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Driven mostly by the search for chemical syntheses under biocompatible conditions, so called "click" chemistry rapidly became a growing field of research. The resulting simple one-pot reactions are so far only scarcely accompanied by an adequate optimization via comparably straightforward and robust analysis techniques possessing short set-up times. Here, we report on a fast and reliable calibration-free online NMR monitoring approach for technical mixtures. It combines a versatile fluidic system, continuous-flow measurement of H-1 spectra with a time interval of 20 s per spectrum, and a robust, fully automated algorithm to interpret the obtained data. As a proof-of-concept, the thiol-ene coupling between N-boc cysteine methyl ester and ally] alcohol was conducted in a variety of non-deuterated solvents while its time-resolved behaviour was characterized with step tracer experiments. Overlapping signals in online spectra during thiol-ene coupling could be deconvoluted with a spectral model using indirect hard modeling and were subsequently converted to either molar ratios (using a calibration free approach) or absolute concentrations (using 1-point calibration). For various solvents the kinetic constant k for pseudo-first order reaction was estimated to be 3.9 h(-1) at 25 degrees C. The obtained results were compared with direct integration of non-overlapping signals and showed good agreement with the implemented mass balance. (C) 2017 Elsevier Inc. All rights reserved.
Planar bis(1,2-dithiooxalato)nickelate(II), [Ni(dto)]2− reacts in aqueous solutions with lanthanide ions (Ln3+) to form pentanuclear, hetero-bimetallic complexes of the general composition [{Ln(H2O)n}2{Ni(dto)2}3]·xH2O. (n = 4 or 5; x = 9–12). The complex [{Ho(H2O)5}2{Ni(dto)2}3]·10H2O, Ho2Ni3, was synthesized and characterized by single crystal X-ray structure analysis and powder diffraction. The Ho2Ni3 complex crystallizes as monoclinic crystals in the space group P21/c. The channels and cavities, appearing in the crystal packing of the complex molecules, are occupied by a varying amount of non-coordinated water molecules.
Class IIa histone deacetylases (HDACs) show extremely low enzymatic activity and no commonly accepted endogenous substrate is known today. Increasing evidence suggests that these enzymes exert their effect rather through molecular recognition of acetylated proteins and recruiting other proteins like HDAC3 to the desired target location. Accordingly, class IIa HDACs like bromodomains have been suggested to act as “Readers” of acetyl marks, whereas enzymatically active HDACs of class I or IIb are called “Erasers” to highlight their capability to remove acetyl groups from acetylated histones or other proteins. Small-molecule ligands of class IIa histone deacetylases (HDACs) have gained tremendous attention during the last decade and have been suggested as pharmaceutical targets in several indication areas such as cancer, Huntington's disease and muscular atrophy. Up to now, only enzyme activity assays with artificial chemically activated trifluoroacetylated substrates are in use for the identification and characterization of new active compounds against class IIa HDACs. Here, we describe the first binding assay for this class of HDAC enzymes that involves a simple mix-and-measure procedure and an extraordinarily robust fluorescence lifetime readout based on [1,3]dioxolo[4,5-f]benzodioxole-based ligand probes. The principle of the assay is generic and can also be transferred to class I HDAC8.
Low-energy electrons (LEEs) play an important role in DNA radiation damage. Here we present a method to quantify LEE induced strand breakage in well-defined oligonucleotide single strands in terms of absolute cross sections. An LEE irradiation setup covering electron energies <500 eV is constructed and optimized to irradiate DNA origami triangles carrying well-defined oligonucleotide target strands. Measurements are presented for 10.0 and 5.5 eV for different oligonucleotide targets. The determination of absolute strand break cross sections is performed by atomic force microscopy analysis. An accurate fluence determination ensures small margins of error of the determined absolute single strand break cross sections sigma SSB. In this way, the influence of sequence modification with the radiosensitive 5-Fluorouracil (U-5F) is studied using an absolute and relative data analysis. We demonstrate an increase in the strand break yields of U-5F containing oligonucleotides by a factor of 1.5 to 1.6 compared with non-modified oligonucleotide sequences when irradiated with 10 eV electrons.
We present a rigorous method to set up a system-bath Hamiltonian for the coupling of adsorbate vibrations (the system) to surface phonons (the bath). The Hamiltonian is straightforward to derive and exact up to second order in the environment coordinates, thus capable of treating one- and two-phonon contributions to vibration-phonon coupling. The construction of the Hamiltonian uses orthogonal coordinates for system and bath modes, is based on an embedded cluster approach, and generalizes previous Hamiltonians of a similar type, but avoids several (additional) approximations. While the parametrization of the full Hamiltonian is in principle feasible by a first principles quantum mechanical treatment, here we adopt in the spirit of a QM/MM model a combination of density functional theory (“QM”, for the system) and a semiempirical forcefield (“MM”, for the bath). We apply the Hamiltonian to a fully H-covered Si(100)-(2 × 1) surface, using Fermi’s Golden Rule to obtain vibrational relaxation rates of various H–Si bending modes of this system. As in earlier work it is found that the relaxation is dominated by two-phonon contributions because of an energy gap between the Si–H bending modes and the Si phonon bands. We obtain vibrational lifetimes (of the first excited state) on the order of 2 ps at K. The lifetimes depend only little on the type of bending mode (symmetric vs. antisymmetric, parallel vs. perpendicular to the Si2H2 dimers). They decrease by a factor of about two when heating the surface to 300 K. We also study isotope effects by replacing adsorbed H atoms by deuterium, D. The Si–D bending modes are shifted into the Si phonon band of the solid, opening up one-phonon decay channels and reducing the lifetimes to few hundred fs.
Accurate Valence Ionization Energies from Kohn-Sham Eigenvalues with the Help of Potential Adjustors
(2017)
An accurate yet computationally very efficient and formally well justified approach to calculate molecular ionization potentials is presented and tested. The first as well as higher ionization potentials are obtained as the negatives of the Kohn-Sham eigenvalues of the neutral molecule after adjusting the eigenvalues by a recently [Gorling Phys. Rev. B 2015, 91, 245120] introduced potential adjustor for exchange-correlation potentials. Technically the method is very simple. Besides a Kohn-Sham calculation of the neutral molecule, only a second Kohn-Sham calculation of the cation is required. The eigenvalue spectrum of the neutral molecule is shifted such that the negative of the eigenvalue of the highest occupied molecular orbital equals the energy difference of the total electronic energies of the cation minus the neutral molecule. For the first ionization potential this simply amounts to a Delta SCF calculation. Then, the higher ionization potentials are obtained as the negatives of the correspondingly shifted Kohn-Sham eigenvalues. Importantly, this shift of the Kohn-Sham eigenvalue spectrum is not just ad hoc. In fact, it is formally necessary for the physically correct energetic adjustment of the eigenvalue spectrum as it results from ensemble density-functional theory. An analogous approach for electron affinities is equally well obtained and justified. To illustrate the practical benefits of the approach, we calculate the valence ionization energies of test sets of small- and medium-sized molecules and photoelectron spectra of medium-sized electron acceptor molecules using a typical semilocal (PBE) and two typical global hybrid functionals (B3LYP and PBE0). The potential adjusted B3LYP and PBE0 eigenvalues yield valence ionization potentials that are in very good agreement with experimental values, reaching an accuracy that is as good as the best G(0)W(0) methods, however, at much lower computational costs. The potential adjusted PBE eigenvalues result in somewhat less accurate ionization energies, which, however, are almost as accurate as those obtained from the most commonly used G(0)W(0) variants.
Six N-alkylpyridinium salts [CnPy](2)[MCl4] (n = 4 or 12 and M = Co, Cu, Zn) were synthesized, and their structure and thermal properties were studied. The [C4Py](2)[MCl4] compounds are monoclinic and crystallize in the space group P2(1)/n. The crystals of the longer chain analogues [C12Py](2)[MCl4] are triclinic and crystallize in the space group P (1) over bar. Above the melting temperature, all compounds are ionic liquids (ILs). The derivatives with the longer C12 chain exhibit liquid crystallinity and the shorter chain compounds only show a melting transition. Consistent with single-crystal analysis, electron paramagnetic resonance spectroscopy suggests that the [CuCl4](2-) ions in the Cu-based ILs have a distorted tetrahedral geometry.
Six N-alkylpyridinium salts [CnPy](2)[MCl4] (n = 4 or 12 and M = Co, Cu, Zn) were synthesized, and their structure and thermal properties were studied. The [C4Py](2)[MCl4] compounds are monoclinic and crystallize in the space group P2(1)/n. The crystals of the longer chain analogues [C12Py](2)[MCl4] are triclinic and crystallize in the space group P (1) over bar. Above the melting temperature, all compounds are ionic liquids (ILs). The derivatives with the longer C12 chain exhibit liquid crystallinity and the shorter chain compounds only show a melting transition. Consistent with single-crystal analysis, electron paramagnetic resonance spectroscopy suggests that the [CuCl4](2-) ions in the Cu-based ILs have a distorted tetrahedral geometry.
The article describes the synthesis and properties of alpha-((4-cyanobenzoyl)oxy)-omega-methyl poly(ethylene glycol), the first poly(ethylene glycol) stabilizer for metal nanoparticles that is based on a cyano rather than a thiol or thiolate anchor group. The silver particles used to evaluate the effectiveness of the new stabilizer typically have a bimodal size distribution with hydrodynamic diameters of ca. 13 and ca. 79 nm. Polymer stability was evaluated as a function of the pH value both for the free stabilizer and for the polymers bound to the surface of the silver nanoparticles using H-1 NMR spectroscopy and zeta potential measurements. The polymer shows a high stability between pH 3 and 9. At pH 12 and higher the polymer coating is degraded over time suggesting that alpha-((4-cyanobenzoyl) oxy)-omega-methyl poly(ethylene glycol) is a good stabilizer for metal nanoparticles in aqueous media unless very high pH conditions are present in the system. The study thus demonstrates that cyano groups can be viable alternatives to the more conventional thiol/thiolate anchors.
microRNAs (miRNAs) have been identified as high-value drug targets. A widely applied strategy in miRNA inhibition is the use of antisense agents. However, it has been shown that oligonucleotides are poorly cell permeable because of their complex chemical structure and due to their negatively charged backbone. Consequently, the general application of oligonucleotides in therapy is limited. Since miRNAs’ functions are executed exclusively by the Argonaute 2 protein, we therefore describe a protocol for the design of a novel miRNA inhibitor class: antagonists of the miRNA-Argonaute 2 protein complex, so-called anti-miR-AGOs, that not only block the crucial binding site of the target miRNA but also bind to the protein’s active site. Due to their lower molecular weight and, thus, more drug-like chemical structure, the novel inhibitor class may show better pharmacokinetic properties than reported oligonucleotide inhibitors, enabling them for potential therapeutic use.
Background: Malaria is an old life-threatening parasitic disease that is still affecting many people, mainly children living in sub-Saharan Africa. Availability of effective antimalarial drugs played a significant role in the treatment and control of malaria. However, recent information on the emergence of P. falciparum parasites resistant to one of the artemisinin-based combination therapies suggests the need for discovery of new drug molecules. Therefore, this study aimed to evaluate the antiplasmodial activity of extracts, fractions and isolated compound from medicinal plants traditionally used in the treatment of malaria in Tanzania. Methods: Dry powdered plant materials were extracted by cold macerations using different solvents. Norcaesalpin D was isolated by column chromatography from dichloromethane root extract of Caesalpinia bonducella and its structure was assigned based on the spectral data. Crude extracts, fractions and isolated compound were evaluated for antiplasmodial activity against chloroquine-sensitive P. falciparum (3D7), chloroquine-resistant P. falciparum (Dd2, K1) and artemisinin-resistant P. falciparum (IPC 5202 Battambang, IPC 4912 Mondolkiri) strains using the parasite lactate dehydrogenase assay. Results: The results indicated that extracts of Erythrina schliebenii, Holarrhena pubescens, Dissotis melleri and C. bonducella exhibited antiplasmodial activity against Dd2 parasites. Ethanolic root extract of E. schliebenii had an IC50 of 1.87 mu g/mL while methanolic and ethanolic root extracts of H. pubescens exhibited an IC50 = 2.05 mu g/mL and IC50 = 2.43 mu g/mL, respectively. Fractions from H. pubescens and C. bonducella roots were found to be highly active against K1, Dd2 and artemisinin-resistant parasites. Norcaesalpin D from C. bonducella root extract was active with IC50 of 0.98, 1.85 and 2.13 mu g/mL against 3D7, Dd2 and IPC 4912-Mondolkiri parasites, respectively. Conclusions: Antiplasmodial activity of norcaesalpin D and extracts of E. schliebenii, H. pubescens, D. melleri and C. bonducella reported in this study requires further attention for the discovery of antimalarial lead compounds for future drug development.
Background: In Kenya, several species of the genus Maytenus are used in traditional medicine to treat many diseases including malaria. In this study, phytochemical constituents and extracts of Maytenus undata, M. putterlickioides, M. senegalensis and M. heterophylla were evaluated to determine compound/s responsible for antimalarial activity.
Objective: To isolate antiplasmodial compounds from these plant species which could be used as marker compounds in the standardization of their extracts as a phytomedicine for malaria.
Methods: Constituents were isolated through activity-guided fractionation of the MeOH/CHCl3 (1:1) extracts and in vitro inhibition of Plasmodium falciparum. Cytotoxicity was evaluated using Vero cells and the compounds were elucidated on the basis of NMR spectroscopy.
Results: Fractionation of the extracts resulted in the isolation of ten known compounds. Compound 1 showed promising antiplasmodial activity with IC50, 3.63 and 3.95 ng/ml against chloroquine sensitive (D6) and resistant (W2) P. falciparum, respectively and moderate cytotoxicity (CC50, 37.5 ng/ml) against Vero E6 cells. The other compounds showed weak antiplasmodial (IC50 > 1.93 mu g/ml) and cytotoxic (CC50 > 39.52 mu g/ml) activities against P. falciparum and Vero E6 cells, respectively.
Conclusion: (20 alpha)-3-hydroxy-2-oxo-24-nor-friedela-1(10),3,5,7-tetraen-carboxylic acid-(29)-methyl-ester (pristimerin) (1) was the most active marker and lead compound that warrants further investigation as a template for the development of new antimalarial drugs. Pristimerin is reported for the first time in M. putterlickioides. 3-Hydroxyolean-12-en-28-oic acid (oleanolic acid) (5), stigmast-5-en-3-ol (beta-sitosterol) (6), 3-oxo-28-friedelanoic acid (7), olean-12-en-3-ol (beta-amyrin) (8), lup-20(29)-en-3-ol (lupeol) (9) and lup-20(29)-en-3-one (lupenone) (10) are reported for the first time in M. undata.
2-Deoxy-D-ribose-5-phosphate aldolase (DERA) is a biocatalyst that is capable of converting acetaldehyde and a second aldehyde as acceptor into enantiomerically pure mono- and diyhydroxyaldehydes, which are important structural motifs in a number of pharmaceutically active compounds. However, substrate as well as product inhibition requires a more-sophisticated process design for the synthesis of these motifs. One way to do so is to the couple aldehyde conversion with transport processes, which, in turn, would require an immobilization of the enzyme within a thin film that can be deposited on a membrane support. Consequently, we developed a fabrication process for such films that is based on the formation of DERA-poly(N-isopropylacrylamide) conjugates that are subsequently allowed to self-assemble at an air-water interface to yield the respective film. In this contribution, we discuss the conjugation conditions, investigate the interfacial properties of the conjugates, and, finally, demonstrate a successful film formation under the preservation of enzymatic activity.
Materials based on biodegradable polyesters, such as poly(butylene terephthalate) (PBT) or poly(butylene terephthalate-co-poly(alkylene glycol) terephthalate) (PBTAT), have potential application as pro-regenerative scaffolds for bone tissue engineering. Herein, the preparation of films composed of PBT or PBTAT and an engineered spider silk protein, (eADF4(C16)), that displays multiple carboxylic acid moieties capable of binding calcium ions and facilitating their biomineralization with calcium carbonate or calcium phosphate is reported. Human mesenchymal stem cells cultured on films mineralized with calcium phosphate show enhanced levels of alkaline phosphatase activity suggesting that such composites have potential use for bone tissue engineering.
