätzlich photovernetzte Schichten aus PNIPAM hergestellt und ebenfalls ellipsometrisch vermessen. Im Vergleich zu PNIPAM verläuft der Phasenübergang der Schichten aus den Copolymeren mit Oligo(ethylenglykol)-seitenketten (OEG Copolymere) über einen größeren Temperaturbereich. Mit Licht einer Wellenlänge > 300 nm wurden die photosensitiven Benzophenongruppen selektiv angeregt. Bei der Verwendung kleinerer Wellenlängen vernetzten die Copolymerschichten auch ohne die Anwesenheit der lichtempfindlichen Benzophenongruppen. Dieser Effekt ließ sich zur kontrollierten Immobilisierung und Vernetzung der OEG Copolymere einsetzen. Als weitere Methode zur Immobilisierung der Copolymere wurde die Anbindung über Amidbindungen untersucht. Dazu wurden OEG Copolymere mit dem carboxylgruppenhaltigen 2 Succinyloxyethylmethacrylat (MES) auf mit 3 Aminopropyldimethylethoxysilan (APDMSi) silanisierte Siliziumwafer rotationsbeschichtet, und mit dem oligomeren α, ω Diamin Jeffamin® ED 900 vernetzt. Die Vernetzungsreaktion erfolgte ohne weitere Zusätze durch Erhitzen der Proben. Die Hydrogelschichten waren anschließend stabil und zeigten neben thermoresponsivem auch pH responsives Verhalten. Um zu untersuchen, ob die Phasenübergangstemperatur durch eine Proteinbindung beeinflusst werden kann, wurde ein polymerisierbares Biotinderivat 2 Biotinyl-aminoethylmethacrylat (BAEMA) in das thermoresponsive Copolymer eingebaut. Der Einfluss des biotinbindenen Proteins Avidin auf das thermoresponsive Verhalten des Copolymers in Lösung wurde untersucht. Die spezifische Bindung von Avidin an das biotinylierte Copolymer verschob die Übergangstemperatur deutlich zu höheren Temperaturen. Kontrollversuche zeigten, dass dieses Verhalten auf eine selektive Proteinbindung zurückzuführen ist. Thermoresponsive OEG Copolymere mit photovernetzbaren Gruppen aus BPEM und Biotingruppen aus BAEMA wurden über Rotationsbeschichtung auf Gold- und auf Siliziumoberflächen aufgetragen und durch UV Strahlung vernetzt. Die spezifische Bindung von Avidin an die Copolymerschicht wurde mit Oberflächenplasmonenresonanz und Ellipsometrie untersucht. Die Bindungskapazität der Schichten war umso größer, je kleiner der Vernetzeranteil, d. h. je größer die Maschenweite des Netzwerkes war. Die Quellbarkeit der Schichten wurde durch die Avidinbindung erhöht. Bei hochgequollenen Systemen verursachte eine Mehrfachbindung des tetravalenten Avidins allerdings eine zusätzliche Quervernetzung des Polymernetzwerkes. Dieser Effekt wirkt der erhöhten Quellbarkeit durch die Avidinbindung entgegen und lässt die Polymernetzwerke schrumpfen.
Die Dissertation beschreibt die Herstellung von ringförmigen Verbindungen (Naphthalenophanen) mit Hilfe der Dehydro-Diels-Alder-Reaktion, wobei immer Enantiomerenpaare auftreten. Es wird der diastereoselektive Aufbau von Naphthalenophanen und der enantiomeren reine Aufbau von Biarylen untersucht. Desweiteren werden die physikalischen Eigenschaften der erhaltenen Verbindungen, wie die Phosphoreszenz, Trennbarkeit der entstehenden Enantiomere und die Ringspannung beschrieben.
Modifizierung von Silikonelastomeren mit organischen Dipolen für Dielektrische Elastomer Aktuatoren
(2013)
Ein Dielektrischer Elastomer Aktuator (DEA) ist ein dehnbarer Kondensator, der aus einem Elastomerfilm besteht, der sich zwischen zwei flexiblen Elektroden befindet. Bei Anlegen einer elektrischen Spannung, ziehen sich die Elektroden aufgrund elektrostatischer Wechselwirkungen an, wodurch das Elastomer in z-Richtung zusammengepresst wird und sich dementsprechend in der x-,y-Ebene ausdehnt. Hierdurch werden Aktuationsbewegungen erreicht, welche sehr präzise über die Spannung gesteuert werden können. Zusätzlich sind DEAs kostengünstig, leicht und aktuieren geräuschlos. DEAs können beispielsweise für Produkte im medizinischen Bereich oder für optischer Komponenten genutzt werden. Ebenso kann aus diesen Bauteilen Strom erzeugt werden. Das größte Hindernis für eine weite Implementierung dieser Materialien liegt in den erforderlichen hohen Spannungen zum Erzeugen der Aktuationsbewegung, welche sich tendenziell im Kilovolt-Bereich befinden. Dies macht die Elektronik teuer und die Bauteile unsicher für Anwender. Um geringere Betriebsspannungen für die DEAs zu erreichen, sind signifikante Materialverbesserungen - insbesondere des verwendeten Elastomers - erforderlich. Um dies zu erreichen, können die dielektrischen Eigenschaften (Permittivität) der Elastomere gesteigert und/oder deren Steifigkeit (Young-Modul) gesenkt werden. In der vorliegenden Arbeit konnte die Aktuationsleistung von Silikonfilmen durch die Addition organischer Dipole erheblich verbessert werden. Hierfür wurde ein Verfahren etabliert, um funktionalisierte Dipole kovalent an das Polymernetzwerk zu binden. Dieser als "One-Step-Verfahren" bezeichnete Ansatz ist einfach durchzuführen und es werden homogene Filme erhalten. Die Dipoladdition wurde anhand verschiedener Silikone erprobt, die sich hinsichtlich ihrer mechanischen Eigenschaften unterschieden. Bei maximalem Dipolgehalt verdoppelte sich die Permittivität aller untersuchten Silikone und die Filme wurden deutlich weicher. Hierbei war festzustellen, dass die Netzwerkstruktur der verwendeten Silikone einen erheblichen Einfluss auf die erreichte Aktuationsdehnung hat. Abhängig vom Netzwerk erfolgte eine enorme Steigerung der Aktuationsleistung im Bereich von 100 % bis zu 4000 %. Dadurch können die Betriebsspannungen in DEAs deutlich abgesenkt werden, so dass sie tendenziell bei Spannungen unterhalb von einem Kilovolt betrieben werden können.
Die Entwicklung neuer Verfahren für die Rückführung von Palladium aus Altmaterialien, wie gebrauchten Autoabgaskatalysatoren, in den Stoffstromkreislauf ist sowohl aus ökologischer als auch ökonomischer Sicht erstrebenswert. In dieser Arbeit wurden neue Flüssig-Flüssig- und Fest-Flüssig-Extraktionsmittel entwickelt, mit denen Palladium(II) aus einer oxidierenden, salzsauren Laugungslösung, die neben Palladium auch Platin und Rhodium sowie zahlreiche unedle Metalle enthält, zurückgewonnen werden kann. Die neuen Extraktionsmittel ungesättigte monomere 1,2-Dithioether und oligomere Ligandenmischungen mit vicinalen Dithioether-Einheiten – sind im Gegensatz zu vielen in der Literatur aufgeführten Extraktionsmitteln hochselektiv. Aufgrund ihrer geometrischen und elektronischen Präorganisation bilden sie mit Palladium(II) stabile quadratisch-planare Chelatkomplexe. Für die Entwicklung des Flüssig-Flüssig-Extraktionsmittels wurde eine Reihe von ungesättigten 1,2-Dithioetherliganden dargestellt, welche auf einer starren 1,2-Dithioethen-Einheit, die in ein variierendes elektronenziehendes Grundgerüst eingebettet ist, basieren und polare Seitenketten besitzen. Neben der Bestimmung der Kristallstrukturen der Liganden und ihrer Palladiumdichlorid-Komplexe wurden die elektro- und photochemischen Eigenschaften, die Komplexstabilität und das Verhalten in Lösung untersucht. In Flüssig-Flüssig-Extraktionsuntersuchungen konnte gezeigt werden, dass einige der neuen Liganden industriell genutzten Extraktionsmitteln durch eine schnellere Einstellung des Extraktionsgleichgewichts überlegen sind. Anhand von Kriterien, die für eine industrielle Nutzbarkeit entscheidend sind, wie: guter Oxidationsbeständigkeit, einer hohen Extraktionsausbeute (auch bei hohen Salzsäurekonzentrationen der Speiselösung), schneller Extraktionskinetik und einer hohen Selektivität für Palladium(II) wurde aus der Reihe der sechs Liganden ein geeignetes Flüssig-Flüssig-Extraktionsmittel ausgewählt: 1,2-Bis(2-methoxyethylthio)benzen. Mit diesem wurde ein praxisnahes Flüssig-Flüssig-Extraktionssystem entwickelt. Nach der schrittweisen Adaption der wässrigen Phase von einer Modelllösung hin zu der oxidierenden, salzsauren Laugungslösung erfolgte die Auswahl eines geeigneten großtechnisch, einsetzbaren Lösemittels (1,2-Dichlorbenzen) und eines effizienten Reextraktionsmittels (0,5 M Thioharnstoff in 0,1 M HCl). Die hohe Palladium(II)-Selektivität dieses Flüssig-Flüssig-Extraktionssystems konnte verifiziert und seine Wiederverwendbarkeit und Praxistauglichkeit unter Beweis gestellt werden. Weiterhin wurde gezeigt, dass sich beim Kontakt mit oxidierenden Medien aus dem Dithioether 1,2-Bis(2-methoxyethylthio)benzen geringe Mengen des Thioethersulfoxids 1-(2-Methoxyethylsulfinyl)-2-(2-methoxyethylthio)benzen bilden. Dieses wird im sauren Milieu protoniert und beschleunigt die Extraktion wie ein Phasentransferkatalysator, ohne jedoch die Palladium(II)-Selektivität herabzusetzen. Die Kristallstruktur des Palladiumdichlorid-Komplexes des Tioethersulfoxids zeigt, dass der unprotonierte Ligand Palladium(II), analog zum Dithioether, über die chelatisierenden Schwefelatome koordiniert. Verschiedene Mischungen von Oligo(dithioether)-Liganden und der monomere Ligand 1,2-Bis(2-methoxyethylthio)benzen dienten als Extraktionsmittel für Fest-Flüssig-Extraktionsversuche mit SIRs (solvent impregnated resins) und wurden zu diesem Zweck auf hydrophilem Kieselgel und organophilem Amberlite® XAD 2 adsorbiert. Die Oligo(dithioether)-Liganden basieren auf 1,2-Dithiobenzen oder 1,2-Dithiomaleonitril-Einheiten, welche über Tris(oxyethylen)ethylen- oder Trimethylen-Brücken miteinander verknüpft sind. Mit Hilfe von Batch-Versuchen konnte gezeigt werden, dass sich strukturelle Unterschiede - wie die Art der chelatisierenden Einheit, die Art der verbrückenden Ketten und das Trägermaterial - auf die Extraktionsausbeuten, die Extraktionskinetik und die Beladungskapazität auswirken. Die kieselgelhaltigen SIRs stellen das Extraktionsgleichgewicht viel schneller ein als die Amberlite® XAD 2-haltigen. Jedoch bleiben die Extraktionsmittel auf Amberlite® XAD 2, im Gegensatz zu Kieselgel, dauerhaft haften. Im salzsauren Milieu sind die 1,2-Dithiobenzen-derivate besser als Extraktionsmittel geeignet als die 1,2-Dithiomaleonitrilderivate. In Säulenversuchen mit der oxidierenden, salzsauren Laugungslösung und wiederverwendbaren, mit 1,2-Dithiobenzenderivaten imprägnierten, Amberlite® XAD 2-haltigen SIRs zeigte sich, dass für die Realisierung hoher Beladungskapazitäten sehr geringe Pumpraten benötigt werden. Trotzdem konnte die gute Palladium(II)-Selektivität dieser Festphasenmaterialien demonstriert werden. Allerdings wurden in den Eluaten im Gegensatz zu den Eluaten, die aus Flüssig-Flüssig-Extraktion resultierten neben dem Palladium auch geringe Mengen an Platin, Aluminium, Eisen und Blei gefunden.
The present thesis is to be brought into line with the current need for alternative and sustainable approaches toward energy management and materials design. In this context, carbon in particular has become the material of choice in many fields such as energy conversion and storage. Herein, three main topics are covered: 1)An alternative synthesis strategy toward highly porous functional carbons with tunable porosity using ordinary salts as porogen (denoted as “salt templating”) 2)The one-pot synthesis of porous metal nitride containing functional carbon composites 3)The combination of both approaches, enabling the generation of highly porous composites with finely tunable properties All approaches have in common that they are based on the utilization of ionic liquids, salts which are liquid below 100 °C, as precursors. Just recently, ionic liquids were shown to be versatile precursors for the generation of heteroatom-doped carbons since the liquid state and a negligible vapor pressure are highly advantageous properties. However, in most cases the products do not possess any porosity which is essential for many applications. In the first part, “salt templating”, the utilization of salts as diverse and sustainable porogens, is introduced. Exemplarily shown for ionic liquid derived nitrogen- and nitrogen-boron-co-doped carbons, the control of the porosity and morphology on the nanometer scale by salt templating is presented. The studies within this thesis were conducted with the ionic liquids 1-Butyl-3-methyl-pyridinium dicyanamide (Bmp-dca), 1-Ethyl-3-methyl-imidazolium dicyanamide (Emim-dca) and 1 Ethyl 3-methyl-imidazolium tetracyanoborate (Emim-tcb). The materials are generated through thermal treatment of precursor mixtures containing one of the ionic liquids and a porogen salt. By simple removal of the non-carbonizable template salt with water, functional graphitic carbons with pore sizes ranging from micro- to mesoporous and surface areas up to 2000 m2g-1 are obtained. The carbon morphologies, which presumably originate from different onsets of demixing, mainly depend on the nature of the porogen salt whereas the nature of the ionic liquid plays a minor role. Thus, a structural effect of the porogen salt rather than activation can be assumed. This offers an alternative to conventional activation and templating methods, enabling to avoid multiple-step and energy-consuming synthesis pathways as well as employment of hazardous chemicals for the template removal. The composition of the carbons can be altered via the heat-treatment procedure, thus at lower synthesis temperatures rather polymeric carbonaceous materials with a high degree of functional groups and high surface areas are accessible. First results suggest the suitability of the materials for CO2 utilization. In order to further illustrate the potential of ionic liquids as carbon precursors and to expand the class of carbons which can be obtained, the ionic liquid 1-Ethyl-3-methyl-imidazolium thiocyanate (Emim-scn) is introduced for the generation of nitrogen-sulfur-co-doped carbons in combination with the already studied ionic liquids Bmp-dca and Emim-dca. Here, the salt templating approach should also be applicable eventually further illustrating the potential of salt templating, too. In the second part, a one-pot and template-free synthesis approach toward inherently porous metal nitride nanoparticle containing nitrogen-doped carbon composites is presented. Since ionic liquids also offer outstanding solubility properties, the materials can be generated through the carbonization of homogeneous solutions of an ionic liquid acting as nitrogen as well as carbon source and the respective metal precursor. The metal content and surface area are easily tunable via the initial metal precursor amount. Furthermore, it is also possible to synthesize composites with ternary nitride nanoparticles whose composition is adjustable by the metal ratio in the precursor solution. Finally, both approaches are combined into salt templating of the one-pot composites. This opens the way to the one-step synthesis of composites with tunable composition, particle size as well as precisely controllable porosity and morphology. Thereby, common synthesis strategies where the product composition is often negatively affected by the template removal procedure can be avoided. The composites are further shown to be suitable as electrodes for supercapacitors. Here, different properties such as porosity, metal content and particle size are investigated and discussed with respect to their influence on the energy storage performance. Because a variety of ionic liquids, metal precursors and salts can be combined and a simple closed-loop process including salt recycling is imaginable, the approaches present a promising platform toward sustainable materials design.
Various synthetic approaches were explored towards the preparation of poly(N-substituted glycine) homo/co-polymers (a.k.a. polypeptoids). In particular, monomers that would facilitate in the preparation of bio-relevant polymers via either chain- or step-growth polymerization were targeted. A 3-step synthetic approach towards N-substituted glycine N-carboxyanhydrides (NNCA) was implemented, or developed, and optimized allowing for an efficient gram scale preparation of the aforementioned monomer (chain-growth). After exploring several solvents and various conditions, a reproducible and efficient ring-opening polymerization (ROP) of NNCAs was developed in benzonitrile (PhCN). However, achieving molecular weights greater than 7 kDa required longer reaction times (>4 weeks) and sub-sequentially allowed for undesirable competing side reactions to occur (eg. zwitterion monomer mechanisms). A bulk-polymerization strategy provided molecular weights up to 11 kDa within 24 hours but suffered from low monomer conversions (ca. 25%). Likewise, a preliminary study towards alcohol promoted ROP of NNCAs suffered from impurities and a suspected alternative activated monomer mechanism (AAMM) providing poor inclusion of the initiator and leading to multi-modal dispersed polymeric systems. The post-modification of poly(N-allyl glycine) via thiol-ene photo-addition was observed to be quantitative, with the utilization of photo-initiators, and facilitated in the first glyco-peptoid prepared under environmentally benign conditions. Furthermore, poly(N-allyl glycine) demonstrated thermo-responsive behavior and could be prepared as a semi-crystalline bio-relevant polymer from solution (ie. annealing). Initial efforts in preparing these polymers via standard poly-condensation protocols were insufficient (step-growth). However, a thermally induced side-product, diallyl diketopiperazine (DKP), afforded the opportunity to explore photo-induced thiol-ene and acyclic diene metathesis (ADMET) polymerizations. Thiol-ene polymerization readily led to low molecular weight polymers (<2.5 kDa), that were insoluble in most solvents except heated amide solvents (ie. DMF), whereas ADMET polymerization, with diallyl DKP, was unsuccessful due to a suspected 6 member complexation/deactivation state of the catalyst. This understanding prompted the preparation of elongated DKPs most notably dibutenyl DKP. SEC data supports the aforementioned understanding but requires further optimization studies in both the preparation of the DKP monomers and following ADMET polymerization. This work was supported by NMR, GC-MS, FT-IR, SEC-IR, and MALDI-Tof MS characterization. Polymer properties were measured by UV-Vis, TGA, and DSC.
Cellulose is the most abundant biopolymer on earth. In this work it has been used, in various forms ranging from wood to fully processed laboratory grade microcrystalline cellulose, to synthesise a variety of metal and metal carbide nanoparticles and to establish structuring and patterning methodologies that produce highly functional nano-hybrids. To achieve this, the mechanisms governing the catalytic processes that bring about graphitised carbons in the presence of iron have been investigated. It was found that, when infusing cellulose with an aqueous iron salt solution and heating this mixture under inert atmosphere to 640 °C and above, a liquid eutectic mixture of iron and carbon with an atom ratio of approximately 1:1 forms. The eutectic droplets were monitored with in-situ TEM at the reaction temperature where they could be seen dissolving amorphous carbon and leaving behind a trail of graphitised carbon sheets and subsequently iron carbide nanoparticles. These transformations turned ordinary cellulose into a conductive and porous matrix that is well suited for catalytic applications. Despite these significant changes on the nanometre scale the shape of the matrix as a whole was retained with remarkable precision. This was exemplified by folding a sheet of cellulose paper into origami cranes and converting them via the temperature treatment in to magnetic facsimiles of those cranes. The study showed that the catalytic mechanisms derived from controlled systems and described in the literature can be transferred to synthetic concepts beyond the lab without loss of generality. Once the processes determining the transformation of cellulose into functional materials were understood, the concept could be extended to other metals and metal-combinations. Firstly, the procedure was utilised to produce different ternary iron carbides in the form of MxFeyC (M = W, Mn). None of those ternary carbides have thus far been produced in a nanoparticle form. The next part of this work encompassed combinations of iron with cobalt, nickel, palladium and copper. All of those metals were also probed alone in combination with cellulose. This produced elemental metal and metal alloy particles of low polydispersity and high stability. Both features are something that is typically not associated with high temperature syntheses and enables to connect the good size control with a scalable process. Each of the probed reactions resulted in phase pure, single crystalline, stable materials. After showing that cellulose is a good stabilising and separating agent for all the investigated types of nanoparticles, the focus of the work at hand is shifted towards probing the limits of the structuring and pattering capabilities of cellulose. Moreover possible post-processing techniques to further broaden the applicability of the materials are evaluated. This showed that, by choosing an appropriate paper, products ranging from stiff, self-sustaining monoliths to ultra-thin and very flexible cloths can be obtained after high temperature treatment. Furthermore cellulose has been demonstrated to be a very good substrate for many structuring and patterning techniques from origami folding to ink-jet printing. The thereby resulting products have been employed as electrodes, which was exemplified by electrodepositing copper onto them. Via ink-jet printing they have additionally been patterned and the resulting electrodes have also been post functionalised by electro-deposition of copper onto the graphitised (printed) parts of the samples. Lastly in a preliminary test the possibility of printing several metals simultaneously and thereby producing finely tuneable gradients from one metal to another have successfully been made. Starting from these concepts future experiments were outlined. The last chapter of this thesis concerned itself with alternative synthesis methods of the iron-carbon composite, thereby testing the robustness of the devolved reactions. By performing the synthesis with partly dissolved scrap metal and pieces of raw, dry wood, some progress for further use of the general synthesis technique were made. For example by using wood instead of processed cellulose all the established shaping techniques available for wooden objects, such as CNC milling or 3D prototyping, become accessible for the synthesis path. Also by using wood its intrinsic well defined porosity and the fact that large monoliths are obtained help expanding the prospect of using the composite. It was also demonstrated in this chapter that the resulting material can be applied for the environmentally important issue of waste water cleansing. Additionally to being made from renewable resources and by a cheap and easy one-pot synthesis, the material is recyclable, since the pollutants can be recovered by washing with ethanol. Most importantly this chapter covered experiments where the reaction was performed in a crude, home-built glass vessel, fuelled – with the help of a Fresnel lens – only by direct concentrated sunlight irradiation. This concept carries the thus far presented synthetic procedures from being common laboratory syntheses to a real world application. Based on cellulose, transition metals and simple equipment, this work enabled the easy one-pot synthesis of nano-ceramic and metal nanoparticle composites otherwise not readily accessible. Furthermore were structuring and patterning techniques and synthesis routes involving only renewable resources and environmentally benign procedures established here. Thereby it has laid the foundation for a multitude of applications and pointed towards several future projects reaching from fundamental research, to application focussed research and even and industry relevant engineering project was envisioned.
Metals are often used in environments that are conducive to corrosion, which leads to a reduction in their mechanical properties and durability. Coatings are applied to corrosion-prone metals such as aluminum alloys to inhibit the destructive surface process of corrosion in a passive or active way. Standard anticorrosive coatings function as a physical barrier between the material and the corrosive environment and provide passive protection only when intact. In contrast, active protection prevents or slows down corrosion even when the main barrier is damaged. The most effective industrially used active corrosion inhibition for aluminum alloys is provided by chromate conversion coatings. However, their toxicity and worldwide restriction provoke an urgent need for finding environmentally friendly corrosion preventing systems. A promising approach to replace the toxic chromate coatings is to embed particles containing nontoxic inhibitor in a passive coating matrix. This work presents the development and optimization of effective anticorrosive coatings for the industrially important aluminum alloy, AA2024-T3 using this approach. The protective coatings were prepared by dispersing mesoporous silica containers, loaded with the nontoxic corrosion inhibitor 2-mercaptobenzothiazole, in a passive sol-gel (SiOx/ZrOx) or organic water-based layer. Two types of porous silica containers with different sizes (d ≈ 80 and 700 nm, respectively) were investigated. The studied robust containers exhibit high surface area (≈ 1000 m² g-1), narrow pore size distribution (dpore ≈ 3 nm) and large pore volume (≈ 1 mL g-1) as determined by N2 sorption measurements. These properties favored the subsequent adsorption and storage of a relatively large amount of inhibitor as well as its release in response to pH changes induced by the corrosion process. The concentration, position and size of the embedded containers were varied to ascertain the optimum conditions for overall anticorrosion performance. Attaining high anticorrosion efficiency was found to require a compromise between delivering an optimal amount of corrosion inhibitor and preserving the coating barrier properties. This study broadens the knowledge about the main factors influencing the coating anticorrosion efficiency and assists the development of optimum active anticorrosive coatings doped with inhibitor loaded containers.
