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Diese Arbeit befasst sich mit der Synthese und der Charakterisierung von thermoresponsiven Polymeren und ihrer Immobilisierung auf festen Oberflächen als nanoskalige dünne Schichten. Dabei wurden thermoresponsive Polymere vom Typ der unteren kritischen Entmischungstemperatur (engl.: lower critical solution temperature, LCST) verwendet. Sie sind bei niedrigeren Temperaturen im Lösungsmittel gut und nach Erwärmen oberhalb einer bestimmten kritischen Temperatur nicht mehr löslich; d. h. sie weisen bei einer bestimmten Temperatur einen Phasenübergang auf. Als Basismaterial wurden verschiedene thermoresponsive und biokompatible Polymere basierend auf Diethylenglykolmethylethermethacrylat (MEO2MA) und Oligo(ethylenglykol)methylethermethacrylat (OEGMA475, Mn = 475 g/ mol) über frei radikalische Copolymerisation synthetisiert. Der thermoresponsive Phasenübergang der Copolymere wurde in wässriger Lösung und in gequollenen vernetzten dünnen Schichten beobachtet. Außerdem wurde untersucht, inwiefern eine selektive Proteinbindung an geeignete funktionalisierte Copolymere die Phasenübergangstemperatur beeinflusst. Die thermoresponsiven Copolymere wurden über photovernetzbare Gruppen auf festen Oberflächen immobilisiert. Die nötigen lichtempfindlichen Vernetzereinheiten wurden mittels des polymerisierbaren Benzophenonderivates 2 (4 Benzoylphenoxy)ethylmethacrylat (BPEM) in das Copolymer integriert. Dünne Filme der Copolymere mit ca. 100 nm Schichtdicke wurden über Rotationsbeschichtung auf Siliziumwafer aufgeschleudert und anschließend durch Bestrahlung mit UV Licht vernetzt und auf der Oberfläche immobilisiert. Die Filme sind stabiler je größer der Vernetzeranteil und je größer die Molmasse der Copolymere ist. Bei einem Waschprozess nach der Vernetzung wird beispielsweise aus einem Film mit moderater Molmasse und geringem Vernetzeranteil mehr unvernetztes Copolymer ausgewaschen als bei einem höhermolekularen Copolymer mit hohem Vernetzeranteil. Die Quellbarkeit der Polymerschichten wurde mit Ellipsometrie untersucht. Sie ist größer je geringer der Vernetzeranteil in den Copolymeren ist. Schichten aus thermoresponsiven OEG Copolymeren zeigen einen Volumenphasenübergang vom Typ der LCST. Der thermoresponsive Kollaps der Schichten ist komplett reversibel, die Kollapstemperatur kann über die Zusammensetzung der Copolymere eingestellt werden. Für einen Vergleich dieser Eigenschaften mit dem gut charakterisierten und derzeit wohl am häufigsten untersuchten thermoresponsiven Polymer Poly(N-isopropylacrylamid) (PNIPAM) wurden zusätzlich photovernetzte Schichten aus PNIPAM hergestellt und ebenfalls ellipsometrisch vermessen. Im Vergleich zu PNIPAM verläuft der Phasenübergang der Schichten aus den Copolymeren mit Oligo(ethylenglykol)-seitenketten (OEG Copolymere) über einen größeren Temperaturbereich. Mit Licht einer Wellenlänge > 300 nm wurden die photosensitiven Benzophenongruppen selektiv angeregt. Bei der Verwendung kleinerer Wellenlängen vernetzten die Copolymerschichten auch ohne die Anwesenheit der lichtempfindlichen Benzophenongruppen. Dieser Effekt ließ sich zur kontrollierten Immobilisierung und Vernetzung der OEG Copolymere einsetzen. Als weitere Methode zur Immobilisierung der Copolymere wurde die Anbindung über Amidbindungen untersucht. Dazu wurden OEG Copolymere mit dem carboxylgruppenhaltigen 2 Succinyloxyethylmethacrylat (MES) auf mit 3 Aminopropyldimethylethoxysilan (APDMSi) silanisierte Siliziumwafer rotationsbeschichtet, und mit dem oligomeren α, ω Diamin Jeffamin® ED 900 vernetzt. Die Vernetzungsreaktion erfolgte ohne weitere Zusätze durch Erhitzen der Proben. Die Hydrogelschichten waren anschließend stabil und zeigten neben thermoresponsivem auch pH responsives Verhalten. Um zu untersuchen, ob die Phasenübergangstemperatur durch eine Proteinbindung beeinflusst werden kann, wurde ein polymerisierbares Biotinderivat 2 