Calcium carbonate formation
(2017)
Cholesteryl Hemisuccinate Monolayers Efficiently Control Calcium Phosphate Nucleation and Growth
(2017)
The article describes the phase behavior of cholesteryl hemisuccinate at the air-liquid interface and its effect on calcium phosphate (CP) mineralization. The amphiphile forms stable monolayers with phase transitions at the air-liquid interface from a gas to a tilted liquid-condensed (TLC) and finally to an untilted liquid-condensed (ULC) phase. CP mineralization beneath these monolayers leads to crumpled CP layers made from individual plates. The main crystal phase is octacalcium phosphate (OCP) along with a minor fraction of hydroxyapatite (HAP), as confirmed by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, bright field transmission electron microscopy, and electron diffraction.
Composition inversion takes place in equimolar solid mixtures of sodium or ammonium carbonate and calcium chloride with respect to the combination of anions and cations leading to the corresponding chloride and calcite in complete conversion. The transformation takes place spontaneously under a variety of different situations, even in a powdery mixture resting under ambient conditions. Powder X-ray diffraction data and scanning electron microscopy micrographs are presented to describe the course of the reaction and to characterize the reaction products. The incomplete reaction in the interspace between two compressed tablets of pure starting materials leads to an electric potential due to the presence of uncompensated charges.
New Si-phenyl-substituted silacyclohexanes and 3-silatetrahydropyrans have been synthesized and studied with respect to the conformational equilibria of the heterosix-membered ring by low temperature C-13 NMR spectroscopy and quantum chemical calculations. For 1-methoxy-1-phenylsilacyclohexane 1 and 3-phenyl-3-silatetrahydropyran 4 the conformational equilibria could be frozen and assigned. The Ph-ax reversible arrow Ph-eq equilibrium constants at 103 K are 2.21 for 1 and 4.59 for 4. In complete agreement with former studies of similar silicon compounds, molecules 1 and 4 prefer to adopt the Pheq conformation. The conformational equilibria of 1-hydroxy-1-phenylsilacydohexane 2 and 3-hydroxy-3-phenyl-3-silatetrahydropyran 3 could not be frozen at 100 K and proved to be heavily one-sided (if not anancomeric). Obviously, there is a general trend of predominance of Phax conformer in the gas phase and of Pheq in solution. For the isolated molecules of silanols 2 and 3, calculations allowed to explain the axial predominance of the phenyl group by a larger polarization of the Si-Ph than of the Si-O bond in the Phax conformer and additional destabilization of 3-Ph-eq conformer by repulsion of unidirectional dipoles of the endocyclic oxygen lone pair and of the highly polar axial Si-O bond.
Conformational transition of peptide-functionalized cryogels enabling shape-memory capability
(2017)
In order to modulate the emission of BODIPY fluorophores, they were connected to a diarylethene (DAE) photoswitch via phenylene-ethynylene linkers of different lengths and orientations. The latter allowed for modulation of the electronic coupling in the prepared four BODIPY-DAE dyads, which were compared also to appropriate BODIPY and DAE model compounds by steady state as well as time-resolved spectroscopies. In their open isomers, all dyads show comparable luminescence behavior indicative of an unperturbed BODIPY fluorophore. In strong contrast, in the closed isomers the BODIPY emission is efficiently quenched but the deactivation mechanism depends on the nature of the linker. The most promising dyad was rendered water-soluble by means of micellar encapsulation and aqueous suspensions were investigated by fluorescence spectroscopy and microscopy. Our results (i) illustrate that the electronic communication between the BODIPY and DAE units can indeed be fine-tuned by the nature of the linker to achieve fluorescence modulation while maintaining photoswitchability and (ii) highlight potential applications to image and control biological processes with high spatio-temporal resolution.
The mechanism of the primary ammonium/tertiary amine-mediated ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) was investigated. Kinetic analyses revealed that the normal amine mechanism (NAM) together with a dormant-active chain end equilibrium were responsible for the controlled nature of this polymerization pathway, but that the polymerization also proceeded via the activated monomer mechanism (AMM). Mixtures of primary amines (1 equiv) and tertiary amines (0-1.5 equiv) were therefore tested to confirm the co-existence of the NAM and AMM and determine the limits for a controlled polymerization. For tertiary amine molar fractions smaller than 0.8 equiv, the reaction times were greatly reduced (compared to primary amine-initiated polymerization) without compromising the control of the reaction. Hence, the polymerization of NCA can proceed in a controlled manner even when the AMM contributes to the overall chain growth mechanism. (C) 2017 Elsevier Ltd. All rights reserved.
The title compound, erioflorin, C19H24O6 [systematic name: (1aR,3S,4Z,5aR,8aR,9R,10aR)-1a, 2,3,5a, 7,8,8a, 9,10,10a-decahydro-3-hydroxy-4,10a-dimethyl-8-methylidene-7-oxooxireno[5,6] cyclodeca[1,2-b]furan-9-yl methacrylate], is a tricyclic germacrane sesquiterpene lactone, which was isolated from Podanthus mitiqui (L.). The compound crystallizes in the space group P2(1)2(1)2(1), and its molecular structure consists of a methacrylic ester of a ten-membered ring sesquiterpenoid annelated with an epoxide and a butyrolactone. The structure is stabilized by one intramolecular C-H center dot center dot center dot O hydrogen bond. An O-H center dot center dot center dot O hydrogen bond and further C-H center dot center dot center dot O interactions can be observed in the packing.
The title compound, erioflorin, C19H24O6 [systematic name: (1aR,3S,4Z,5aR,8aR,9R,10aR)-1a, 2,3,5a, 7,8,8a, 9,10,10a-decahydro-3-hydroxy-4,10a-dimethyl-8-methylidene-7-oxooxireno[5,6] cyclodeca[1,2-b]furan-9-yl methacrylate], is a tricyclic germacrane sesquiterpene lactone, which was isolated from Podanthus mitiqui (L.). The compound crystallizes in the space group P2(1)2(1)2(1), and its molecular structure consists of a methacrylic ester of a ten-membered ring sesquiterpenoid annelated with an epoxide and a butyrolactone. The structure is stabilized by one intramolecular C-H center dot center dot center dot O hydrogen bond. An O-H center dot center dot center dot O hydrogen bond and further C-H center dot center dot center dot O interactions can be observed in the packing.
In dieser Arbeit werden drei Themen im Zusammenhang mit den spektroskopischen Eigenschaften von Cumarin- (Cou) und DBD-Farbstoffen ([1,3]Dioxolo[4,5-f][1,3]benzodioxol) behandelt. Der erste Teil zeigt die grundlegende spektroskopische Charakterisierung von 7-Aminocumarinen und ihre potentielle Anwendung als Fluoreszenzsonde für Fluoreszenzimmunassays. Im zweiten Teil werden mit die photophysikalischen Eigenschaften der Cumarine genutzt um Cou- und DBD-funktionalisierte Oligo-Spiro-Ketal-Stäbe (OSTK) und ihre Eigenschaften als Membransonden zu untersuchen. Der letzte Teil beschäftigt sich mit der Synthese und der Charakterisierung von Cou- und DBD-funktionalisierten Polyprolinen als Referenzsysteme für schwefelfunktionalisierte OSTK-Stäbe und ihrer Kopplung an Goldnanopartikel.
Immunochemische Analysemethoden sind in der klinischen Diagnostik sehr erfolgreich und werden heute auch für die Nahrungsmittelkontrolle und Überwachung von Umweltfragen mit einbezogen. Dadurch sind sie von großem Interesse für weitere Forschungen. Unter den verschiedenen Immunassays zeichnen sich lumineszenzbasierte Formate durch ihre herausragende Sensitivität aus, die dieses Format für zukünftige Anwendungen besonders attraktiv macht. Die Notwendigkeit von Multiparameterdetektionsmöglichkeiten erfordert einen Werkzeugkasten mit Farbstoffen, um die biochemische Reaktion in ein optisch detektierbares Signal umzuwandeln. Hier wird bei einem Multiparameteransatz jeder Analyt durch einen anderen Farbstoff mit einer einzigartigen Emissionsfarbe, die den blauen bis roten Spektralbereich abdecken, oder eine einzigartige Abklingzeit detektiert. Im Falle eines kompetitiven Immunassayformats wäre für jeden der verschiedenen Farbstoffe ein einzelner Antikörper erforderlich. In der vorliegenden Arbeit wird ein leicht modifizierter Ansatz unter Verwendung einer Cumarineinheit, gegen die hochspezifische monoklonale Antikörper (mAb) erzeugt wurden, als grundlegendes Antigen präsentiert. Durch eine Modifikation der Stammcumarineinheit an einer Position des Moleküls, die für die Erkennung durch den Antikörper nicht relevant ist, kann auf den vollen Spektralbereich von blau bis tiefrot zugegriffen werden. In dieser Arbeit wird die photophysikalische Charakterisierung der verschiedenen Cumarinderivate und ihrer entsprechenden Immunkomplexe mit zwei verschiedenen, aber dennoch hochspezifischen, Antikörpern präsentiert. Die Cumarinfarbstoffe und ihre Immunkomplexe wurden durch stationäre und zeitaufgelöste Absorptions- sowie Fluoreszenzemissionsspektroskopie charakterisiert. Darüber hinaus wurden Fluoreszenzdepolarisationsmessungen durchgeführt, um die Daten zu vervollständigen, die die verschiedenen Bindungsmodi der beiden Antikörper betonten. Im Gegensatz zu häufig eingesetzten Nachweissystemen wurde eine massive Fluoreszenzverstärkung bei der Bildung des Antikörper-Farbstoffkomplexes bis zu einem Faktor von 50 gefunden. Wegen der leichten Emissionsfarbenänderung durch das Anpassen der Cumarinsubstitution in der für die Antigenbindung nicht relevanten Position des Elternmoleküls, ist eine Farbstoff-Toolbox vorhanden, die bei der Konstruktion von kompetitiven Multiparameterfluoreszenzverstärkungsimmunassays verwendet werden kann.
Oligo-Spiro-Thio-Ketal-Stäbe werden aufgrund ihres hydrophoben Rückgrats leicht in Doppellipidschichten eingebaut und deshalb als optische Membransonde verwendet. Wegen ihres geringen Durchmessers wird nur eine minimale Störung der Doppellipidschicht verursacht. Durch die Markierung mit Fluoreszenzfarbstoffen sind neuartige Förster-Resonanz-Energietransfersonden mit hoch definierten relativen Orientierungen der Übergangsdipolmomente der Donor- und Akzeptorfarbstoffe zugänglich und macht die Klasse der OSTK-Sonden zu einem leistungsstarken, flexiblen Werkzeugkasten für optische Biosensoranwendungen. Mit Hilfe von stationären und zeitaufgelösten Fluoreszenzexperimenten wurde der Einbau von Cumarin- und DBD markierten OSTK-Stäben in großen unilamellaren Vesikeln untersucht und die Ergebnisse durch Fluoreszenzdepolarisationsmessungen untermauert.
Der letzte Teil dieser Arbeit beschäftigt sich mit der Synthese und Charakterisierung von Cou- und DBD-funktionalisierten Polyprolinen und ihrer Kopplung an Goldnanopartikel. Die farbstoffmarkierten Polyproline konnten erfolgreich hergestellt werden. Es zeigten sich deutlich Einflüsse auf die spektroskopischen Eigenschaften der Farbstoffe durch die Bindung an die Polyprolinhelix. Die Kopplung an die 5 nm großen AuNP konnte erfolgreich durchgeführt werden. Die Erfahrungen, die durch die Kopplung der Polyproline an die AuNP, gewonnen wurde, ist die Basis für eine Einzelmolekül-AFM-FRET-Nanoskopie mit OSTK-Stäben.
Among modern functional materials, the class of nitrogen-containing carbons combines non-toxicity and sustainability with outstanding properties. The versatility of this materials class is based on the opportunity to tune electronic and catalytic properties via the nitrogen content and –motifs: This ranges from the electronically conducting N-doped carbon, where few carbon atoms in the graphitic lattice are substituted by nitrogen, to the organic semiconductor graphitic carbon nitride (g-C₃N₄), with a structure based on tri-s-triazine units.
In general, composites can reveal outstanding catalytic properties due to synergistic behavior, e.g. the formation of electronic heterojunctions. In this thesis, the formation of an “all-carbon” heterojunction was targeted, i.e. differences in the electronic properties of the single components were achieved by the introduction of different nitrogen motives into the carbon lattice. Such composites are promising as metal-free catalysts for the photocatalytic water splitting. Here, hydrogen can be generated from water by light irradiation with the use of a photocatalyst. As first part of the heterojunction, the organic semiconductor g-C₃N₄ was employed, because of its suitable band structure for photocatalytic water splitting, high stability and non-toxicity. The second part was chosen as C₂N, a recently discovered semiconductor. Compared to g-C₃N₄, the less nitrogen containing C₂N has a smaller band gap and a higher absorption coefficient in the visible light range, which is expected to increase the optical absorption in the composite eventually leading to an enhanced charge carrier separation due to the formation of an electronic heterojunction.
The aim of preparing an “all-carbon” composite included the research on appropriate precursors for the respective components g-C₃N₄ and C₂N, as well as strategies for appropriate structuring. This was targeted by applying precursors which can form supramolecular pre-organized structures. This allows for more control over morphology and atom patterns during the carbonization process.
In the first part of this thesis, it was demonstrated how the photocatalytic activity of g-C₃N₄ can be increased by the targeted introduction of defects or surface terminations. This was achieved by using caffeine as a “growth stopping” additive during the formation of the hydrogen-bonded supramolecular precursor complexes. The increased photocatalytic activity of the obtained materials was demonstrated with dye degradation experiments.
The second part of this thesis was focused on the synthesis of the second component C₂N. Here, a deep eutectic mixture from hexaketocyclohexane and urea was structured using the biopolymer chitosan. This scaffolding resulted in mesoporous nitrogen-doped carbon monoliths and beads. CO₂- and dye-adsorption experiments with the obtained monolith material revealed a high isosteric heat of CO₂-adsorption and showed the accessibility of the monolithic pore system to larger dye molecules. Furthermore, a novel precursor system for C₂N was explored, based on organic crystals from squaric acid and urea. The respective C₂N carbon with an unusual sheet-like morphology could be synthesized by carbonization of the crystals at 550 °C. With this precursor system, also microporous C₂N carbon with a BET surface area of 865 m²/g was obtained by “salt-templating” with ZnCl₂.
Finally, the preparation of a g-C₃N₄/C₂N “all carbon” composite heterojunction was attempted by the self-assembly of g-C₃N₄ and C₂N nanosheets and tested for photocatalytic water splitting. Indeed, the composites revealed high rates of hydrogen evolution when compared to bulk g-C₃N₄. However, the increased catalytic activity was mainly attributed to the high surface area of the nanocomposites rather than to the composition. With regard to alternative composite synthesis ways, first experiments indicated N-Methyl-2-pyrrolidon to be suitable for higher concentrated dispersion of C₂N nanosheets. Eventually, the results obtained in this thesis provide precious synthetic contributions towards the preparation and processing of carbon/nitrogen compounds for energy applications.