Für den Einsatz in Autobatterien gibt es besondere Anforderungen an den Elektrolyten im Bereich der Energie- und Leistungsdichten, um beispielsweise thermische Verluste gering zu halten. Hochleitfähige Elektrolyte mit Leitfähigkeiten im Millisiemensbereich sind hier ebenso notwendig wie auch sichere, d.h. möglichst nicht brennbare und einen niedrigen Dampfdruck besitzende Materialien. Um diese Vorgaben zu erreichen, ist es notwendig, einen polymeren Separator zu entwickeln, welcher auf brennbare organische Lösungsmittel verzichtet und damit eine drastische Steigerung der Sicherheit gewährleistet. Gleichzeitig müssen hierbei die Leistungsvorgaben bezüglich der Leitfähigkeit erfüllt werden. Zu diesem Zweck wurde ein Konzept basierend auf der Kombination von einer polymeren sauerstoffreichen Matrix und einer ionischen Flüssigkeit entwickelt und verifiziert. Dabei wurden folgende Erkenntnisse gewonnen: 1. Es wurden neuartige diacrylierte sauerstoffreiche Matrixkomponenten mit vielen Carbonylfunktionen, für eine gute Lithiumleitfähigkeit, synthetisiert. 2. Es wurden mehrere neue ionische Flüssigkeiten sowohl auf Imidazolbasis als auch auf Ammoniumbasis synthetisiert und charakterisiert. 3. Die Einflüsse der Kationenstruktur und der Einfluss der Gegenionen im Bezug auf Schmelzpunkte und Leitfähigkeiten wurden untersucht. 4. Aus den entwickelten Materialien wurden Blendsysteme hergestellt und mittels Impedanzspektrometrie untersucht: Leitfähigkeiten von 10-4S/cm bei Raumtemperatur sind realisierbar. 5. Die Blendsysteme wurden auf ihre thermische Stabilität hin untersucht: Stabilitäten bis 250°C sind erreichbar. Dabei wird keine kristalline Struktur beobachtet.
Der Förster-Resonanzenergietransfer (FRET) liefert einen wichtigen Beitrag bei der Untersuchung kleinskaliger biologischer Systeme und Prozesse. Möglich wird dies durch die r-6-Abhängigkeit des FRET, die es erlaubt Abstände und strukturelle Änderungen weit unterhalb der Beugungsgrenze des Lichts mit hoher Sensitivität und geringem Aufwand zu bestimmen. Die besonderen photophysikalischen Eigenschaften von Terbiumkomplexen (LTC) und Quantenpunkten (QD) machen sie zu geeigneten Kandidaten für hochsensitive und störungsarme Multiplex-Abstandsmessungen in biologischen Systemen und Prozessen. Die Abstandsbestimmungen setzen jedoch eine genaueste Kenntnis des Mechanismus des Energietransfers von LTC auf QD ebenso voraus, wie das Wissen um Größe und Gestalt letzterer. Quantenpunkte haben im Vergleich zu biologischen Strukturen ähnliche Dimensionen und können nicht als punktförmig betrachtet werden, wie es bei einfacheren Farbstoffen möglich ist. Durch ihre Form kommt es zu einer Abstandsverteilung innerhalb des Donor-Akzeptorsystems. Dies beeinflusst den Energietransfer und damit die experimentellen Ergebnisse. In dieser Arbeit wurde der Energietransfer von LTC auf QD untersucht, um zu einer Aussage hinsichtlich des Mechanismus der Energieübertragung und der dabei zu berücksichtigenden photophysikalischen und strukturellen Parameter von LTC und QD zu gelangen. Mit der Annahme einer Abstandsverteilung sollten die Größen der Quantenpunkte bestimmt und der Einfluss von Form und Gestalt auf den Energietransfer betrachtet werden. Die notwendigen theoretischen und praktischen Grundlagen wurden eingangs dargestellt. Daran schlossen sich Messungen zur photophysikalischen Charakterisierung der Donoren und Akzeptoren an, die Grundlage der Berechnung der FRET-Parameter waren. Die Förster-Radien zeigten die für den FRET von LTC auf QD typischen extrem hohen Werte von bis zu 11 nm. Zeitaufgelöste Messungen der FRET-induzierten Lumineszenz der Donoren und Akzeptoren in den beiden biomolekularen Modellsystemen Zink-Histidin und Biotin-Streptavidin beschlossen den praktischen Teil. Als Donor wurde Lumi4Tb gebunden an ein Peptid bzw. Streptavidin genutzt, Akzeptoren waren fünf verschiedene, kommerziell erhältliche Quantenpunkte mit Carboxyl- bzw. Biotinfunktionalisierung. Bei allen Donor-Akzeptor-Paarungen konnte FRET beobachtet und ausgewertet werden. Es konnte gezeigt werden, dass die gesamte Emission des Terbiums zum Energietransfer beiträgt und der Orientierungsfaktor ² den Wert 2/3 annimmt. Die Charakterisierung der Bindungsverhältnisse innerhalb der FRET-Paare von LTC und QD über Verteilungsfunktionen bietet über die Form der Verteilungskurve die Möglichkeit Aussagen über die Gestalt der FRET-Partner zu treffen. So war es möglich, die mittlere Form der Quantenpunkte als Sphäre zu bestimmen. Dies entsprach, insbesondere bei den in z-Richtung des Kristallgitters elongierten Quantenpunkten, nicht den Erwartungen. Dieser Befund ermöglicht daher bei zukünftigen Messungen eine Verbesserung der Genauigkeit bei Abstandsbestimmungen mit Quantenpunkten. Neben der Ermittlung der die FRET-Verteilung bestimmenden Gestalt der Quantenpunkte konnte im Rahmen dieser Arbeit anhand vergleichender Messungen die Dicke der Polymerhülle der QD bestimmt und so gezeigt werden, dass FRET-Paare aus lumineszenten Terbiumkomplexen und Quantenpunkten in der Lage sind, Abstände im Nano- bis Sub-Nanometerbereich aufzulösen.
Die Photophysik und Photochemie von Flavinen sind aufgrund ihrer biologischen Funktion, inbesondere von Flavoproteinen, von großen Interesse. Flavoproteine spielen eine große Rolle in einer Vielzahl von biologischen Prozessen, z.B. Biolumineszenz, Entfernung von Radikalen, die bei oxidativem Stress entstehen, Photosynthese und DNA-Reparatur. Die spektroskopischen Eigenschaften des Flavin-Cofaktors machen diesen zu einem natürlichen Reporter für Veränderungen innerhalb des aktiven Zentrums. Deshalb sind die Flavoproteine eine der am meisten untersuchten Enzymfamilien. Eine biologische Aktivität des Flavins führt über einen elektronisch angeregten Zustand, wo dann, abhängig von der Aminosäureumgebung, ein bestimmter Mechanismus zu einem biologischen Prozess führt (Photozyklus). Ein wichtiges Analysetool zum Verständnis des anfänglichen Photoanregungsschritts der Flavine sind die elektronische und die Schwingungsspektroskopie. In dieser Arbeit wurden die Prozesse von Riboflavin (RF) während und nach optischer Anregung mit theoretischen Mitteln beleuchtet. Dazu wurden quantenchemische Berechnungen für Schwingungsspektren (vibratorische) von Riboflavin, auch Laktoflavin oder Vitamin B2 genannt, dem Grundmolekül der Chromophore biologischer Blaulichtrezeptoren, in dessen elektronischem Grundzustand und dessen niedrigsten angeregten Zustand durchgeführt. Weiterhin wurden vibronische (vibratorische+elektronische) Absorptionsspektren und ein vibronisches Emissionsspektrum berechnet. Die so berechneten Schwingungs- und elektronischen Spektren sind in guter qualitativer wie quantitativer Übereinstimmung mit gemessenen Werten, und helfen so, die experimentellen Signale der Photoanregung von Flavinen zuzuweisen. Unmittelbar nach der Photoanregung wurde ein Verlust des Doppelbindungscharakters im polaren Bereich des Ringssystems beobachtet, was zu der vibronischen Feinstruktur im elektronischen Absorptions- und Emissionsspektrum führte. Hier zeigte sich zudem, dass neben den vibronischen Effekten auch die Lösungsmitteleffekte wichtig für das quantitative Verständnis der Photophysik der Flavine in Lösung sind. Um Details des optischen Anregungsprozesses als initialen, elementaren Schritt zur Signalweiterleitung zu entschlüsseln, wurden ultraschnelle (femtosekundenaufgelöste) Experimente durchgeführt, die die Photoaktivierung des Flavins untersuchen. Diese Arbeit soll zu einem weiteren Verständnis und der Interpretation dieser Experimente durch das Studium der Post-Anregungsschwingungsdynamik von Riboflavin und mikrosolvatisiertem Riboflavin beitragen. Dazu wurde eine 200 fs lange Molekulardynamik in angeregten Zuständen betrachtet. Durch die Analyse charakteristischer Atombewegungen und durch die Berechnungen zeitaufgelöster Emissionsspektren fand man heraus, dass nach der optischen Anregung Schwingungen im Ringssystem des Riboflavins einsetzen. Mit Hilfe dieser Berechnungen kann die Umverteilung der Energie im angeregten Zustand beobachtet werden. Neben den theoretischen Untersuchungen zu Riboflavin in der Gasphase und auch in Lösung wurde ein Modell für eine BLUF (Blue-Light Photoreceptor Using Flavin) Domäne, ein Flavin benutzender Photorezeptor, erstellt. Hierbei zeigt sich, dass man die in dieser Arbeit angewendeten Analysemethoden auch auf biologisch relevante Systeme anwenden kann.
The aim of this thesis is the quantum dynamical study of two examples of scanning tunneling microscope (STM)-controllable, Si(100)(2x1) surface-mounted switches of atomic and molecular scale. The first example considers the switching of single H-atoms between two dangling-bond chemisorption sites on a Si-dimer of the Si(100) surface (Grey et al., 1996). The second system examines the conformational switching of single 1,5-cyclooctadiene molecules chemisorbed on the Si(100) surface (Nacci et al., 2008). The temporal dynamics are provided by the propagation of the density matrix in time via an according set of equations of motion (EQM). The latter are based on the open-system density matrix theory in Lindblad form. First order perturbation theory is used to evaluate those transition rates between vibrational levels of the system part. In order to account for interactions with the surface phonons, two different dissipative models are used, namely the bilinear, harmonic and the Ohmic bath model. IET-induced vibrational transitions in the system are due to the dipole- and the resonance-mechanism. A single surface approach is used to study the influence of dipole scattering and resonance scattering in the below-threshold regime. Further, a second electronic surface was included to study the resonance-induced switching in the above-threshold regime. Static properties of the adsorbate, e.g., potentials and dipole function and potentials, are obtained from quantum chemistry and used within the established quantum dynamical models.
Entwicklung multi-stimuli sensitiver Materialien auf der Basis von flüssigkristallinen Elastomeren
(2012)
Aufgrund der zunehmenden technischen Ansprüche der Gesellschaft sind sich aktiv bewegende Polymere in den Mittelpunkt aktueller Forschung gerückt. Diese spielen bei Anwen-dungen im Bereich von künstlichen Muskeln und Implantaten für die minimal invasive Chirurgie eine wichtige Rolle. Vor allem Formänderungs- und Formgedächtnispolymere stehen dabei im wissenschaftlichen Fokus. Während die kontaktlose Deformation einer permanenten Form in eine temporäre metastabile Form, charakteristisch für Formände-rungspolymere ist, kann bei Formgedächtnis-Materialien die temporäre Form, aufgrund der Ausbildung reversibler, temporärer Netzpunkte, fixiert werden. Ein Polymermaterial, das eine Kombination beider Funktionen aufweist würde zu einem Material führen welches kontaktlos in eine temporäre Form deformiert und in dieser fixiert werden kann. Zusätzlich würde aufgrund der kontaktlosen Deformation die Reversibilität dieser Funktion gewähr-leistet sein. Ein solches Material ist bislang noch nicht beschrieben worden. In dieser Arbeit wird untersucht, ob durch die Kopplung zweier separat schaltbarer, be-kannter Funktionen eine neue schaltbare Funktion erzielt werden kann. Daher wurden multi-stimuli sensitive Materialien entwickelt die eine Kopplung des Formänderungs- und des Formgedächtniseffektes aufweisen. Dazu wurden zwei Konzepte entwickelt, die sich hinsichtlich der Reihenfolge der verwendeten Stimuli unterscheiden. Im ersten Konzept wurden flüssigkristalline Elastomere basie-rend auf Azobenzenderivaten aufgebaut und hinsichtlich der Kombination des licht-induzierten Formänderungseffektes mit dem thermisch-induzierten Formgedächtniseffekt untersucht. Diese orientierten Netzwerke weisen oberhalb der Glasübergangstemperatur (Tg) eine kontaktlose Verformung (Biegung) durch Bestrahlung mit UV-Licht des geeigneten Wellenlängenbereichs auf, wodurch eine temporäre Form erhalten wurde. Hierbei spielt der Vernetzungsgrad eine entscheidende Rolle bezüglich der Ausprägung dieser Biegung. Eine fixierte, temporäre Form konnte durch gleichzeitiges Abkühlen des Materials unterhalb von Tg während der Bestrahlung mit UV-Licht erhalten werden. Nach erneutem Aufheizen über Tg konnte die Originalform wiederhergestellt werden. Dieser Vorgang konnte reversibel durchgeführt werden. Damit wurde gezeigt, dass eine neue schaltbare Funktion erzielt wurde, die auf der Kopplung des lichtinduzierten Formänderungs- mit dem thermisch-induzierten Formgedächtniseffekt basiert. Die Abstimmung der einzelnen Funktion wird in diesem Konzept über die Morphologie des Systems gewährleistet. Diese neue Funktion ermöglicht eine kontaktlose Deformation des Materials in eine temporäre Form, welche fixiert werden kann. Im zweiten Konzept wurde eine Kopplung des thermisch induzierten Formänderungs- mit dem licht-induzierten Formgedächtniseffekt angestrebt. Um dies zu realisieren wurden nematisch, flüssigkristalline Hauptkettenelastomere (NMC-LCE) entwickelt, die eine nied-rige Übergangstemperatur der nematischen in die isotrope Phase (TNI), als auch einen aus-geprägten thermisch induzierten Formänderungseffekt aufweisen. Zusätzlich wurde eine photosensitive Schicht aufgebaut, die Cinnamylidenessigsäuregruppen in der Seitenkette eines Polysiloxanrückgrates aufweist. Die Reversibilität der photoinduzierten [2+2]-Cycloaddition konnte für dieses photosensitive Polymer beobachtet werden, wodurch die-ses Polymersystem in der Lage ist reversible temporäre Netzpunkte, aufgrund der Bestrah-lung mit UV-Licht, auszubilden. Die kovalente Anbindung der photosensitiven Schicht an die Oberfläche des flüssigkristallinen Kerns wurde erfolgreich durchgeführt, wodurch ein Multi-Komponenten-System aufgebaut wurde. Die Kombination des thermisch-induzierten Formänderungs- mit dem licht-induzierten Formgedächtniseffektes wurde anhand dieses Systems untersucht. Während die Einzelkomponenten die erforderliche Funktion zeigten, ist hier noch Arbeit in der Abstimmung beider Strukturen zu leisten. Insbesondere die Variation der Schichtdicken beider Komponenten steht im Fokus zukünftiger Arbeiten. In dieser Arbeit wurde durch die Kopplung von zwei separat schaltbaren, bekannten Funktionen eine neue schaltbare Funktion erzielt. Dies setzt voraus, dass die Einzelkomponenten hinsichtlich einer Funktion schaltbar sind und in einem Material integriert werden können. Des Weiteren müssen die beiden Funktionen mit unterschiedlichen Stimuli geschaltet werden. Ein wichtiger Schritt bei der Kopplung der Funktionen, ist die Abstimmung der beiden Komponenten. Dies kann über die Variation der Morphologie oder der Struktur erzielt werden. Anhand der Vielzahl der vorhandenen stimuli-sensitiven Materialien sind verschiedene Kopplungsmöglichkeiten vorhanden. Demnach wird erwartet, dass auf diesem Gebiet weitere neue Funktionen erzielt werden können.
Typische assoziative Verdicker für wässrige Systeme basieren auf linearen, doppelt hydrophob endmodifizierten Poly(ethylenglykolen) (PEGs). Diese Polymere aggregieren aufgrund ihrer Struktur in wässriger Lösung und bilden ein Netzwerk aus verbrückten Polymer-Mizellen. Dabei kann ein Polymer-Molekül maximal zwei Mizellen miteinander verbinden. Bisher ist unklar, wie die Anzahl der Endgruppen eines verzweigten, mehrfach hydrophob endmodifizierten hydrophilen Polymers die Struktur und Dynamik solcher Netzwerke beeinflusst. Die Synthese verzweigter Polymere auf PEG-Basis erfolgt mittels lebender ionischer Polymerisation und ist experimentell aufwändig. Das Einführen hydrophober Endgruppen erfordert zusätzliche Synthese-Schritte. In dieser Arbeit wurden hydrophile Sternpolymere mit hydrophoben Endgruppen in einem Schritt hergestellt. Dazu wurde die Technik der radikalischen Polymerisation unter Kettenübertragung durch reversible Addition und anschließende Fragmentierung (reversible addition-fragmentation chain transfer, RAFT) genutzt. Die Synthese der Sternpolymere erfolgte von einem multifunktionalen Kern, der die R-Gruppe der RAFT-Kettenüberträger (chain transfer agents, CTAs) bildete. Die dazu benötigten CTAs wurden so konzipiert, dass mit ihrer Hilfe sowohl die Anzahl der Arme des Sternpolymers (von 2 bis 4), als auch die Länge der hydrophoben Endgruppe (C4, C12, C18) variiert werden konnte. Der große Vorteil der RAFT-Polymerisation ist, dass sie viele polare Monomere für die Synthese der hydrophilen Arme des Sternpolymers toleriert. In dieser Arbeit wurden als Modell-Monomere Oligo(ethylenglykol)methylether-acrylat (OEGA) und N,N-Dimethylacrylamid (DMA) eingesetzt. Beide Monomere bilden nicht-ionische hydrophile Polymere. Poly(OEGA) ist ein Kammpolymer, das auf PEG basiert. Poly(DMA) besitzt dagegen eine deutlich kompaktere Struktur. Die erhaltenen amphiphilen Sternpolymere wurden umfassend molekular charakterisiert. Die Molmassen wurden mit verschiedenen GPC-Systemen bestimmt und der Grad der Endgruppenfunktionalisierung wurde mittels UV/Vis- und 1H-NMR-Spektroskopie überprüft. Die Polymerisation von OEGA zeigt mit den CTAs einige Charakteristika der Polymerisation mit reversibler Deaktivierung (RDRP, auch „kontrollierte radikalische Polymerisation“), wird aber durch Kettenübertragung zum Monomer bzw. Polymer gestört. Diese Nebenreaktion ist auf die Struktur des Monomers als Oligoether zurückzuführen. Bei allen untersuchten Polymerisationen von DMA mit den multifunktionalen CTAs steigt die Molmasse linear mit dem Umsatz. Die erhaltenen Polymere zeigen durchweg monomodale und enge Molmassenverteilungen (PDI ≤ 1,2). Die Molmassen lassen sich in einem weiten Bereich von 25 kg/mol bis 150 kg/mol einstellen und die Endgruppen der Polymere bleiben zu 90 % erhalten. Während die Polymerisation von DMA sowohl mit den di- als auch den trifunktionalen CTAs innerhalb von 3 h zu quantitativen Umsätzen verläuft, wird der quantitative Umsatz des Monomers bei der Polymerisation mit tetrafunktionalen CTAs erst nach 4 h erreicht. Diese Verzögerung ist auf eine Retardierung in der Anfangsphase der Polymerisation zurückzuführen, die sich aus der besonderen Struktur der tetrafunktionalen CTAs erklärt. Auf dem System zur Polymerisation von DMA aufbauend ließen sich Gradienten-Block-Copolymere in Eintopfreaktionen herstellen. Dazu wurde nach Erreichen des quantitativen Umsatzes von DMA ein zweites Monomer zur Reaktionsmischung gegeben. Mit Ethylacrylat (EtA) wurden so lineare amphiphile symmetrische Triblock-Copolymere erhalten. Dabei wurde die Länge des hydrophoben Blocks durch unterschiedliche Mengen an EtA variiert. Mit N,N-Diethylacrylamid (DEA) wurden lineare symmetrische Triblock-Copolymere sowie 3-Arm Stern-Diblock-Copolymere hergestellt, die über einen thermisch schaltbaren zweiten Block verfügen. Bei diesen Polymeren lässt sich die Länge des hydrophoben Teils in situ durch Veränderung der Temperatur variieren. Das Verhalten der amphiphilen Sternpolymere in wässriger Lösung und in Mikroemulsion wurde im Rahmen einer Kooperation an der TU Berlin mit Hilfe von Kleinwinkel-Neutronenstreuung (SANS), dynamischer Lichtstreuung (DLS) und Rheologie untersucht. Die Polymere wirken durch Assoziation der hydrophoben Endgruppen als effektive Verdicker sowohl allein in wässriger Lösung als auch in Mikroemulsion. Die Struktur des gebildeten Netzwerks hängt dabei von der Konzentration des Polymers in der Lösung und der Länge der Endgruppe (Hydrophobie) ab. Die dynamischen Eigenschaften der Lösungen werden außerdem durch die Anzahl der Arme der Polymere bestimmt.
In this work new fluorinated and non-fluorinated mono- and bifunctional trithiocarbonates of the structure Z-C(=S)-S-R and Z-C(=S)-S-R-S-C(=S)-Z were synthesized for the use as chain transfer agents (CTAs) in the RAFT-process. All newly synthesized CTAs were tested for their efficiency to moderate the free radical polymerization process by polymerizing styrene (M3). Besides characterization of the homopolymers by GPC measurements, end- group analysis of the synthesized block copolymers via 1H-, 19F-NMR, and in some cases also UV-vis spectroscopy, were performed attaching suitable fluorinated moieties to the Z- and/or R-groups of the CTAs. Symmetric triblock copolymers of type BAB and non-symmetric fluorine end- capped polymers were accessible using the RAFT process in just two or one polymerization step. In particular, the RAFT-process enabled the controlled polymerization of hydrophilic monomers such as N-isopropylacrylamide (NIPAM) (M1) as well as N-acryloylpyrrolidine (NAP) (M2) for the A-blocks and of the hydrophobic monomers styrene (M3), 2-fluorostyrene (M4), 3-fluorostyrene (M5), 4-fluorostyrene (M6) and 2,3,4,5,6-pentafluorostyrene (M7) for the B-blocks. The properties of the BAB-triblock copolymers were investigated in dilute, concentrated and highly concentrated aqueous solutions using DLS, turbidimetry, 1H- and 19F-NMR, rheology, determination of the CMC, foam height- and surface tension measurements and microscopy. Furthermore, their ability to stabilize emulsions and microemulsions and the wetting behaviour of their aqueous solutions on different substrates was investigated. The behaviour of the fluorine end-functionalized polymers to form micelles was studied applying DLS measurements in diluted organic solution. All investigated BAB-triblock copolymers were able to form micelles and show surface activity at room temperature in dilute aqueous solution. The aqueous solutions displayed moderate foam formation. With different types and concentrations of oils, the formation of emulsions could be detected using a light microscope. A boosting effect in microemulsions could not be found adding BAB-triblock copolymers. At elevated polymer concentrations, the formation of hydrogels was proved applying rheology measurements.