Biotinyl-aminoethylmethacrylat (BAEMA) in das thermoresponsive Copolymer eingebaut. Der Einfluss des biotinbindenen Proteins Avidin auf das thermoresponsive Verhalten des Copolymers in Lösung wurde untersucht. Die spezifische Bindung von Avidin an das biotinylierte Copolymer verschob die Übergangstemperatur deutlich zu höheren Temperaturen. Kontrollversuche zeigten, dass dieses Verhalten auf eine selektive Proteinbindung zurückzuführen ist. Thermoresponsive OEG Copolymere mit photovernetzbaren Gruppen aus BPEM und Biotingruppen aus BAEMA wurden über Rotationsbeschichtung auf Gold- und auf Siliziumoberflächen aufgetragen und durch UV Strahlung vernetzt. Die spezifische Bindung von Avidin an die Copolymerschicht wurde mit Oberflächenplasmonenresonanz und Ellipsometrie untersucht. Die Bindungskapazität der Schichten war umso größer, je kleiner der Vernetzeranteil, d. h. je größer die Maschenweite des Netzwerkes war. Die Quellbarkeit der Schichten wurde durch die Avidinbindung erhöht. Bei hochgequollenen Systemen verursachte eine Mehrfachbindung des tetravalenten Avidins allerdings eine zusätzliche Quervernetzung des Polymernetzwerkes. Dieser Effekt wirkt der erhöhten Quellbarkeit durch die Avidinbindung entgegen und lässt die Polymernetzwerke schrumpfen.
Novel hydrogels based on hydroxyethyl starch modified with polyethylene glycol methacrylate (HES-P(EG)(6)MA) were developed as delivery system for the controlled release of proteins. Since the drug release behavior is supposed to be related to the pore structure of the hydrogel network the pore sizes were determined by cryo-SEM, which is a mild technique for imaging on a nanometer scale. The results showed a decreasing pore size and an increase in pore homogeneity with increasing polymer concentration. Furthermore, the mesh sizes of the hydrogels were calculated based on swelling data. Pore and mesh size were significantly different which indicates that both structures are present in the hydrogel. The resulting structural model was correlated with release data for bulk hydrogel cylinders loaded with FITC-dextran and hydrogel microspheres loaded with FITC-IgG and FITC-dextran of different molecular size. The initial release depended much on the relation between hydrodynamic diameter and pore size while the long term release of the incorporated substances was predominantly controlled by degradation of the network of the much smaller meshes.
Biotin is an essential vitamin that is, on the one hand, relevant for the metabolism, gene expression and in the cellular response to DNA damage and, on the other hand, finds numerous applications in biotechnology. The functionality of biotin is due to two particular sub-structures, the ring structure and the side chain with carboxyl group. The heterocyclic ring structure results in the capability of biotin to form strong intermolecular hydrogen and van der Waals bonds with proteins such as streptavidin, whereas the carboxyl group can be employed to covalently bind biotin to other complex molecules. Dissociative electron attachment (DEA) to biotin results in a decomposition of the ring structure and the carboxyl group, respectively, within resonant features in the energy range 0-12 eV, thereby preventing the capability of biotin for intermolecular binding and covalent coupling to other molecules. Specifically, the fragment anions (M-H)(-), (M-O)(-), C3N2O-, CH2O2-, OCN-, CN-, OH- and O- are observed, and exemplarily the DEA cross section of OCN- formation is determined to be 3 x 10(-19) cm(2). To study the response of biotin to electrons within a complex condensed environment, we use the DNA origami technique and determine a dissociation yield of (1.1 +/- 0.2) x 10(-14) cm(2) at 18 eV electron energy, which represents the most relevant energy for biomolecular damage induced by secondary electrons. The present results thus have important implications for the use of biotin as a label in radiation experiments.