There is a tremendous demand for highly Na+-selective fluoroionophores to monitor the top analyte Na+ in life science. Here, we report a systematic route to develop highly Na+/K+ selective fluorescent probes. Thus, we synthesized a set of fluoroionophores 1, 3, 4, 5, 8 and 9 (see Scheme 1) to investigate the Na+/K+ selectivity and Na(+-)complex stability in CH3CN and H2O. These Na+-probes bear different 15-crown-5 moieties to bind Na+ stronger than K+. In the set of the diethylaminocoumarin-substituted fluoroionophores 1-5, the following trend of fluorescence quenching 1 > 3 > 2 > 4 > 5 in CH3CN was observed. Therefore, the flexibility of the aza-15-crown-5 moieties in 1-4 determines the conjugation of the nitrogen lone pair with the aromatic ring. As a consequence, 1 showed in CH3CN the highest Na+-induced fluorescence enhancement (FE) by a factor of 46.5 and a weaker K+ induced FE of 3.7. The Na+-complex stability of 1-4 in CH3CN is enhanced in the following order of 2 > 4 > 3 > 1, assuming that the O-atom of the methoxy group in the ortho-position, as shown in 2, strengthened the Na+-complex formation. Furthermore, we found for the N( o-methoxyphenyl) aza-15-crown-5 substituted fluoroionophores 2, 8 and 9 in H2O, an enhanced Na+-complex stability in the following order 8 > 2 > 9 and an increased Na+/K+ selectivity in the reverse order 9 > 2 > 8. Notably, the Na+-induced FE of 8 (FEF = 10.9), 2 (FEF = 5.0) and 9 (FEF = 2.0) showed a similar trend associated with a decreased K+-induced FE [8 (FEF = 2.7) > 2 (FEF = 1.5) > 9 (FEF = 1.1)]. Here, the Na+-complex stability and Na+/K+ selectivity is also influenced by the fluorophore moiety. Thus, fluorescent probe 8 (K-d = 48 mm) allows high-contrast, sensitive, and selective Na+ measurements over extracellular K+ levels. A higher Na+/K+ selectivity showed fluorescent probe 9, but also a higher Kd value of 223 mm. Therefore, 9 is a suitable tool to measure Na+ concentrations up to 300 mm at a fluorescence emission of 614 nm.
Development of a reliable and environmentally friendly synthesis for fluorescence carbon nanodots
(2017)
Carbon nanodots (CNDs) have generated considerable attention due to their promising properties, e.g. high water solubility, chemical inertness, resistance to photobleaching, high biocompatibility and ease of functionalization. These properties render them ideal for a wide range of functions, e.g. electrochemical applications, waste water treatment, (photo)catalysis, bio-imaging and bio-technology, as well as chemical sensing, and optoelectronic devices like LEDs. In particular, the ability to prepare CNDs from a wide range of accessible organic materials makes them a potential alternative for conventional organic dyes and semiconductor quantum dots (QDs) in various applications. However, current synthesis methods are typically expensive and depend on complex and time-consuming processes or severe synthesis conditions and toxic chemicals. One way to reduce overall preparation costs is the use of biological waste as starting material. Hence, natural carbon sources such as pomelo peal, egg white and egg yolk, orange juice, and even eggshells, to name a few; have been used for the preparation of CNDs. While the use of waste is desirable, especially to avoid competition with essential food production, most starting-materials lack the essential purity and structural homogeneity to obtain homogeneous carbon dots. Furthermore, most synthesis approaches reported to date require extensive purification steps and have resulted in carbon dots with heterogeneous photoluminescent properties and indefinite composition. For this reason, among others, the relationship between CND structure (e.g. size, edge shape, functional groups and overall composition) and photophysical properties is yet not fully understood. This is particularly true for carbon dots displaying selective luminescence (one of their most intriguing properties), i.e. their PL emission wavelength can be tuned by varying the excitation wavelength.
In this work, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain CNDs with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch, carboxylic acids and Tris-EDTA (TE) buffer as carbon- and nitrogen source, respectively. The presented microwave-assisted hydrothermal precursor carbonization (MW-hPC) is characterized by its cost-efficiency, simplicity, short reaction times, low environmental footprint, and high yields of approx. 80% (w/w). Furthermore, only a single synthesis step is necessary to obtain homogeneous water-soluble CNDs with no need for further purification.
Depending on starting materials and reaction conditions different types of CNDs have been prepared. The as-prepared CNDs exhibit reproducible, highly homogeneous and favourable PL properties with narrow emission bands (approx. 70nm FWHM), are non-blinking, and are ready to use without need for further purification, modification or surface passivation agents. Furthermore, the CNDs are comparatively small (approx. 2.0nm to 2.4nm) with narrow size distributions; are stable over a long period of time (at least one year), either in solution or as a dried solid; and maintain their PL properties when re-dispersed in solution. Depending on CND type, the PL quantum yield (PLQY) can be adjusted from as low as 1% to as high as 90%; one of the highest reported PLQY values (for CNDs) so far.
An essential part of this work was the utilization of a microwave synthesis reactor, allowing various batch sizes and precise control over reaction temperature and -time, pressure, and heating- and cooling rate, while also being safe to operate at elevated reaction conditions (e.g. 230 ±C and 30 bar). The hereby-achieved high sample throughput allowed, for the first time, the thorough investigation of a wide range of synthesis parameters, providing valuable insight into the CND formation. The influence of carbon- and nitrogen source, precursor concentration and -combination, reaction time and -temperature, batch size, and post-synthesis purification steps were carefully investigated regarding their influence on the optical properties of as-synthesized CNDs. In addition, the change in photophysical properties resulting from the conversion of CND solution into solid and back into the solution was investigated. Remarkably, upon freeze-drying the initial brown CND-solution turns into a non-fluorescent white/slightly yellow to brown solid which recovers PL in aqueous solution. Selected CND samples were also subject to EDX, FTIR, NMR, PL lifetime (TCSPC), particle size (TEM), TGA and XRD analysis. Besides structural characterization, the pH- and excitation dependent PL characteristics (i.e. selective luminescence) were examined; giving inside into the origin of photophysical properties and excitation dependent behaviour of CNDs. The obtained results support the notion that for CNDs the nature of the surface states determines the PL properties and that excitation dependent behaviour is caused by the “Giant Red-Edge Excitation Shift” (GREES).
In this work, a sensor system based on thermoresponsive materials is developed by utilizing a modular approach. By synthesizing three different key monomers containing either a carboxyl, alkene or alkyne end group connected with a spacer to the methacrylic polymerizable unit, a flexible copolymerization strategy has been set up with oligo ethylene glycol methacrylates. This allows to tune the lower critical solution temperature (LCST) of the polymers in aqueous media. The molar masses are variable thanks to the excurse taken in polymerization in ionic liquids thus stretching molar masses from 25 to over 1000 kDa. The systems that were shown shown to be effective in aqueous solution could be immobilized on surfaces by copolymerizing photo crosslinkable units. The immobilized systems were formulated to give different layer thicknesses, swelling ratios and mesh sizes depending on the demand of the coupling reaction.
The coupling of detector units or model molecules is approached via reactions of the click chemistry pool, and the reactions are evaluated on their efficiency under those aspects, too. These coupling reactions are followed by surface plasmon resonance spectroscopy (SPR) to judge efficiency. With these tools at hand, Salmonella saccharides could be selectively detected by SPR. Influenza viruses were detected in solution by turbidimetry in solution as well as by a copolymerized solvatochromic dye to track binding via the changes of the polymers’ fluorescence by said binding event. This effect could also be achieved by utilizing the thermoresponsive behavior. Another demonstrator consists of the detection system bound to a quartz surface, thus allowing the virus detection on a solid carrier.
The experiments show the great potential of combining the concepts of thermoresponsive materials and click chemistry to develop technically simple sensors for large biomolecules and viruses.
Polyplexes, composed of Salmon DNA and very small gold nanoparticles embedded into a dendritic glycopolymer architecture of sugar-modified poly(ethyleneimine) (PEI-Mal) with a molar mass of about 25,000 g/mol, were characterized by dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (mu-DSC) and transmission electron microscopy (TEM). The PEI-Mal-entrapped gold nanoparticles of about 2 nm in diameter influence the polyplex formation of the hyperbranched PEI containing bulky maltose, and in consequence the DNA is more compactized in the inner part of spherical polyplex particles of about 150 nm in diameter. The resulting more compact core shell polyplex particles with embedded gold nanoparticles in the outer polymer shell will be used as components in forthcoming gene delivery experiments. (C) 2017 Elsevier B.V. All rights reserved.
The combination of stimuli-responsive polymers and proteins that can transport drugs is a promising approach for drug delivery. The formation of ferritin-poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) conjugates by atom-transfer radical polymerization from the protein macroinitiator is described. PDMAEMA is a dual-stimuli-responsive polymer and the thermo- and pH-responsive properties of the resulting conjugates are studied in detail with dynamic light scattering (DLS). Additionally, it is demonstrated that the lower critical solution temperature (LCST) of the protein-polymer conjugates can be further adjusted by the ionic strength of the solution. The conjugates are also characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), matrix-assisted laser desorption ionization-time of flight (MALDI-ToF) mass spectrometry, and NMR spectroscopy. The obtained MALDI-ToF mass spectra are exceptional for protein-polymer conjugates and have not been so often reported.
The synthesis of new N,N-dimethyl carbamoyl 5-aryloxytetrazoles have been reported. Their dynamic H-1-NMR via rotation about C-N bonds in moiety of urea group [a; CO-NMe2 and b; (2-tetrazolyl)N-CO rotations] in the solvents CDCl3 (223-333 K) and DMSO (298-363 K) is studied. Accordingly, the free energies of activation, obtained 16.5 and 16.9 kcal mol(-1) respectively, attributed to the conformational isomerization about the Me2N-C=O bond (a rotation). Moreover, a and b barrier to rotations in 5-((4-methylphenoxy)-N,N-dimethyl-2H-tetrazole-2-carboxamide (P) also were computed at level of B3LYP using 6-311++G** basis set. The optimized geometry parameters are in good agreement with X-ray structure data. The computation of energy barrier for a and b was determined 16.9 and 2.5 kcal mol(-1), respectively. The former is completely in agreement with the result obtained via dynamic NMR. X-ray structure analysis data demonstrate that just 2-acylated tetrazole was formed in the case of 5-(p-tolyloxy)-N,N-dimethyl-2H-tetrazole-2-carboxamide. X-ray data also revealed a planar trigonal orientation of the Me2N group which is coplanar to carbonyl group with the partial double-bond C-N character. It also demonstrates the synperiplanar position of C=O group with tetrazolyl ring. On average, in solution the plane containing carbonyl bond is almost perpendicular to the plane of the tetrazolyl ring (because of steric effects as confirmed by B3LY12/6-311++G**) while the plane containing Me2N group is coplanar with carbonyl bond which is in contrast with similar urea derivatives and it demonstrates the unusually high rotational energy barrier of these compounds. (C) 2016 Elsevier B.V. All rights reserved.
Complexation with dissolved humic matter can be crucial in controlling the mobility of toxic or radioactive contaminant metals. For speciation and transport modelling, a dynamic equilibrium process is commonly assumed, where association and dissociation run permanently. This is, however, questionable in view of reported observations of a growing resistance to dissociation over time. In this study, the isotope exchange principle was employed to gain direct insight into the dynamics of the complexation equilibrium, including kinetic inertisation phenomena. Terbium(III), an analogue of trivalent actinides, was used as a representative of higher-valent metals. Isotherms of binding to (flocculated) humic acid, determined by means of Tb-160 as a radiotracer, were found to be identical regardless of whether the radioisotope was introduced together with the bulk of stable Tb-159 or subsequently after pre-equilibration for up to 3 months. Consequently, there is a permanent exchange of free and humic-bound Tb since all available binding sites are occupied in the plateau region of the isotherm. The existence of a dynamic equilibrium was thus evidenced. There was no indication of an inertisation under these experimental conditions. If the small amount of Tb-160 was introduced prior to saturation with Tb-159, the expected partial desorption of Tb-160 occurred at much lower rates than observed for the equilibration process in the reverse procedure. In addition, the rates decreased with time of pre-equilibration. Inertisation phenomena are thus confined to the stronger sites of humic molecules (occupied at low metal concentrations). Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium. Since, however, metal-humic interaction remains reversible, exchange of metals between humic carriers and mineral surfaces cannot be neglected on the long time scale to be considered in predictive transport models.
Editorial
(2017)
Photothermal therapy is a novel approach to destroy cancer cells by an increase of temperature due to laser illumination of gold nanoparticles (GNPs) that are incorporated into the cells. Here, we study the decomposition of DNA nucleobases via irradiation of gold nanoparticles with ns-laser pulses. The kinetics of the adsorption and decomposition process is described by a theoretical model based on the Langmuir assumptions and correlated with experimentally determined reaction rates revealing a strong influence of the nucleobase specific adsorption. Beside the four nucleobases, their brominated analogs, which are potential radiosensitizers in cancer therapy, are also investigated and show a significant modification of the decomposition rates. The fastest decomposition rates are observed for adenine, 8-bromoadenine, 8-bromoguanine and 5-bromocytosine. These results are in good agreement with the relative adsorption rates that are determined from the aggregation kinetics of the GNPs taking the effect of an inhomogeneous surface into account. For adenine and its brominated analog, the decomposition products are further analyzed by surface enhanced Raman scattering (SERS) indicating a strong fragmentation of the molecules into their smallest subunits.
A series of new sulfobetaine methacrylates, including nitrogen-containing saturated heterocycles, was synthesised by systematically varying the substituents of the zwitterionic group. Radical polymerisation via the RAFT (reversible addition–fragmentation chain transfer) method in trifluoroethanol proceeded smoothly and was well controlled, yielding polymers with predictable molar masses. Molar mass analysis and control of the end-group fidelity were facilitated by end-group labeling with a fluorescent dye. The polymers showed distinct thermo-responsive behaviour of the UCST (upper critical solution temperature) type in an aqueous solution, which could not be simply correlated to their molecular structure via an incremental analysis of the hydrophilic and hydrophobic elements incorporated within them. Increasing the spacer length separating the ammonium and the sulfonate groups of the zwitterion moiety from three to four carbons increased the phase transition temperatures markedly, whereas increasing the length of the spacer separating the ammonium group and the carboxylate ester group on the backbone from two to three carbons provoked the opposite effect. Moreover, the phase transition temperatures of the analogous polyzwitterions decreased in the order dimethylammonio > morpholinio > piperidinio alkanesulfonates. In addition to the basic effect of the polymers’ precise molecular structure, the concentration and the molar mass dependence of the phase transition temperatures were studied. Furthermore, we investigated the influence of added low molar mass salts on the aqueous-phase behaviour for sodium chloride and sodium bromide as well as sodium and ammonium sulfate. The strong effects evolved in a complex way with the salt concentration. The strength of these effects depended on the nature of the anion added, increasing in the order sulfate < chloride < bromide, thus following the empirical Hofmeister series. In contrast, no significant differences were observed when changing the cation, i.e. when adding sodium or ammonium sulfate.
Contactless pressure monitoring based on Forster resonance energy transfer between donor/acceptor pairs immobilized within elastomers is demonstrated. The donor/acceptor energy transfer is employed by dispersing terbium(III) tris[(2-hydroxybenzoyl)-2-aminoethyl] amine complex (LLC, donor) and CdSe/ZnS quantum dots (QD655, acceptor) in styrene-ethylene/buthylene-styrene (SEBS) and poly(dimethylsiloxane) (PDMS). The continuous monitoring of QD luminescence showed a reversible intensity change as the pressure signal is alternated between two stable states indicating a pressure sensitivity of 6350 cps kPa(-1). Time-resolved measurements show the pressure impact on the FRET signal due to an increase of decay time (270 ms up to 420 ms) for the donor signal and parallel drop of decay time (170 mu s to 155 mu s) for the acceptor signal as the net pressure applied. The LLC/QD655 sensors enable a contactless readout as well as space resolved monitoring to enable miniaturization towards smaller integrated stretchable opto-electronics. Elastic FRET sensors can potentially lead to developing profitable analysis systems capable to outdo conventional wired electronic systems (inductive, capacitive, ultrasonic and photoelectric sensors) especially for point-of-care diagnostics, biological monitoring required for wearable electronics.
A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo)switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z -> E) by the same wavelength of light, which normally triggers E -> Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways.
Die Elektrosprayionisation (ESI) ist eine der weitverbreitetsten Ionisationstechniken für flüssige Pro-ben in der Massen- und Ionenmobilitäts(IM)-Spektrometrie. Aufgrund ihrer schonenden Ionisierung wird ESI vorwiegend für empfindliche, komplexe Moleküle in der Biologie und Medizin eingesetzt. Überdies ist sie allerdings für ein sehr breites Spektrum an Substanzklassen anwendbar. Die IM-Spektrometrie wurde ursprünglich zur Detektion gasförmiger Proben entwickelt, die hauptsächlich durch radioaktive Quellen ionisiert werden. Sie ist die einzige analytische Methode, bei der Isomere in Echtzeit getrennt und über ihre charakteristische IM direkt identifiziert werden können. ESI wurde in den 90ger Jahren durch die Hill Gruppe in die IM-Spektrometrie eingeführt. Die Kombination wird bisher jedoch nur von wenigen Gruppen verwendet und hat deshalb noch ein hohes Entwick-lungspotential. Ein vielversprechendes Anwendungsfeld ist der Einsatz in der Hochleistungs-flüssigkeitschromatographie (HPLC) zur mehrdimensionalen Trennung. Heutzutage ist die HPLC die Standardmethode zur Trennung komplexer Proben in der Routineanalytik. HPLC-Trennungsgänge sind jedoch häufig langwierig und der Einsatz verschiedener Laufmittel, hoher Flussraten, von Puffern, sowie Laufmittelgradienten stellt hohe Anforderungen an die Detektoren. Die ESI-IM-Spektrometrie wurde in einigen Studien bereits als HPLC-Detektor eingesetzt, war dort bisher jedoch auf Flussratensplitting oder geringe Flussraten des Laufmittels beschränkt.