Porous materials (e.g. zeolites, activated carbon, etc.) have found various applications in industry, such as the use as sorbents, catalyst supports and membranes for separation processes. Recently, much attention has been focused on synthesizing porous polymer materials. A vast amount of tailor-made polymeric systems with tunable properties has been investigated. Very often, however, the starting substances for these polymers are of petrochemical origin, and the processes are all in all not sustainable. Moreover, the new polymers have challenged existing characterizing methodologies. These have to be further developed to address the upcoming demands of the novel materials. Some standard techniques for the analysis of porous substances like nitrogen sorption at 77 K do not seem to be sufficient to answer all arising questions about the microstructure of such materials. In this thesis, microporous polymers from an abundant natural resource, betulin, will be presented. Betulin is a large-scale byproduct of the wood industry, and its content in birch bark can reach 30 wt.%. Based on its rigid structure, polymer networks with intrinsic microporosity could be synthesized and characterized. Apart from standard nitrogen and carbon dioxide sorption at 77 K and 273 K, respectively, gas sorption has been examined not only with various gases (hydrogen and argon) but also at various temperatures. Additional techniques such as X-ray scattering and xenon NMR have been utilized to enable insight into the microporous structure of the material. Starting from insoluble polymer networks with promising gas selectivities, soluble polyesters have been synthesized and processed to a cast film. Such materials are feasible for membrane applications in gas separation. Betulin as a starting compound for polyester synthesis has aided to prepare, and for the first time to thoroughly analyse a microporous polyester with respect to its pores and microstructure. It was established that nitrogen adsorption at 87 K can be a better method to solve the microstructure of the material. In addition to that, other betulin-based polymers such as polyurethanes and polyethylene glycol bioconjugates are presented. Altogether, it has been shown that as an abundant natural resource betulin is a suitable and cheap starting compound for some polymers with various potential applications.
The present work is devoted to establishing of a new generation of self-healing anti-corrosion coatings for protection of metals. The concept of self-healing anticorrosion coatings is based on the combination of the passive part, represented by the matrix of conventional coating, and the active part, represented by micron-sized capsules loaded with corrosion inhibitor. Polymers were chosen as the class of compounds most suitable for the capsule preparation. The morphology of capsules made of crosslinked polymers, however, was found to be dependent on the nature of the encapsulated liquid. Therefore, a systematic analysis of the morphology of capsules consisting of a crosslinked polymer and a solvent was performed. Three classes of polymers such as polyurethane, polyurea and polyamide were chosen. Capsules made of these polymers and eight solvents of different polarity were synthesized via interfacial polymerization. It was shown that the morphology of the resulting capsules is specific for every polymer-solvent pair. Formation of capsules with three general types of morphology, such as core-shell, compact and multicompartment, was demonstrated by means of Scanning Electron Microscopy. Compact morphology was assumed to be a result of the specific polymer-solvent interactions and be analogues to the process of swelling. In order to verify the hypothesis, pure polyurethane, polyurea and polyamide were synthesized; their swelling behavior in the solvents used as the encapsulated material was investigated. It was shown that the swelling behavior of the polymers in most cases correlates with the capsules morphology. Different morphologies (compact, core-shell and multicompartment) were therefore attributed to the specific polymer-solvent interactions and discussed in terms of “good” and “poor” solvent. Capsules with core-shell morphology are formed when the encapsulated liquid is a “poor” solvent for the chosen polymer while compact morphologies are formed when the solvent is “good”. Multicompartment morphology is explained by the formation of infinite networks or gelation of crosslinked polymers. If gelation occurs after the phase separation in the system is achieved, core-shell morphology is present. If gelation of the polymer occurs far before crosslinking is accomplished, further condensation of the polymer due to the crosslinking may lead to the formation of porous or multicompartment morphologies. It was concluded that in general, the morphology of capsules consisting of certain polymer-solvent pairs can be predicted on the basis of polymer-solvent behavior. In some cases, the swelling behavior and morphology may not match. The reasons for that are discussed in detail in the thesis. The discussed approach is only capable of predicting capsule morphology for certain polymer-solvent pairs. In practice, the design of the capsules assumes the trial of a great number of polymer-solvent combinations; more complex systems consisting of three, four or even more components are often used. Evaluation of the swelling behavior of each component pair of such systems becomes unreasonable. Therefore, exploitation of the solubility parameter approach was found to be more useful. The latter allows consideration of the properties of each single component instead of the pair of components. In such a manner, the Hansen Solubility Parameter (HSP) approach was used for further analysis. Solubility spheres were constructed for polyurethane, polyurea and polyamide. For this a three-dimensional graph is plotted with dispersion, polar and hydrogen bonding components of solubility parameter, obtained from literature, as the orthogonal axes. The HSP of the solvents are used as the coordinates for the points on the HSP graph. Then a sphere with a certain radius is located on a graph, and the “good” solvents would be located inside the sphere, while the “poor” ones are located outside. Both the location of the sphere center and the sphere radius should be fitted according to the information on polymer swelling behavior in a number of solvents. According to the existing correlation between the capsule morphology and swelling behavior of polymers, the solvents located inside the solubility sphere of a polymer give capsules with compact morphologies. The solvents located outside the solubility sphere of the solvent give either core-shell or multicompartment capsules in combination with the chosen polymer. Once the solubility sphere of a polymer is found, the solubility/swelling behavior is approximated to all possible substances. HSP theory allows therefore prediction of polymer solubility/swelling behavior and consequently the capsule morphology for any given substance with known HSP parameters on the basis of limited data. The latter makes the theory so attractive for application in chemistry and technology, since the choice of the system components is usually performed on the basis of a large number of different parameters that should mutually match. Even slight change of the technology sometimes leads to the necessity to find the analogue of this or that solvent in a sense of solvency but carrying different chemistry. Usage of the HSP approach in this case is indispensable. In the second part of the work examples of the HSP application for the fabrication of capsules with on-demand-morphology are presented. Capsules with compact or core-shell morphology containing corrosion inhibitors were synthesized. Thus, alkoxysilanes possessing long hydrophobic tail, combining passivating and water-repelling properties, were encapsulated in polyurethane shell. The mechanism of action of the active material required core-shell morphology of the capsules. The new hybrid corrosion inhibitor, cerium diethylhexyl phosphate, was encapsulated in polyamide shells in order to facilitate the dispersion of the substance and improve its adhesion to the coating matrix. The encapsulation of commercially available antifouling agents in polyurethane shells was carried out in order to control its release behavior and colloidal stability. Capsules with compact morphology made of polyurea containing the liquid corrosion inhibitor 2-methyl benzothiazole were synthesized in order to improve the colloidal stability of the substance. Capsules with compact morphology allow slower release of the liquid encapsulated material compared to the core-shell ones. If the “in-situ” encapsulation is not possible due to the reaction of the oil-soluble monomer with the encapsulated material, a solution was proposed: loading of the capsules should be performed after monomer deactivation due to the accomplishment of the polymerization reaction. Capsules of desired morphologies should be preformed followed by the loading step. In this way, compact polyurea capsules containing the highly effective but chemically active corrosion inhibitors 8-hydroxyquinoline and benzotriazole were fabricated. All the resulting capsules were successfully introduced into model coatings. The efficiency of the resulting “smart” self-healing anticorrosion coatings on steel and aluminium alloy of the AA-2024 series was evaluated using characterization techniques such as Scanning Vibrating Electron Spectroscopy, Electrochemical Impedance Spectroscopy and salt-spray chamber tests.
Ein viel diskutiertes Thema unserer Zeit ist die Zukunft der Energiegewinnung und Speicherung. Dabei nimmt die Nanowissenschaft eine bedeutende Rolle ein; sie führt zu einer Effizienzsteigerung bei der Speicherung und Gewinnung durch bereits bekannte Materialien und durch neue Materialien. In diesem Zusammenhang ist die Chemie Wegbereiter für Nanomaterialien. Allerdings führen bisher die meisten bekannten Synthesen von Nanopartikeln zu undefinierten Partikeln. Eine einfache, kostengünstige und sichere Synthese würde die Möglichkeit einer breiten Anwendung und Skalierbarkeit bieten. In dieser Arbeit soll daher die Darstellung der einfachen Synthese von Mangannitrid-, Aluminiumnitrid-, Lithiummangansilicat-, Zirkonium-oxinitrid- und Mangancarbonatnanopartikel betrachtet werden. Dabei werden die sogenannte Harnstoff-Glas-Route als eine Festphasensynthese und die Solvothermalsynthese als typische Flüssigphasensynthese eingesetzt. Beide Synthesewege führen zu definierten Partikelgrößen und interessanten Morphologien und ermöglichen eine Einflussnahme auf die Produkte. Im Falle der Synthese der Mangannitridnanopartikel mithilfe der Harnstoff-Glas-Route führt diese zu Nanopartikeln mit Kern-Hülle-Struktur, deren Einsatz als Konversionsmaterial erstmalig vorgestellt wird. Mit dem Ziel einer leichteren Anwendung von Nanopartikeln wird eine einfache Beschichtung von Oberflächen mit Nanopartikeln mithilfe der Rotationsbeschichtung beschrieben. Es entstand ein Gemisch aus MnN0,43/MnO-Nanopartikeln, eingebettet in einem Kohlenstofffilm, dessen Untersuchung als Konversionsmaterial hohe spezifische Kapazitäten (811 mAh/g) zeigt, die die von dem konventionellen Anodenmaterial Graphit (372 mAh/g) übersteigt. Neben der Synthese des Anodenmaterials wurde ebenfalls die des Kathodenmaterials Li2MnSiO4-Nanopartikeln mithilfe der Harnstoff-Glas-Route vorgestellt. Mithilfe der Synthese von Zirkoniumoxinitridnanopartikeln Zr2ON2 kann eine einfache Einflussnahme auf das gewünschte Produkt durch die Variation derReaktionsbedingungen, wie Harnstoffmenge oder Reaktionstemperatur, bei der Harnstoff-Glas-Route demonstriert werden. Der Zusatz von kleinsten Mengen an Ammoniumchlorid vermeidet, dass sich Kohlenstoff im Endprodukt bildet und führt so zu gelben Zr2ON2-Nanopartikeln mit einer Größe d = 8 nm, die Halbleitereigen-schaften besitzen. Die Synthese von Aluminiumnitridnanopartikeln führt zu kristallinen Nanopartikeln, die in eine amorphe Matrix eingebettet sind. Die Solvothermalsynthese von Mangancarbonatnanopartikel lässt neue Morphologien in Form von Nanostäbchen entstehen, die zu schuppenartigen sphärischen Überstrukturen agglomeriert sind.
Taking advantage of ATRP and using functionalized initiators, different functionalities were introduced in both α and ω chain-ends of synthetic polymers. These functionalized polymers could then go through modular synthetic pathways such as click cycloaddition (copper-catalyzed or copper-free) or amidation to couple synthetic polymers to other synthetic polymers, biomolecules or silica monoliths. Using this general strategy and designing these co/polymers so that they are thermoresponsive, yet bioinert and biocompatible with adjustable cloud point values (as it is the case in the present thesis), the whole generated system becomes "smart" and potentially applicable in different branches. The applications which were considered in the present thesis were in polymer post-functionalization (in situ functionalization of micellar aggregates with low and high molecular weight molecules), hydrophilic/hydrophobic tuning, chromatography and bioconjugation (enzyme thermoprecipitation and recovery, improvement of enzyme activity). Different α-functionalized co/polymers containing cholesterol moiety, aldehyde, t-Boc protected amine, TMS-protected alkyne and NHS-activated ester were designed and synthesized in this work.
The underlying motivation for the work carried out for this thesis was the growing need for more sustainable technologies. The aim was to synthesize a “palette” of functional nanomaterials using the established technique of hydrothermal carbonization (HTC). The incredible diversity of HTC was demonstrated together with small but steady advances in how HTC can be manipulated to tailor material properties for specific applications. Two main strategies were used to modify the materials obtained by HTC of glucose, a model precursor representing biomass. The first approach was the introduction of heteroatoms, or “doping” of the carbon framework. Sulfur was for the first time introduced as a dopant in hydrothermal carbon. The synthesis of sulfur and sulfur/nitrogen doped microspheres was presented whereby it was shown that the binding state of sulfur could be influenced by varying the type of sulfur source. Pyrolysis may additionally be used to tune the heteroatom binding states which move to more stable motifs with increasing pyrolysis temperature. Importantly, the presence of aromatic binding states in the as synthesized hydrothermal carbon allows for higher heteroatom retention levels after pyrolysis and hence more efficient use of dopant sources. In this regard, HTC may be considered as an “intermediate” step in the formation of conductive heteroatom doped carbon. To assess the novel hydrothermal carbons in terms of their potential for electrochemical applications, materials with defined nano-architectures and high surface areas were synthesized via templated, as well as template-free routes. Sulfur and/or nitrogen doped carbon hollow spheres (CHS) were synthesized using a polystyrene hard templating approach and doped carbon aerogels (CA) were synthesized using either the albumin directed or borax-mediated hydrothermal carbonization of glucose. Electrochemical testing showed that S/N dual doped CHS and aerogels derived via the albumin approach exhibited superior catalytic performance compared to solely nitrogen or sulfur doped counterparts in the oxygen reduction reaction (ORR) relevant to fuel cells. Using the borax mediated aerogel formation, nitrogen content and surface area could be tuned and a carbon aerogel was engineered to maximize electrochemical performance. The obtained sample exhibited drastically improved current densities compared to a platinum catalyst (but lower onset potential), as well as excellent long term stability. In the second approach HTC was carried out at elevated temperatures (550 °C) and pressure (50 bar), corresponding to the superheated vapor regime (htHTC). It was demonstrated that the carbon materials obtained via htHTC are distinct from those obtained via ltHTC and subsequent pyrolysis at 550 °C. No difference in htHTC-derived material properties could be observed between pentoses and hexoses. The material obtained from a polysaccharide exhibited a slightly lower degree of carbonization but was otherwise similar to the monosaccharide derived samples. It was shown that in addition to thermally induced carbonization at 550 °C, the SHV environment exhibits a catalytic effect on the carbonization process. The resulting materials are chemically inert (i.e. they contain a negligible amount of reactive functional groups) and possess low surface area and electronic conductivity which distinguishes them from carbon obtained from pyrolysis. Compared to the materials presented in the previous chapters on chemical modifications of hydrothermal carbon, this makes them ill-suited candidates for electronic applications like lithium ion batteries or electrocatalysts. However, htHTC derived materials could be interesting for applications that require chemical inertness but do not require specific electronic properties. The final section of this thesis therefore revisited the latex hard templating approach to synthesize carbon hollow spheres using htHTC. However, by using htHTC it was possible to carry out template removal in situ because the second heating step at 550 °C was above the polystyrene latex decomposition temperature. Preliminary tests showed that the CHS could be dispersed in an aqueous polystyrene latex without monomer penetrating into the hollow sphere voids. This leaves the stagnant air inside the CHS intact which in turn is promising for their application in heat and sound insulating coatings. Overall the work carried out in this thesis represents a noteworthy development in demonstrating the great potential of sustainable carbon materials.
In this work, the synthesis of biopolymer-based hydrogel networks with defined architecture is presented. In order to obtain materials with defined properties, the chemoselective copper-catalyzed azide-alkyne cycloaddition (or Click Chemistry) was used for the synthesis of gelatin-based hydrogels. Alkyne-functionalized gelatin was reacted with four different diazide crosslinkers above its sol-gel transition to suppress the formation of triple helices. By variation of the crosslinking density and the crosslinker flexibility, the swelling (Q: 150-470 vol.-%;) and the Young’s and shear moduli (E: 50 kPa - 635 kPa, G’: 0.1 kPa - 16 kPa) could be tuned in the kPa range. In order to understand the network structure, a method based on the labelling of free functional groups within the hydrogel was developed. Gelatin-based hydrogels were incubated with alkyne-functionalized fluorescein to detect the free azide groups, resulting from the formation of dangling chains. Gelatin hydrogels were also incubated with azido-functionalized fluorescein to check the presence of alkyne groups available for the attachment of bioactive molecules. By using confocal laser scanning microscopy and fluorescence spectroscopy, the amount of crosslinking, grafting and free alkyne groups could be determined. Dangling chains were observed in samples prepared by using an excess of crosslinker and also when using equimolar amounts of alkyne:azide. In the latter case the amount of dangling chains was affected by the crosslinker structure. Specifically, 0.1% of dangling chains were found using 4,4’-diazido-2,2’-stilbene-disulfonic acid as cosslinker, 0.06% with 1,8-diazidooctane, 0.05% with 1,12-diazidododecane and 0.022 % with PEG-diazide. This observation could be explained considering the structure of the crosslinkers. During network formation, the movements of the gelatin chains are restricted due to the formation of covalent netpoints. A further crosslinking will be possible only in the case of crosslinker that are flexible and long enough to reach another chain. The method used to obtain defined gelatin-based hydrogels enabled also the synthesis of hyaluronic acid-based hydrogels with tailorable properties. Alkyne-functionalized hyaluronic acid was crosslinked with three different linkers having two terminal azide functionalities. By variation of the crosslinking density and crosslinker type, hydrogels with elastic moduli in the range of 0.5-3 kPa have been prepared. The variation of the crosslinking density and crosslinker type had furthermore an influence also on the hydrolytic and enzymatic degradation of gelatin-based hydrogels. Hydrogels with a low crosslinker amount experienced a faster decrease in mass loss and elastic modulus compared to hydrogels with higher crosslinker content. Moreover, the structure of the crosslinker had a strong influence on the enzymatic degradation. Hydrogels containing a crosslinker with a rigid structure were much more resistant to enzymatic degradation than hydrogels containing a flexible crosslinker. During hydrolytic degradation, the hydrogel became softer while maintaining the same outer dimensions. These observations are in agreement with a bulk degradation mechanism, while the decrease in size of the hydrogels during enzymatic degradation suggested a surface erosion mechanism. Because of the use of small amount of crosslinker (0.002 mol.% 0.02 mol.%) the networks synthesized can still be defined as biopolymer-based hydrogels. However, they contain a small percentage of synthetic residues. Alternatively, a possible method to obtain biopolymer-based telechelics, which could be used as crosslinkers, was investigated. Gelatin-based fragments with defined molecular weight were obtained by controlled degradation of gelatin with hydroxylamine, due to its specific action on asparaginyl-glycine bonds. The reaction of gelatin with hydroxylamine resulted in fragments with molecular weights of 15, 25, 37, and 50 kDa (determined by SDS-PAGE) independently of the reaction time and conditions. Each of these fragments could be potentially used for the synthesis of hydrogels in which all components are biopolymer-based materials.
This work describes the synthesis and characterization of stimuli-responsive polymers made by reversible addition-fragmentation chain transfer (RAFT) polymerization and the investigation of their self-assembly into “smart” hydrogels. In particular the hydrogels were designed to swell at low temperature and could be reversibly switched to a collapsed hydrophobic state by rising the temperature. Starting from two constituents, a short permanently hydrophobic polystyrene (PS) block and a thermo-responsive poly(methoxy diethylene glycol acrylate) (PMDEGA) block, various gelation behaviors and switching temperatures were achieved. New RAFT agents bearing tert-butyl benzoate or benzoic acid groups, were developed for the synthesis of diblock, symmetrical triblock and 3-arm star block copolymers. Thus, specific end groups were attached to the polymers that facilitate efficient macromolecular characterization, e.g by routine 1H-NMR spectroscopy. Further, the carboxyl end-groups allowed functionalizing the various polymers by a fluorophore. Because reports on PMDEGA have been extremely rare, at first, the thermo-responsive behavior of the polymer was investigated and the influence of factors such as molar mass, nature of the end-groups, and architecture, was studied. The use of special RAFT agents enabled the design of polymer with specific hydrophobic and hydrophilic end-groups. Cloud points (CP) of the polymers proved to be sensitive to all molecular variables studied, namely molar mass, nature and number of the end-groups, up to relatively high molar masses. Thus, by changing molecular parameters, CPs of the PMDEGA could be easily adjusted within the physiological interesting range of 20 to 40°C. A second responsivity, namely to light, was added to the PMDEGA system via random copolymerization of MDEGA with a specifically designed photo-switchable azobenzene acrylate. The composition of the copolymers was varied in order to determine the optimal conditions for an isothermal cloud point variation triggered by light. Though reversible light-induced solubility changes were achieved, the differences between the cloud points before and after the irradiation were small. Remarkably, the response to light differed from common observations for azobenzene-based systems, as CPs decreased after UV-irradiation, i.e with increasing content of cis-azobenzene units. The viscosifying and gelling abilities of the various block copolymers made from PS and PMDEGA blocks were studied by rheology. Important differences were observed between diblock copolymers, containing one hydrophobic PS block only, the telechelic symmetrical triblock copolymers made of two associating PS termini, and the star block copolymers having three associating end blocks. Regardless of their hydrophilic block length, diblock copolymers PS11 PMDEGAn were freely flowing even at concentrations as high as 40 wt. %. In contrast, all studied symmetrical triblock copolymers PS8-PMDEGAn-PS8 formed gels at low temperatures and at concentrations as low as 3.5 wt. % at best. When heated, these gels underwent a gel-sol transition at intermediate temperatures, well below the cloud point where phase separation occurs. The gel-sol transition shifted to markedly higher transition temperatures with increasing length of the hydrophilic inner block. This effect increased also with the number of arms, and with the length of the hydrophobic end blocks. The mechanical properties of the gels were significantly altered at the cloud point and liquid-like dispersions were formed. These could be reversibly transformed into hydrogels by cooling. This thesis demonstrates that high molar mass PMDEGA is an easily accessible, presumably also biocompatible and at ambient temperature well water-soluble, non-ionic thermo-responsive polymer. PMDEGA can be easily molecularly engineered via the RAFT method, implementing defined end-groups, and producing different, also complex, architectures, such as amphiphilic triblock and star block copolymers, having an analogous structure to associative telechelics. With appropriate design, such amphiphilic copolymers give way to efficient, “smart” viscosifiers and gelators displaying tunable gelling and mechanical properties.
The need to reduce humankind reliance on fossil fuels by exploiting sustainably the planet renewable resources is a major driving force determining the focus of modern material research. For this reason great interest is nowadays focused on finding alternatives to fossil fuels derived products/materials. For the short term the most promising substitute is undoubtedly biomass, since it is the only renewable and sustainable alternative to fossil fuels as carbon source. As a consequence efforts, aimed at finding new synthetic approaches to convert biomass and its derivatives into carbon-based materials, are constantly increasing. In this regard, hydrothermal carbonisation (HTC) has shown to be an effective means of conversion of biomass-derived precursors into functional carbon materials. However the attempts to convert raw biomass, in particular lignocellulosic one, directly into such products have certainly been rarer. Unlocking the direct use of these raw materials as carbon precursors would definitely be beneficial in terms of HTC sustainability. For this reason, in this thesis the HTC of carbohydrate and protein-rich biomass was systematically investigated, in order to obtain more insights on the potentials of this thermochemical processing technique in relation to the production of functional carbon materials from crude biomass. First a detailed investigation on the HTC conversion mechanism of lignocellulosic biomass and its single components (i.e. cellulose, lignin) was developed based on a comparison with glucose HTC, which was adopted as a reference model. In the glucose case it was demonstrated that varying the HTC temperature allowed tuning the chemical structure of the synthesised carbon materials from a highly cross-linked furan-based structure (T = 180oC) to a carbon framework composed of polyaromatic arene-like domains. When cellulose or lignocellulosic biomass was used as carbon precursor, the furan rich structure could not be isolated at any of the investigated processing conditions. These evidences were indicative of a different HTC conversion mechanism for cellulose, involving reactions that are commonly observed during pyrolytic processes. The evolution of glucose-derived HTC carbon chemical structure upon pyrolysis was also investigated. These studies revealed that upon heat treatment (Investigated temperatures 350 – 900 oC) the furan-based structure was progressively converted into highly curved aromatic pre-graphenic domains. This thermal degradation process was observed to produce an increasingly more hydrophobic surface and considerable microporosity within the HTC carbon structure. In order to introduce porosity in the HTC carbons derived from lignocellulosic biomass, KOH chemical activation was investigated as an HTC post-synthesis functionalisation step. These studies demonstrated that HTC carbons are excellent precursors for the production of highly microporous activated carbons (ACs) and that the porosity development upon KOH chemical activation is dependent on the chemical structure of the HTC carbon, tuned by employing different HTC temperatures. Preliminary testing of the ACs for CO2 capture or high pressure CH4 storage yielded very promising results, since the measured uptakes of both adsorbates (i.e. CO2 and CH4) were comparable to top-performing and commercially available adsorbents, usually employed for these end-applications. The combined use of HTC and KOH chemical activation was also employed to produce highly microporous N-doped ACs from microalgae. The hydrothermal treatment of the microalgae substrate was observed to cause the depletion of the protein and carbohydrate fractions and the near complete loss (i.e. 90%) of the microalgae N-content, as liquid hydrolysis/degradation products. The obtained carbonaceous product showed a predominantly aliphatic character indicating the presence of alkyl chains presumably derived from the lipid fractions. Addition of glucose to the initial reaction mixture was found out to be extremely beneficial, because it allowed the fixation of a higher N amount, in the algae derived HTC carbons (i.e. 60%), and the attainment of higher product yields (50%). Both positive effects were attributed to Maillard type cascade reactions taking place between the monosaccharides and the microalgae derived liquid hydrolysis/degradation products, which were in this way recovered from the liquid phase. KOH chemical activation of the microalgae/glucose mixture derived HTC carbons produced highly microporous N-doped carbons. Although the activation process led to a major reduction of the N-content, the retained N-amount in the ACs was still considerable. These features render these materials ideal candidates for supercapacitors electrodes, since they provide extremely high surface areas, for the formation of electric double-layer, coupled to abundant heteroatom doping (i.e. N and O) necessary to obtain a pseudocapacitance contribution.