In this paper, we present quantum dynamical calculations on electron correlation dynamics in atoms and molecules using explicitly time-dependent ab initio configuration interaction theory. The goals are (i) to show that in which cases it is possible to switch off the electronic correlation by ultrashort laser pulses, and (ii) to understand the temporal evolution and the time scale on which it reappears. We characterize the appearance of correlation through electron-electron scattering when starting from an uncorrelated state, and we identify pathways for the preparation of a Hartree-Fock state from the correlated, true ground state. Exemplary results for noble gases, alkaline earth elements, and selected molecules are provided. For Mg we show that the uncorrelated state can be prepared using a shaped ultrashort laser pulse.
Effect of ionic strength and layer number on swelling of polyelectrolyte multilayers in water vapour
(2013)
The swelling behavior of polyelectrolyte multilayers (PEMs) of poly(sodium-4 styrene sulfonate) (PSS) and poly(diallyl dimethyl ammonium chloride) (PDADMAC) prepared from aqueous solution of 0.1 M and 0.5 M NaCl are investigated by ellipsometry and Atomic Force Microscopy (AFM). From 1 double-layer up to 4 double-layers of 0.1 M NaCl, the amount of swelling water in the PEMs decreases with increasing number of adsorbed double layers due to an increase in polyelectrolyte density as a result of the attraction between the positively charged outermost PDADMAC layer and the Si substrate. From 6 double layers to 30 double layers, the attraction is reduced due to a much larger distance between substrate and outermost layer leading to a much lower polyelectrolyte density and higher swelling water. In PEMs prepared from aqueous solution of 0.5 M NaCl, the amount of water constantly increases which is related to a monotonically decreasing polyelectrolyte density with increasing number of polyelectrolyte layers. Studies of the surface topology also indicate a transition from a more substrate affected interphase behavior to a continuum properties of the polyelectrolyte multilayers. The threshold for the transition from interphase to continuum behavior depends on the preparation conditions of the PEM.
DNA nanotechnology holds great promise for the fabrication of novel plasmonic nanostructures and the potential to carry out single-molecule measurements using optical spectroscopy. Here, we demonstrate for the first time that DNA origami nanostructures can be exploited as substrates for surface-enhanced Raman scattering (SERS). Gold nanoparticles (AuNPs) have been arranged into dimers to create intense Raman scattering hot spots in the interparticle gaps. AuNPs (15 nm) covered with TAMRA-modified DNA have been placed at a nominal distance of 25 nm to demonstrate the formation of Raman hot spots. To control the plasmonic coupling between the nanoparticles and thus the field enhancement in the hot spot, the size of AuNPs has been varied from 5 to 28 nm by electroless Au deposition. By the precise positioning of a specific number of TAMRA molecules in these hot spots, SERS with the highest sensitivity down to the few-molecule level is obtained.
In many biological and environmental applications spatially resolved sensing of molecular oxygen is desirable. A powerful tool for distributed measurements is optical time domain reflectometry (OTDR) which is often used in the field of telecommunications. We combine this technique with a novel optical oxygen sensor dye, triangular-[4] phenylene (TP), immobilized in a polymer matrix. The TP luminescence decay time is 86 ns. The short decay time of the sensor dye is suitable to achieve a spatial resolution of some meters. In this paper we present the development and characterization of a reflectometer in the UV range of the electromagnetic spectrum as well as optical oxygen sensing with different fiber arrangements.
In many biological and environmental applications spatially resolved sensing of molecular oxygen is desirable. A powerful tool for distributed measurements is optical time domain reflectometry (OTDR) which is often used in the field of telecommunications. We combine this technique with a novel optical oxygen sensor dye, triangular-[4] phenylene (TP), immobilized in a polymer matrix. The TP luminescence decay time is 86 ns. The short decay time of the sensor dye is suitable to achieve a spatial resolution of some meters. In this paper we present the development and characterization of a reflectometer in the UV range of the electromagnetic spectrum as well as optical oxygen sensing with different fiber arrangements.