In dieser kumulativen Doktorarbeit konnte daher erstmals ein ESI IM-Spektrometer als HPLC-Detektor für den Flussratenbereich von 200-1500 μl/min entwickelt werden. Anhand von fünf Publi-kationen wurden (1) über eine umfassende Charakterisierung die Eignung des Spektrometers als HPLC-Detektor festgestellt, (2) ausgewählte komplexe Trenngänge präsentiert und (3) die Anwen-dung zum Reaktionsmonitoring und (4, 5) mögliche Weiterentwicklungen gezeigt.
Erfolgreich konnten mit dem selbst-entwickelten ESI IM-Spektrometer typische HPLC-Bedingungen wie Wassergehalte im Laufmittel von bis zu 90%, Pufferkonzentrationen von bis zu 10 mM, sowie Nachweisgrenzen von bis zu 50 nM erreicht werden. Weiterhin wurde anhand der komplexen Trennungsgänge (24 Pestizide/18 Aminosäuren) gezeigt, dass die HPLC und die IM-Spektrometrie eine hohe Orthogonalität besitzen. Eine effektive Peakkapazität von 240 wurde so realisiert. Auf der HPLC-Säule koeluierende Substanzen konnten über die Driftzeit getrennt und über ihre IM identifi-ziert werden, sodass die Gesamttrennzeiten erheblich minimiert werden konnten. Die Anwend-barkeit des ESI IM-Spektrometers zur Überwachung chemischer Synthesen wurde anhand einer dreistufigen Reaktion demonstriert. Es konnten die wichtigsten Edukte, Zwischenprodukte und Produkte aller Stufen identifiziert werden. Eine quantitative Auswertung war sowohl über eine kurze HPLC-Vortrennung als auch durch die Entwicklung eines eigenen Kalibrierverfahrens, welches die Ladungskonkurrenz bei ESI berücksichtigt, ohne HPLC möglich. Im zweiten Teil der Arbeit werden zwei Weiterentwicklungen des Spektrometers präsentiert. Eine Möglichkeit ist die Reduzierung des Drucks in den intermediären Bereich (300 - 1000 mbar) mit dem Ziel der Verringerung der benötigten Spannungen. Mithilfe von Streulichtbildern und Strom-Spannungs-Kurven wurden für geringe Drücke eine verminderte Freisetzung der Analyt-Ionen aus den Tropfen festgestellt. Die Verluste konnten jedoch über höhere elektrische Feldstärken ausgeglichen werden, sodass gleiche Nachweisgrenzen bei 500 mbar und bei 1 bar erreicht wurden. Die zweite Weiterentwicklung ist ein neuartiges Ionentors mit Pulsschaltung, welches eine Verdopplung der Auflösung auf bis zu R > 100 bei gleicher Sensitivität ermöglichte. Eine denkbare Anwendung im Bereich der Peptidanalytik wurde mit beachtlichen Auflösungen der Peptide von R = 90 gezeigt.
Magnetische Eisenoxidnanopartikel werden bereits seit geraumer Zeit erfolgreich als MRT-Kontrastmittel in der klinischen Bildgebung eingesetzt. Durch Optimierung der magnetischen Eigenschaften der Nanopartikel kann die Aussagekraft von MR-Aufnahmen verbessert und somit der diagnostische Wert einer MR-Anwendung weiter erhöht werden. Neben der Verbesserung bestehender Verfahren wird die bildgebende Diagnostik ebenso durch die Entwicklung neuer Verfahren, wie dem Magnetic Particle Imaging, vorangetrieben. Da hierbei das Messsignal von den magnetischen Nanopartikeln selbst erzeugt wird, birgt das MPI einen enormen Vorteil hinsichtlich der Sensitivität bei gleichzeitig hoher zeitlicher und räumlicher Auflösung. Da es aktuell jedoch keinen kommerziell vertriebenen in vivo-tauglichen MPI-Tracer gibt, besteht ein dringender Bedarf an geeigneten innovativen Tracermaterialien. Daraus resultierte die Motivation dieser Arbeit biokompatible und superparamagnetische Eisenoxidnanopartikel für den Einsatz als in vivo-Diagnostikum insbesondere im Magnetic Particle Imaging zu entwickeln. Auch wenn der Fokus auf der Tracerentwicklung für das MPI lag, wurde ebenso die MR-Performance bewertet, da geeignete Partikel somit alternativ oder zusätzlich als MR-Kontrastmittel mit verbesserten Kontrasteigenschaften eingesetzt werden könnten.
Die Synthese der Eisenoxidnanopartikel erfolgte über die partielle Oxidation von gefälltem Eisen(II)-hydroxid und Green Rust sowie eine diffusionskontrollierte Kopräzipitation in einem Hydrogel.
Mit der partiellen Oxidation von Eisen(II)-hydroxid und Green Rust konnten erfolgreich biokompatible und über lange Zeit stabile Eisenoxidnanopartikel synthetisiert werden. Zudem wurden geeignete Methoden zur Formulierung und Sterilisierung etabliert, wodurch zahlreiche Voraussetzungen für eine Anwendung als in vivo-Diagnostikum geschaffen wurden. Weiterhin ist auf Grundlage der MPS-Performance eine hervorragende Eignung dieser Partikel als MPI-Tracer zu erwarten, wodurch die Weiterentwicklung der MPI-Technologie maßgeblich vorangetrieben werden könnte. Die Bestimmung der NMR-Relaxivitäten sowie ein initialer in vivo-Versuch zeigten zudem das große Potential der formulierten Nanopartikelsuspensionen als MRT-Kontrastmittel. Die Modifizierung der Partikeloberfläche ermöglicht ferner die Herstellung zielgerichteter Nanopartikel sowie die Markierung von Zellen, wodurch das mögliche Anwendungsspektrum maßgeblich erweitert wurde.
Im zweiten Teil wurden Partikel durch eine diffusionskontrollierte Kopräzipitation im Hydrogel, wobei es sich um eine bioinspirierte Modifikation der klassischen Kopräzipitation handelt, synthetisiert, wodurch Partikel mit einer durchschnittlichen Kristallitgröße von 24 nm generiert werden konnten. Die Bestimmung der MPS- und MR-Performance elektrostatisch stabilisierter Partikel ergab vielversprechende Resultate. In Vorbereitung auf die Entwicklung eines in vivo-Diagnostikums wurden die Partikel anschließend erfolgreich sterisch stabilisiert, wodurch der kolloidale Zustand in MilliQ-Wasser über lange Zeit aufrechterhalten werden konnte. Durch Zentrifugation konnten die Partikel zudem erfolgreich in verschiedene Größenfraktionen aufgetrennt werden. Dies ermöglichte die Bestimmung der idealen Aggregatgröße dieses Partikelsystems in Bezug auf die MPS-Performance.
Polymer degradation occurs under physiological conditions in vitro and in vivo, especially when bonds susceptible to hydrolysis are present in the polymer. Understanding of the degradation mechanism, changes of material properties over time, and overall rate of degradation is a necessary prerequisite for the knowledge-based design of polymers with applications in biomedicine. Here, hydrolytic degradation studies of gelatin-based networks synthesized by copper-catalyzed azide-alkyne cycloaddition reaction are reported, which were performed with or without addition of an enzyme. In all cases, networks with a stilbene as crosslinker proofed to be more resistant to degradation than when an octyl diazide was used. Without addition of an enzyme, the rate of degradation was ruled by the crosslinking density of the network and proceeded via a bulk degradation mechanism. Addition of Clostridium histolyticum collagenase resulted in a much enhanced rate of degradation, which furthermore occurred via surface erosion. The mesh size of the hydrogels (>7nm) was in all cases larger than the hydrodynamic radius of the enzyme (4.5nm) so that even in very hydrophilic networks with large mesh size enzymes may be used to induce a fast surface degradation mechanism. This observation is of general interest when designing hydrogels to be applied in the presence of enzymes, as the degradation mechanism and material performance are closely interlinked. Copyright (c) 2016 John Wiley & Sons, Ltd.
Polymeric biomaterials are of specific relevance in medical and pharmaceutical applications due to their wide range of tailorable properties and functionalities. The knowledge about interactions of biomaterials with their biological environment is of crucial importance for developing highly sophisticated medical devices. To achieve optimal in vivo performance, a description at the molecular level is required to gain better understanding about the surface of synthetic materials for tailoring their properties. This is still challenging and requires the comprehensive characterization of morphological structures, polymer chain arrangements and degradation behaviour. The review discusses selected aspects for evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer methods as powerful techniques for studying interfacial properties, such as morphological and degradation processes. The combination of spectroscopic, microscopic and scattering methods with the Langmuir techniques adapted to polymers can substantially improve the understanding of their in vivo behaviour.
Non-Born–Oppenheimer quantum dynamics of H+ 2 excited by shaped one-cycle laser pulses linearly polarised along the molecular axis have been studied by the numerical solution of the time-dependent Schrödinger equation within a three-dimensional model, including the internuclear separation, R, and the electron coordinates z and ρ. Laser carrier frequencies corresponding to the wavelengths λ l = 25 nm through λ l = 400 nm were used and the amplitudes of the pulses were chosen such that the energy of H+ 2 was close to its dissociation threshold at the end of any laser pulse applied. It is shown that there exists a characteristic oscillation frequency ωosc ≃ 0.2265 au (corresponding to the period of τosc ≃ 0.671 fs and the wavelength of λosc ≃ 201 nm) that manifests itself as a ‘carrier’ frequency of temporally shaped oscillations of the time-dependent expectation values ⟨z ⟩ and ⟨∂V/∂z ⟩ that emerge at the ends of the laser pulses and exist on a timescale of at least 50 fs. Time-dependent expectation values ⟨ρ⟩ and ⟨∂V /∂ρ⟩ of the optically passive degree of freedom, ρ, demonstrate post-laser-field oscillations at two basic frequencies ωρ 1 ≈ ωosc and ωρ 2 ≈ 2ωosc. Power spectra associated with the electronic motion show higher- and lower-order harmonics with respect to the driving field.
Four metal organic frameworks with similar topology but different chemical environment inside the pore structure, namely, IFP-1, IFP-3, IFP-5, and IFP-7, have been investigated with respect to the separation potential for olefin paraffin mixtures as well as the influence of the different linkers on adsorption properties using experiments and Monte Carlo simulations. All IFP structures show a higher adsorption of ethane compared to ethene with the exception of IFP-7 which shows no selectivity in breakthrough experiments. For propane/propane separation, all adsorbents show a higher adsorption for the olefin. The experimental results agree quite well with the simulated values except for the IFP-7, which is presumably due to the flexibility of the structure. Moreover, the experimental and simulated isotherms were confirmed with breakthrough experiments that render IFP-1, IFP-3, and IFP-5 as suitable for the purification of ethene from ethane.
This work presents a fabrication of thermoresponsive plasmonic core-satellite nanoassemblies. The structure has a silica nanoparticle core surrounded by gold nanoparticle satellites using thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) chains as scaffolds. The thiol-terminated PNIPAM shell is densely grafted on the silica core via surface-initiated reversible addition-fragmentation chain transfer polymerization and used to anchor numerous gold nanoparticle satellites with a tunable stoichiometry. Below and above lower critical solution temperature, the chain conformation of PNIPAM reversibly changes between swollen and shrunken state. The reversible change of the polymer size varies the refractive index of the local medium surrounding the satellites and the distance between them. The two effects together lead to the thermoresponsive plasmonic properties of the nanoassemblies. Under different satellite densities, two distinctive plasmonic features appear.
New hybrid clay materials with good affinity for phosphate ions were developed from a combination of biomass-Carica papaya seeds (PS) and Musa paradisiaca (Plantain peels-PP), ZnCl2 and Kaolinite clay to produce iPS-HYCA and iPP-HYCA composite adsorbents respectively. Functionalization of these adsorbents with an organosilane produced NPS-HYCA and NPP-HYCA composite adsorbents. The pH(pzc) for the adsorbents were 7.83, 6.91, 7.66 and 6.55 for iPS-HYCA, NPS-HYCA, iPP-HYCA and NPP-HYCA respectively. Using the Brouer-Sotolongo isotherm model which best predict the adsorption capacity of composites for phosphate, iPP-HYCA, iPS-HYCA, NPP-HYCA, and NPS-HYCA composite adsorbents respectively. When compared with some commercial resins, the amino-functionalized adsorbents had better adsorption capacities. Furthermore, amino-functionalized adsorbents showed improved adsorption capacity and rate of phosphate uptake (as much as 40-fold), as well as retain 94% (for NPS-HYCA) and 84.1% (for NPP-HYCA) efficiency for phosphate adsorption after 5 adsorption-desorption cycles (96 h of adsorption time with 100 mg/L of phosphate ions) as against 37.5% (for iPS-HYCA) and 35% (for iPP-HYCA) under similar conditions. In 25 min desorption of phosphate ion attained equilibrium. These new amino-functionalized hybrid clay composite adsorbents, which were prepared by a simple means that is sustainable, have potentials for the efficient capture of phosphate ions from aqueous solution. They are quickly recovered from aqueous solution, non-biodegradable (unlike many biosorbent) with potentials to replace expensive adsorbents in the future. They have the further advantage of being useful in the recovery of phosphate for use in agriculture which could positively impact the global food security programme. (C) 2017 Elsevier Ltd. All rights reserved.
The article describes the synthesis and properties of new ionogels for ion transport. A new preparation process using an organic linker, bis(3-(trimethoxysilyl) propyl) amine (BTMSPA), yields stable organosilica matrix materials. The second ionogel component, the ionic liquid 1-methyl-3-(4-sulfobutyl) imidazolium 4-methylbenzenesulfonate, [BmimSO(3)H][PTS], can easily be prepared with near-quantitative yields. [BmimSO(3)H][PTS] is the proton conducting species in the ionogel. By combining the stable organosilica matrix with the sulfonated ionic liquid, mechanically stable, and highly conductive ionogels with application potential in sensors or fuel cells can be prepared.
Artificial light harvesting complexes find applications in artificial photosynthesis, photovoltaics and light harvesting chemical sensors. They are used to enhance the absorption of light of a reaction center which is often represented by a single acceptor. Here, we present different light harvesting systems on DNA origami structures and analyze systematically the light harvesting efficiency. By changing the number and arrangement of different fluorophores (FAM as donor, Cy3 as transmitter and Cy5 as acceptor molecules) the light harvesting efficiency is optimized to create a broadband absorption and to improve the antenna effect 1 (including two energy transfer steps) from 0.02 to 1.58, and the antenna effect 2 (including a single energy transfer step) from 0.04 to 8.7, i.e. the fluorescence emission of the acceptor is significantly higher when the light-harvesting antenna is excited at lower wavelength compared to direct excitation of the acceptor. The channeling of photo energy to the acceptor proceeds by Forster Resonance Energy Transfer (FRET) and we carefully analyze also the FRET efficiency of the different light harvesting systems. Accordingly, the antenna effect can be tuned by modifying the stoichiometry of donor, transmitter and acceptor dyes, whereas the FRET efficiency is mainly governed by the spectroscopic properties of dyes and their distances.