In this work, the development of a new molecular building block, based on synthetic peptides derived from decorin, is presented. These peptides represent a promising basis for the design of polymer-based biomaterials that mimic the ECM on a molecular level and exploit specific biological recognition for technical applications. Multiple sequence alignments of the internal repeats of decorin that formed the inner and outer surface of the arch-shaped protein were used to develop consensus sequences. These sequences contained conserved sequence motifs that are likely to be related to structural and functional features of the protein. Peptides representative for the consensus sequences were synthesized by microwave-assisted solid phase peptide synthesis and purified by RP-HPLC, with purities higher than 95 mol%. After confirming the desired masses by MALDI-TOF-MS, the primary structure of each peptide was investigated by 1H and 2D NMR, from which a full assignment of the chemical shifts was obtained. The characterization of the peptides conformation in solution was performed by CD spectroscopy, which demonstrated that using TFE, the peptides from the outer surface of decorin show a high propensity to fold into helical structures as observed in the original protein. To the contrary, the peptides from the inner surface did not show propensity to form stable secondary structure. The investigation of the binding capability of the peptides to Collagen I was performed by surface plasmon resonance analyses, from which all but one of the peptides representing the inner surface of decorin showed binding affinity to collagen with values of dissociation constant between 2•10-7 M and 2.3•10-4 M. On the other hand, the peptides representative for the outer surface of decorin did not show any significant interaction to collagen. This information was then used to develop experimental demonstration for the binding capabilities of the peptides from the inner surface of decorin to collagen even when used in more complicated situations close to possible appications. With this purpose, the peptide (LRELHLNNN) which showed the highest binding affinity to collagen (2•10-7 M) was functionalized with an N-terminal triple bond in order to obtain a peptide dimer via copper(I)-catalyzed cycloaddition reaction with 4,4'-diazidostilbene-2,2'-disulfonic acid. Rheological measurements showed that the presence of the peptide dimer was able to enhance the elastic modulus (G') of a collagen gel from ~ 600 Pa (collagen alone) to ~ 2700 Pa (collagen and peptide dimer). Moreover, it was shown that the mechanical properties of a collagen gel can be tailored by using different molar ratios of peptide dimer respect to collagen. The same peptide, functionalized with the triple bond, was used to obtain a peptide-dye conjugate by coupling it with N-(5'-azidopentanoyl)-5-aminofluorescein. An aqueous solution (5 vol% methanol) of the peptide dye conjugate was injected into a collagen and a hyaluronic acid (HA) gel and images of fluorescence detection showed that the diffusion of the peptide was slower in the collagen gel compared to the HA gel. The third experimental demonstration was gained using the peptide (LSELRLHNN) which showed the lower binding affinity (2.3•10-4 M) to collagen. This peptide was grafted to hyaluronic acid via EDC-chemistry, with a degree of functionalization of 7 ± 2 mol% as calculated by 1H-NMR. The grafting was further confirmed by FTIR and TGA measurements, which showed that the onset of decomposition for the HA-g-peptide decreased by 10 °C compared to the native HA. Rheological measurements showed that the elastic modulus of a system based on collagen and HA-g-peptide increased by almost two order of magnitude (G' = 200 Pa) compared to a system based on collagen and HA (G' = 0.9 Pa). Overall, this study showed that the synthetic peptides, which were identified from decorin, can be applied as potential building blocks for biomimetic materials that function via biological recognition.
Mechanistische und kinetische Untersuchungen von komplexen zellulären Prozessen in situ sind in den vergangenen Jahren durch den Einsatz photoaktivierbarer Biomoleküle, sogenannter caged Verbindungen, möglich geworden. Bei den caged Verbindungen handelt es sich um photolabile inaktive Derivate von biologisch aktiven Molekülen, aus denen durch ultraviolettes Licht mit Hilfe einer photochemischen Reaktion die natürliche, biologisch aktive Substanz schnell freigesetzt werden kann. Im Rahmen der vorliegenden Arbeit wurden caged Verbindungen von den Neurotransmittern Octopamin und Dopamin, dem Octopamin-Antagonist Epinastin, den Proteinsyntheseinhibitoren Emetin und Anisomycin, dem Protonophor CCCP und dem Riechstoff Bourgeonal hergestellt. Zur Synthese dieser caged Verbindungen wurden sowohl bekannte als auch verschiedene im Rahmen dieser Arbeit neu entwickelte photolabile Schutzgruppen mit einem (Cumarin-4-yl)methyl- bzw. einem 2-Nitrobenzyl-Gerüst eingesetzt. Entsprechende Syntheseverfahren wurden erarbeitet. Anschließend erfolgte eine umfassende physikalisch-chemische sowie photochemische Charakterisierung der erhaltenen caged Verbindungen. Dabei wurde besonders auf gute Löslichkeit in Wasser bei physiologischer Ionenstärke, schnelle und effiziente Photoreaktivität, hohe Extinktion bei Wellenlängen von 350-430 nm und gute solvolytische Stabilität bei geringer Toxizität der freigesetzten Schutzgruppe geachtet. Ein Schwerpunkt bei der photochemischen Charakterisierung bildeten die Untersuchungen zur Quantifizierung der 2-Photonen-Anregung, uncaging action cross-sections, der Cumarinylmethyl-caged Verbindungen, aufgrund ihrer Bedeutung für die Photofreisetzung von Biomolekülen, da die gleichzeitige Absorption von 2 IR-Photonen eine höhere dreidimensionale Auflösung und eine wesentlich tiefere Gewebepenetration erlaubt. Mit Hilfe von Kooperationspartnern wurden zeitaufgelösten Fluoreszenz- und IR-Messungen an verschiedenen (Cumarin-4-yl)methoxycarbonyl-caged Modellverbindungen durchgeführt, mit denen die Geschwindigkeitskonstanten k1 und kdecarb des Photolysemechanismus ermittelt wurde. Am Ende folgten die Anwendungserprobungen ausgewählter caged Verbindungen in einem Translationsassay bzw. in Zelluntersuchungen.
The needs for sustainable energy generation, but also a sustainable chemistry display the basic motivation of the current thesis. By different single investigated cases, which are all related to the element carbon, the work can be devided into two major topics. At first, the sustainable synthesis of “useful” carbon materials employing the process of hydrothermal carbonisation (HC) is described. In the second part, the synthesis of heteroatom - containing carbon materials for electrochemical and fuel cell applications employing ionic liquid precursors is presented. On base of a thorough review of the literature on hydrothermolysis and hydrothermal carbonisation of sugars in addition to the chemistry of hydroxymethylfurfural, mechanistic considerations of the formation of hydrothermal carbon are proposed. On the base of these reaction schemes, the mineral borax, is introduced as an additive for the hydrothermal carbonisation of glucose. It was found to be a highly active catalyst, resulting in decreased reaction times and increased carbon yields. The chemical impact of borax, in the following is exploited for the modification of the micro- and nanostructure of hydrothermal carbon. From the borax - mediated aggregation of those primary species, widely applicable, low density, pure hydrothermal carbon aerogels with high porosities and specific surface areas are produced. To conclude the first section of the thesis, a short series of experiments is carried out, for the purpose of demonstrating the applicability of the HC model to “real” biowaste i.e. watermelon waste as feedstock for the production of useful materials. In part two cyano - containing ionic liquids are employed as precursors for the synthesis of high - performance, heteroatom - containing carbon materials. By varying the ionic liquid precursor and the carbonisation conditions, it was possible to design highly active non - metal electrocatalyst for the reduction of oxygen. In the direct reduction of oxygen to water (like used in polymer electrolyte fuel cells), compared to commercial platinum catalysts, astonishing activities are observed. In another example the selective and very cost efficient electrochemical synthesis of hydrogen peroxide is presented. In a last example the synthesis of graphitic boron carbon nitrides from the ionic liquid 1 - Ethyl - 3 - methylimidazolium - tetracyanoborate is investigated in detail. Due to the employment of unreactive salts as a new tool to generate high surface area these materials were first time shown to be another class of non - precious metal oxygen reduction electrocatalyst.
Within this work, three physicochemical methods for the hydrophobization of initially hydrophilic solid particles are investigated. The modified particles are then used for the stabilization of oil-in-water (o/w) emulsions. For all introduced methods electrostatic interactions between strongly or weakly charged groups in the system are es-sential. (i) Short chain alkylammonium bromides (C4 – C12) adsorb on oppositely charged solid particles. Macroscopic contact angle measurements of water droplets under air and hexane on flat silica surfaces in dependency of the surface charge density and alkylchain-length allow the calculation of the surface energy and give insights into the emulsification properties of solid particles modified with alkyltrimethylammonium bromides. The measure-ments show an increase of the contact angle with increasing surface charge density, due to the enhanced adsorp-tion of the oppositely charged alkylammonium bromides. Contact angles are higher for longer alkylchain lengths. The surface energy calculations show that in particular the surface-hexane or surface-air interfacial en-ergy is being lowered upon alkylammonium adsorption, while a significant increase of the surface-water interfa-cial energy occurs only at long alkyl chain lengths and high surface charge densities. (ii) The thickness and the charge density of an adsorbed weak polyelectrolyte layer (e.g. PMAA, PAH) influence the wettability of nanoparticles (e.g. alumina, silica, see Scheme 1(b)). Furthermore, the isoelectric point and the pH range of colloidal stability of particle-polyelectrolyte composites depend on the thickness of the weak polye-lectrolyte layer. Silica nanoparticles with adsorbed PAH and alumina nanoparticles with adsorbed PMAA be-come interfacially active and thus able to stabilize o/w emulsions when the degree of dissociation of the polye-lectrolyte layer is below 80 %. The average droplet size after emulsification of dodecane in water depends on the thickness and the degree of dissociation of the adsorbed PE-layer. The visualization of the particle-stabilized o/w emulsions by cryogenic SEM shows that for colloidally stable alumina-PMAA composites the oil-water interface is covered with a closely packed monolayer of particles, while for the colloidally unstable case closely packed aggregated particles deposit on the interface. (iii) By emulsifying a mixture of the corrosion inhibitor 8-hydroxyquinoline (8-HQ) and styrene with silica nanoparticles a highly stable o/w emulsion can be obtained in a narrow pH window. The amphoteric character of 8-HQ enables a pH dependent electrostatic interaction with silica nanoparticles, which can render them interfa-cially active. Depending on the concentration and the degree of dissociation of 8-HQ the adsorption onto silica results from electrostatic or aromatic interactions between 8-HQ and the particle-surface. At intermediate amounts of adsorbed 8-HQ the oil wettability of the particles becomes sufficient for stabilizing o/w emulsions. Cryogenic SEM visualization shows that the particles arrange then in a closely packed shell consisting of partly of aggregated domains on the droplet interface. For further increasing amounts of adsorbed 8-HQ the oil wet-tability is reduced again and the particles ability to stabilize emulsions decreases. By the addition of hexadecane to the oil phase the size of the droplets can be reduced down to 200 nm by in-creasing the silica mass fraction. Subsequent polymerization produces corrosion inhibitor filled (20 wt-%) poly-styrene-silica composite particles. The measurement of the release of 8-hydroxyquinoline shows a rapid increase of 8-hydroxyquinoline in a stirred aqueous solution indicating the release of the total content in less than 5 min-utes. The method is extended for the encapsulation of other organic corrosion inhibitors. The silica-polymer-inhibitor composite particles are then dispersed in a water based alkyd emulsion, and the dispersion is used to coat flat aluminium substrates. After drying and cross-linking the polmer-film Confocal Laser Scanning Micros-copy is employed revealing a homogeneous distribution of the particles in the film. Electrochemical Impedance Spectroscopy in aqueous electrolyte solutions shows that films with aggregated particle domains degrade with time and don’t provide long-term corrosion protection of the substrate. However, films with highly dispersed particles have high barrier properties for corrosive species. The comparison of films containing silica-polystyrene composite particles with and without 8-hydroxyquinoline shows higher electrochemical impedances when the inhibitor is present in the film. By applying the Scanning Vibrating Electrode Technique the localized corrosion rate in the fractured area of scratched polymer films containing the silica-polymer-inhibitor composite particles is studied. Electrochemical corrosion cannot be suppressed but the rate is lowered when inhibitor filled composite particles are present in the film. By depositing six polyelectrolyte layers on particle stabilized emulsion droplets their surface morphology changes significantly as shown by SEM visualization. When the oil wettability of the outer polyelectrolyte layer increases, the polyelectrolyte coated droplets can act as emulsion stabilizers themselves by attaching onto bigger oil droplets in a closely packed arrangement. In the presence of 3 mM LaCl3 8-HQ hydrophobized silica particles aggregate strongly on the oil-water inter-face. The application of an ultrasonic field can remove two dimensional shell-compartments from the droplet surface, which are then found in the aqueous bulk phase. Their size ranges up to 1/4th of the spherical particle shell.
Block copolymers are receiving increasing attention in the literature. Reports on amphiphilic block copolymers have now established the basis of their self-assembly behavior: aggregate sizes, morphologies and stability can be explained from the absolute and relative block lengths, the nature of the blocks, the architecture and also solvent selectiveness. In water, self-assembly of amphiphilic block copolymers is assumed to be driven by the hydrophobic. The motivation of this thesis is to study the influence on the self-assembly in water of A b B type block copolymers (with A hydrophilic) of the variation of the hydrophilicity of B from non-soluble (hydrophobic) to totally soluble (hydrophilic). Glucose-modified polybutadiene-block-poly(N-isopropylacrylamide) copolymers were prepared and their self-assembly behavior in water studied. The copolymers formed vesicles with an asymmetric membrane with a glycosylated exterior and poly(N-isopropylacrylamide) on the inside. Above the low critical solution temperature (LCST) of poly(N-isopropylacrylamide), the structure collapsed into micelles with a hydrophobic PNIPAM core and glycosylated exterior. This collapse was found to be reversible. As a result, the structures showed a temperature-dependent interaction with L-lectin proteins and were shown to be able to encapsulate organic molecules. Several families of double hydrophilic block copolymers (DHBC) were prepared. The blocks of these copolymers were biopolymers or polymer chimeras used in aqueous two-phase partition systems. Copolymers based on dextran and poly(ethylene glycol) blocks were able to form aggregates in water. Dex6500-b-PEG5500 copolymer spontaneously formed vesicles with PEG as the “less hydrophilic” barrier and dextran as the solubilizing block. The aggregates were found to be insensitive to the polymer's architecture and concentration (in the dilute range) and only mildly sensitive to temperature. Variation of the block length, yielded different morphologies. A longer PEG chain seemed to promote more curved aggregates following the inverse trend usually observed in amphiphilic block copolymers. A shorter dextran promoted vesicular structures as usually observed for the amphiphilic counterparts. The linking function was shown to have an influence of the morphology but not on the self-assembly capability in itself. The vesicles formed by dex6500-b-PEG5500 showed slow kinetics of clustering in the presence of Con A lectin. In addition both dex6500-b-PEG5500 and its crosslinked derivative were able to encapsulate fluorescent dyes. Two additional dextran-based copolymers were synthesized, dextran-b-poly(vinyl alcohol) and dextran-b-poly(vinyl pyrrolidone). The study of their self-assembly allowed to conclude that aqueous two-phase systems (ATPS) is a valid source of inspiration to conceive DHBCs capable of self-assembling. In the second part the principle was extended to polypeptide systems with the synthesis of a poly(N-hydroxyethylglutamine)-block-poly(ethylene glycol) copolymer. The copolymer that had been previously reported to have emulsifying properties was able to form vesicles by direct dissolution of the solid in water. Last, a series of thermoresponsive copolymers were prepared, dextran-b-PNIPAMm. These polymers formed aggregates below the LCST. Their structure could not be unambiguously elucidated but seemed to correspond to vesicles. Above the LCST, the collapse of the PNIPAM chains induced the formation of stable objects of several hundreds of nanometers in radius that evolved with increasing temperature. The cooling of these solution below LCST restored the initial aggregates. This self-assembly of DHBC outside any stimuli of pH, ionic strength, or temperature has only rarely been described in the literature. This work constituted the first formal attempt to frame the phenomenon. Two reasons were accounted for the self-assembly of such systems: incompatibility of the polymer pairs forming the two blocks (enthalpic) and a considerable solubility difference (enthalpic and entropic). The entropic contribution to the positive Gibbs free energy of mixing is believed to arise from the same loss of conformational entropy that is responsible for “the hydrophobic effect” but driven by a competition for water of the two blocks. In that sense this phenomenon should be described as the “hydrophilic effect”.
In this thesis, simulations of laser-driven many-electron dynamics in molecules are presented, i.e., the interaction between molecules and an electromagnetic field is demonstrated. When a laser field is applied to a molecular system, a population of higher electronic states takes place as well as other processes, e.g. photoionization, which is described by an appropriate model. Also, a finite lifetime of an excited state can be described by such a model. In the second part, a method is postulated that is capable of describing electron correlation in a time-dependent scheme. This is done by introducing a single-electron entropy that is at least temporarily minimized in a further step.
Conventional energy sources are diminishing and non-renewable, take million years to form and cause environmental degradation. In the 21st century, we have to aim at achieving sustainable, environmentally friendly and cheap energy supply by employing renewable energy technologies associated with portable energy storage devices. Lithium-ion batteries can repeatedly generate clean energy from stored materials and convert reversely electric into chemical energy. The performance of lithium-ion batteries depends intimately on the properties of their materials. Presently used battery electrodes are expensive to be produced; they offer limited energy storage possibility and are unsafe to be used in larger dimensions restraining the diversity of application, especially in hybrid electric vehicles (HEVs) and electric vehicles (EVs). This thesis presents a major progress in the development of LiFePO4 as a cathode material for lithium-ion batteries. Using simple procedure, a completely novel morphology has been synthesized (mesocrystals of LiFePO4) and excellent electrochemical behavior was recorded (nanostructured LiFePO4). The newly developed reactions for synthesis of LiFePO4 are single-step processes and are taking place in an autoclave at significantly lower temperature (200 deg. C) compared to the conventional solid-state method (multi-step and up to 800 deg. C). The use of inexpensive environmentally benign precursors offers a green manufacturing approach for a large scale production. These newly developed experimental procedures can also be extended to other phospho-olivine materials, such as LiCoPO4 and LiMnPO4. The material with the best electrochemical behavior (nanostructured LiFePO4 with carbon coating) was able to delive a stable 94% of the theoretically known capacity.
Die vorliegende Arbeit beschäftigt sich mit der Synthese und Charakterisierung mesoporöser monolithischer Silica und deren Hybridmaterialien mit Ionischen Flüssigkeiten (ILs, ionic liquids). Zur Synthese der Silicaproben wurde ein Sol-Gel-Verfahren, ausgehend von einer Präkursorverbindung wie Tetramethylorthosilicat angewendet. Der Katalysator mit der geringsten Basizität führte zum Material mit der kleinsten Porengröße und der größten spezifischen Oberfläche. Eine Kombination von porösen Silica mit ILs führt zur Materialklasse der Silica-Ionogele. Diese Hybridmaterialien verbinden die Eigenschaften eines porösen Festkörpers mit denen einer IL (Leitfähigkeit, weites elektrochemisches Fenster, gute thermische Stabilität) und bieten vielfältige Einsatzmöglichkeiten z.B. in der Katalyse- Solar- und Sensortechnik. Um diese Materialien für ihren Verwendungszweck zu optimieren, bedarf es deren umfassenden Charakterisierung. Daher wurde in der vorliegenden Arbeit das thermische Verhalten von Silica-Ionogelen unter Verwendung verschiedener 1-Ethyl-3-methylimidazolium [Emim]-basierter ILs untersucht. Interessanterweise zeigen die untersuchten ILs deutliche Änderungen in ihrem thermischen Verhalten, wenn diese in porösen Materialien eingeschlossen werden (Confinement). Während sich die untersuchten reinen ILs durch klar unterscheidbare Phasenübergänge auszeichnen, konnten für die entsprechenden Hybridmaterialien deutlich schwächer ausgeprägte Übergänge beobachtet werden. Einzelne Phasenübergänge wurden unterdrückt (Glas- und Kristallisationsübergänge), während z.B. Schmelzübergänge in verbreiterten Temperaturbereichen, zum Teil als einzeln getrennte Schmelzpeaks beobachtet wurden. Diese Untersuchungen belegen deutliche Eigenschaftsänderungen der ILs in eingeschränkten Geometrien. Über Festkörper-NMR-Spektroskopie konnte außerdem gezeigt werden, daß die ILs in den mesoporösen Silicamaterialien eine unerwartet hohe Mobilität aufweisen. Die ILs können als quasi-flüssig bezeichnet werden und zeigen die nach bestem Wissen höchste Mobilität, die bisher für vergleichbare Hybridmaterialien beobachtet wurde. Durch Verwendung von funktionalisierten Präkursoren, sowie der Wahl der Reaktionsbedingungen, kann die Oberfläche der Silicamaterialien chemisch funktionalisiert werden und damit die Materialeigenschaften in der gewünschten Weise beeinflußt werden. In der vorliegenden Arbeit wurde der Einfluß der Oberflächenfunktionalität auf das thermische Verhalten hin untersucht. Dazu wurden zwei verschiedene Möglichkeiten der Funktionalisierung angewendet und miteinander verglichen. Bei der in-situ-Funktionalisierung wird die chemische Funktionalität während der Sol-Gel-Synthese über ein entsprechend funktionalisiertes Silan mit in das Silicamaterial einkondensiert. Eine postsynthetische Funktionalisierung erfolgt durch Reaktion der Endgruppen eines Silicamaterials mit geeigneten Reaktionspartnern. Um den Einfluß der physikalischen Eigenschaften der Probe auf die Reaktion zu untersuchen, wurden pulverisierte und monolithische Silicamaterialien miteinander verglichen. Im letzten Teil der Arbeit wurde die Vielfältigkeit, mit der Silicamaterialien postsynthetisch funktionalisiert werden können demonstriert. Durch die Kenntnis von Struktur-Eigenschaftsbeziehungen können die Eigenschaften von Silica-Ionogelen durch die geeignete Kombination von fester und mobiler Phase in der gewünschten Weise verändert werden. Die vorliegende Arbeit soll einen Beitrag zur Untersuchung dieser Beziehungen leisten, um das Potential dieser interessanten Materialien für Anwendungen nutzen zu können.