Sulfonated polyanilines have become promising building blocks in the construction of biosensors, and therefore we use here differently substituted polymer forms to investigate the role of their structural composition and properties in achieving a direct electron transfer with the redox enzyme pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH). To this end, new copolymers containing different ratios of 2-methoxyaniline-5-sulfonic acid (MAS), 3-aminobenzenesulfonic acid (ABS) and 3-aminobenzoic acid (AB) units have been chemically synthesized. All polymers have been studied with respect to their ability to react directly with PQQ-GDH. This interaction has been monitored initially in solution, and subsequently on electrode surfaces. The results show that only copolymers with MAS and aniline units can directly react with PQQ-GDH in solution; the background can be mainly ascribed to the emeraldine salt redox state of the polymer, allowing rather easy reduction. However, when polymers and the enzyme are immobilized on the surface of carbon nanotube-containing electrodes, direct bioelectrocatalysis is also feasible in the case of copolymers composed of ABS/AB and MAS/AB units, existing initially in pernigraniline base form. This verifies that a productive interaction of the enzyme with differently substituted polymers is feasible when the electrode potential can be used to drive the reaction towards the oxidation of the substrate-reduced enzyme. These results clearly demonstrate that enzyme electrodes based on sulfonated polyanilines and direct bioelectrocatalysis can be successfully constructed.
Die Dissertation beschreibt die Herstellung von ringförmigen Verbindungen (Naphthalenophanen) mit Hilfe der Dehydro-Diels-Alder-Reaktion, wobei immer Enantiomerenpaare auftreten. Es wird der diastereoselektive Aufbau von Naphthalenophanen und der enantiomeren reine Aufbau von Biarylen untersucht. Desweiteren werden die physikalischen Eigenschaften der erhaltenen Verbindungen, wie die Phosphoreszenz, Trennbarkeit der entstehenden Enantiomere und die Ringspannung beschrieben.
Calcium phosphate nanofibers with a diameter of only a few nanometers and a cotton-ball-like aggregate morphology have been reported several times in the literature. Although fiber formation seems reproducible in a variety of conditions, the crystal structure and chemical composition of the fibers have been elusive. Using scanning transmission electron microscopy, low dose electron (nano)diffraction, energy-dispersive X-ray spectroscopy, and energy- filtered transmission electron microscopy, we have assigned crystal structures and chemical compositions to the fibers. Moreover, we demonstrate that the mineralization process yields true polymer/calcium phosphate hybrid materials where the block copolymer template is closely associated with the calcium phosphate.
Calcium phosphate nanofibers with a diameter of only a few nanometers and a cotton-ball-like aggregate morphology have been reported several times in the literature. Although fiber formation seems reproducible in a variety of conditions, the crystal structure and chemical composition of the fibers have been elusive. Using scanning transmission electron microscopy, low dose electron (nano) diffraction, energy-dispersive X-ray spectroscopy, and energy-filtered transmission electron microscopy, we have assigned crystal structures and chemical compositions to the fibers. Moreover, we demonstrate that the mineralization process yields true polymer/calcium phosphate hybrid materials where the block copolymer template is closely associated with the calcium phosphate.
Calcium phosphate nanofibers with a diameter of only a few nanometers and a cotton-ball-like aggregate morphology have been reported several times in the literature. Although fiber formation seems reproducible in a variety of conditions, the crystal structure and chemical composition of the fibers have been elusive. Using scanning transmission electron microscopy, low dose electron (nano)diffraction, energy-dispersive X-ray spectroscopy, and energy-filtered transmission electron microscopy, we have assigned crystal structures and chemical compositions to the fibers. Moreover, we demonstrate that the mineralization process yields true polymer/calcium phosphate hybrid materials where the block copolymer template is closely associated with the calcium phosphate.