A new type of self-organized materials based on cholesteric networks filled with photoactive side-chain copolymer is being developed. Supramolecular helical structure of cholesteric polymer network resulting in the selective reflection is used as a photonic scaffold. Photochromic azobenzene-containing nematic copolymer is embedded in cholesteric scaffold and utilized as a photoactive media for optical pattering. 1D and 2D transmission diffraction gratings are successfully recorded in composite films by holographic technique. For the first time the possibility to create selective reflection gratings in cholesteric material mimicking the natural optical properties of cholesteric mesophase is demonstrated. That enables the coexistence of two selective gratings, where one has an intrinsic cholesteric periodic helical structure and the other is a holographic grating generated in photochromic polymer. The full-polymer composites provide high light-induced optical anisotropy due to effective photo-orientation of side-chain fragments of the azobenzene-containing liquid crystalline polymer, and prevent the degradation of the helical superstructure maintaining all optical properties of cholesteric mesophase. The proposed class of optical materials could be easily applied to a broad range of polymeric materials with specific functionality. The versatility of the adjustment and material preprogramming combined with high optical performance makes these materials a highly promising candidate for modern optical and photonic applications.
Functional nanoporous carbon-based materials derived from oxocarbon-metal coordination complexes
(2017)
Nanoporous carbon based materials are of particular interest for both science and industry due to their exceptional properties such as a large surface area, high pore volume, high electroconductivity as well as high chemical and thermal stability. Benefiting from these advantageous properties, nanoporous carbons proved to be useful in various energy and environment related applications including energy storage and conversion, catalysis, gas sorption and separation technologies. The synthesis of nanoporous carbons classically involves thermal carbonization of the carbon precursors (e.g. phenolic resins, polyacrylonitrile, poly(vinyl alcohol) etc.) followed by an activation step and/or it makes use of classical hard or soft templates to obtain well-defined porous structures. However, these synthesis strategies are complicated and costly; and make use of hazardous chemicals, hindering their application for large-scale production. Furthermore, control over the carbon materials properties is challenging owing to the relatively unpredictable processes at the high carbonization temperatures.
In the present thesis, nanoporous carbon based materials are prepared by the direct heat treatment of crystalline precursor materials with pre-defined properties. This synthesis strategy does not require any additional carbon sources or classical hard- or soft templates. The highly stable and porous crystalline precursors are based on coordination compounds of the squarate and croconate ions with various divalent metal ions including Zn2+, Cu2+, Ni2+, and Co2+, respectively. Here, the structural properties of the crystals can be controlled by the choice of appropriate synthesis conditions such as the crystal aging temperature, the ligand/metal molar ratio, the metal ion, and the organic ligand system. In this context, the coordination of the squarate ions to Zn2+ yields porous 3D cube crystalline particles. The morphology of the cubes can be tuned from densely packed cubes with a smooth surface to cubes with intriguing micrometer-sized openings and voids which evolve on the centers of the low index faces as the crystal aging temperature is raised. By varying the molar ratio, the particle shape can be changed from truncated cubes to perfect cubes with right-angled edges.
These crystalline precursors can be easily transformed into the respective carbon based materials by heat treatment at elevated temperatures in a nitrogen atmosphere followed by a facile washing step. The resulting carbons are obtained in good yields and possess a hierarchical pore structure with well-organized and interconnected micro-, meso- and macropores. Moreover, high surface areas and large pore volumes of up to 1957 m2 g-1 and 2.31 cm3 g-1 are achieved, respectively, whereby the macroscopic structure of the precursors is preserved throughout the whole synthesis procedure.
Owing to these advantageous properties, the resulting carbon based materials represent promising supercapacitor electrode materials for energy storage applications. This is exemplarily demonstrated by employing the 3D hierarchical porous carbon cubes derived from squarate-zinc coordination compounds as electrode material showing a specific capacitance of 133 F g-1 in H2SO4 at a scan rate of 5 mV s-1 and retaining 67% of this specific capacitance when the scan rate is increased to 200 mV s-1.
In a further application, the porous carbon cubes derived from squarate-zinc coordination compounds are used as high surface area support material and decorated with nickel nanoparticles via an incipient wetness impregnation. The resulting composite material combines a high surface area, a hierarchical pore structure with high functionality and well-accessible pores. Moreover, owing to their regular micro-cube shape, they allow for a good packing of a fixed-bed flow reactor along with high column efficiency and a minimized pressure drop throughout the packed reactor. Therefore, the composite is employed as heterogeneous catalyst in the selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran showing good catalytic performance and overcoming the conventional problem of column blocking.
Thinking about the rational design of 3D carbon geometries, the functions and properties of the resulting carbon-based materials can be further expanded by the rational introduction of heteroatoms (e.g. N, B, S, P, etc.) into the carbon structures in order to alter properties such as wettability, surface polarity as well as the electrochemical landscape. In this context, the use of crystalline materials based on oxocarbon-metal ion complexes can open a platform of highly functional materials for all processes that involve surface processes.
Im Rahmen dieser Arbeit wurden zum einen erste Oligospiro(thio)ketal (OS(T)K)-basierte Modellsysteme (molekulare Sonden) für abstandsabhängige Messungen mittels Förster-Resonanz-Energietransfer (FRET) und zum anderen Sensorfluorophore, basierend auf einem DBD-Fluorophor und BAPTA, zur Messung der intrazellulären Calcium-Konzentration dargestellt.
Für die Synthese von molekularen Sonden für abstandsabhängige Messungen wurden verschiedenste einfach- und doppelt-markierte OS(T)K-Stäbe entwickelt und spektroskopisch untersucht. Die OS(T)K-Stäbe, sogenannte molekulare Stäbe, dienten als starre Abstandshalter zwischen den Fluorophoren. Als Fluorophore wurden Derivate von 6,7-Dihydroxy-4-methylcoumarin (Donor) und Acyl-DBD (Akzeptor) verwendet, die zusammen ein FRET-Paar bilden. Die Fluorophore wurden so funktionalisiert, dass sie sowohl unbeweglich bzw. „starr“, als auch beweglich bzw. „flexibel“ an den OS(T)K-Stab gebunden werden konnten. Für die Synthese der OS(T)K-Stäbe wurden ebenfalls eine Reihe an unterschiedlich langen und kurzen Stabbausteinen synthetisiert. Auf diese Weise wurden eine Vielzahl an verschiedensten einfach- und doppelt-markierten OS(T)K-Stäben dargestellt, deren Fluorophore sowohl „starr“ als auch „flexibel“ gebunden sind. Die dargestellten Stäbe wurden in verschiedensten Lösungsmitteln spektroskopisch untersucht, um anschließend das Verhalten in Vesikel, die eine biomimetische Umgebung darstellen, zu beurteilen. Es wurde festgestellt, dass sich die Stäbe erfolgreich in die Vesikelmembran einlagerten und hohe FRET-Effizienzen aufweisen.
Des Weiteren wurde ein FRET-Paar dargestellt, das sich durch 2-Photonenabsorpion im NIR-Bereich anregen lässt. Es wurde in den lebenden Zellen mittels Fluoreszenzlebenszeitmikroskopie (FLIM) untersucht.
Zur Untersuchung von intrazellulärem Calcium wurden zwei verschiedene DBD-Fluorophore über einen kurzen Linker mit dem Calcium-Chelator BAPTA verknüpft. Die dargestellten Fluorophore wurden sowohl in vitro als auch in vivo auf ihre Calcium-Sensitivität überprüft. Mittels FLIM wurden in lebenden Zellen die Fluoreszenzlebenszeitverteilungen der Fluorophore nach Calcium-Konzentrationsänderungen detektiert.
The field of nanophotonics focuses on the interaction between electromagnetic radiation and matter on the nanometer scale. The elements of nanoscale photonic devices can transfer excitation energy non-radiatively from an excited donor molecule to an acceptor molecule by Förster resonance energy transfer (FRET). The efficiency of this energy transfer is highly dependent on the donor-acceptor distance. Hence, in these nanoscale photonic devices it is of high importance to have a good control over the spatial assembly of used fluorophores. Based on molecular self-assembly processes, various nanostructures can be produced. Here, DNA nanotechnology and especially the DNA origami technique are auspicious self-assembling methods. By using DNA origami nanostructures different fluorophores can be introduced with a high local control to create a variety of nanoscale photonic objects. The applications of such nanostructures range from photonic wires and logic gates for molecular computing to artificial light harvesting systems for artificial photosynthesis.
In the present cumulative doctoral thesis, different FRET systems on DNA origami structures have been designed and thoroughly analyzed. Firstly, the formation of guanine (G) quadruplex structures from G rich DNA sequences has been studied based on a two-color FRET system (Fluorescein (FAM)/Cyanine3 (Cy3)). Here, the influences of different cations (Na+ and K+), of the DNA origami structure and of the DNA sequence on the G-quadruplex formation have been analyzed. In this study, an ion-selective K+ sensing scheme based on the G-quadruplex formation on DNA origami structures has been developed. Subsequently, the reversibility of the G-quadruplex formation on DNA origami structures has been evaluated. This has been done for the simple two-color FRET system which has then been advanced to a switchable photonic wire by introducing additional fluorophores (FAM/Cy3/Cyanine5 (Cy5)/IRDye®700). In the last part, the emission intensity of the acceptor molecule (Cy5) in a three-color FRET cascade has been tuned by arranging multiple donor (FAM) and transmitter (Cy3) molecules around the central acceptor molecule. In such artificial light harvesting systems, the excitation energy is absorbed by several donor and transmitter molecules followed by an energy transfer to the acceptor leading to a brighter Cy5 emission. Furthermore, the range of possible excitation wavelengths is extended by using several different fluorophores (FAM/Cy3/Cy5). In this part of the thesis, the light harvesting efficiency (antenna effect) and the FRET efficiency of different donor/transmitter/acceptor assemblies have been analyzed and the artificial light harvesting complex has been optimized in this respect.
General Synthetic Route toward Highly Dispersed Metal Clusters Enabled by Poly(ionic liquid)s
(2017)
The ability to synthesize a broad spectrum of metal clusters (MCs) with their size controllable on a subnanometer scale presents an enticing prospect for exploring nanosize-dependent properties. Here we report an innovative design of a capping agent from a polytriazolium poly(ionic liquid) (PIL) in a vesicular form in solution that allows for crafting a variety of MCs including transition metals, noble metals, and their bimetallic alloy with precisely controlled sizes (similar to 1 nm) and record-high catalytic performance. The ultrastrong stabilization power is a result of an unusual synergy between the conventional binding sites in the heterocyclic cations in PIL and an in situ generated polycarbene structure induced simultaneously to the reduction reaction.
Nanolenses are linear chains of differently-sized metal nanoparticles, which can theoretically provide extremely high field enhancements. The complex structure renders their synthesis challenging and has hampered closer analyses so far. Here, the technique of DNA origami was used to self-assemble DNA-coated 10 nm, 20 nm, and 60 nm gold or silver nanoparticles into gold or silver nanolenses. Three different geometrical arrangements of gold nanolenses were assembled, and for each of the three, sets of single gold nanolenses were investigated in detail by atomic force microscopy, scanning electron microscopy, dark-field scattering and Raman spectroscopy. The surface-enhanced Raman scattering (SERS) capabilities of the single nanolenses were assessed by labelling the 10 nm gold nanoparticle selectively with dye molecules. The experimental data was complemented by finite-difference time-domain simulations. For those gold nanolenses which showed the strongest field enhancement, SERS signals from the two different internal gaps were compared by selectively placing probe dyes on the 20 nm or 60 nm gold particles. The highest enhancement was found for the gap between the 20 nm and 10 nm nanoparticle, which is indicative of a cascaded field enhancement. The protein streptavidin was labelled with alkyne groups and served as a biological model analyte, bound between the 20 nm and 10 nm particle of silver nanolenses. Thereby, a SERS signal from a single streptavidin could be detected. Background peaks observed in SERS measurements on single silver nanolenses could be attributed to amorphous carbon. It was shown that the amorphous carbon is generated in situ.
Nanolenses are self-similar chains of metal nanoparticles, which can theoretically provide extremely high field enhancements. Yet, the complex structure renders their synthesis challenging and has hampered closer analyses so far. Here, DNA origami is used to self-assemble 10, 20, and 60 nm gold nanoparticles as plasmonic gold nanolenses (AuNLs) in solution and in billions of copies. Three different geometrical arrangements are assembled, and for each of the three designs, surface-enhanced Raman scattering (SERS) capabilities of single AuNLs are assessed. For the design which shows the best properties, SERS signals from the two different internal gaps are compared by selectively placing probe dyes. The highest Raman enhancement is found for the gap between the small and medium nanoparticle, which is indicative of a cascaded field enhancement.
In der vorliegenden Arbeit konnte gezeigt werden, dass die beiden verwendeten Amphiphile mit Cholesterol als hydrophoben Block, gute Template für die Mineralisation von Calciumphosphat an der Wasser/Luft-Grenzfläche sind. Mittels Infrarot-Reflexions-Absorptions-Spektroskopie (IRRAS), Röntgenphotoelektronenspektroskopie (XPS), Energie dispersiver Röntgenspektroskopie (EDXS), Elektronenbeugung (SAED) und hochauflösende Transmissionselektronenmikroskopie (HRTEM) konnte die erfolgreiche Mineralisation von Calciumphosphat für beide Amphiphile an der Wasser/Luft-Grenzfläche nachgewiesen werden. Es konnte auch gezeigt werden, dass das Phasenverhalten der beiden Amphiphile und die bei der Mineralisation von Calciumphosphat gebildeten Kristallphasen nicht identisch sind. Beide Amphiphile üben demnach einen unterschiedlichen Einfluss auf den Mineralisationsverlauf aus.
Beim CHOL-HEM konnte sowohl nach 3 h als auch nach 5 h Octacalciumphosphat (OCP) als einzige Kristallphase mittels XPS, SAED, HRTEM und EDXS nachgewiesen werden. Das A-CHOL hingegen zeigte bei der Mineralisation von Calciumphosphat nach 1 h zunächst eine nicht eindeutig identifizierbare Vorläuferphase aus amorphen Calciumphosphat, Brushit (DCPD) oder OCP. Diese wandelte sich dann nach 3 h und 5 h in ein Gemisch, bestehend aus OCP und ein wenig Hydroxylapatit (HAP) um.
Die Schlussfolgerung daraus ist, dass das CHOL-HEM in der Lage ist, dass während der Mineralisation entstandene OCP zu stabilisieren. Dies geschieht vermutlich durch die Adsorption des Amphiphils bevorzugt an der OCP Oberfläche in [100] Orientierung. Dadurch wird die Spaltung entlang der c-Achse unterdrückt und die Hydrolyse zum HAP verhindert.
Das A-CHOL ist hingegen sterisch anspruchsvoller und kann wahrscheinlich aufgrund seiner Größe nicht so gut an der OCP Kristalloberfläche adsorbieren verglichen zum CHOL HEM. Das CHOL-HEM kann also die Hydrolyse von OCP zu HAP besser unterdrücken als das A-CHOL. Da jedoch auch beim A-CHOL nach einer Mineralisationszeit von 5 h nur wenig HAP zu finden ist, wäre auch hier ein Stabilisierungseffekt der OCP Kristalle möglich. Um eine genaue Aussage darüber treffen zu können, sind jedoch zusätzliche Kontrollexperimente notwendig. Es wäre zum einen denkbar, die Mineralisationsexperimente über einen längeren Zeitraum durchzuführen. Diese könnten zeigen, ob das CHOL-HEM die Hydrolyse vom OCP zum HAP komplett unterdrückt. Außerdem könnte nachgewiesen werden, ob beim A-CHOL das OCP weiter zum HAP umgesetzt wird oder ob ein Gemisch beider Kristallphasen erhalten bleibt.
Um die Mineralisation an der Wasser/Luft-Grenzfläche mit der Mineralisation in Bulklösung zu vergleichen, wurden zusätzlich Mineralisationsexperimente in Bulklösung durchgeführt. Dazu wurden Nitrilotriessigsäure (NTA) und Ethylendiamintetraessigsäure (EDTA) als Mineralisationsadditive verwendet, da NTA unter anderem der Struktur der hydrophilen Kopfgruppe des A-CHOLs ähnelt. Es konnte gezeigt werden, dass ein Vergleich der Mineralisation an der Grenzfläche mit der Mineralisation in Bulklösung nicht ohne weiteres möglich ist. Bei der Mineralisation in Bulklösung wird bei tiefen pH-Werten DCPD und bei höheren pH-Werten HAP gebildet. Diese wurde mittels Röntgenpulverdiffraktometrie Messungen nachgewiesen und durch Infrarotspektroskopie bekräftigt. Die Bildung von OCP wie an der Wasser/Luft-Grenzfläche konnte nicht beobachtet werden.