In the present thesis, the self-assembly of multi thermoresponsive block copolymers in dilute aqueous solution was investigated by a combination of turbidimetry, dynamic light scattering, TEM measurements, NMR as well as fluorescence spectroscopy. The successive conversion of such block copolymers from a hydrophilic into a hydrophobic state includes intermediate amphiphilic states with a variable hydrophilic-to-lipophilic balance. As a result, the self-organization is not following an all-or-none principle but a multistep aggregation in dilute solution was observed. The synthesis of double thermoresponsive diblock copolymers as well as triple thermoresponsive triblock copolymers was realized using twofold-TMS labeled RAFT agents which provide direct information about the average molar mass as well as residual end group functionality from a routine proton NMR spectrum. First a set of double thermosensitive diblock copolymers poly(N-n-propylacrylamide)-b-poly(N-ethylacrylamide) was synthesized which differed only in the relative size of the two blocks. Depending on the relative block lengths, different aggregation pathways were found. Furthermore, the complementary TMS-labeled end groups served as NMR-probes for the self-assembly of these diblock copolymers in dilute solution. Reversible, temperature sensitive peak splitting of the TMS-signals in NMR spectroscopy was indicative for the formation of mixed star-/flower-like micelles in some cases. Moreover, triple thermoresponsive triblock copolymers from poly(N-n-propylacrylamide) (A), poly(methoxydiethylene glycol acrylate) (B) and poly(N-ethylacrylamide) (C) were obtained from sequential RAFT polymerization in all possible block sequences (ABC, BAC, ACB). Their self-organization behavior in dilute aqueous solution was found to be rather complex and dependent on the positioning of the different blocks within the terpolymers. Especially the localization of the low-LCST block (A) had a large influence on the aggregation behavior. Above the first cloud point, aggregates were only observed when the A block was located at one terminus. Once placed in the middle, unimolecular micelles were observed which showed aggregation only above the second phase transition temperature of the B block. Carrier abilities of such triple thermosensitive triblock copolymers tested in fluorescence spectroscopy, using the solvatochromic dye Nile Red, suggested that the hydrophobic probe is less efficiently incorporated by the polymer with the BAC sequence as compared to ABC or ACB polymers above the first phase transition temperature. In addition, due to the problem of increasing loss of end group functionality during the subsequent polymerization steps, a novel concept for the one-step synthesis of multi thermoresponsive block copolymers was developed. This allowed to synthesize double thermoresponsive di- and triblock copolymers in a single polymerization step. The copolymerization of different N-substituted maleimides with a thermosensitive styrene derivative (4-vinylbenzyl methoxytetrakis(oxyethylene) ether) led to alternating copolymers with variable LCST. Consequently, an excess of this styrene-based monomer allowed the synthesis of double thermoresponsive tapered block copolymers in a single polymerization step.
Nanoporous carbon materials are widely used in industry as adsorbents or catalyst supports, whilst becoming increasingly critical to the developing fields of energy storage / generation or separation technologies. In this thesis, the combined use of carbohydrate hydrothermal carbonisation (HTC) and templating strategies is demonstrated as an efficient route to nanostructured carbonaceous materials. HTC is an aqueous-phase, low-temperature (e.g. 130 – 200 °C) carbonisation, which proceeds via dehydration / poly-condensation of carbon precursors (e.g. carbohydrates and their derivatives), allowing facile access to highly functional carbonaceous materials. Whilst possessing utile, modifiable surface functional groups (e.g. -OH and -C=O-containing moieties), materials synthesised via HTC typically present limited accessible surface area or pore volume. Therefore, this thesis focuses on the development of fabrication routes to HTC materials which present enhanced textural properties and well-defined porosity. In the first discussed synthesis, a combined hard templating / HTC route was investigated using a range of sacrificial inorganic templates (e.g. mesoporous silica beads and macroporous alumina membranes (AAO)). Via pore impregnation of mesoporous silica beads with a biomass-derived carbon source (e.g. 2-furaldehyde) and subsequent HTC at 180 oC, an inorganic / carbonaceous hybrid material was produced. Removal of the template component by acid etching revealed the replication of the silica into mesoporous carbonaceous spheres (particle size ~ 5 μm), representing the inverse morphological structure of the original inorganic body. Surface analysis (e.g. FTIR) indicated a material decorated with hydrophilic (oxygenated) functional groups. Further thermal treatment at increasingly elevated temperatures (e.g. at 350, 550, 750 oC) under inert atmosphere allowed manipulation of functionalities from polar hydrophilic to increasingly non-polar / hydrophobic structural motifs (e.g. extension of the aromatic / pseudo-graphitic nature), thus demonstrating a process capable of simultaneous control of nanostructure and surface / bulk chemistry. As an extension of this approach, carbonaceous tubular nanostructures with controlled surface functionality were synthesised by the nanocasting of uniform, linear macropores of an AAO template (~ 200 nm). In this example, material porosity could be controlled, showing increasingly microporous tube wall features as post carbonisation temperature increased. Additionally, by taking advantage of modifiable surface groups, the introduction of useful polymeric moieties (i.e. grafting of thermoresponsive poly(N-isopropylacrylamide)) was also demonstrated, potentially enabling application of these interesting tubular structures in the fields of biotechnology (e.g. enzyme immobilization) and medicine (e.g. as drug micro-containers). Complimentary to these hard templating routes, a combined HTC / soft templating route for the direct synthesis of ordered porous carbonaceous materials was also developed. After selection of structural directing agents and optimisation of synthesis composition, the F127 triblock copolymer (i.e. ethylene oxide (EO)106 propylene oxide (PO)70 ethylene oxide (EO)106) / D-Fructose system was extensively studied. D-Fructose was found to be a useful carbon precursor as the HTC process could be performed at 130 oC, thus allowing access to stable micellular phase. Thermolytic template removal from the synthesised ordered copolymer / carbon composite yielded functional cuboctahedron single crystalline-like particles (~ 5 μm) with well ordered pore structure of a near perfect cubic Im3m symmetry. N2 sorption analysis revealed a predominantly microporous carbonaceous material (i.e. Type I isotherm, SBET = 257 m2g-1, 79 % microporosity) possessing a pore size of ca. 0.9 nm. The addition of a simple pore swelling additive (e.g. trimethylbenzene (TMB)) to this system was found to direct pore size into the mesopore size domain (i.e. Type IV isotherm, SBET = 116 m2g-1, 60 % mesoporosity) generating pore size of ca. 4 nm. It is proposed that in both cases as HTC proceeds to generate a polyfuran-like network, the organised block copolymer micellular phase is essentially “templated”, either via hydrogen bonding between hydrophilic poly(EO) moiety and the carbohydrate or via hydrophobic interaction between hydrophobic poly(PO) moiety and forming polyfuran-like network, whilst the additive TMB presumably interact with poly(PO) moieties, thus swelling the hydrophobic region expanding the micelle template size further into the mesopore range.
Towards greener stationary phases : thermoresponsive and carbonaceous chromatographic supports
(2011)
Polymers which are sensitive towards external physical, chemical and electrical stimuli are termed as ‘intelligent materials’ and are widely used in medical and engineering applications. Presently, polymers which can undergo a physical change when heat is applied at a certain temperature (cloud point) in water are well-studied for this property in areas of separation chemistry, gene and drug delivery and as surface modifiers. One example of such a polymer is the poly (N-isopropylacrylamide) PNIPAAM, where it is dissolved well in water below 32 oC, while by increasing the temperature further leads to its precipitation. In this work, an alternative polymer poly (2-(2-methoxy ethoxy)ethyl methacrylate-co- oligo(ethylene glycol) methacrylate) (P(MEO2MA-co-OEGMA)) is studied due to its biocompatibility and the ability to vary its cloud points in water. When a layer of temperature responsive polymer was attached to a single continuous porous piece of silica-based material known as a monolith, the thermoresponsive characteristic was transferred to the column surfaces. The hybrid material was demonstrated to act as a simple temperature ‘switch’ in the separation of a mixture of five steroids under water. Different analytes were observed to be separated under varying column temperatures. Furthermore, more complex biochemical compounds such as proteins were also tested for separation. The importance of this work is attributed to separation processes utilizing environmentally friendly conditions, since harsh chemical environments conventionally used to resolve biocompounds could cause their biological activities to be rendered inactive.
In this thesis entitled “Saccharide Recognition - Boronic acids as Receptors in Polymeric Networks” different aspects of boronic acid synthesis, their analysis and incorporation or attachment to different polymeric networks and characterisation thereof were investigated. The following key aspects were considered: • Provision of a variety of different characterised arylboronic acids and benzoboroxoles • Attachment of certain derivatives to nanoparticles and the characterisation of saccharide binding by means of isothermal titration calorimetry and displacement assay (ARS) to enhance the association constant to saccharides at pH 7.4 • Enhancement of selectivity in polymeric systems by means of molecular imprinting using fructose as template and a polymerisable benzoboroxole as functional monomer for the recognition at pH 7.4 (Joined by a diploma thesis of F. Grüneberger) • Development of biomimetic saccharide structures and the development of saccharide (especially glucose and fructose) binding MIPs by using these structures as template molecules. In the first part of the thesis different arylboronic acid derivatives were synthesised and their binding to glucose or fructose was investigated by means of isothermal titration calorimetry (ITC). It could be derived, which is in parallel to the literature, that derivatives bearing a methylhydroxyl-group in ortho-position to the boron (benzoboroxole) exhibit in most cases a two-fold higher association constant compared to the corresponding phenylboronic acid derivative. To gain a deeper understanding NMR spectroscopy and mass spectrometry with the benzoboroxole and glucose or fructose was performed. It could be shown that the exchange rate in terms of NMR time scale is quite slow since in titration experiments new peaks appeared. Via mass spectrometry of a mixture between benzoboroxole and glucose or fructose, different binding stoichiometries could be detected showing that the binding of saccharides is comparable with their binding to phenylboronic acid. In addition, the use of Alizarin Red S as an electrochemical reporter was described for the first time to monitor the saccharide binding to arylboronic acids not only with spectroscopy. Here, the redox behaviour and the displacement were recorded by cyclic voltammograms. In the second part different applications of boronic acids in polymeric networks were investigated. The attachment of benzoboroxoles to nanoparticles was investigated and monitored by means of isothermal titration calorimetry and a colourimetric assay with Alizarin Red S as the report dye. The investigations by isothermal titration calorimetry compared the fructose binding of arylboronic acids and benzoboroxoles coupled to these nanoparticles and “free” in solution. It could be shown that the attached derivatives showed a higher binding constant due to an increasing entropy term. This states for possible multivalent binding combined with a higher water release. Since ITC could not characterise the binding of glucose to these nanoparticles due to experimental restrictions the glucose binding at pH 7.4 was shown with ARS. Here, the displacement of ARS by fructose and also glucose could be followed and consequently these nanoparticles can be used for saccharide determination. Within this investigation also the temperature stability of these nanoparticles was examined and after normal sterilisation procedures (121°C, 20 min.) the binding behaviour was still unchanged. To target the selectivity of the used polymeric networks, molecular imprinting was used as a technique for creating artificial binding pockets on a molecular scale. As functional monomer 3-methacrylamidobenzoboroxole was introduced for the recognition of fructose. In comparison to polymers prepared with vinylphenylboronic acid the benzoboroxole containing polymer had a stronger binding at pH 7.4 which was shown for the first time. In addition, another imprinted polymer was synthesised especially for the recognition of glucose and fructose employing biomimetic saccharide analogues as template molecule. The advantage to use the saccharide analogues is the defined template-functional monomer complex during the polymerisation which is not the case, for example, for glucose-boronic acid interaction. The biomimetic character was proven through structural superimposition of crystal structures of the analogues with already described crystal structures of boronic acid esters of glucose and fructose. A molecularly imprinted polymer was synthesised with vinylphenylboronic acid as the functional monomer to show that both glucose and fructose are able to bind to the polymer which was predicted by the structural similarity of the analogues. The major scientific contributions of this thesis are • the determination of binding constants for some, not yet reported saccharide – boronic acid / benzoboroxole pairs, • the use of ARS as electrochemical reporter for saccharide detection, • the thermodynamic characterisation of a saccharide binding nanoparticle system containing benzoboroxole and functioning at pH 7.4, • the use of a polymerisable benzoboroxole as functional monomer for saccharide recognition in neutral, aqueous environments • and the synthesis and utilisation of biomimetic saccharide analogues as template molecules especially for the development of a glucose binding MIP.
In this thesis chemical reactions under hydrothermal conditions were explored, whereby emphasis was put on green chemistry. Water at high temperature and pressure acts as a benign solvent. Motivation to work under hydrothermal conditions was well-founded in the tunability of physicochemical properties with temperature, e.g. of dielectric constant, density or ion product, which often resulted in surprising reactivity. Another cornerstone was the implementation of the principles of green chemistry. Besides the use of water as solvent, this included the employment of a sustainable feedstock and the sensible use of resources by minimizing waste and harmful intermediates and additives. To evaluate the feasibility of hydrothermal conditions for chemical synthesis, exemplary reactions were performed. These were carried out in a continuous flow reactor, allowing for precise control of reaction conditions and kinetics measurements. In most experiments a temperature of 200 °C in combination with a pressure of 100 bar was chosen. In some cases the temperature was even raised to 300 °C. Water in this subcritical range can also be found in nature at hydrothermal vents on the ocean floor. On the primitive earth, environments with such conditions were however present in larger numbers. Therefore we tested whether biologically important carbohydrates could be formed at high temperature from the simple, probably prebiotic precursor formaldehyde. Indeed, this formose reaction could be carried out successfully, although the yield was lower compared to the counterpart reaction under ambient conditions. However, striking differences regarding selectivity and necessary catalysts were observed. At moderate temperatures bases and catalytically active cations like Ca2+ are necessary and the main products are hexoses and pentoses, which accumulate due to their higher stability. In contrast, in high-temperature water no catalyst was necessary but a slightly alkaline solution was sufficient. Hexoses were only formed in negligible amounts, whereas pentoses and the shorter carbohydrates accounted for the major fraction. Amongst the pentoses there was some preference for the formation of ribose. Even deoxy sugars could be detected in traces. The observation that catalysts can be avoided was successfully transferred to another reaction. In a green chemistry approach platform chemicals must be produced from sustainable resources. Carbohydrates can for instance be employed as a basis. They can be transformed to levulinic acid and formic acid, which can both react via a transfer hydrogenation to the green solvent and biofuel gamma-valerolactone. This second reaction usually requires catalysis by Ru or Pd, which are neither sustainable nor low-priced. Under hydrothermal conditions these heavy metals could be avoided and replaced by cheap salts, taking advantage of the temperature dependence of the acid dissociation constant. Simple sulfate was recognized as a temperature switchable base. With this additive high yield could be achieved by simultaneous prevention of waste. In contrast to conventional bases, which create salt upon neutralization, a temperature switchable base becomes neutral again when cooled down and thus can be reused. This adds another sustainable feature to the high atom economy of the presented hydrothermal synthesis. In a last study complex decomposition pathways of biomass were investigated. Gas chromatography in conjunction with mass spectroscopy has proven to be a powerful tool for the identification of unknowns. It was observed that several acids were formed when carbohydrates were treated with bases at high temperature. This procedure was also applied to digest wood. Afterwards it was possible to fermentate the solution and a good yield of methane was obtained. This has to be regarded in the light of the fact that wood practically cannot be used as a feedstock in a biogas factory. Thus the hydrothermal pretreatment is an efficient means to employ such materials as well. Also the reaction network of the hydrothermal decomposition of glycine was investigated using isotope-labeled compounds as comparison for the unambiguous identification of unknowns. This refined analysis allowed the identification of several new molecules and pathways, not yet described in literature. In summary several advantages could be taken from synthesis in high-temperature water. Many catalysts, absolutely necessary under ambient conditions, could either be completely avoided or replaced by cheap, sustainable alternatives. In this respect water is not only a green solvent, but helps to prevent waste and preserves resources.
Das Hauptziel dieser Arbeit ist das Verständnis der molekularen Kristallisation, sowohl mit als auch ohne polymere Additive, als einen mehrstufigen Prozess. Dieser beinhaltet eine transiente flüssig-flüssig Phasentrennung, die Nukleation von Nanokristallen in der dichten flüssigen Precursor-Phase so wie eine anschließende nanokristalline Selbstorganisation. Die Arbeit beginnt mit Untersuchungen an einem quaternären Modelsystem bestehend aus DL-Glutamat (Glu), Polyethylenimin (PEI), Wasser und Ethanol. Das Phasendiagramm dieses quaternären Systems wird durch Variation der Glu/PEI w/w und Wasser/EtOH v/v Verhältnisse bestimmt, wobei Präzpitat aus polymerinduzierten flüssigen Precursor, Koazervate oder homogene Mischungen erhalten werden Das thermodynamisch stabile Koazervat kann als Referenz für das Verständnis von flüssigen Precursorn angesehen werden, welche in der Natur metastabil und transient sind. Der mehrstufige Mechanismus der Glu-Präzipitation mit PEI als Additiv wird dann mittels Neutronen Kleinwinkelstreuung untersucht. Dies zeigt, dass die ursprünglich gebildeten flüssigen Precursor noch vor der Nukleation von Nanokristallen einen Wechsel von Wachstum und Koaleszenz durchlaufen. Die Ergebnisse aus optischer- und Eletronenmikroskopie zeigen, dass sowohl die flüssigen Precursor Superstrukturen ausbilden als auch, dass die Nukleation von Nanoplättchen in jedem einzelnen Precursor Tropfen von statten geht. Dies geschieht noch bevor sich die Nanoplättchen selbst in einer radialen Orientierung ausrichten. Diese Studie liefert die Kinetik der Präzipitation von organischen Stoffen in Gegenwart von polymeren Additiven. Eine ähnliche Vorgehensweise wie für die Herstellung von Mikrokügelchen kann für die Darstellung von gemusterten Filmen angewandt werden. Die homogene Nukleation von Nanopartikeln (NPs) findet während der Verdampfung einer quarternären DL-Lys·HCl-Polyacrylsäure-Wasser-Ethanol Dispersion auf einer hydrophilen Oberfläche statt. Die darauffolgende vollständige Verdampfung löst die Mesokristallisation eines kontinuierlichen sphärolithischen dünnen Films aus, welcher sich wiederum in einen mesokristallinen dünnen Film umwandelt. Mesokristalline Filme mit 4 Hierarchiestufen bzw. auch periodische Filme werden durch die Verdampfung der Mikrokügelchen-Dispersion erhalten. Die Ergebnisse zeigen, dass die Verdampfung eine einfache aber effektive Methode zur Herstellung von verschieden gemusterten hierarchischen Filmen darstellt. Nicht-klassische Kristallisation wird auch in der Abwesenheit von polymeren Additiven beobachtet. Wir verfolgen mittels Rasterkraftmikroskop (AFM) die Nukleation und das Wachstum einer neuen molekularen Schicht auf wachsenden DL-Glu·H2O Kristallen aus übersättigter Mutterlauge. Die Bildung einer neuen molekularen Schicht verläuft durch die Anlagerung von amorphen Nanopartikeln. Das Schrumpfen der NPs zusammen mit der strukturellen Änderung von dreidimensionalen NPs zu 2D Schichten wird während dieses Relaxationsprozesses beobachtet. Schließlich kommt es zu der Ausbildung einer neuen molekularen Schicht. Die Bildung einer molekularen Schicht durch die Anlagerung von Nanopartikeln aus der Lösung und die darauffolgende Relaxation liefert ein abweichendes Bild zu der bisher gängigen klassischen Theorie des Kristallwachstums.
Poröse Sol-Gel-Materialien finden in vielen Bereichen Anwendung bzw. sind Gegenstand der aktuellen Forschung. Zu diesen Bereichen zählen sowohl klassische Anwendungen, wie z. B. die Verwendung als Katalysator, Molekularsieb oder Trockenmittel, als auch nichtklassische Anwendungen, wie z. B. der Einsatz als Kontrastmittel in der Magnet-Resonanz-Tomographie oder in Form von dünnen Zeolithfilmen als Isolatoren in Mikrochips. Auch für den Einsatz in der Photonik werden poröse Materialien in Betracht gezogen, wie die Entwicklung des Zeolith-Farbstoff-Lasers zeigt. Mikroporöse Zeolithe können generell über einfache Ionenaustauschreaktionen mit Lanthanoidionen in lumineszente Materialien umgewandelt werden. Neben der Erzeugung eines lumineszenten Materials, dessen Lumineszenzeigenschaften charakterisiert werden müssen, bietet die Nutzung von Lanthanoidionen die Möglichkeit diese Ionen als Sonde zur Charakterisierung der Ion-Wirt-Wechselwirkungen zu funktionalisieren, was z. B. in Bezug auf die Anwendung als Katalysator von großer Bedeutung ist. Dabei werden die einzigartigen Lumineszenzeigenschaften der Lanthanoidionen, in diesem Fall von Europium(III) und Terbium(III), genutzt. In dieser Arbeit wurden Lanthanoid-dotierte mikroporöse Zeolithe, mikroporös-mesoporöse Hybridmaterialien und mesoporöse Silikate hinsichtlich ihrer Lumineszenzeigenschaften und ihrer Wechselwirkung des Wirtsmaterials mit den Lanthanoidionen mittels zeitaufgelöster Lumineszenzspektroskopie untersucht. Zeitaufgelöste Emissionsspektren (TRES) liefern dabei sowohl Informationen in der Wellenlängen- als auch in der Zeitdomäne. Erstmalig wurden die TRES mittels einer umfangreichen Auswertemethodik behandelt. Neben der Anpassung des Abklingverhaltens mit einer diskreten Zahl von Exponentialfunktionen, wurden unterstützend auch Abklingzeitverteilungsanalysen durchgeführt. Zeitaufgelöste flächennormierte Emissionsspektren (TRANES), eine Erweiterung der normalen TRES, konnten erstmals zur Bestimmung der Zahl der emittierenden Lanthanoidspezies in porösen Materialien genutzt werden. Durch die Berechnung der Decayassoziierten Spektren (DAS) konnten den Lanthanoidspezies die entsprechenden Lumineszenzspektren zugeordnet werden. Zusätzlich konnte, speziell im Fall der Europium-Lumineszenz, durch Kombination von zeitlicher und spektraler Information das zeitabhängige Asymmetrieverhältnis R und die spektrale Evolution des 5D0-7F0-Übergangs mit der Zeit t untersucht und somit wesentliche Informationen über die Verteilung der Europiumionen im Wirtsmaterial erhalten werden. Über die Abklingzeit und das Asymmetrieverhältnis R konnten Rückschlüsse auf die Zahl der OH-Oszillatoren in der ersten Koordinationssphäre und die Symmetrie der Koordinationsumgebung gezogen werden. Für die mikroporösen und mikroporös-mesoporösen Materialien wurden verschiedene Lanthanoidspezies, im Regelfall zwei, gefunden, welche entsprechend der beschriebenen Methoden charakterisiert wurden. Diese Lanthanoidspezies konnten Positionen in den Materialien zugeordnet werden, die sich im tief Inneren des Porensystems oder auf bzw. nahe der äußeren Oberfläche oder in den Mesoporen befinden. Erstere Spezies ist aufgrund ihrer Position im Material gut vor Feuchtigkeitseinflüssen geschützt, was sich deutlich in entsprechend langen Lumineszenzabklingzeiten äußert. Zusätzlich ist diese Europiumspezies durch unsymmetrische Koordinationsumgebung charakterisiert, was auf einen signifikanten Anteil an Koordination der Lanthanoidionen durch die Sauerstoffatome im Wirtsgitter zurückzuführen ist. Ionen, die sich nahe oder auf der äußeren Oberfläche befinden, sind dagegen für Feuchtigkeit zugänglicher, was in kürzeren Lumineszenzabklingzeiten und einer symmetrischeren Koordinationsumgebung resultiert. Der Anteil von Wassermolekülen in der ersten Koordinationssphäre ist hier deutlich größer, als bei den Ionen, die sich tiefer im Porensystem befinden und entspricht in vielen Fällen der Koordinationszahl eines vollständig hydratisierten Lanthanoidions. Auch der Einfluss von Oberflächenmodifikationen auf die Speziesverteilung und das Verhalten der Materialien gegenüber Feuchtigkeit wurde untersucht. Dabei gelang es den Einfluss der Feuchtigkeit auf die Lumineszenzeigenschaften und die Speziesverteilung durch die Oberflächenmodifikation zu verringern und die Lumineszenzeigenschaften teilweise zu konservieren. Im Fall der mesoporösen Silikamonolithe wurde auch eine heterogene Verteilung der Lanthanoidionen im Porensystem gefunden. Hier wechselwirkt ein Teil der Ionen mit der Porenwand, während sich die restlichen Ionen in der wäßrigen Phase innerhalb des Porensystems aufhalten. Das Aufbringen von Oberflächenmodifikationen führte zu einer Wechselwirkung der Ionen mit diesen Oberflächenmodifikationen, was sich in Abhängigkeit von der Oberflächenbeladung in den enstprechenden Lumineszenzeigenschaften niederschlug.