Two synthetic approaches to functionalize plant oil derived platform chemicals were investigated. For this purpose, methyl 10-undecenoate, which can be obtained by pyrolysis of castor oil, was used in olefin cross-metathesis under neat conditions forming an unsaturated a,?-acetoxy ester. A catalyst screening with 11 different ruthenium-based metathesis catalysts was performed, revealing that well-suited catalysts allow for full conversion and very good cross-metathesis selectivity at a loading of only 0.5?mol%. An alternative possibility to the aforementioned synthetic method is a palladium-catalyzed reaction of methyl 10-undecenoate with acetic acid in the presence of dimethyl sulfoxide. Here, the formation of linear and branched unsaturated acetoxy esters as well as a ketone was observed. The conversion as well as the selectivity of this procedure was studied under different reaction conditions and compared to the cross-metathesis results. Based on the successful functionalization of methyl 10-undecenoate, methyl oleate was investigated in this palladium-catalyzed C?H activation reaction. Due to the lower reactivity of the internal double bond the desired acetoxy ester was only obtained in moderate conversion in this case. In summary, this study clearly shows that palladium-catalyzed functionalization of unsaturated fatty compounds via C?H activation is an attractive alternative to the well-established olefin cross-metathesis procedure.
Cross metathesis of allyl alcohols how to suppress and how to promote double bond isomerization
(2013)
Under standard conditions the cross metathesis of allyl alcohols and methyl acrylate is accompanied by the formation of ketones, resulting from uncontrolled and undesired double bond isomerization. By conducting the CM in the presence of phenol, the catalyst loading and the reaction time required for quantiative conversion can be reduced, and isomerization can be suppressed. On the other hand, consecutive isomerization can be deliberately promoted by evaporating excess methyl acrylate after completing cross metathesis and by adding a base or silane as chemical triggers.
Under standard conditions the cross metathesis of allyl alcohols and methyl acrylate is accompanied by the formation of ketones, resulting from uncontrolled and undesired double bond isomerization. By conducting the CM in the presence of phenol, the catalyst loading and the reaction time required for quantiative conversion can be reduced, and isomerization can be suppressed. On the other hand, consecutive isomerization can be deliberately promoted by evaporating excess methyl acrylate after completing cross metathesis and by adding a base or silane as chemical triggers.
The non-ionic monomer (methoxy diethylene glycol) acrylate is copolymerized with its azodye-functionalized acrylate analogue using reversible addition-fragmentation chain transfer (RAFT) polymerization. Copolymerization is increasingly difficult with increasing amounts of the azo-dye-bearing monomer. The resulting water-soluble polymers are thermosensitive, exhibiting lower critical solution temperature (LCST) behavior, which can be modulated by the photoinduced trans-cis isomerization of the dye. While already small contents of the hydrophobic azobenzene group reduce the phase-transition temperatures of the copolymers strongly, photoisomerization of the apolar trans-state to the more-polar cis-state has only a small effect, and decreases rather than increases the cloud points.
Continuous synthesis of pyridocarbazoles and initial photophysical and bioprobe characterization
(2013)
Pyridocarbazoles when ligated to transition metals yield high affinity kinase inhibitors. While batch photocyclizations enable the synthesis of these heterocycles, the non-oxidative Mallory reaction only provides modest yields and difficult to purify mixtures. We demonstrate here that a flow-based Mallory cyclization provides superior results and enables observation of a clear isobestic point. The flow method allowed us to rapidly synthesize ten pyridocarbazoles and for the first time to document their interesting photophysical attributes. Preliminary characterization reveals that these molecules might be a new class of fluorescent bioprobe.
The transport of bioactive compounds to the site of action is a great challenge. A promising approach to overcome application-related problems is the development of targeting colloidal transport systems, such as micelles which are equipped with uptake mediating moieties. Here, we investigated a set of novel lipopeptides which exhibit a surfactant-like structure due to attachment of two palmitoyl chains to the Nterminus of cationic or anionic amino acid sequences. We analyzed the association behavior of these lipopeptides by using 5(6)-carboxyfluorescein (CF)-labeled derivatives as a fluorescent probe and different spectroscopic methods such as fluorescence anisotropy and fluorescence correlation spectroscopy (FCS). The photophysical properties as well as the diffusion and rotational movements of the CF-labeled lipopeptides were exploited to determine the cmc and the size of the micelles consisting of lipopeptides. We could distinguish cationic and anionic lipopeptides by their association behavior and by studying the interactions with mouse brain capillary endothelial cells (b.end3). The cationic derivatives turned out to be very strong surfactants with a very low cmc in the micromolar range (0.5-14 mu M). The unique combination of micelle-forming property and cell-penetrating ability can pave the road for the development of a novel class of efficient drug carrier systems.