Es konnte auch gezeigt werden, dass beide Additive NTA und EDTA einen unterschiedlichen Einfluss auf den Verlauf der Mineralisation nehmen. So unterscheiden sich zum einen die Morphologien des gebildeten DCPDs und zum anderen wurde beispielsweise in Anwesenheit von 10 und 15 mM NTA neben DCPD auch HAP bei einem Ausgangs-pH-Wert von 7 nachgewiesen.
Da unser Augenmerk speziell auf der Mineralisation von Calciumphosphat an der Wasser/Luft-Grenzfläche liegt, könnten Folgeexperimente wie beispielsweise GIXD Messungen durchgeführt werden. Dadurch wäre es möglich, einen Überblick über die gebildeten Kristallphasen nach unterschiedlichen Reaktionszeiten direkt auf dem Trog zu erhalten.
Es konnte weiterhin gezeigt werden, dass auch einfache Amphiphile in der Lage sind, die Mineralisation von Calciumphosphat zu steuern. Amphiphile mit Cholesterol als hydrophoben Block bilden offensichtlich besonders stabile Monolagen an der Wasser/Luft-Grenzfläche. Eine Untersuchung des Einflusses ähnlicher Amphiphile mit unterschiedlichen hydrophilen Kopfgruppen auf das Mineralisationsverhalten von Calciumphosphat wäre durchaus interessant.
We present a fluorescence excitation-emission-matrix spectrometer with superior data acquisition rates over previous instruments. Light from a white light emitting diode (LED) source is dispersed onto a digital micromirror array (DMA) and encoded using binary n-size Walsh functions ("barcodes"). The encoded excitation light is used to irradiate the liquid sample and its fluorescence is dispersed and detected using a conventional array spectrometer. After exposure to excitation light encoded in n different ways, the 2-dimensional excitation-emission-matrix (EEM) spectrum is obtained by inverse Hadamard transformation. Using this technique we examined the kinetics of the fluorescence of rhodamine B as a function of temperature and the acid-driven demetalation of chlorophyll into pheophytin-a. For these experiments, EEM spectra with 31 excitation channels and 2048 emission channels were recorded every 15 s. In total, data from over 3000 EEM spectra were included in this report. It is shown that the increase in data acquisition rate can be as high as [{n(n + 1)}/2]-fold over conventional EEM spectrometers. Spectral acquisition rates of more than two spectra per second were demonstrated.
Halloysites as tubular alumosilicates are introduced as inexpensive natural nanoparticles to form and stabilize oil-water emulsions. This stabilized emulsion is shown to enable efficient interfacial catalytic reactions. Yield, selectivity, and product separation can be tremendously enhanced, e.g., for the hydroformylation reaction of dodecene to tridecanal. In perspective, this type of formulation may be used for oil spill dispersions. The key elements of the described formulations are clay nanotubes (halloysites) which are highly anisometric, can be filled by helper molecules, and are abundantly available in thousands of tons, making this technology scalable for industrial applications.
Herstellung anisotroper Kolloide mittels templatgesteuerter Assemblierung und Kontaktdruckverfahren
(2017)
Diese Arbeit befasste sich mit neuen Konzepten zur Darstellung anisotroper Partikelsysteme durch Anordnung von funktionalisierten Partikeln unter Zuhilfenahme etablierter Methoden wie der templatgestützten Assemblierung von Partikeln und dem Mikrokontaktdruck.
Das erste Teilprojekt beschäftigte sich mit der kontrollierten Herstellung von Faltenstrukturen im Mikro- bis Nanometerbereich. Die Faltenstrukturen entstehen durch die Relaxation eines Systems bestehend aus zwei übereinander liegender Schichten unterschiedlicher Elastizität. In diesem Fall wurden Falten auf einem elastischen PDMS-Substrat durch Generierung einer Oxidschicht auf der Substratoberfläche mittels Plasmabehandlung erzeugt. Die Dicke der Oxidschicht, die über verschiedene Parameter wie Behandlungszeit, Prozessleistung, Partialdruck des plasmaaktiven Gases, Vernetzungsgrad, Deformation sowie Substratdicke einstellbar war, bestimmte Wellenlänge und Amplitude der Falten.
Das zweite Teilprojekt hatte die Darstellung komplexer, kolloidaler Strukturen auf Basis supramolekularer Wechselwirkungen zum Ziel. Dazu sollte vor allem die templatgestützte Assemblierung von Partikeln sowohl an fest-flüssig als auch flüssig-flüssig Grenzflächen genutzt werden. Für Erstere sollten die in Teilprojekt 1 hergestellten Faltenstrukturen als Templat, für Letztere Pickering-Emulsionen zur Anwendung kommen. Im ersten Fall wurden verschiedene, modifizierte Silicapartikel und Magnetitnanopartikel, deren Größe und Oberflächenfunktionalität (Cyclodextrin-, Azobenzol- und Arylazopyrazolgruppen) variierte, in Faltenstrukturen angeordnet. Die Anordnung hing dabei nicht nur vom gewählten Verfahren, sondern auch von Faktoren wie der Partikelkonzentration, der Oberflächenladung oder dem Größenverhältnis der Partikel zur Faltengeometrie ab.
Die Kombination von Cyclodextrin (CD)- und Arylazopyrazol-modifizierten Partikeln ermöglichte, auf Basis einer Wirt-Gast-Wechselwirkung zwischen den Partikeltypen und einer templatgesteuerten Anordnung, die Bildung komplexer und strukturierter Formen in der Größenordnung mehrerer Mikrometer. Dieses System kann einerseits als Grundlage für die Herstellung verschiedener Janus-Partikel herangezogen werden, andererseits stellt die gerichtete Vernetzung zweier Partikelsysteme zu größeren Aggregaten den Grundstein für neuartige, funktionale Materialien dar. Neben der Anordnung an fest-flüssig Grenzflächen konnte außerdem nachgewiesen werden, dass Azobenzol-funktionalisierte Silicapartikel in der Lage sind, Pickering-Emulsionen über mehrere Monate zu stabilisieren. Die Stabilität und Größe der Emulsionsphase kann über Parameter, wie das Volumenverhältnis und die Konzentration, gesteuert werden. CD-funktionalisierte Silicapartikel besaßen dagegen keine Grenzflächenaktivität, während es CD-basierten Polymeren wiederum möglich war, durch die Ausbildung von Einschlusskomplexen mit den hydrophoben Molekülen der Ölphase stabile Emulsionen zu bilden. Dagegen zeigte die Kombination zwei verschiedener Partikelsysteme keinen oder einen destabilisierenden Effekt bezüglich der Ausbildung von Emulsionen.
Im letzten Teilprojekt wurde die Herstellung multivalenter Silicapartikel mittels Mikrokontaktdruck untersucht. Die Faltenstrukturen wurden dabei als Stempel verwendet, wodurch es möglich war, die Patch-Geometrie über die Wellenlänge der Faltenstrukturen zu steuern. Als Tinte diente das positiv geladene Polyelektrolyt Polyethylenimin (PEI), welches über elektrostatische Wechselwirkungen auf unmodifizierten Silicapartikeln haftet. Im Gegensatz zum Drucken mit flachen Stempeln fiel dabei zunächst auf, dass sich die Tinte bei den Faltenstrukturen nicht gleichmäßig über die gesamte Substratfläche verteilt, sondern hauptsächlich in den Faltentälern vorlag. Dadurch handelte es sich bei dem Druckprozess letztlich nicht mehr um ein klassisches Mikrokontaktdruckverfahren, sondern um ein Tiefdruckverfahren. Über das Tiefdruckverfahren war es dann aber möglich, sowohl eine als auch beide Partikelhemisphären gleichzeitig und mit verschiedenen Funktionalitäten zu modifizieren und somit multivalente Silicapartikel zu generieren. In Abhängigkeit der Wellenlänge der Falten konnten auf einer Partikelhemisphäre zwei bis acht Patches abgebildet werden. Für die Patch-Geometrie, sprich Größe und Form der Patches, spielten zudem die Konzentration der Tinte auf dem Stempel, das Lösungsmittel zum Ablösen der Partikel nach dem Drucken sowie die Stempelhärte eine wichtige Rolle. Da die Stempelhärte aufgrund der variierenden Dicke der Oxidschicht bei verschiedenen Wellenlängen nicht kontant ist, wurden für den Druckprozess meist Abgüsse der Faltensubstrate verwendet. Auf diese Weise war auch die Vergleichbarkeit bei variierender Wellenlänge gewährleistet. Neben dem erfolgreichen Nachweis der Modifikation mittels Tiefdruckverfahren konnte auch gezeigt werden, dass über die Komplexierung mit PEI negativ geladene Nanopartikel auf die Partikeloberfläche aufgebracht werden können.
The valorization of carbohydrates is one of the most promising fields in green chemistry, as it enables to produce bulk chemicals and fuels out of renewable and abundant resources, instead of further exploiting fossil feedstocks. The focus in this thesis is the conversion of fructose, using dehydration and hydrodeoxygenation reactions. The main goal is to find an easy continuous process, including the solubility of the sugar in a green solvent, the conversion over a solid acid as well as over a metal@tungsten carbide catalyst.
At the beginning of this thesis, solid acid catalysts are synthesized by using carbohydrate material like glucose and starch at high temperatures (up to 600 °C). Additionally a third carbon is synthesized, using an activation method based on Ca(OH)2. After carbonization and further sulfonation, using fuming sulfuric acid, the three resulting catalysts are characterized together with sulfonated carbon black and Amberlyst 15 as references. In order to test all solid acid catalysts in reaction, a 250 mm x 4.6 mm stainless steel column is used as a fixed-bed continuous reactor. The temperature (110 °C to 250 °C) and residence time (2 to 30 minutes) is varied, and a direct relationship between contact time and selectivity is determined. The reaction mechanism, as well as the product distribution is showing a dehydration step of fructose towards 5-hydroxymethylfurfural (HMF). These furan-ring molecules are considered as “sleeping giants”, due to the possibility of using them as fuel, but also for upgrading them to chemicals like terephthalic acid or p-xylene. Consecutive reactions are producing levulinic acid, as well as condensation products with ethanol and formic acid. The activated carbon is additionally showing a 2 % yield of 2,5-Dimethylfuran (DMF) production, pointing towards the extraordinary properties of this catalyst. Without a metal catalyst present, what is normally necessary for hydrogenation reactions, a transferhydrogenation (with formic acid) is observed. The active catalyst was therefore carbon itself, what activated the hydrogen on its surface. This phenomenon was just very rarely observed so far. Expensive noble metals are the material of choice, when it comes to hydrogenation reactions nowadays and cheaper alternatives are necessary.
By postulating a similar electronic structure of tungsten carbide (WC) to platinum by Lewy and Boudart, research is focusing on the replacement of Pt. The production of nano-sized tungsten carbide particles (7.5 ± 2.5 nm, 70 m2 g-1) is enabled by the so called “urea glass route” and its catalytic performances are compared to commercial material. It is shown, that the activity is strongly dependent on the size of the particles as well as the surface area. Nano-sized tungsten carbide is showing activity for hydrogenation reactions under mild conditions (maximum 150 °C, 30 bar). This material therefore opens up new possibilities for replacing the rare and expensive platinum with tungsten carbide based catalysts.
Additionally different metal nanoparticles of palladium, copper and nickel are deposited on top of WC to further promote its reactivity. The nickel nanoparticles are strongly connected to WC and showed the best activity as well as selectivity for upgrading HMF with hydrodeoxygenation. The Ni@WC is not leaching and is showing very good hydrodeoxygenation properties with DMF yields up to 90 percent. Copper@WC is not showing good activity and palladium@WC enables undesired consecutive reactions, hydrogenating the furan ring system.
In order to enable the upgrade of fructose to DMF directly in a continuous system, the current H CUBE Pro TM hydrogenation system is customized with a second reaction column. A 250 mm x 4.6 mm stainless steel reactor column is connected ahead of the hydrogen insertion, enabling the dehydration of fructose to HMF derivatives, before pumping these products into the second column for hydrogenation. The overall residence time in the two column reactor system is 14 minutes. The overall results are an almost full conversion with a yield of 38.5 % DMF and 47 % yield of EL. The main disadvantage is the formation of higher mass products, so called humins, which start depositing on top of the catalysts, blocking their active sites.
In general it can be stated, that a two column system goes along with a higher investment as well as more maintenance costs, compared to a one column catalytic approach. To develop a catalyst, which is on the one hand able to dehydrate as well as hydrodeoxygenate the reactants, is aimed for at the last part of the thesis. The activated carbon however shows already activity for hydrodeoxygenation without any metal present and offers itself therefore as an alternative to overcome the temperature instability of Amberlyst 15 (max. 120 °C) for a combined DMF production directly from fructose. The activity for the upgrade to DMF is increased from 2 % to 12 % DMF yield in one mixed continuous column.
In order to scale up the entire one column approach, an 800 mm x 28.5 mm inner diameter column was planned and manufactured. The system is scaled up and assembled, whereas this flow reactor system is able to be run with 50 mL min-1 maximum flow rate, to stand a pressure of maximum 100 bar and be heated to around 500 °C. The tubing and connections, as well as the used devices are planned according to be safe and easy in use. The scaled-up approach offers a reaction column 120 times bigger (510 ml) then the first extension of the commercial system. This further extension offers the possibility of ranging between 1 and 1000 mL min-1, making it possible to use the approach in pilot plant applications.
The new K+-selective fluorescent probes 1 and 2 were obtained by Cu-I-catalyzed 1,3-dipolar azide alkyne cycloaddition (CuAAC) reactions of an alkyne-substituted [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD) ester fluorophore with azido-functionalized N-phenylaza-18-crown-6 ether and N-(o-isopropoxy) phenylaza-18-crown-6 ether, respectively. Probes 1 and 2 allow the detection of K+ in the presence of Na+ in water by fluorescence enhancement (2.2 for 1 at 2000mm K+ and 2.5 for 2 at 160mm K+). Fluorescence lifetime measurements in the absence and presence of K+ revealed bi-exponential decay kinetics with similar lifetimes, however with different proportions changing the averaged fluorescence decay times ((f(av))). For 1 a decrease of (f(av)) from 12.4 to 9.3ns and for 2 an increase from 17.8 to 21.8ns was observed. Variation of the substituent in ortho position of the aniline unit of the N-phenylaza-18-crown-6 host permits the modulation of the K-d value for a certain K+ concentration. For example, substitution of H in 1 by the isopropoxy group (2) decreased the K-d value from >300mm to 10mm. 2 was chosen for studying the efflux of K+ from human red blood cells (RBC). Upon addition of the Ca2+ ionophor ionomycin to a RBC suspension in a buffer containing Ca2+, the fluorescence of 2 slightly rose within 10min, however, after 120min a significant increase was observed.
In nature, proteins self-assemble into various structures with different dimensions. To construct these nanostructures in laboratories, normally proteins with different symmetries are selected. However, most of these approaches are engineering-intensive and highly dependent on the accuracy of the protein design. Herein, we report that a simple native protein LecA assembles into one-dimensional nanoribbons and nanowires, two-dimensional nanosheets, and three-dimensional layered structures controlled mainly by small-molecule assembly-inducing ligands RnG (n = 1, 2, 3, 4, 5) with varying numbers of ethylene oxide repeating units. To understand the formation mechanism of the different morphologies controlled by the small-molecule structure, molecular simulations were performed from microscopic and mesoscopic view, which presented a clear relationship between the molecular structure of the ligands and the assembled patterns. These results introduce an easy strategy to control the assembly structure and dimension, which could shed light on controlled protein assembly.
The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of amino-substituted heteraromatic six-membered ring systems such as pyrylium/thiopyrylium analogues have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the existing aromaticity of the studied compounds. Due to strong conjugation of six-membered ring pi-electrons and lone pairs of the exo-cyclic amino substituents (restricted rotation about partial C,N double bonds) the interplay of still aromatic and already dominating trimethine cyanine/merocyanine-like substructures can be estimated. (C) 2017 Elsevier Ltd. All rights reserved.