Magnetische Nanopartikel bieten ein großes Potential, da sie einerseits die Eigenschaften ihrer Bulk-Materialien besitzen und anderseits, auf Grund ihrer Größe, über komplett unterschiedliche magnetische Eigenschaften verfügen können; Superparamagnetismus ist eine dieser Eigenschaften. Die meisten etablierten Anwendungen magnetischer Nanopartikel basieren heutzutage auf Eisenoxiden. Diese bieten gute magnetische Eigenschaften, sind chemisch relativ stabil, ungiftig und lassen sich auf vielen Synthesewegen relativ einfach herstellen. Die magnetischen Eigenschaften der Eisenoxide sind materialabhängig aber begrenzt, weshalb nach anderen Verbindungen mit besseren Eigenschaften gesucht werden muss. Eisencarbid (Fe3C) kann eine dieser Verbindungen sein. Dieses besitzt vergleichbare positive Eigenschaften wie Eisenoxid, jedoch viel bessere magnetische Eigenschaften, speziell eine höhere Sättigungsmagnetisierung. Bis jetzt wurde Fe3C hauptsächlich in Gasphasenabscheidungsprozessen synthetisiert oder als Nebenprodukt bei der Synthese von Kohlenstoffstrukturen gefunden. Eine Methode, mit der gezielt Fe3C-Nanopartikel und andere Metallcarbide synthetisiert werden können, ist die „Harnstoff-Glas-Route“. Neben den Metallcarbiden können mit dieser Methode auch die entsprechenden Metallnitride synthetisiert werden, was die breite Anwendbarkeit der Methode unterstreicht. Die „Harnstoff-Glas-Route“ ist eine Kombination eines Sol-Gel-Prozesses mit einer anschließenden carbothermalen Reduktion/Nitridierung bei höheren Temperaturen. Sie bietet den Vorteil einer einfachen und schnellen Synthese verschiedener Metallcarbide/nitride. Der Schwerpunkt in dieser Arbeit lag auf der Synthese von Eisencarbiden/nitriden, aber auch Nickel und Kobalt wurden betrachtet. Durch die Variation der Syntheseparameter konnten verschiedene Eisencarbid/nitrid Nanostrukturen synthetisiert werden. Fe3C-Nanopartikel im Größenbereich von d = 5 – 10 nm konnten, durch die Verwendung von Eisenchlorid, hergestellt werden. Die Nanopartikel weisen durch ihre geringe Größe superparamagnetische Eigenschaften auf und besitzen, im Vergleich zu Eisenoxid Nanopartikeln im gleichen Größenbereich, eine höhere Sättigungsmagnetisierung. Diese konnten in fortführenden Experimenten erfolgreich in ionischen Flüssigkeiten und durch ein Polymer-Coating, im wässrigen Medium, dispergiert werden. Desweiteren wurde durch ein Templatieren mit kolloidalem Silika eine mesoporöse Fe3C-Nanostruktur hergestellt. Diese konnte erfolgreich in der katalytischen Spaltung von Ammoniak getestet werden. Mit der Verwendung von Eisenacetylacetonat konnten neben Fe3C-Nanopartikeln, nur durch Variation der Reaktionsparameter, auch Fe7C3- und Fe3N-Nanopartikel synthetisiert werden. Speziell für die Fe3C-Nanopartikel konnte die Sättigungsmagnetisierung, im Vergleich zu den mit Eisenchlorid synthetisierten Nanopartikeln, nochmals erhöht werden. Versuche mit Nickelacetat führten zu Nickelnitrid (Ni3N) Nanokristallen. Eine zusätzliche metallische Nickelphase führte zu einer Selbstorganisation der Partikel in Scheiben-ähnliche Überstrukturen. Mittels Kobaltacetat konnten, in Sphären aggregierte, metallische Kobalt Nanopartikel synthetisiert werden. Kobaltcarbid/nitrid war mit den gegebenen Syntheseparametern nicht zugänglich.
The creation of complex polymer structures has been one of the major research topics over the last couple of decades. This work deals with the synthesis of (block co-)polymers, the creation of complex and stimuli-responsive aggregates by self-assembly, and the cross-linking of these structures. Also the higher-order self-assembly of the aggregates is investigated. The formation of poly-2-oxazoline based micelles in aqueous solution and their simultaneous functionalization and cross-linking using thiol-yne chemistry is e.g. presented. By introducing pH responsive thiols in the core of the micelles the influence of charged groups in the core of micelles on the entire structure can be studied. The charging of these groups leads to a swelling of the core and a decrease in the local concentration of the corona forming block (poly(2-ethyl-2-oxazoline)). This decrease in concentration yields a shift in the cloud point temperature to higher temperatures for this Type I thermoresponsive polymer. When the swelling of the core is prohibited, e.g. by the introduction of sufficient amounts of salt, this behavior disappears. Similar structures can be prepared using complex coacervate core micelles (C3Ms) built through the interaction of weakly acidic and basic polymer blocks. The advantage of these structures is that two different stabilizing blocks can be incorporated, which allows for more diverse and complex structures and behavior of the micelles. Using block copolymers with either a polyanionic or a polycationic block C3Ms could be created with a corona which contains two different soluble nonionic polymers, which either have a mixed corona or a Janus type corona, depending on the polymers that were chosen. Using NHS and EDC the micelles could easily be cross-linked by the formation of amide bonds in the core of the micelles. The higher-order self-assembly behavior of these core cross-linked complex coacervate core micelles (C5Ms) was studied. Due to the cross-linking the micelles are stabilized towards changes in pH and ionic strength, but polymer chains are also no longer able to rearrange. For C5Ms with a mixed corona likely network structures were formed upon the collapse of the thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm), whereas for Janus type C5Ms well defined spherical aggregates of micelles could be obtained, depending on the pH of the solution. Furthermore it could be shown that Janus micelles can adsorb onto inorganic nanoparticles such as colloidal silica (through a selective interaction between PEO and the silica surface) or gold nanoparticles (by the binding of thiol end-groups). Asymmetric aggregates were also formed using the streptavidin-biotin binding motive. This is achieved by using three out of the four binding sites of streptavidin for the binding of one three-arm star polymer, end-functionalized with biotin groups. A homopolymer with one biotin end-group can be used to occupy the last position. This binding of two different polymers makes it possible to create asymmetric complexes. This phase separation is theoretically independent of the kind of polymer since the structure of the protein is the driving force, not the intrinsic phase separation between polymers. Besides Janus structures also specific cross-linking can be achieved by using other mixing ratios.
Gesunde sowie qualitativ hochwertige Nahrungsmittel sind wichtige Voraussetzungen, um einerseits die Lebensmittelsicherheit entlang der Wertschöpfungskette (Wachstum, Verarbeitung, Lagerung und Transport) und andererseits einen vorbeugenden Verbraucherschutz zu gewährleisten. Die Belastung der Nahrung mit Rückständen jeglicher Art war in letzter Zeit häufig Mittelpunkt heftiger öffentlicher Diskussionen. Zahlreiche Untersuchungen haben gezeigt, dass unter bestimmten Bedingungen durch Pilze gebildete Giftstoffe, so genannte Mykotoxine, die Ernteprodukte belasten und es bei deren Verzehr durch Menschen oder Tiere zu Vergiftungen kommen kann. Die FAO schätzt, dass etwa 25% der Weltproduktion von Nahrungsmitteln mit Mykotoxinen kontaminiert und in 20% der Getreideernte der Europäischen Union messbare Konzentrationen an Mykotoxinen detektierbar sind. Damit die Lebensmittelsicherheit weiterhin gewährleistet bleibt, werden neben den Routinemethoden schnellere und zerstörungsfreie Methoden benötigt, um die Lebensmittel direkt vor Ort auf Schimmelpilze und deren Mykotoxine zu untersuchen. In dieser Arbeit wird das Potenzial von ausgewählten optisch-basierten spektroskopischen Methoden für die in-situ bzw. in-line Detektion von Schimmelpilzen sowie Mykotoxinen in Getreide(produkten) untersucht. Es werden Absorptions- und Reflexionsmethoden einerseits und Fluoreszenztechniken andererseits eingesetzt. Die spektroskopischen Methoden werden dabei auf Proben unterschiedlicher Komplexität angewandt - beginnend mit der Untersuchung der photophysikalischen Eigenschaften der reinen Mykotoxine in Lösung über künstlich mit verschiedenen Mykotoxinen kontaminierten Getreideproben bis hin zu mit Pilzen befallenem Getreide und hochveredelte Lebensmittel (Wein und Bier) als Proben höchster Komplexität.
Mit Seitenkettenpolystyrenen wurde ein neues Synthesekonzept für phosphoreszente polymere LED-Materialien aufgestellt und experimentell verifiziert. Zunächst erfolgten auf Grundlage strukturell einfacher Verbindungen Untersuchungen zum Einfluss von Spacern zwischen aktiven Seitengruppen und dem Polystyrenrückgrat. Es wurden Synthesemethoden für die Monomere etabliert, durch die aktive Elemente - Elektronen- und Lochleiter - mit und ohne diesen Spacer zugänglich sind. Durch Kombination dieser Monomere waren unter Hinzunahme von polymerisierbaren Iridium-Komplexen in unterschiedlicher Emissionswellenlänge statistische Terpolymere darstellbar. Es wurde gezeigt, dass die Realisierung bestimmter Verhältnisse zwischen Loch-, Elektronenleiter und Triplettemitter in ausreichender Molmasse möglich ist. Die Glasstufen der Polymere zeigten eine deutliche Strukturabhängigkeit. Auf die Lage der Grenzorbitale übten die Spacer nahezu keinen Einfluss aus. Die unterschiedlichen Makromoleküle kamen in polymeren Licht emittierenden Dioden (PLEDs) zum Einsatz, wobei ein deutlicher Einfluss der Spacereinheiten auf die Leistungscharakteristik der PLEDs festzustellen war: Sowohl Effizienz, Leuchtdichte wie auch Stromdichte waren durch den Einsatz der kompakten Makromoleküle ohne Spacer deutlich höher. Diese Beobachtungen begründeten sich hauptsächlich in der Verwendung der aliphatischen Spacer, die den Anteil im Polymer erhöhten, der keine Konjugation und damit elektrisch isolierende Eigenschaften besaß. Diese Schlussfolgerungen waren mit allen drei realisierten Emissionsfarben grün, rot und blau verifizierbar. Die besten Messergebnisse erzielte eine PLED aus einem grün emittierenden und spacerlosen Terpolymer mit einer Stromeffizienz von etwa 28 cd A-1 (bei 6 V) und einer Leuchtdichte von 3200 cd m-2 (bei 8 V). Ausgehend von obigen Ergebnissen konnten neue Matrixmaterialien aus dem Bereich verdampfbarer Moleküle geringer Molmasse in das Polystyrenseitenkettenkonzept integriert werden. Es wurden Strukturvariationen sowohl von loch- wie auch von elektronenleitenden Verbindungen als Homopolymere dargestellt und als molekular dotierte Systeme in PLEDs untersucht. Sieben verschiedene lochleitende Polymere mit Triarylamin-Grundkörper und drei elektronendefizitäre Polymere auf der Basis von Phenylbenzimidazol konnten erfolgreich in den Polymeransatz integriert werden. Spektroskopische und elektrochemische Untersuchungen zeigten kaum eine Veränderung der Charakteristika zwischen verdampfbaren Molekülen und den dargestellten Makromolekülen. Diese ladungstransportierenden Makro-moleküle wurden als polymere Matrizes molekular dotiert und lösungsbasiert zu Einschicht-PLEDs verarbeitet. Als aussichtsreichstes Lochleiterpolymer dieser Reihe, mit einer Strom-effizenz von etwa 33 cd A-1 (bei 8 V) und einer Leuchtdichte von 6700 cd m-2 (bei 10 V), stellte sich ein Triarylaminderivat mit Carbazolsubstituenten heraus. Als geeignetstes Matrixmaterial für die Elektronenleitung wurde ein meta-verknüpftes Di-Phenylbenzimidazol ausfindig gemacht, das in der PLED eine Stromeffizienz von etwa 20 cd A-1 (bei 8 V) und eine Leuchtdichte von 7100 cd m-2 (bei 10 V) erzielte. Anschließend wurden die geeignetsten Monomere zu Copolymeren kombiniert: Die lochleitende Einheit bildete ein carbazolylsubstituiertes Triarylamin und die elektronen-leitende Einheit war ein disubstituiertes Phenylbenzimidazol. Dieses Copolymer diente im Folgenden dazu, PLEDs zu realisieren und die Leistungsdaten mit denen eines Homopolymer-blends zu vergleichen, wobei der Blend die bessere Leistungscharakteristik zeigte. Mit dem Homopolymerblend waren Bauteileffizienzen von annähernd 30 cd A-1 (bei 10 V) und Leuchtdichten von 6800 cd m-2 neben einer Verringerung der Einsatzspannung realisierbar. Für die abschließende Darstellung bipolarer Blockcopolymere wurde auf die Nitroxid-vermittelte Polymerisation zurückgegriffen. Mit dieser Technik waren kontrollierte radikalische Polymersiationen mit ausgewählten Monomeren in unterschiedlichen Block-längen durchführbar. Diese Blockcopolymere kamen als molekular dotierte Matrizes in phosphoreszenten grün emittierenden PLEDs zum Einsatz. Die Bauteile wurden sowohl mit statistischen Copolymeren, wie auch mit Homopolymerblends in gleicher Zusammensetzung aber unterschiedlichem Polymerisationsgrad hinsichtlich der Leistungscharakteristik verglichen. Kernaussage dieser Untersuchungen ist, dass hochmolekulare Systeme eine bessere Leistungscharakteristik aufweisen als niedermolekulare Matrizes. Über Rasterkraft-mikroskopie konnte eine Phasenseparation in einem Größenbereich von etwa 10 nm für den hochmolekularen Homopolymerblend nachgewiesen werden. Für die Blockcopolymere war es nicht möglich eine Phasenseparation zu beobachten, was vorwiegend auf deren zu geringe Blocklänge zurückgeführt wurde.
Von der Natur geschaffene Polymere faszinieren Polymerforscher durch ihre spezielle auf eine bestimmte Aufgabe ausgerichtete Funktionalität. Diese ergibt sich aus ihrer Bausteinabfolge uber die Ausbildung von Uberstrukturen. Dazu zählen zum Beispiel Proteine (Eiweiße), aus deren Gestalt sich wichtige Eigenschaften ergeben. Diese Struktureigenschaftsbeziehung gilt ebenso für funktionelle synthetische Makromoleküle. Demzufolge kann die Kontrolle der Monomersequenz in Polymeren bedeutend für die resultierende Form des Polymermoleküls sein. Obwohl die Synthese von synthetischen Polymeren mit der Komplexität und der Größe von Proteinen in absehbarer Zeit wahrscheinlich nicht gelingen wird, können wir von der Natur lernen, um neuartige Polymermaterialien mit definierten Strukturen (Sequenzen) zu synthetisieren. Deshalb ist die Entwicklung neuer und besserer Techniken zur Strukturkontrolle von großem Interesse für die Synthese von Makromolekülen, die perfekt auf ihre Funktion zugeschnitten sind. Im Gegensatz zu der Anzahl fortgeschrittener Synthesestrategien zum Design aus- gefallener Polymerarchitekturen – wie zum Beispiel Sterne oder baumartige Polymere (Dendrimere) – gibt es vergleichsweise wenig Ansätze zur echten Sequenzkontrolle in synthetischen Polymeren. Diese Arbeit stellt zwei unterschiedliche Techniken vor, mit denen die Monomersequenz innerhalb eines Polymers kontrolliert werden kann. Gerade bei den großtechnisch bedeutsamen radikalischen Polymerisationen ist die Sequenzkontrolle schwierig, weil die chemischen Bausteine (Monomere) sehr reaktiv sind. Im ersten Teil dieser Arbeit werden die Eigenschaften zweier Monomere (Styrol und N-substituiertes Maleinimid) geschickt ausgenutzt, um in eine Styrolkette definierte und lokal scharf abgegrenzte Funktionssequenzen einzubauen. Uber eine kontrollierte radikalische Polymerisationsmethode (ATRP) wurden in einer Ein-Topf-Synthese über das N-substituierte Maleinimid chemische Funktionen an einer beliebigen Stelle der Polystyrolkette eingebaut. Es gelang ebenfalls, vier unterschiedliche Funktionen in einer vorgegebenen Sequenz in die Polymerkette einzubauen. Diese Technik wurde an zwanzig verschiedenen N-substituierten Maleinimiden getestet, die meisten konnten erfolgreich in die Polymerkette integriert werden. In dem zweiten in dieser Arbeit vorgestellten Ansatz zur Sequenzkontrolle, wurde der schrittweise Aufbau eines Oligomers aus hydrophoben und hydrophilen Segmenten (ω-Alkin-Carbonsäure bzw. α-Amin-ω-Azid-Oligoethylenglycol) an einem löslichen Polymerträger durchgeführt. Das Oligomer konnte durch die geschickte Auswahl der Verknüpfungsreaktionen ohne Schutzgruppenstrategie synthetisiert werden. Der lösliche Polymerträger aus Polystyrol wurde mittels ATRP selbst synthetisiert. Dazu wurde ein Startreagenz (Initiator) entwickelt, das in der Mitte einen säurelabilen Linker, auf der einen Seite die initiierende Einheit und auf der anderen die Ankergruppe für die Anbindung des ersten Segments trägt. Der lösliche Polymerträger ermöglichte einerseits die schrittweise Synthese in Lösung. Andererseits konnten überschüssige Reagenzien und Nebenprodukte zwischen den Reaktionsschritten durch Fällung in einem Nicht-Lösungsmittel einfach abgetrennt werden. Der Linker ermöglichte die Abtrennung des Oligomers aus jeweils drei hydrophoben und hydrophilen Einheiten nach der Synthese.
One of the main issues with the use of nickel titanium alloy (NiTi) implants in cardiovascular implants (stents) is that these devices must be of very high quality in order to avoid subsequent operations due to failing stents. For small stents with diameters below ca. 2 mm, however, stent characterization is not straightforward. One of the main problems is that there are virtually no methods to characterize the interior of the NiTi tubes used for fabrication of these tiny stents. The current paper reports on a robust hybrid actuator for the characterization of NiTi tubes prior to stent fabrication. The method is based on a polymer/hydrogel/magnetic nanoparticle hybrid material and allows for the determination of the inner diameter at virtually all places in the raw NiTi tubes. Knowledge of the inner structure of the raw NiTi tubes is crucial to avoid regions that are not hollow or regions that are likely to fail due to defects inside the raw tube. The actuator enables close contact of a magnetic polymer film with the inner NiTi tube surface. The magnetic signal can be detected from outside and be used for a direct mapping of the tube interior. As a result, it is possible to detect critical regions prior to expensive and slow stent fabrication processes.
Um Prozesse in biologischen Systemen auf molekularer Ebene zu untersuchen, haben sich vor allem fluoreszenzspektroskopische Methoden bewährt. Die Möglichkeit, einzelne Moleküle zu beobachten, hat zu einem deutlichen Fortschritt im Verständnis von elementaren biochemischen Prozessen geführt. Zu einer der bekanntesten Methoden der Einzelmolekülspektroskopie zählt die Fluoreszenz-Korrelations-Spektroskopie (FCS), mit deren Hilfe intramolekulare und diffusionsgesteuerte Prozesse in einem Zeitbereich von µs bis ms untersucht werden können. Durch die Verwendung von sog. Fluoreszenzsonden können Informationen über deren molekulare Mikroumgebung erhalten werden. Insbesondere für die konfokale Mikroskopie und die Einzelmolekülspektroskopie werden Fluoreszenzfarbstoffe mit einer hohen Photostabilität und hohen Fluoreszenzquantenausbeute benötigt. Aufgrund ihrer hohen Fluoreszenzquantenausbeute und der Möglichkeit, maßgeschneiderte“ Farbstoffe in einem breiten Spektralbereich für die Absorption und Fluoreszenz zu entwickeln, sind Cyaninfarbstoffe von besonderem Interesse für bioanalytische Anwendungen. Als Fluoreszenzmarker finden diese Farbstoffe insbesondere in der klinischen Diagnostik und den Lebenswissenschaften Verwendung. Die in dieser Arbeit verwendeten Farbstoffe DY-635 und DY-647 sind zwei typische Vertreter dieser Farbstoffklasse. Durch Modifizierung können die Farbstoffe kovalent an biologisch relevante Moleküle gebunden werden. Aufgrund ihres Absorptionsmaximums oberhalb von 630nm werden sie insbesondere in der Bioanalytik eingesetzt. In der vorliegenden Arbeit wurden die spektroskopischen Eigenschaften der Cyaninfarbstoffe DY-635 und DY-647 in biomimetischen und biologischen Modellsystemen untersucht. Zur Charakterisierung wurden dabei neben der Absorptionsspektroskopie insbesondere fluoreszenzspektroskopische Methoden verwendet. Dazu zählen die zeitkorrelierte Einzelphotonenzählung zur Ermittlung des Fluoreszenzabklingverhaltens, Fluoreszenz-Korrelations-Spektroskopie (FCS) zur Beobachtung von Diffusions- und photophysikalischen Desaktivierungsprozessen und die zeitaufgelöste Fluoreszenzanisotropie zur Untersuchung der Rotationsdynamik und Beweglichkeit der Farbstoffe im jeweiligen Modellsystem. Das Biotin-Streptavidin-System wurde als Modellsystem für die Untersuchung von Protein-Ligand-Wechselwirkungen verwendet, da der Bindungsmechanismus weitgehend aufgeklärt ist. Nach Bindung der Farbstoffe an Streptavidin wurde eine erhebliche Veränderung in den Absorptions- und Fluoreszenzeigenschaften beobachtet. Es wird angenommen, dass diese spektralen Veränderungen durch Wechselwirkung von benachbarten, an ein Streptavidintetramer gebundenen Farbstoffmolekülen und Bildung von H-Dimeren verursacht wird. Für das System Biotin-Streptavidin ist bekannt, dass während der Bindung des Liganden (Biotin) an das Protein eine Konformationsänderung auftritt. Anhand von zeitaufgelösten Fluoreszenzanisotropieuntersuchungen konnte in dieser Arbeit gezeigt werden, dass diese strukturellen Veränderungen zu einer starken Einschränkung der Beweglichkeit des Farbstoffes DY-635B führen. Liegt eine Mischung von ungebundenem und Streptavidin-gebundenem Farbstoff vor, können die Anisotropieabklingkurven nicht nach einem exponentiellen Verlauf angepasst werden. Es konnte im Rahmen dieser Arbeit gezeigt werden, dass in diesem Fall die Auswertung mit Hilfe des Assoziativen Anisotropiemodells möglich ist, welches eine Unterscheidung der Beiträge aus den zwei verschiedenen Mikroumgebungen ermöglicht. Als zweites Modellsystem dieser Arbeit wurden Mizellen des nichtionischen Tensids Tween-20 eingesetzt. Mizellen bilden eines der einfachsten Systeme, um die Mikroumgebung einer biologischen Membran nachzuahmen. Sind die Farbstoffe in den Mizellen eingelagert, so kommt es zu keiner Veränderung der Mizellgröße. Die ermittelten Werte des Diffusionskoeffizienten der mizellar eingelagerten Farbstoffe spiegeln demzufolge die Translationsbewegung der Tween-20-Mizellen wider. Die Beweglichkeit der Farbstoffe innerhalb der Tween-20-Mizellen wurde durch zeitaufgelöste Fluoreszenzanisotropiemessungen untersucht. Neben der „Wackelbewegung“, entsprechend dem wobble-in-a-cone-Modell, wird zusätzlich noch die laterale Diffusion der Farbstoffe entlang der Mizelloberfläche beschrieben.