In various biological systems and small scale technological applications particles transiently bind to a cylindrical surface. Upon unbinding the particles diffuse in the vicinal bulk before rebinding to the surface. Such bulk-mediated excursions give rise to an effective surface translation, for which we here derive and discuss the dynamic equations, including additional surface diffusion. We discuss the time evolution of the number of surface-bound particles, the effective surface mean squared displacement, and the surface propagator. In particular, we observe sub- and superdiffusive regimes. A plateau of the surface mean-squared displacement reflects a stalling of the surface diffusion at longer times. Finally, the corresponding first passage problem for the cylindrical geometry is analysed.
Starting from the conveniently available ex-chiral pool building block (R,R)-hexa-1,5-diene-3,4-diol, the ten-membered ring lactones stagonolide E and curvulide A were synthesized using a bidirectional olefin-metathesis functionalization of the terminal double bonds. Key steps are (i) a site-selective cross metathesis, (ii) a highly diastereoselective extended tethered RCM to furnish a (Z,E)-configured dienyl carboxylic acid and (iii) a Ru-lipase-catalyzed dynamic kinetic resolution to establish the desired configuration at C9. Ring closure was accomplished by macrolactonization. Curvulide A was synthesized from stagonolide E through Sharpless epoxidation.
Awards
(2013)
An asymmetric variant of the dehydro-Diels-Alder (DDA) reaction has been developed and applied in the atropselective synthesis of various (1,5)naphthalenophanes. Whereas the suitability of the photochemically induced DDA (PDDA) was limited, the thermally induced DDA provided the desired product, depending on the chiral auxiliary used and the length of the linker, with nearly perfect stereoselectivity. Furthermore, the mechanism of the DDA was investigated by means of DFT calculations, and a stepwise mechanism involving 1,4-biradicals was suggested.
1,2-Diketones were synthesized from styrenes by combining a cross metathesis and a Ru-catalyzed alkene oxidation to an assisted tandem catalytic sequence. The synthesis relies on the use of just one metathesis precatalyst, which was in situ converted to the oxidation catalyst by addition of an alkyl hydroperoxide as a chemical trigger and oxidant. The one-flask sequence can be extended beyond 1,2-diketones to quinoxalines, by condensation of the oxidation products with ortho-phenylenediamine.
Assessment of coupled cluster theory and more approximate methods for hydrogen bonded systems
(2013)
To assess the accuracy of post-Hartree-Fock methods like CCSD(T), MP3, MP2.5, MP2, SCS-MP2, SOS-MP2, and DFT-SAPT, we evaluated several effects going beyond valence-correlated CCSD(T). For 16 small hydrogen bonded systems, CCSD(T) achieves an RMS error of 0.17 kJ/mol in the dissociation energy compared to our best estimate, which is a composite method akin to W4 theory. The error of CCSD(T) is thus much lower than for atomization energies. MP2 is surprisingly accurate for these systems with an RMS error of 1.3 kJ/mol. MP2.5 yields a clear improvement over MP2 (RMS of 0.5 kJ/mol) but still has an error about 3 times as large as CCSD(T) for the absolute RMS and almost 10 times as large for the relative RMS. error. Neither SCS-MP2, SOS-MP2, nor DFT-SAPT yield lower errors than MP2. With a Delta CCSD(T) correction to MP2, the basis set limit is readily achieved when employing diffuse functions-without these, the convergence is rather slow.