Noninvasive imaging in the root soil compartment is mandatory for improving knowledge about root soil interactions and uptake processes which eventually control crop growth and productivity. Here we propose a method of MRI T-1 relaxation mapping to investigate water uptake patterns, and as second example, in combination with neutron tomography (NT), property changes in the rhizosphere. The first part demonstrates quantification of solute enrichment by advective transport to the roots due to water uptake. This accumulation is counterbalanced by net downward flow and dispersive spreading. One can furthermore discriminate between zones of high accumulation patterns and zones with much less enrichment. This behavior persists over days. The second part presents the novel combination of MRI with neutron tomography to couple static, proton density information of roots and their interface to the surrounding soil with information about the local water dynamics, reflected by NMR relaxation times. The root soil interface of a broad bean plant is characterized by slightly increasing MRI and NT signal intensity but decreasing T-1 relaxation time indicating locally changed soil properties.
The performance of organic photovoltaic blend devices is critically dependent on the polymer:fullerene interface. These interfaces are expected to impact the structural and thermal properties of the polymer with regards to the conjugated backbone planarity and transition temperatures during annealing/cooling processes. Here, we report the impact of fullerene intercalation on structural and thermal properties of poly(2,5-bis(3-tetradecylthiophen-2-yOthieno[3,2-b]thiophene (PBTTT), a highly stable material known to exhibit liquid crystalline behavior. We undertake a detailed systematic study of the extent of intercalation in the PBTTT:fullerene blend, considering the use of four different fullerene derivatives and also varying the loading ratios. Resonant Raman spectroscopy allows morphology in situ during controlled heating and cooling. We find that small fullerene molecules readily intercalate into PBTTT crystallites, resulting in a planarization of the polymer backbone, but high fullerene loading ratios or larger fullerenes result in nonintercalated domains. During cooling from melt, nonintercalated blend films are found to return to their original morphology and reproduce all thermal transitions on cooling with minimal hysteresis. Intercalated blend films show significant hysteresis on cooling due to the crystallized fullerene attempting to reintercalate. The strongest hysteresis is for intercalated blend films with excess fullerene loading ratio, which form a distinct nanoribbon morphology and exhibit a reduced geminate recombination rate. These results reveal that careful consideration should be taken during device fabrication, as postdeposition thermal treatments significantly impact the charge generation and recombination dynamics.
Fluorinating conjugated polymers is a proven strategy for creating high performance materials in polymer solar cells, yet few studies have investigated the importance of the fluorination method. We compare the performance of three fluorinated systems: a poly(benzodithieno-dithienyltriazole) (PBnDT-XTAZ) random copolymer where 50% of the acceptor units are difluorinated, PBnDT-mFTAZ where every acceptor unit is monofluorinated, and a 1:1 physical blend of the difluorinated and nonfluorinated polymer. All systems have the same degree of fluorination (50%) yet via different methods (chemically vs physically, random vs regular). We show that these three systems have equivalent photovoltaic behavior:,similar to 5.2% efficiency with a short-circuit current (J(sc)) at,similar to 11 mA cm(-2), an open-circuit voltage (v(oc)) at 0.77 V, and a fill factor (FF) of similar to 60%. Further investigation of these three systems demonstrates that the charge generation, charge extraction, and charge transfer state are essentially identical for the three studied systems. Transmission electron microscopy shows no significant differences in the morphologies. All these data illustrate that it is possible to improve performance not only via regular or random fluorination but also by physical addition via a ternary blend. Thus, our results demonstrate the versatility of incorporating fluorine in the active layer of polymer solar cells to enhance device performance.
Polyplexes between a double-stranded Salmon DNA and hyperbranched poly(ethyleneimine) (PEI) as well as a maltosylated PEI-Mal were incorporated into a gelatin/chitosan hydrogel scaffold. Calorimetric experiments of the polyplexes show a decrease of the melting temperature in presence of PEI and a peak splitting in presence of PEI-Mal, which can be interpreted to a partial compaction of the DNA strands in presence of PEI-Mal. When the polyplexes are incorporated into a gelatin/chitosan scaffold in the swollen state, the DNA melting peaks at 90 and 93 degrees C, respectively, indicate in both cases the release of the DNA at the surface of the hydrogel scaffold in a more compact form. Specific interactions between the PEI-Mal shell and gelatin are responsible for the tuning of the release properties in presence of the maltose units in the hyperbranched PEI.
Surfactants are required for the formation and stabilization of hydrophobic polymeric particles in aqueous environment. In order to form submicron particles of varying sizes from oligo[3-(S)-sec-butylmorpholine-2,5-dione]diols ((OBMD)-diol), different surfactants were investigated. As new surfactants, four-armed star-shaped oligo(ethylene glycol)s of molecular weights of 5-20 kDa functionalized with desamino-tyrosine (sOEG-DAT) resulted in smaller particles with lower PDI than with desaminotyrosyl tyrosine (sOEG-DATT) in an emulsion/solvent evaporation method. In a second set of experiments, sOEG-DAT of M-n= 10 kDa was compared with the commonly employed emulsifiers polyvinylalcohol (PVA), polyoxyethylene (20) sorbitan monolaurate (Tween 20), and D-alpha-tocopherol polyethylene glycol succinate (VIT E-TPGS) for OBMD particle preparation. sOEG-DAT allowed to systematically change sizes in a range of 300 up to 900 nm with narrow polydispersity, while in the other cases, a lower size range (250-400 nm, PVA; 300 nm, Tween 20) or no effective particle formation was observed. The ability of tailoring particle size in a broad range makes sOEG-DAT of particular interest for the formation of oligodepsipeptide particles, which can further be investigated as drug carriers for controlled delivery. (C) 2016 Elsevier B.V. All rights reserved.
A series of new fluorescent dye bearing monomers, including glycomonomers, based on maleamide and maleic esteramide was synthesized. The dye monomers were incorporated by radical copolymerization into thermo-responsive poly(N-vinyl-caprolactam) that displays a lower critical solution temperature (LCST) in aqueous solution. The effects of the local molecular environment on the polymers' luminescence, in particular on the fluorescence intensity and the extent of solvatochromism, were investigated below as well as above the phase transition. By attaching substituents of varying size and polarity in the close vicinity of the fluorophore, and by varying the spacer groups connecting the dyes to the polymer backbone, we explored the underlying structure-property relationships, in order to establish rules for successful sensor designs, e.g., for molecular thermometers. Most importantly, spacer groups of sufficient length separating the fluorophore from the polymer backbone proved to be crucial for obtaining pronounced temperature regulated fluorescence responses.
Microwave heating (MW)-assisted synthesis has been widely applied as an alternative method for the chemical synthesis of organic and inorganic materials. In this work, we report MW-assisted synthesis of three isostructural 3D frameworks with a flexible linker arm of the chelating linker 2-substituted imidazolate- 4-amide-5-imidate, named IFP-7-MW (M = Zn, R = OMe), IFP-8-MW (M = Co; R = OMe) and IFP-10-MW (M = Co; R = OEt) (IFP = Imidazolate Framework Potsdam). These chelating ligands were generated in situ by partial hydrolysis of 2-substituted 4,5-dicyanoimidazoles under MW-and also conventional electrical heating (CE)-assisted conditions in DMF. The structure of these materials was determined by IR spectroscopy and powder X-ray diffraction (PXRD) and the identity of the materials synthesized under CE-conditions was established. Materials obtained from MW-heating show many fold enhancement of CO2 and H-2 uptake capacities, compared to the analogous CE-heating method based materials. To understand the inner pore-sizes of IFP structures and variations of gas sorptions, we performed positron annihilation lifetime spectroscopy (PALS), which shows that MW-assisted materials have smaller pore sizes than materials synthesized under CE-conditions. The "kinetically controlled" MW-synthesized material has an inherent ability to trap extra linkers, thereby reducing the pore sizes of CE-materials to ultra/micropores. These ultramicropores are responsible for high gas sorption.
The decomposition of anthracene endoperoxides has been investigated under various conditions. Thermolyses proceed via radical intermediates and afford anthracenes and rearrangement products, depending on the substitution pattern. Interestingly, not only the O-O but also the C-O bond can be cleaved homolytically. Under basic conditions fragmentations take place, affording anthraquinone, and reactive oxygen species. This mechanism explains the often observed decomposition of endoperoxides during work-up. Finally, an acid-catalyzed cleavage has been observed under release of hydrogen peroxide. The results should be interesting for the mechanistic understanding of peroxide decomposition and the endoperoxides might serve as mild sources of reactive oxygen species for future applications. Copyright (C) 2016 John Wiley & Sons, Ltd.
Despite the myriad of organic donor:acceptor materials, only few systems have emerged in the life of organic solar cells to, exhibit considerable reduced bimolecular recombination, with respect to the random encounter rate given by the Langevin equation. Monte Carlo simulations have revealed that the rate constant of the formation of electron-hole bound states depends on the random encounter of opposite charges and is nearly given by the Langevin equation for the domain sizes relevant to efficient bulk heterojunction systems. Recently, three studies :suggested that charge transfer states dissociating much faster than their decay rate to the ground state, can result in reduced bimolecular recombination by lowering the recombination rate to the ground state as a loss pathway. A separate study identified another loss pathway and suggested that forbidden back electron transfer from triplet charge transfer states to triplet excitons is a key to achieving reduced recombination. Herein we further explain the reduced bimolecular recombination by investigating the limitations of these two proposals. By solving kinetic rate equations for a BHJ system with realistic rates, we show that both of these previously presented conditions must only be held at the same time fora system to exhibit non-Langevin behavior. We demonstrate that suppression of both of the parallel loss channels of singlet and triplet states can be achieved through increasing the dissociation rate of the charge transfer states; a crucial requirement to achieve a high charge carrier extraction efficiency.
Ionogels (IGs) based on poly(methyl methacrylate) (PMMA) and the metal-containing ionic liquids (ILs) bis-1-butyl-3-methlimidazolium tetrachloridocuprate(II), tetrachloride cobaltate(II), and tetrachlorido manganate(II) have been synthesized and their mechanical and electrical properties have been correlated with their microstructure. Unlike many previous examples, the current IGs show a decreasing stability in stress-strain experiments on increasing IL fractions. The conductivities of the current IGs are lower than those observed in similar examples in the literature. Both effects are caused by a two-phase structure with micrometer-sized IL-rich domains homogeneously dispersed an IL-deficient continuous PMMA phase. This study demonstrates that the IL-polymer miscibility and the morphology of the IGs are key parameters to control the (macroscopic) properties of IGs.
A new isoflavone, 8-prenylmilldrone (1), and four new rotenoids, oblarotenoids A-D (2-5), along with nine known compounds (6-14), were isolated from the CH2Cl2/CH3OH (1:1) extract of the leaves of Millettia oblata ssp. teitensis by chromatographic separation. The purified compounds were identified by NMR spectroscopic and mass spectrometric analyses, whereas the absolute configurations of the rotenoids were established on the basis of chiroptical data and in some cases by single-crystal X-ray crystallography. Maximaisoflavone J (11) and oblarotenoid C (4) showed weak activity against the human breast cancer cell line MDA-MB-231 with IC50 values of 33.3 and 93.8 mu M, respectively.
High oxygen permeable [poly(TMSP)] nanofibers incorporating porphyrin macrocycle as luminescence indicators were prepared by electrospinning technique. The porphyrins involves were modified by i) introducing phenylacetylide substituents on the para position of the phenyl moieties and ii) varying the metal centers [Pt(II) or Pd(II)] of the meso-tetrakisphenylporphyrins. A set of nanofibers; (Pt-TPP)NF, (Pd-TPP)NF, (Pt-TPA)NF and (Pd-TPA)NF were obtained to study their structure-activity relationship toward oxygen. The lifetime-based technique was privileged to take advantage of their long-lived phosphorescent properties. A two-fold enhancement was observed for (Pt-TPA)NF and (Pd-TPA)NF compared to (Pt-TPP)NF and (Pd-TPP)NF demonstrating the positive effect of the phenylacetylide moieties on the lifetime. Also, Silver nanoparticles were included in nanofibers to investigate their influence on lifetime-based oxygen sensitivity, showing that the presence of AgNPs only affects (Pd-TPA)NF.
Lignin valorization
(2017)
The topic of this project is the use of lignin as alternative source of aromatic building blocks and oligomers to fossil feedstocks. Lignin is known as the most abundant aromatic polymer in nature and is isolated from the lignocellulosic component of plants by different possible extraction treatments. Both the biomass source and the extraction method affect the structure of the isolated lignin, therefore influencing its further application. Lignin was extracted from beech wood by two different hydrothermal alkaline treatments, which use NaOH and Ba(OH)2 as base and by an acid-catalyzed organosolv process. Moreover, lignin was isolated from bamboo, beech wood and coconut by soda treatment of the biomasses. A comparison of the structural features of such isolated lignins was performed through the use of a wide range of analytical methods. Alkaline lignins resulted in a better candidate as carbon precursor and macromonomers for the synthesis of polymer than organosolv lignin. In fact, alkaline lignins showed higher residual mass after carbonization and higher content of the reactive hydroxy functionalities. In contrast, the lignin source turned out to slightly affect the lignin hydroxyl content.
One of the most common lignin modifications is its deconstruction to obtain aromatic molecules, which can be used as starting materials for the synthesis of fine chemicals. Lignin deconstruction leads to a complex mixture of aromatic molecules. A gas chromatographic analytical method was developed to characterize the mixture of products obtained by lignin deconstruction via heterogeneous catalytic hydrogenolysis. The analytical protocol allowed the quantification of three main groups of molecules by means of calibration curves, internal standard and a preliminary silylation step of the sample. The analytical method was used to study the influence of the hydrogenolysis catalyst, temperature and system (flow and batch reactor) on the yield and selectivity of the aromatic compounds.
Lignin extracted from beech wood by a hydrothermal process using Ba(OH)2 as base, was functionalized by aromatic nitration in order to add nitrogen functionalities. The final goal was the synthesis of a nitrogen doped carbon. Nitrated lignin was reduced to the amino form in order to compare the influence of different nitrogen functionalities on the porosity of the final carbon. The carbons were obtained by ionothermal treatment of the precursors in the presence of the eutectic salt mixture KCl/ZnCl2 Such synthesized carbons showed micro-, macro- and mesoporosity and were tested for their electrocatalytic activity towards the oxygen reduction reaction. Mesoporous carbon derived from nitro lignin displayed the highest electrocatalytic activity.
Lignins isolated from coconut, beech wood and bamboo were used as macromonomers for the synthesis of biobased polyesters. A condensation reaction was performed between lignin and a hyper branched poly(ester-amine), previously obtained by condensation of triethanolamine and adipic acid. The influence of the lignin source and content on the thermochemical and mechanical properties of the final material was investigated. The prepolymer showed adhesive properties towards aluminum and its shear strength was therefore measured. The gluing properties of such synthesized glues turned out to be independent from the lignin source but affected by the amount of lignin in the final material.
This work shows that, although still at a laboratory scale, the valorization of lignin can overcome the critical issues of lignin´s structure variability and complexity.
In virtue of the rising demand for metal-free polymeric materials, organocatalytic polymerization has emerged and blossomed unprecedentedly in the past 15 years into an appealing research area and a powerful arsenal for polymer synthesis. In addition to the inherent merits as being metal-free, small molecule organocatalysts have also provided opportunities to develop alternative and, in many cases, more expedient synthetic approaches toward macromolecular architectures, that play a crucial role in shaping the properties of the obtained polymers. A majority of preliminary studies exploring for new catalysts, catalytic mechanisms and optimized polymerization conditions are extended to application of the catalytic systems on rational design and controlled synthesis of various macromolecular architectures. Such endeavors are described in this review, categorized by the architectural elements including chain structure (types, sequence and composition of monomeric units constituting the polymer chains), topological structure (the fashion different polymer chains are covalently attached to each other within the macromolecule) and functionality (position and amount of functional groups that endow the entire macromolecule with specific chemical, physico-chemical or biological properties). (C) 2017 Published by Elsevier B.V.