With the rise of nanotechnology in the last decade, nanofluidics has been established as a research field and gained increased interest in science and industry. Natural aqueous nanofluidic systems are very complex, there is often a predominance of liquid interfaces or the fluid contains charged or differently shaped colloids. The effects, promoted by these additives, are far from being completely understood and interesting questions arise with regards to the confinement of such complex fluidic systems. A systematic study of nanofluidic processes requires designing suitable experimental model nano – channels with required characteristics. The present work employed thin liquid films (TLFs) as experimental models. They have proven to be useful experimental tools because of their simple geometry, reproducible preparation, and controllable liquid interfaces. The thickness of the channels can be adjusted easily by the concentration of electrolyte in the film forming solution. This way, channel dimensions from 5 – 100 nm are possible, a high flexibility for an experimental system. TLFs have liquid IFs of different charge and properties and they offer the possibility to confine differently shaped ions and molecules to very small spaces, or to subject them to controlled forces. This makes the foam films a unique “device” available to obtain information about fluidic systems in nanometer dimensions. The main goal of this thesis was to study nanofluidic processes using TLFs as models, or tools, and to subtract information about natural systems plus deepen the understanding on physical chemical conditions. The presented work showed that foam films can be used as experimental models to understand the behavior of liquids in nano – sized confinement. In the first part of the thesis, we studied the process of thinning of thin liquid films stabilized with the non – ionic surfactant n – dodecyl – β – maltoside (β – C₁₂G₂) with primary interest in interfacial diffusion processes during the thinning process dependent on surfactant concentration 64. The surfactant concentration in the film forming solutions was varied at constant electrolyte (NaCl) concentration. The velocity of thinning was analyzed combining previously developed theoretical approaches. Qualitative information about the mobility of the surfactant molecules at the film surfaces was obtained. We found that above a certain limiting surfactant concentration the film surfaces were completely immobile and they behaved as non – deformable, which decelerated the thinning process. This follows the predictions for Reynolds flow of liquid between two non – deformable disks. In the second part of the thesis, we designed a TLF nanofluidic system containing rod – like multivalent ions and compared this system to films containing monovalent ions. We presented first results which recognized for the first time the existence of an additional attractive force in the foam films based on the electrostatic interaction between rod – like ions and oppositely charged surfaces. We may speculate that this is an ion bridging component of the disjoining pressure. The results show that for films prepared in presence of spermidine the transformation of the thicker CF to the thinnest NBF is more probable as films prepared with NaCl at similar conditions of electrostatic interaction. This effect is not a result of specific adsorption of any of the ions at the fluid surfaces and it does not lead to any changes in the equilibrium properties of the CF and NBF. Our hypothesis was proven using the trivalent ion Y3+ which does not show ion bridging. The experimental results are compared to theoretical predictions and a quantitative agreement on the system’s energy gain for the change from CF to NBF could be obtained. In the third part of the work, the behavior of nanoparticles in confinement was investigated with respect to their impact on the fluid flow velocity. The particles altered the flow velocity by an unexpected high amount, so that the resulting changes in the dynamic viscosity could not be explained by a realistic change of the fluid viscosity. Only aggregation, flocculation and plug formation can explain the experimental results. The particle systems in the presented thesis had a great impact on the film interfaces due to the stabilizer molecules present in the bulk solution. Finally, the location of the particles with respect to their lateral and vertical arrangement in the film was studied with advanced reflectivity and scattering methods. Neutron Reflectometry studies were performed to investigate the location of nanoparticles in the TLF perpendicular to the IF. For the first time, we study TLFs using grazing incidence small angle X – ray scattering (GISAXS), which is a technique sensitive to the lateral arrangement of particles in confined volumes. This work provides preliminary data on a lateral ordering of particles in the film.
Nanofibrous mats are interesting scaffold materials for biomedical applications like tissue engineering due to their interconnectivity and their size dimension which mimics the native cell environment. Electrospinning provides a simple route to access such fiber meshes. This thesis addresses the structural and functional control of electrospun fiber mats. In the first section, it is shown that fiber meshes with bimodal size distribution could be obtained in a single-step process by electrospinning. A standard single syringe set-up was used to spin concentrated poly(ε-caprolactone) (PCL) and poly(lactic-co-glycolic acid) (PLGA) solutions in chloroform and meshes with bimodal-sized fiber distribution could be directly obtained by reducing the spinning rate at elevated humidity. Scanning electron microscopy (SEM) and mercury porosity of the meshes suggested a suitable pore size distribution for effective cell infiltration. The bimodal fiber meshes together with unimodal fiber meshes were evaluated for cellular infiltration. While the micrometer fibers in the mixed meshes generate an open pore structure, the submicrometer fibers support cell adhesion and facilitate cell bridging on the large pores. This was revealed by initial cell penetration studies, showing superior ingrowth of epithelial cells into the bimodal meshes compared to a mesh composed of unimodal 1.5 μm fibers. The bimodal fiber meshes together with electrospun nano- and microfiber meshes were further used for the inorganic/organic hybrid fabrication of PCL with calcium carbonate or calcium phosphate, two biorelevant minerals. Such composite structures are attractive for the potential improvement of properties such as stiffness or bioactivity. It was possible to encapsulate nano and mixed sized plasma-treated PCL meshes to areas > 1 mm2 with calcium carbonate using three different mineralization methods including the use of poly(acrylic acid). The additive seemed to be useful in stabilizing amorphous calcium carbonate to effectively fill the space between the electrospun fibers resulting in composite structures. Micro-, nano- and mixed sized fiber meshes were successfully coated within hours by fiber directed crystallization of calcium phosphate using a ten-times concentrated simulated body fluid. It was shown that nanofibers accelerated the calcium phosphate crystallization, as compared to microfibers. In addition, crystallizations performed at static conditions led to hydroxyapatite formations whereas in dynamic conditions brushite coexisted. In the second section, nanofiber functionalization strategies are investigated. First, a one-step process was introduced where a peptide-polymer-conjugate (PLLA-b-CGGRGDS) was co-spun with PLGA in such a way that the peptide is enriched on the surface. It was shown that by adding methanol to the chloroform/blend solution, a dramatic increase of the peptide concentration at the fiber surface could be achieved as determined by X-ray photoelectron spectroscopy (XPS). Peptide accessibility was demonstrated via a contact angle comparison of pure PLGA and RGD-functionalized fiber meshes. In addition, the electrostatic attraction between a RGD-functionalized fiber and a silica bead at pH ~ 4 confirmed the accessibility of the peptide. The bioactivity of these RGD-functionalized fiber meshes was demonstrated using blends containing 18 wt% bioconjugate. These meshes promoted adhesion behavior of fibroblast compared to pure PLGA meshes. In a second functionalization approach, a modular strategy was investigated. In a single step, reactive fiber meshes were fabricated and then functionalized with bioactive molecules. While the electrospinning of the pure reactive polymer poly(pentafluorophenyl methacrylate) (PPFPMA) was feasible, the inherent brittleness of PPFPMA required to spin a PCL blend. Blends and pure PPFPMA showed a two-step functionalization kinetics. An initial fast reaction of the pentafluorophenyl esters with aminoethanol as a model substance was followed by a slow conversion upon further hydrophilization. This was analysed by UV/Vis-spectroscopy of the pentaflurorophenol release upon nucleophilic substitution with the amines. The conversion was confirmed by increased hydrophilicity of the resulting meshes. The PCL/PPFPMA fiber meshes were then used for functionalization with more complex molecules such as saccharides. Aminofunctionalized D-Mannose or D-Galactose was reacted with the active pentafluorophenyl esters as followed by UV/Vis spectroscopy and XPS. The functionality was shown to be bioactive using macrophage cell culture. The meshes functionalized with D-Mannose specifically stimulated the cytokine production of macrophages when lipopolysaccharides were added. This was in contrast to D-Galactose- or aminoethanol-functionalized and unfunctionalized PCL/PPFPMA fiber mats.
Contents: Production and Applications of Chitin and Chitosan Krill as a promising raw material for the production of chitin in Europe - Containerized plant for producing chitin - Preparation and characterization of chitosan from Mucorales - Chitosan from Absidia orchidis - Scaling up of lactic acid fermentation of prawn wastes in packed-bed column reactor for chitin recovery - Preparation of chitin by acetic acid fermentation - Inter-source reproducibility of the chitin deacetylation process - Comparative analysis of chitosans from insects and crustacea - Effect of the rate of deacetylation on the physico-chemical properties of cuttlefish chitosan - Deacetylation of chitin by fungal enzymes - Production of partially degraded chitosan with desired molecular weight - Chitin-containing materials Mycoton for wounds treatment - Biological activity of selected forms of chitosan - Application of chitosan on the preservation quality of cut flowers - Preparation and characterization of chitosan films: application in cell cultures - Transport phenomena in chitin gels - Symplex membranes of chitosan and sulphoethylcellulose - Preparation and use of chitosan-Ca pectinate pellets - Bioseparation of protein from cheese whey by using chitosan coagulation and ultrafiltration membranes - Preparation of silk fibroin/chitosan fiber - Preparation of paper sheets containing microcrystalline chitosan - Applications of chitosan in textile printing - Permanent modification of fibrous materials with biopolymers - Ion exchanger from chitosan - Chitosan in waste water treatment - The immobilization of tyrosinase on chitin and chitosan and its possible use in wastewater treatment - Utilization of modified chitosan in aqueous system treatment Biomaterials Chemical and preclinical studies on 6-oxychitin - Diverse biological effects of fungal chitin-glucan complex - Effect of concentration of neutralizing agent on chitosan membrane properties - Preliminary investigation of the compatibility of a chitosan-based peritoneal dialysis solution - Influence of chitosan on the growth of several cellular lines - A new chitosan containing phosphonic group with chelating properties - Biocompatibility of chitin materials using cell culture method Oral Administration of Chitosan Recent results in the oral administration of chitosan - Reduction of absorption of dietary lipids and cholesterol by chitosan, its derivatives and special formulations - Chitosan in weight reduction: results from a large scale consumer study - Conformation of chitosan ascorbic acid salt - Trimethylated chitosans as safe absorption enhancers for transmucosal delivery of peptide drugs - Chitosan derivates as intestinal penetration enhancers of the peptide drug buserelin in vivo and in vitro - Chitosan microparticles for oral vaccination: optimization and characterization - Effect of chitosan in enhancing drug delivery across buccal mucosa - Influence of chitosans on permeability of human intestinal epithelial (Caco-2) cells: The effect of molecular weight, degree of deacetylation and exposure time - Oral polymeric N-acetyl-D-glucosamine as potential treatment for patients with osteoarthritis - Clinicoimmunological efficiency of the chitin-containing drug Mycoton in complex treatment of a chronic hepatitis - Interactions of chitin, chitosan, N-laurylchitosan, and N-dimethylaminopropyl chitosan with olive oil - The chitin-containing preparation Mycoton in a pediatric gastroenterology case - Antifungal activity and release behaviour of cross-linked chitosan films incorporated with chlorhexidine gluconate - Release of N-acetyl-D-glucosamine from chitosan in saliva - Physical and Physicochemical Properties Recent approach of metal binding by chitosan and derivatives - As(V) sorption on molybdate-impregnated chitosan gel beads (MICB) - Influence of medium pH on the biosorption of heavy metals by chitin-containing sorbent Mycoton - Comparative studies on molecular chain parameters of polyelectrolyte chains: the stiffness parameter B and temperature coefficient of intrinsic viscosity of chitosans and poly(diallyldimethylammonium chloride) - Crystalline behavior of chitosan - The relationship between the crystallinity and degree of deacetylation of chitin from crab shell - Reversible water-swellable chitin gel: modulation of swellability - Syneresis aspects of chitosan based gel systems - In situ chitosan gelation using the enzyme tyrosinase - Preparation and characterization of controlling pore size chitosan membranes - Fabrication of porous chitin matrices - Changes of polydispersity and limited molecular weight of ultrasonic treated chitosan - A statistical evaluation of IR spectroscopic methods to determine the degree of acetylation of ?-chitin and chitosan - Products of alkaline hydrolysis of dibutyrylchitin: chemical composition and DSC investigation - Chitosan emulsification properties Chemistry of Chitin and Chitosan Chemically modified chitinous materials: preparation and properties - Progress on the modification of chitosan - The graft copolymerization of chitosan with methyl acrylate using an organohalide-manganese carbonyl coinitiator system - Grafting of 4-vinylpyridine, maleic acid and maleic anhydride onto chitin and chitosan - Peptide synthesis on chitosan/chitin - Graft copolymerization of methyl methacrylate onto mercapto-chitin - Thermal depolymerization of chitosan salts - Radiolysis and sonolysis of chitosan - two convenient techniques for a controlled reduction of molecular weight - Thermal and UV degradation of chitosan - Heat-induced physicochemical changes in highly deacetylated chitosan - Chitosan fiber and its chemical N-modification at the fiber state for use as functional materials - Preparation of a fiber reactive chitosan derivative with enhanced microbial activity - Chromatographic separation of rare earths with complexane types of chemically modified chitosan - The effects of detergents on chitosan - Chitosan-alginate PEC films prepared from chitosan of different molecular weights - Enzymology of Chitin and Chitosan Biosynthesis and Degradation Enzymes of chitin metabolism for the design of antifungals - Enzymatic degradation of chitin by microorganisms - Kinetic behaviours of chitinase isozymes - An acidic chitinase from gizzards of broiler (Gallus gallus L.) - On the contribution of conserved acidic residues to catalytic activity of chitinase B from Serratia marcescens - Detection, isolation and preliminary characterisation of a new hyperthermophilic chitinase from the anaerobic archaebacterium Thermococcus chitonophagus - Biochemical and genetic engineering studies on chitinase A from Serratia marcescens - Induction of chitinase production by Serratia marcescens, using a synthetic N-acetylglucosamine derivative - Libraries of chito-oligosaccharides of mixed acetylation patterns and their interactions with chitinases - Approaches towards the design of new chitinase inhibitors - Allosamidin inhibits the fragmentation and autolysis of Penicillium chrysogenum - cDNA encoding chitinase in the midge, Chironomus tentans - Extraction and purification of chitosanase from Bacillus cereus - Substrate binding mechanism of chitosanase from Streptomyces sp. N174 - Chitosanase-catalyzed hydrolysis of 4-methylumbelliferyl ?-chitotrioside - A rust fungus turns chitin into chitosan upon plant tissue colonization to evade recognition by the host - Antibiotic kanosamine is an inhibitor of chitin biosynthesis in fungi - PCR amplification of chitin deacetylase genes - Amplification of antifungal effect of GlcN-6-P synthase and chitin synthase inhibitors - ?-N-Acetylhexosaminidases: two enzyme families, two mechanisms - Purification and characterisation of chitin deacetylase from Absidia orchidis - Effect of aluminium ion on hydrolysis reaction of carboxymethyl- and dihydroxypropyl-chitin with lysozyme - Structure and function relatioship of human N-acetyl-D-glucosamine 2-epimerase (renin binding protein) - Identification of active site residue(s)
Injection of a mixture of HAuCl4 and cellulose dissolved in the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride [Bmim]Cl into aqueous NaBH4 leads to colloidal gold nanoparticle/cellulose hybrid precipitates. This process is a model example for a very simple and generic approach towards (noble) metal/cellulose hybrids, which could find applications in sensing, sterile filtration, or as biomaterials.
From the dichloromethane-methanol (1:1) extract of the seed pods of Derris trifoliata, a new flavanone derivative (S)-lupinifolin 4´-methyl ether was isolated. In addition, the known flavonoids lupinifolin and rotenone were identified. The structures were determined on the basis of spectroscopic evidence. Lupinfolin showed moderate in vitro antiplasmodial activity against the D6 (chloroquine-sensitive) and W2 (chloroquineresistant) strains of Plasmodium falciparum. The different parts of this plant showed larvicidal activities against Aedes aegypti and rotenoids were identified as the active principles.
From the seedpods of Tephrosia elata, a new β-hydroxydihydrochalcone named (S)-elatadihydrochalcone was isolated. In addition, the known flavonoids obovatachalcone, obovatin, obovatin methyl ether and deguelin were identified. The structures were determined on the basis of spectroscopic evidence. The crude extract and the flavonoids obtained from the seedpods of this plant showed antiplasmodial activities. The literature NMR data on β-hydroxydihydrochalcones is reviewed and the identity of some of the compounds assigned β-hydroxydihydrochalcone skeleton is questioned.
BACKGROUND: There is an increased need to replace materials derived from fossil sources by renewables. Sugar-cane derived carbohydrates are very abundant in Brazil and are the cheapest sugars available in the market, with more than 400 million tons of sugarcane processed in the year 2007. The objective of this work was to study the preparation of sugar acrylates from free sugars and free acrylic acid, thus avoiding the previous preparation of protected sugar derivatives, such as glycosides, or activated acrylates, such as vinyl acrylate. RESULTS: Lipase catalyzed esterification of three mono- and two disaccharides with acrylic acid, in the presence or absence of molecular sieves was investigated. The reactions were monitored by high-performance liquid chromatography (HPLC) and the products were analyzed by matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry. The main products are mono- and diacrylates, while higher esters are formed as minor products. The highest conversion to sugar acrylates was observed for the D-glucose and D-fructose, followed by D-xylose and D-maltose. Molecular sieves had no pronounced effect on the conversion CONCLUSIONS: A feasible method is described to produce and to characterize sugar acrylates, including those containing more than two acrylate groups. The process for production of these higher esters could potentially be optimized further to produce molecules for cross-linking in acrylate polymerization and other applications. The direct enzymatic esterification of free carbohydrates with acrylic acid is unprecedented.
Growth of phytopathogenic fungi in the presence of partially acetylated chitooligosaccharides
(2008)
Four phytopathogenic fungi were cultivated up to six days in media containing chitooligosaccharide mixtures differing in average DP and FA. The three different mixtures were named Q3 (which contained oligosaccharides ofDP2–DP10, withDP2–DP7 asmain components), Q2 (which contained oligosaccharides of DP2–DP12, with DP2–DP10 as main components) and Q1 (which derived from Q2 and contained oligomers of DP5–DP8 with hexamer and a heptamer as the main components). The novel aspect of this work is the description of the effect of mixtures of oligosaccharides with different and known composition on fungal growth rates. The growth rate of Alternaria alternata and Rhizopus stolonifer was initially inhibited by Q3 and Q2 at higher concentrations. Q1 had a growth stimulating effect on these two fungi. Growth of Botrytis cinerea was inhibited by Q3 and Q2, while Q1 had no effect on the growth of this fungus. Growth of Penicillium expansum was only slightly inhibited by higher concentrations of sample Q3, while Q2 and Q1 had no effect. The inhibition of growth rates or their resistance toward chitooligosaccharides correlated with the absence or presence of chitinolytic enzymes in the culture media, respectively.
From the roots of the African plant Bulbine frutescens (Asphodelaceae), two unprecedented novel dimeric phenylanthraquinones, named joziknipholones A and B, possessing axial and centrochirality, were isolated, together with six known compounds. Structural elucidation of the new metabolites was achieved by spectroscopic and chiroptical methods, by reductive cleavage of the central bond between the monomeric phenylanthraquinone and -anthrone portions with sodium dithionite, and by quantum chemical CD calculations. Based on the recently revised absolute axial configuration of the parent phenylanthraquinones, knipholone and knipholone anthrone, the new dimers were attributed to possess the P-configuration (i.e., with the acetyl portions below the anthraquinone plane) at both axes in the case of joziknipholone A, whereas in joziknipholone B, the knipholone part was found to be M-configured. Joziknipholones A and B are active against the chloroquine resistant strain K1 of the malaria pathogen, Plasmodium falciparum, and show moderate activity against murine leukemic lymphoma L5178y cells.
Molecular photoswitches are attracting much attention lately mostly because of their possible applications in nano technology, and their role in biology. One of the widely studied representatives of photochromic molecules is azobenzene (AB). With light, by a static electric field, or with tunneling electrons this specie can be "switched" from the flat and energetically more stable trans form, into the compact cis form. The back reaction can be induced optically or thermally. Quantum chemical calculations, mostly based on density functional theory, on the AB molecule, AB derivatives and related systems are presented. All the calculations were done for isolated species, however, with implications for latest experimental results aiming at the switching of surface mounted ABs. In some of these experiments, it is assumed that the switching process is substrate mediated, by attaching an electron or a hole to the adsorbate forming short-lived anion or cation resonances. Therefore, we calculated also cationic and anionic ABs in this work. An influence of external electric fields on the potential energy surfaces, was also studied. Further, by the type, number and positioning of various substituent groups, systematic changes on activation energies and rates for the thermal cis-to-trans isomerization can be enforced. The nature of the transition state for ground state isomerization was investigated. Applying Eyring's transition state theory, trends in activation energies and rates were predicted and are, where a comparison was possible, in good agreement with experimental data. Further, thermal isomerization was studied in solution, for which a polarizable continuum model was employed. The influence of substitution and an environment leaves its traces on structural properties of molecules and quantitative appearance of calculated UV/Vis spectra, as well. Finally, an explicit treatment of a solid substrate was demonstrated for the conformational switching, by scanning tunneling microscope, of a 1,5-cyclooctadiene (COD) molecule at a Si(001) surface, treated by a cluster model. At first, we studied energetics and potential energy surfaces along relevant switching coordinates by quantum chemical calculations, followed by the switching dynamics using wave packet methods. We show that, in spite the simplicity of the model, our calculations support the switching of adsorbed COD, by inelastic electron tunneling at low temperatures.
We present an approach to the correlated dynamics of many-electron systems. We show, that the twoelectron reduced density matrix (2RDM) can provide a suitable description of the real time evolution of a system. To achieve this, the hierarchy of equations of motion must be truncated in a practical way. Also, the computational effort, given that the 2RDM is represented by products of two-electron determinants, is discussed, and numerical model calculations are presented.