From the surface exudates of Senecio roseiflorus fourteen known methylated flavonoids and one phenol were isolated and characterized. The structures of these compounds were determined on the basis of their spectroscopic analysis. The surface exudate and the flavonoids isolated showed moderate to good antiplasmodial activity with 5,4'-dihydroxy-7-dimethoxyflavanone having the highest activity against chloroquine-sensitive (D6) and resistant (W2) strains of Plasmodium falciparum, with IC50 values of 3.2 +/- 0.8 and 4.4 +/- 0.01 mu g/mL respectively.
An anionic microporous polymer network prepared by the polymerization of weakly coordinating anions
(2013)
Derivatization of fullerene (C60) with branched aliphatic chains softens C60-based materials and enables the formation of thermotropic liquid crystals and room temperature nonvolatile liquids. This work demonstrates that by carefully tuning parameters such as type, number and substituent position of the branched chains, liquid crystalline C60 materials with mesophase temperatures suited for photovoltaic cell fabrication and room temperature nonvolatile liquid fullerenes with tunable viscosity can be obtained. In particular, compound 1, with branched chains, exhibits a smectic liquid crystalline phase extending from 84°C to room temperature. Analysis of bulk heterojunction (BHJ) organic solar cells with a ca. 100 nm active layer of compound 1 and poly(3-hexylthiophene) (P3HT) as an electron acceptor and an electron donor, respectively, reveals an improved performance (power conversion efficiency, PCE: 1.6 ñ 0.1%) in comparison with another compound, 10 (PCE: 0.5 ñ 0.1%). The latter, in contrast to 1, carries linear aliphatic chains and thus forms a highly ordered solid lamellar phase at room temperature. The solar cell performance of 1 blended with P3HT approaches that of PCBM/P3HT for the same active layer thickness. This indicates that C60 derivatives bearing branched tails are a promising class of electron acceptors in soft (flexible) photovoltaic devices.
Derivatization of fullerene (C60) with branched aliphatic chains softens C60-based materials and enables the formation of thermotropic liquid crystals and room temperature nonvolatile liquids. This work demonstrates that by carefully tuning parameters such as type, number and substituent position of the branched chains, liquid crystalline C60 materials with mesophase temperatures suited for photovoltaic cell fabrication and room temperature nonvolatile liquid fullerenes with tunable viscosity can be obtained. In particular, compound 1, with branched chains, exhibits a smectic liquid crystalline phase extending from 84 °C to room temperature. Analysis of bulk heterojunction (BHJ) organic solar cells with a ca. 100 nm active layer of compound 1 and poly(3-hexylthiophene) (P3HT) as an electron acceptor and an electron donor, respectively, reveals an improved performance (power conversion efficiency, PCE: 1.6 ± 0.1%) in comparison with another compound, 10 (PCE: 0.5 ± 0.1%). The latter, in contrast to 1, carries linear aliphatic chains and thus forms a highly ordered solid lamellar phase at room temperature. The solar cell performance of 1 blended with P3HT approaches that of PCBM/P3HT for the same active layer thickness. This indicates that C60 derivatives bearing branched tails are a promising class of electron acceptors in soft (flexible) photovoltaic devices.
A water soluble fluorescent polymer as a dual colour sensor for temperature and a specific protein
(2013)
We present two thermoresponsive water soluble copolymers prepared via free radical statistical copolymerization of N-isopropylacrylamide (NIPAm) and of oligo(ethylene glycol) methacrylates (OEGMAs), respectively, with a solvatochromic 7-(diethylamino)-3-carboxy-coumarin (DEAC)-functionalized monomer. In aqueous solutions, the NIPAm-based copolymer exhibits characteristic changes in its fluorescence profile in response to a change in solution temperature as well as to the presence of a specific protein, namely an anti-DEAC antibody. This polymer emits only weakly at low temperatures, but exhibits a marked fluorescence enhancement accompanied by a change in its emission colour when heated above its cloud point. Such drastic changes in the fluorescence and absorbance spectra are observed also upon injection of the anti-DEAC antibody, attributed to the specific binding of the antibody to DEAC moieties. Importantly, protein binding occurs exclusively when the polymer is in the well hydrated state below the cloud point, enabling a temperature control on the molecular recognition event. On the other hand, heating of the polymer-antibody complexes releases a fraction of the bound antibody. In the presence of the DEAC-functionalized monomer in this mixture, the released antibody competitively binds to the monomer and the antibody-free chains of the polymer undergo a more effective collapse and inter-aggregation. In contrast, the emission properties of the OEGMA-based analogous copolymer are rather insensitive to the thermally induced phase transition or to antibody binding. These opposite behaviours underline the need for a carefully tailored molecular design of responsive polymers aimed at specific applications, such as biosensing.