Magnetosome Organization in Magnetotactic Bacteria Unraveled by Ferromagnetic Resonance Spectroscopy
(2017)
Magnetotactic bacteria form assemblies of magnetic nanoparticles called magnetosomes. These magnetosomes are typically arranged in chains, but other forms of assemblies such as clusters can be observed in some species and genetic mutants. As such, the bacteria have developed as a model for the understanding of how organization of particles can influence the magnetic properties. Here, we use ferromagnetic resonance spectroscopy to measure the magnetic anisotropies in different strains of Magnetosprillum gtyphiswaldense MSR-1, a bacterial species that is amendable to genetic mutations. We combine our experimental results with a model describing the spectra. The model includes chain imperfections and misalignments following a Fisher distribution function, in addition to the intrinsic magnetic properties of the magnetosomes. Therefore, by applying the model to analyze the ferromagnetic resonance data, the distribution of orientations in the bulk sample can be retrieved in addition to the average magnetosome arrangement. In this way, we quantitatively characterize the magnetosome arrangement in both wild-type cells and Delta mamJ mutants, which exhibit differing magnetosome organization.
The Marangoni contraction of sessile drops of a binary mixture of a volatile and a nonvolatile liquid has been investigated experimentally and theoretically. The origin of the contraction is the locally inhomogeneous evaporation rate of sessile drops. This leads to surface tension gradients and thus to a Marangoni flow. Simulations show that the interplay of Marangoni flow, capillary flow, diffusive transport, and evaporative losses can establish a quasistationary drop profile with an apparent nonzero contact angle even if both liquid components individually wet the substrate completely. Experiments with different solvents, initial mass fractions, and gaseous environments reveal a previously unknown universal power-law relation between the apparent contact angle and the relative undersaturation of the ambient atmosphere: theta(app) similar to (RHeq - RH)(1/3). This experimentally observed power law is in quantitative agreement with simulation results. The exponent can also be inferred from a scaling analysis of the hydrodynamic-evaporative evolution equations of a binary mixture of liquids with different volatilities.
Potato (Solanum tuberosum L.) is one of the most important food crops worldwide. Current potato varieties are highly susceptible to drought stress. In view of global climate change, selection of cultivars with improved drought tolerance and high yield potential is of paramount importance. Drought tolerance breeding of potato is currently based on direct selection according to yield and phenotypic traits and requires multiple trials under drought conditions. Marker-assisted selection (MAS) is cheaper, faster and reduces classification errors caused by noncontrolled environmental effects. We analysed 31 potato cultivars grown under optimal and reduced water supply in six independent field trials. Drought tolerance was determined as tuber starch yield. Leaf samples from young plants were screened for preselected transcript and nontargeted metabolite abundance using qRT-PCR and GC-MS profiling, respectively. Transcript marker candidates were selected from a published RNA-Seq data set. A Random Forest machine learning approach extracted metabolite and transcript markers for drought tolerance prediction with low error rates of 6% and 9%, respectively. Moreover, by combining transcript and metabolite markers, the prediction error was reduced to 4.3%. Feature selection from Random Forest models allowed model minimization, yielding a minimal combination of only 20 metabolite and transcript markers that were successfully tested for their reproducibility in 16 independent agronomic field trials. We demonstrate that a minimum combination of transcript and metabolite markers sampled at early cultivation stages predicts potato yield stability under drought largely independent of seasonal and regional agronomic conditions.
Macrocycles based on L-cystine were synthesized by ring-closing metathesis (RCM) and subsequently polymerized by entropy-driven ring-opening metathesis polymerization (ED-ROMP). Monomer conversion reached similar to 80% in equilibrium and the produced poly (ester-amine-disulfide-alkene)s exhibited apparent molar masses (M-w(app)) of up to 80 kDa and dispersities (D) of similar to 2. The polymers can be further functionalized with acid anhydrides and degraded by reductive cleavage of the main-chain disulfide.
In many laser based ionization techniques with a subsequent drift time separation, the laser pulse generating the ions is considered as the start time to. Therefore, an accurate temporal definition of this event is crucial for the resolution of the experiments. In this contribution, the laser induced plume dynamics of liquids evaporating into atmospheric pressure are visualized for two distinctively different laser pulse widths, Delta t = 6 nanoseconds and Delta tau = 280 microseconds. For ns-pulses the expansion of the generated vapour against atmospheric pressure is found to lead to turbulences inside the gas phase. This results in spatial and temporal broadening of the nascent clouds. A more equilibrated expansion, without artificial smearing of the temporal resolution can, in contrast, be observed to follow mu s-pulse excitation. This leads to the counterintuitive finding that longer laser pulses results in an increased temporal vapour formation definition. To examine if this fume expansion also eventually results in a better definition of ion formation, the nascent vapour plumes were expanded into a linear drift tube ion mobility spectrometer (IMS). This time resolved detection of ion formation corroborates the temporal broadening caused by collisional impeding of the supersonic expansion at atmospheric pressure and the overall better defined ion formation by evaporation with long laser pulses. A direct comparison of the observed results strongly suggests the coexistence of two individual ion formation mechanisms that can be specifically addressed by the use of appropriate laser sources.
ortho-Aryl phenols, synthesized via protecting group free Suzuki-Miyaura coupling of ortho-halophenols and arene boronic acids, undergo a cyclization to dibenzofurans via oxidative C-H activation. The reaction proceeds under microwave irradiation in short reaction times using catalytic amounts of Pd(OAc)(2) without additional ligands.
The molecular structure and conformational preferences of 1-phenyl-1-X-1-silacyclohexanes C5H10Si(Ph,X) (X = F (3), Cl (4)) were studied by gas-phase electron diffraction, low-temperature NMR spectroscopy, and high-level quantum chemical calculations. In the gas phase only three (3) and two (4) stable conformers differing in the axial or equatorial location of the phenyl group and the angle of rotation about the Si-C-ph bond (axi and axo denote the Ph group lying in or out of the X-Si-C-ph plane) contribute to the equilibrium. In 3 the ratio Ph-eq:Ph-axo:Ph-axi is 40(12):55(24):5 and 64:20:16 by experiment and theory, respectively. In 4 the ratio Ph-eq:Ph-axo is 79(15):21(15) and 71:29 by experiment and theory (M06-2X calculations), respectively. The gas-phase electron diffraction parameters are in good agreement with those obtained from theory at the M06-2X/aug-ccPVTZ and MP2/aug-cc-pVTZ levels. Unlike the case for M06-2X, MP2 calculations indicate that 3-Ph-eq conformer lies 0.5 kcal/mol higher than the 3-Ph-axo, conformer. As follows from QTAIM analysis, the phenyl group is more stable when it is located in the axial position but produces destabilization of the silacyclohexane ring: By low temperature NMR spectroscopy the six-membered ring interconversion could be frozen, at 103 K and the present conformational equilibria of 3 and 4 could be determined. The ratio of the conformers is 3-Ph-eq:3-Ph-ax = (75-77):(23-25) and 4-Ph-eq:4-Ph-ax = 82:18.
Water deficit (drought stress) massively restricts plant growth and the yield of crops; reducing the deleterious effects of drought is therefore of high agricultural relevance. Drought triggers diverse cellular processes including the inhibition of photosynthesis, the accumulation of cell-damaging reactive oxygen species and gene expression reprogramming, besides others. Transcription factors (TF) are central regulators of transcriptional reprogramming and expression of many TF genes is affected by drought, including members of the NAC family. Here, we identify the NAC factor JUNGBRUNNEN1 (JUB1) as a regulator of drought tolerance in tomato (Solanum lycopersicum). Expression of tomato JUB1 (SlJUB1) is enhanced by various abiotic stresses, including drought. Inhibiting SlJUB1 by virus-induced gene silencing drastically lowers drought tolerance concomitant with an increase in ion leakage, an elevation of hydrogen peroxide (H2O2) levels and a decrease in the expression of various drought-responsive genes. In contrast, overexpression of AtJUB1 from Arabidopsis thaliana increases drought tolerance in tomato, alongside with a higher relative leaf water content during drought and reduced H2O2 levels. AtJUB1 was previously shown to stimulate expression of DREB2A, a TF involved in drought responses, and of the DELLA genes GAI and RGL1. We show here that SlJUB1 similarly controls the expression of the tomato orthologs SlDREB1, SlDREB2 and SlDELLA. Furthermore, AtJUB1 directly binds to the promoters of SlDREB1, SlDREB2 and SlDELLA in tomato. Our study highlights JUB1 as a transcriptional regulator of drought tolerance and suggests considerable conservation of the abiotic stress-related gene regulatory networks controlled by this NAC factor between Arabidopsis and tomato.
The high interfacial activity of protein-polymer conjugates has inspired their use as stabilizers for Pickering emulsions, resulting in many interesting applications such as synthesis of templated micro-compartments and protocells or vehicles for drug and gene delivery. In this study we report, for the first time, the stabilization of Pickering emulsions with conjugates of a genetically modified transmembrane protein, ferric hydroxamate uptake protein component A (FhuA). The lysine residues of FhuA with open pore (FhuA Delta CVFtev) were modified to attach an initiator and consequently controlled radical polymerization (CRP) carried out via the grafting-from technique. The resulting conjugates of FhuA Delta CVFtev with poly(N-isopropylacrylamide) (PNIPAAm) and poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA), the so-called building blocks based on transmembrane proteins (BBTP), have been shown to engender larger structures. The properties such as pH-responsivity, temperature-responsivity and interfacial activity of the BBTP were analyzed using UV-Vis spectrophotometry and pendant drop tensiometry. The BBTP were then utilized for the synthesis of highly stable Pickering emulsions, which could remain non-coalesced for well over a month. A new UV-crosslinkable monomer was synthesized and copolymerized with NIPAAm from the protein. The emulsion droplets, upon crosslinking of polymer chains, yielded micro-compartments. Fluorescence microscopy proved that these compartments are of micrometer scale, while cryo-scanning electron microscopy and scanning force microscopy analysis yielded a thickness in the range of 11.1 +/- 0.6 to 38.0 +/- 18.2 nm for the stabilizing layer of the conjugates. Such micro-compartments would prove to be beneficial in drug delivery applications, owing to the possibility of using the channel of the transmembrane protein as a gate and the smart polymer chains as trigger switches to tune the behavior of the capsules.
Nanocarriers
(2017)
Ziel der vorliegenden Arbeit war die Synthese und Charakterisierung von anisotropen Goldnanopartikeln in einer geeigneten Polyelektrolyt-modifizierten Templatphase. Der Mittelpunkt bildet dabei die Auswahl einer geeigneten Templatphase, zur Synthese von einheitlichen und reproduzierbaren anisotropen Goldnanopartikeln mit den daraus resultierenden besonderen Eigenschaften. Bei der Synthese der anisotropen Goldnanopartikeln lag der Fokus in der Verwendung von Vesikeln als Templatphase, wobei hier der Einfluss unterschiedlicher strukturbildender Polymere (stark alternierende Maleamid-Copolymere PalH, PalPh, PalPhCarb und PalPhBisCarb mit verschiedener Konformation) und Tenside (SDS, AOT – anionische Tenside) bei verschiedenen Synthese- und Abtrennungsbedingungen untersucht werden sollte.
Im ersten Teil der Arbeit konnte gezeigt werden, dass PalPhBisCarb bei einem pH-Wert von 9 die Bedingungen eines Röhrenbildners für eine morphologische Transformation von einer vesikulären Phase in eine röhrenförmige Netzwerkstruktur erfüllt und somit als Templatphase zur formgesteuerten Bildung von Nanopartikeln genutzt werden kann.
Im zweiten Teil der Arbeit wurde dargelegt, dass die Templatphase PalPhBisCarb (pH-Wert von 9, Konzentration von 0,01 wt.%) mit AOT als Tensid und PL90G als Phospholipid (im Verhältnis 1:1) die effektivste Wahl einer Templatphase für die Bildung von anisotropen Strukturen in einem einstufigen Prozess darstellt. Bei einer konstanten Synthesetemperatur von 45 °C wurden die besten Ergebnisse bei einer Goldchloridkonzentration von 2 mM, einem Gold-Templat-Verhältnis von 3:1 und einer Synthesezeit von 30 Minuten erzielt. Ausbeute an anisotropen Strukturen lag bei 52 % (Anteil an dreieckigen Nanoplättchen von 19 %). Durch Erhöhung der Synthesetemperatur konnte die Ausbeute auf 56 % (29 %) erhöht werden.
Im dritten Teil konnte durch zeitabhängige Untersuchungen gezeigt werden, dass bei Vorhandensein von PalPhBisCarb die Bildung der energetisch nicht bevorzugten Plättchen-Strukturen bei Raumtemperatur initiiert wird und bei 45 °C ein Optimum annimmt.
Kintetische Untersuchungen haben gezeigt, dass die Bildung dreieckiger Nanoplättchen bei schrittweiser Zugabe der Goldchlorid-Präkursorlösung zur PalPhBisCarb enthaltenden Templatphase durch die Dosierrate der vesikulären Templatphase gesteuert werden kann. In umgekehrter Weise findet bei Zugabe der Templatphase zur Goldchlorid-Präkursorlösung bei 45 °C ein ähnlicher, kinetisch gesteuerter Prozess der Bildung von Nanodreiecken statt mit einer maximalen Ausbeute dreieckigen Nanoplättchen von 29 %.
Im letzten Kapitel erfolgten erste Versuche zur Abtrennung dreieckiger Nanoplättchen von den übrigen Geometrien der gemischten Nanopartikellösung mittels tensidinduzierter Verarmungsfällung. Bei Verwendung von AOT mit einer Konzentration von 0,015 M wurde eine Ausbeute an Nanoplättchen von 99 %, wovon 72 % dreieckiger Geometrien hatten, erreicht.
The conformational equilibrium of the axial/equatorial conformers of 4-methylene-cyclohexyl pivalate is studied by dynamic NMR spectroscopy in a methylene chloride/freon mixture. At 153K, the ring interconversion gets slow on the nuclear magnetic resonance timescale, the conformational equilibrium (-G degrees) can be examined, and the barrier to ring interconversion (G(#)) can be determined. The structural influence of sp(2) hybridization on both G degrees and G(#) of the cyclohexyl moiety can be quantified.
Reversible movements of current polymeric actuators stem from the continuous response to signals from a controlling unit, and subsequently cannot be interrupted without stopping or eliminating the input trigger. Here, we present actuators based on cross-linked blends of two crystallizable polymers capable of pausing their movements in a defined manner upon continuous cyclic heating and cooling. This noncontinuous actuation can be adjusted by varying the applied heating and cooling rates. The feasibility of these devices for technological applications was shown in a 140 cycle experiment of free-standing noncontinuous shape shifts, as well as by various demonstrators.
Novel metal-doped bacteriostatic hybrid clay composites for point-of-use disinfection of water
(2017)
This study reports the facile microwave-assisted thermal preparation of novel metal-doped hybrid clay composite adsorbents consisting of Kaolinite clay, Carica papaya seeds and/or plantain peels (Musa paradisiaca) and ZnCl2. Fourier Transformed IR spectroscopy, X-ray diffraction, Scanning Electron Microscopy and Brunauer-Emmett-Teller (BET) analysis are employed to characterize these composite adsorbents. The physicochemical analysis of these composites suggests that they act as bacteriostatic rather than bacteriacidal agents. This bacterostactic action is induced by the ZnO phase in the composites whose amount correlates with the efficacy of the composite. The composite prepared with papaya seeds (PS-HYCA) provides the best disinfection efficacy (when compared with composite prepared with Musa paradisiaca peels-PP-HYCA) against gram-negative enteric bacteria with a breakthrough time of 400 and 700 min for the removal of 1.5 x10(6) cfu/mL S. typhi and V. cholerae from water respectively. At 10(3) cfu/mL of each bacterium in solution, 2 g of both composite adsorbents kept the levels the bacteria in effluent solutions at zero for up to 24 h. Steam regeneration of 2 g of bacteria-loaded Carica papaya prepared composite adsorbent shows a loss of ca. 31% of its capacity even after the 3rd regeneration cycle of 25 h of service time. The composite adsorbent prepared with Carica papaya seeds will be useful for developing simple point-of-use water treatment systems for water disinfection application. This composite adsorbent is comparatively of good performance and shows relatively long hydraulic contact times and is expected to minimize energy intensive traditional treatment processes.