In the first section of the thesis graphitic carbon nitride was for the first time synthesised using the high-temperature condensation of dicyandiamide (DCDA) – a simple molecular precursor – in a eutectic salt melt of lithium chloride and potassium chloride. The extent of condensation, namely next to complete conversion of all reactive end groups, was verified by elemental microanalysis and vibrational spectroscopy. TEM- and SEM-measurements gave detailed insight into the well-defined morphology of these organic crystals, which are not based on 0D or 1D constituents like known molecular or short-chain polymeric crystals but on the packing motif of extended 2D frameworks. The proposed crystal structure of this g-C3N4 species was derived in analogy to graphite by means of extensive powder XRD studies, indexing and refinement. It is based on sheets of hexagonally arranged s-heptazine (C6N7) units that are held together by covalent bonds between C and N atoms. These sheets stack in a graphitic, staggered fashion adopting an AB-motif, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy. This study was contrasted with one of many popular – yet unsuccessful – approaches in the last 30 years of scientific literature to perform the condensation of an extended carbon nitride species through synthesis in the bulk. The second section expands the repertoire of available salt melts introducing the lithium bromide and potassium bromide eutectic as an excellent medium to obtain a new phase of graphitic carbon nitride. The combination of SEM, TEM, PXRD and electron diffraction reveals that the new graphitic carbon nitride phase stacks in an ABA’ motif forming unprecedentedly large crystals. This section seizes the notion of the preceding chapter, that condensation in a eutectic salt melt is the key to obtain a high degree of conversion mainly through a solvatory effect. At the close of this chapter ionothermal synthesis is seen established as a powerful tool to overcome the inherent kinetic problems of solid state reactions such as incomplete polymerisation and condensation in the bulk especially when the temperature requirement of the reaction in question falls into the proverbial “no man’s land” of classical solvents, i.e. above 250 to 300 °C. The following section puts the claim to the test, that the crystalline carbon nitrides obtained from a salt melt are indeed graphitic. A typical property of graphite – namely the accessibility of its interplanar space for guest molecules – is transferred to the graphitic carbon nitride system. Metallic potassium and graphitic carbon nitride are converted to give the potassium intercalation compound, K(C6N8)3 designated according to its stoichiometry and proposed crystal structure. Reaction of the intercalate with aqueous solvents triggers the exfoliation of the graphitic carbon nitride material and – for the first time – enables the access of singular (or multiple) carbon nitride sheets analogous to graphene as seen in the formation of sheets, bundles and scrolls of carbon nitride in TEM imaging. The thus exfoliated sheets form a stable, strongly fluorescent solution in aqueous media, which shows no sign in UV/Vis spectroscopy that the aromaticity of individual sheets was subject to degradation. The final section expands on the mechanism underlying the formation of graphitic carbon nitride by literally expanding the distance between the covalently linked heptazine units which constitute these materials. A close examination of all proposed reaction mechanisms to-date in the light of exhaustive DSC/MS experiments highlights the possibility that the heptazine unit can be formed from smaller molecules, even if some of the designated leaving groups (such as ammonia) are substituted by an element, R, which later on remains linked to the nascent heptazine. Furthermore, it is suggested that the key functional groups in the process are the triazine- (Tz) and the carbonitrile- (CN) group. On the basis of these assumptions, molecular precursors are tailored which encompass all necessary functional groups to form a central heptazine unit of threefold, planar symmetry and then still retain outward functionalities for self-propagated condensation in all three directions. Two model systems based on a para-aryl (ArCNTz) and para-biphenyl (BiPhCNTz) precursors are devised via a facile synthetic procedure and then condensed in an ionothermal process to yield the heptazine based frameworks, HBF-1 and HBF-2. Due to the structural motifs of their molecular precursors, individual sheets of HBF-1 and HBF-2 span cavities of 14.2 Å and 23.0 Å respectively which makes both materials attractive as potential organic zeolites. Crystallographic analysis confirms the formation of ABA’ layered, graphitic systems, and the extent of condensation is confirmed as next-to-perfect by elemental analysis and vibrational spectroscopy.
Analytical ultracentrifugation (AUC) has made an important contribution to polymer and particle characterization since its invention by Svedberg (Svedberg and Nichols 1923; Svedberg and Pederson 1940) in 1923. In 1926, Svedberg won the Nobel price for his scientific work on disperse systems including work with AUC. The first important discovery performed with AUC was to show the existence of macromolecules. Since that time AUC has become an important tool to study polymers in biophysics and biochemistry. AUC is an absolute technique that does not need any standard. Molar masses between 200 and 1014 g/mol and particle size between 1 and 5000 nm can be detected by AUC. Sample can be fractionated into its components due to its molar mass, particle size, structure or density without any stationary phase requirement as it is the case in chromatographic techniques. This very property of AUC earns it an important status in the analysis of polymers and particles. The distribution of molar mass, particle sizes and densities can be measured with the fractionation. Different types of experiments can give complementary physicochemical parameters. For example, sedimentation equilibrium experiments can lead to the study of pure thermodynamics. For complex mixtures, AUC is the main method that can analyze the system. Interactions between molecules can be studied at different concentrations without destroying the chemical equilibrium (Kim et al. 1977). Biologically relevant weak interactions can also be monitored (K ≈ 10-100 M-1). An analytical ultracentrifuge experiment can yield the following information: • Molecular weight of the sample • Number of the components in the sample if the sample is not a single component • Homogeneity of the sample • Molecular weight distribution if the sample is not a single component • Size and shape of macromolecules & particles • Aggregation & interaction of macromolecules • Conformational changes of macromolecules • Sedimentation coefficient and density distribution Such an extremely wide application area of AUC allows the investigation of all samples consisting of a solvent and a dispersed or dissolved substance including gels, micro gels, dispersions, emulsions and solutions. Another fact is that solvent or pH limitation does not exist for this method. A lot of new application areas are still flourishing, although the technique is 80 years old. In 1970s, 1500 AUC were operational throughout the world. At those times, due to the limitation in detection technologies, experimental results were obtained with photographic records. As time passed, faster techniques such as size exclusion chromatography (SEC), light scattering (LS) or SDS-gel electrophoresis occupied the same research fields with AUC. Due to these relatively new techniques, AUC began to loose its importance. In the 1980s, only a few AUC were in use throughout the world. In the beginning of the 1990s a modern AUC -the Optima XL-A - was released by Beckman Instruments (Giebeler 1992). The Optima XL-A was equipped with a modern computerized scanning absorption detector. The addition of Rayleigh Interference Optics is introduced which is called XL-I AUC. Furthermore, major development in computers made the analysis easier with the help of new analysis software. Today, about 400 XL-I AUC exist worldwide. It is usually applied in the industry of pharmacy, biopharmacy and polymer companies as well as in academic research fields such as biochemistry, biophysics, molecular biology and material science. About 350 core scientific publications which use analytical ultracentrifugation are published every year (source: SciFinder 2008 ) with an increasing number of references (436 reference in 2008). A tremendous progress has been made in method and analysis software after digitalization of experimental data with the release of XL-I. In comparison to the previous decade, data analysis became more efficient and reliable. Today, AUC labs can routinely use sophisticated data analysis methods for determination of sedimentation coefficient distributions (Demeler and van Holde 2004; Schuck 2000; Stafford 1992), molar mass distributions (Brookes and Demeler 2008; Brookes et al. 2006; Brown and Schuck 2006), interaction constants (Cao and Demeler 2008; Schuck 1998; Stafford and Sherwood 2004), particle size distributions with Angstrom resolution (Cölfen and Pauck 1997) and the simulations determination of size and shape distributions from sedimentation velocity experiments (Brookes and Demeler 2005; Brookes et al. 2006). These methods are also available in powerful software packages that combines various methods, such as, Ultrascan (Demeler 2005), Sedift/Sedphat (Schuck 1998; Vistica et al. 2004) and Sedanal (Stafford and Sherwood 2004). All these powerful packages are free of charge. Furthermore, Ultrascans source code is licensed under the GNU Public License (http://www.gnu.org/copyleft/gpl.html). Thus, Ultrascan can be further improved by any research group. Workshops are organized to support these software packages. Despite of the tremendous developments in data analysis, hardware for the system has not developed much. Although there are various user developed detectors in research laboratories, they are not commercially available. Since 1992, only one new optical system called “the fluorescence optics” (Schmidt and Reisner, 1992, MacGregor et al. 2004, MacGregor, 2006, Laue and Kroe, in press) has been commercialized. However, except that, there has been no commercially available improvement in the optical system. The interesting fact about the current hardware of the XL-I is that it is 20 years old, although there has been an enormous development in microelectronics, software and in optical systems in the last 20 years, which could be utilized for improved detectors. As examples of user developed detector, Bhattacharyya (Bhattacharyya 2006) described a Multiwavelength-Analytical Ultracentrifuge (MWL-AUC), a Raman detector and a small angle laser light scattering detector in his PhD thesis. MWL-AUC became operational, but a very high noise level prevented to work with real samples. Tests with the Raman detector were not successful due to the low light intensity and thus high integration time is required. The small angle laser light scattering detector could only detect latex particles but failed to detect smaller particles and molecules due to low sensitivity of the detector (a photodiode was used as detector). The primary motivation of this work is to construct a detector which can measure new physico-chemical properties with AUC with a nicely fractionated sample in the cell. The final goal is to obtain a multiwavelength detector for the AUC that measures complementary quantities. Instrument development is an option for a scientist only when there is a huge potential benefit but there is no available commercial enterprise developing appropriate equipment, or if there is not enough financial support to buy it. The first case was our motivation for developing detectors for AUC. Our aim is to use today’s technological advances in microelectronics, programming, mechanics in order to develop new detectors for AUC and improve the existing MWL detector to routine operation mode. The project has multiple aspects which can be listed as mechanical, electronical, optical, software, hardware, chemical, industrial and biological. Hence, by its nature it is a multidisciplinary project. Again by its nature it contains the structural problem of its kind; the problem of determining the exact discipline to follow at each new step. It comprises the risk of becoming lost in some direction. Having that fact in mind, we have chosen the simplest possible solution to any optical, mechanical, electronic, software or hardware problem we have encountered and we have always tried to see the overall picture. In this research, we have designed CCD-C-AUC (CCD Camera UV/Vis absorption detector for AUC) and SLS-AUC (Static Light Scattering detector for AUC) and tested them. One of the SLS-AUC designs produced successful test results, but the design could not be brought to the operational stage. However, the operational state Multiwavelength Analytical Ultracentrifuge (MWL-AUC) AUC has been developed which is an important detector in the fields of chemistry, biology and industry. In this thesis, the operational state Multiwavelength Analytical Ultracentrifuge (MWL-AUC) AUC is to be introduced. Consequently, three different applications of MWL-AUC to the aforementioned disciplines shall be presented. First of all, application of MWL-AUC to a biological system which is a mixture of proteins lgG, aldolase and BSA is presented. An application of MWL-AUC to a mass-produced industrial sample (β-carotene gelatin composite particles) which is manufactured by BASF AG, is presented. Finally, it is shown how MWL-AUC will impact on nano-particle science by investigating the quantum size effect of CdTe and its growth mechanism. In this thesis, mainly the relation between new technological developments and detector development for AUC is investigated. Pioneering results are obtained that indicate the possible direction to be followed for the future of AUC. As an example, each MWL-AUC data contains thousands of wavelengths. MWL-AUC data also contains spectral information at each radial point. Data can be separated to its single wavelength files and can be analyzed classically with existing software packages. All the existing software packages including Ultrascan, Sedfit, Sedanal can analyze only single wavelength data, so new extraordinary software developments are needed. As a first attempt, Emre Brookes and Borries Demeler have developed mutliwavelength module in order to analyze the MWL-AUC data. This module analyzes each wavelength separately and independently. We appreciate Emre Brookes and Borries Demeler for their important contribution to the development of the software. Unfortunately, this module requires huge amount of computer power and does not take into account the spectral information during the analysis. New software algorithms are needed which take into account the spectral information and analyze all wavelengths accordingly. We would like also invite the programmers of Ultrascan, Sedfit, Sedanal and the other programs, to develop new algorithms in this direction.
This work presents the synthesis and the self-assembly of symmetrical amphiphilic ABA and BAB triblock copolymers in dilute, semi-concentrated and highly concentrated aqueous solution. A series of new bifunctional bistrithiocarbonates as RAFT agents was used to synthesise these triblock copolymers, which are characterised by a long hydrophilic middle block and relatively small, but strongly hydrophobic end blocks. As hydrophilic A blocks, poly(N-isopropylacrylamide) (PNIPAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA) were employed, while as hydrophobic B blocks, poly(4-tert-butyl styrene), polystyrene, poly(3,5-dibromo benzyl acrylate), poly(2-ethylhexyl acrylate), and poly(octadecyl acrylate) were explored as building blocks with different hydrophobicities and glass transition temperatures. The five bifunctional trithiocarbonates synthesised belong to two classes: the first are RAFT agents, which position the active group of the growing polymer chain at the outer ends of the polymer (Z-C(=S)-S-R-S-C(=S)-Z, type I). The second class places the active groups in the middle of the growing polymer chain (R-S-C(=S)-Z-C(=S)-S-R, type II). These RAFT agents enable the straightforward synthesis of amphiphilic triblock copolymers in only two steps, allowing to vary the nature of the hydrophobic blocks as well as the length of the hydrophobic and hydrophilic blocks broadly with good molar mass control and narrow polydispersities. Specific side reactions were observed among some RAFT agents including the elimination of ethylenetrithiocarbonate in the early stage of the polymerisation of styrene mediated by certain agents of the type II, while the use of the RAFT agents of type I resulted in retardation of the chain extension of PNIPAM with styrene. These results underline the need of a careful choice of RAFT agents for a given task. The various copolymers self-assemble in dilute and semi-concentrated aqueous solution into small flower-like micelles. No indication for the formation of micellar clusters was found, while only at high concentration, physical hydrogels are formed. The reversible thermoresponsive behaviour of the ABA and BAB type copolymer solutions in water with A made of PNIPAM was examined by turbidimetry and dynamic light scattering (DLS). The cloud point of the copolymers was nearly identical to the cloud point of the homopolymer and varied between 28-32 °C with concentrations from 0.01 to 50 wt%. This is attributed to the formation of micelles where the hydrophobic blocks are shielded from a direct contact with water, so that the hydrophobic interactions of the copolymers are nearly the same as for pure PNIPAM. Dynamic light scattering measurements showed the presence of small micelles at ambient temperature. The aggregate size dramatically increased above the cloud point, indicating a change of aggregate morphology into clusters due to the thermosensitivity of the PNIPAM block. The rheological behaviour of the amphiphilic BAB triblock copolymers demonstrated the formation of hydrogels at high concentrations, typically above 30-35 wt%. The minimum concentration to induce hydrogels decreased with the increasing glass transition temperatures and increasing length of the end blocks. The weak tendency to form hydrogels was attributed to a small share of bridged micelles only, due to the strong segregation regime occurring. In order to learn about the role of the nature of the thermoresponsive block for the aggregation, a new BAB triblock copolymer consisting of short polystyrene end blocks and PMDEGA as stimuli-responsive middle block was prepared and investigated. Contrary to PNIPAM, dilute aqueous solutions of PMDEGA and of its block copolymers showed reversible phase transition temperatures characterised by a strong dependence on the polymer composition. Moreover, the PMDEGA block copolymer allowed the formation of physical hydrogels at lower concentration, i.e. from 20 wt%. This result suggests that PMDEGA has a higher degree of water-swellability than PNIPAM.
Die Kombination von Polymeren mit Peptiden vereint die Eigenschaften beider Stoffklassen miteinander. Dabei können die strukturbildenden Eigenschaften der Peptide genutzt werden, um Polymere zu organisieren. In der vorliegenden Arbeit wurde ein Polymer-Peptid-Konjugat verwendet, das sich in Wasser zu Bändern anordnet. Die treibende Kraft für diesen Prozess ist die Anordnung des Peptidteils zu β-Faltblattstrukturen. Das Polymer-Peptid-Aggregat besitzt einen Peptidkern mit funktionalen Oberflächen, der lateral von einer Polyethylenoxidschale umgeben ist. Durch Änderung der Peptidsequenz war es bisher möglich, die Eigenschaften dieser Fasern zu variieren. In der Arbeit wird ein modularer Ansatz zur vielfältigen Modifizierung einer Polymer-Peptid-Faser entwickelt. So ist es möglich, die Eigenschaften der Fasern einzustellen, ohne die strukturbildende β-Faltblattsequenz verändern zu müssen. Um weitere Funktionen an den Fasern anzubringen, wurde die 1,3-dipolaren Addition verwendet. Diese Reaktion beschreibt die konzertierte Umlagerung eines Azides mit einem Alkin. Sie ist in den meisten Lösungsmitteln unter hohen Ausbeuten durchführbar. Im Rahmen der Arbeit wird die Erzeugung von Aziden untersucht und auf die Polymer-Peptid-Fasern übertragen. Der Diazotransfer stellte dabei die Methode der Wahl dar, so können Azidgruppen aus Aminen gewonnen werden. Unter Verwendung der 1,3-dipolaren Addition konnten verschiedene alkinfunktionale Moleküle kovalent an die azidfunktionalisierten Polymer-Peptid-Fasern gebunden werden. So wurde ein Fluoreszenzfarbstoff an die Fasern gebunden, der eine Abbildung der Fasern mittels konfokaler Mikroskopie erlaubte. Weiterhin wurden die Eigenschaften der Fasern durch Addition dreier carboxylfunktionaler Moleküle modifiziert. Diese Fasern konnten weiter genutzt werden, um Kalzium zu binden. Dabei variierte die Anzahl der gebundenen Kalziumionen in Abhängigkeit der jeweiligen Fasermodifikation erheblich. Weitere Untersuchungen, die Morphologie von Kalziumcarbonatkristallen betreffend, werden aktuell durchgeführt. Die kovalente Anbringung eines reduzierenden Zuckers an die Polymer-Peptid-Fasern erlaubt die Abscheidung von Silber aus Tollens Reagenz. Durch eine Entwicklung analog zur Schwarz-Weiss-Photographie können in nachfolgenden Arbeiten so Silberdrähte in Nanogröße erzeugt werden. An die azidfunktionalen Fasern können weitere funktionale Moleküle angebracht werden, um die Eigenschaften und das Anwendungsspektrum der Polymer-Peptid-Fasern zu erweitern.
New ABC triblock copolymers were synthesized by controlled free-radical polymerization via Reversible Addition-Fragmentation chain Transfer (RAFT). Compared to amphiphilic diblock copolymers, the prepared materials formed more complex self-assembled structures in water due to three different functional units. Two strategies were followed: The first approach relied on double-thermoresponsive triblock copolymers exhibiting Lower Critical Solution Temperature (LCST) behavior in water. While the first phase transition triggers the self-assembly of triblock copolymers upon heating, the second one allows to modify the self-assembled state. The stepwise self-assembly was followed by turbidimetry, dynamic light scattering (DLS) and 1H NMR spectroscopy as these methods reflect the behavior on the macroscopic, mesoscopic and molecular scale. Although the first phase transition could be easily monitored due to the onset of self-assembly, it was difficult to identify the second phase transition unambiguously as the changes are either marginal or coincide with the slow response of the self-assembled system to relatively fast changes of temperature. The second approach towards advanced polymeric micelles exploited the thermodynamic incompatibility of “triphilic” block copolymers – namely polymers bearing a hydrophilic, a lipophilic and a fluorophilic block – as the driving force for self-assembly in water. The self-assembly of these polymers in water produced polymeric micelles comprising a hydrophilic corona and a microphase-separated micellar core with lipophilic and fluorophilic domains – so called multi-compartment micelles. The association of triblock copolymers in water was studied by 1H NMR spectroscopy, DLS and cryogenic transmission electron microscopy (cryo-TEM). Direct imaging of the polymeric micelles in solution by cryo-TEM revealed different morphologies depending on the block sequence and the preparation conditions. While polymers with the sequence hydrophilic-lipophilic-fluorophilic built core-shell-corona micelles with the core being the fluorinated compartment, block copolymers with the hydrophilic block in the middle formed spherical micelles where single or multiple fluorinated domains “float” as disks on the surface of the lipophilic core. Increasing the temperature during micelle preparation or annealing of the aqueous solutions after preparation at higher temperatures induced occasionally a change of the micelle morphology or the particle size distribution. By RAFT polymerization not only the desired polymeric architectures could be realized, but the technique provided in addition a precious tool for molar mass characterization. The thiocarbonylthio moieties, which are present at the chain ends of polymers prepared by RAFT, absorb light in the UV and visible range and were employed for end-group analysis by UV-vis spectroscopy. A variety of dithiobenzoate and trithiocarbonate RAFT agents with differently substituted initiating R groups were synthesized. The investigation of their absorption characteristics showed that the intensity of the absorptions depends sensitively on the substitution pattern next to the thiocarbonylthio moiety and on the solvent polarity. According to these results, the conditions for a reliable and convenient end-group analysis by UV-vis spectroscopy were optimized. As end-group analysis by UV-vis spectroscopy is insensitive to the potential association of polymers in solution, it was advantageously exploited for the molar mass characterization of the prepared amphiphilic block copolymers.
The piezoelectric and pyroelectric properties of oriented films possessing dipole moments are increasingly being used in pressure, acoustic, thermal and optical devices. The performance of these devices in many applications may be enhanced by thin-film technology.The developing Langmuir-Blodgett thin-film deposition technique offers the opportunity to obtain highly oriented and uniform organic-based films in the 10–5000 nm thickness range. Special techniques must be used, however, to assemble these molecules in such a way as to result in polar multilayer films. Several possible deposition techniques are investigated, with one resulting in a polar and pyroelectric film about 50 nm thick.
Controlling interactions in synthetic polymers as precisely as in proteins would have a strong impact on polymer science. Advanced structural and functional control can lead to rational design of, integrated nano- and microstructures. To achieve this, properties of monomer sequence defined oligopeptides were exploited. Through their incorporation as monodisperse segments into synthetic polymers we learned in recent four years how to program the structure formation of polymers, to adjust and exploit interactions in such polymers, to control inorganic-organic interfaces in fiber composites and induce structure in Biomacromolecules like DNA for biomedical applications.
The molecular packing and spatial correlations of two isomeric zwitterionic polymethacrylates and one polyacrylate analog are studied by means of X-ray analysis and conformational calculations. The analysis of the correlation functions and density distribution profiles suggest a double-layered molecular packing which is discussed for the three polymers investigated, with respect to their different chemical structures. Whereas the zwitterionic polymethacrylates studied exhibit liquid-like short-range order, the polyacrylate analog exhibits an ordered double-layered superstructure.
A variety of polymerizable lipids containing a hydrophilic spacer group between the reactive group and the main amphiphilic structure have been synthesized. They were investigated in monolayers, liposomes, and multilayers. When the spacer concept was used, efficient decoupling of the motions of the polymeric chain and the amphiphilic side groups is achieved. Thus, the often found loss of the important fluid phases by polymerization is avoided. Polymeric monolayers of the spacer lipid, prepared either by polymerization in the monolayer or by spreading of prepolymerized lipid, exhibit nearly identical surface pressure-area diagrams. Most distinctly, the successful decoupling of the motions of the polymer main chain and the membrane forming amphiphilic side groups is demonstrated by the self-organization of bulk polymerized spacer lipids to polymeric liposomes. In addition, spacer lipids are able to build polymeric Langmuir-Blodgett multilayers. The decoupling of the polymer main chain and the membrane-forming amphiphilic side groups enables the deposition of already polymeric monolayers onto supports to form defined multilayers. If, alternatively, monomeric monolayers are deposited and polymerized on the support, defects in the layers due to structural changes during the polymerization are avoided by the flexible spacer group.
Dielectric spectroscopy is employed to analyze the molecular dynamics and the charge transport in mixtures of zwitterionic polymers of the type poly{3 [N(-methacryloyloxyalkyl)] N, [N-dimethylammonio propanesulfonate] with sodium iodide in the frequency range of 10²Hz-10(up)7 Hz and in the temperature range of 110 K-400 K. The amount of inorganic salt added varies from 0-200 mol-% relative to the number of zwitterionic groups present in the polymer, contributing strongly to the conductivity. One relaxation process is observed whose relaxation rate depends strongly on the length of the aliphatic spacer between the polymethacrylate main chain and the zwitterionic group. Exhibiting an Arrhenius-like temperature depence with activation energy EA = 47 KJ/mol, this relaxation process is assigned to fluctuation of the quaternary ammonium groups in the side chains. At higher temperatures, the dielectric properties and the conductivity are primarily dominated by the mobile inorganic ions: conductivity strongly depends on the salt concentration, showing a pronounced electrode polarization effect. The frequency and salt concentration, dependences of the conductivity can be quantitatively described as hopping of charge carriers being subject to spatially randomly varying energy barriers. For the low-frequency regime and for the critical frequency marking the onset of the conductivity's dispersion, the Barton-Nakajima-Namikawa (BNN) relationship is fulfilled.
Several zwitterionic polymers were prepared by radical homopolymerization of surfactant monomers which bear diallyl, diene or vinylcyclopropane moieties. These polymer systems were complemented by alternating copolymers of appropriate zwitterionic vinyl compounds. Thus, polymers with reduced (as compared with simple vinylic homopolymers, or statistical copolymers) and well defined density of surfactant side groups are obtained. The solubilities found for these polymers are dominated by polymer geometry rather than by the balance of hydrophilic and hydrophobic fragments, thus corroborating a main-chain spacer model proposed recently. All water-soluble polymers exhibit characteristic features of classical polysoaps, as shown by surface tension measurements and by solubilization of hydrophobic dyes. In contrast, the water-insoluble copolymers are capable to form stable monolayers at the air-water interface.