A water soluble fluorescent polymer as a dual colour sensor for temperature and a specific protein
(2013)
We present two thermoresponsive water soluble copolymers prepared via free radical statistical copolymerization of N-isopropylacrylamide (NIPAm) and of oligo(ethylene glycol) methacrylates (OEGMAs), respectively, with a solvatochromic 7-(diethylamino)-3-carboxy-coumarin (DEAC)- functionalized monomer. In aqueous solutions, the NIPAm-based copolymer exhibits characteristic changes in its fluorescence profile in response to a change in solution temperature as well as to the presence of a specific protein, namely an anti-DEAC antibody. This polymer emits only weakly at low temperatures, but exhibits a marked fluorescence enhancement accompanied by a change in its emission colour when heated above its cloud point. Such drastic changes in the fluorescence and absorbance spectra are observed also upon injection of the anti-DEAC antibody, attributed to the specific binding of the antibody to DEAC moieties. Importantly, protein binding occurs exclusively when the polymer is in the well hydrated state below the cloud point, enabling a temperature control on the molecular recognition event. On the other hand, heating of the polymer–antibody complexes releases a fraction of the bound antibody. In the presence of the DEAC-functionalized monomer in this mixture, the released antibody competitively binds to the monomer and the antibody-free chains of the polymer undergo a more effective collapse and inter-aggregation. In contrast, the emission properties of the OEGMA-based analogous copolymer are rather insensitive to the thermally induced phase transition or to antibody binding. These opposite behaviours underline the need for a carefully tailored molecular design of responsive polymers aimed at specific applications, such as biosensing.
A polymer analogous reaction for the formation of imidazolium and NHC based porous polymer networks
(2013)
A polymer analogous reaction was carried out to generate a porous polymeric network with N-heterocyclic carbenes (NHC) in the polymer backbone. Using a stepwise approach, first a polyimine network is formed by polymerization of the tetrafunctional amine tetrakis(4-aminophenyl)methane. This polyimine network is converted in the second step into polyimidazolium chloride and finally to a polyNHC network. Furthermore a porous Cu(II)-coordinated polyNHC network can be generated. Supercritical drying generates polymer networks with high permanent surface areas and porosities which can be applied for different catalytic reactions. The catalytic properties were demonstrated for example in the activation of CO2 or in the deoxygenation of sulfoxides to the corresponding sulfides.
A polymer analogous reaction for the formation of imidazolium and NHC based porous polymer networks
(2013)
A polymer analogous reaction was carried out to generate a porous polymeric network with N-heterocyclic carbenes (NHC) in the polymer backbone. Using a stepwise approach, first a polyimine network is formed by polymerization of the tetrafunctional amine tetrakis(4-aminophenyl)methane. This polyimine network is converted in the second step into polyimidazolium chloride and finally to a polyNHC network. Furthermore a porous Cu(II)-coordinated polyNHC network can be generated. Supercritical drying generates polymer networks with high permanent surface areas and porosities which can be applied for different catalytic reactions. The catalytic properties were demonstrated for example in the activation of CO2 or in the deoxygenation of sulfoxides to the corresponding sulfides.
A polymer analogous reaction for the formation of imidazolium and NHC based porous polymer networks
(2013)
A polymer analogous reaction was carried out to generate a porous polymeric network with N-heterocyclic carbenes (NHC) in the polymer backbone. Using a stepwise approach, first a polyimine network is formed by polymerization of the tetrafunctional amine tetrakis(4-aminophenyl)methane. This polyimine network is converted in the second step into polyimidazolium chloride and finally to a polyNHC network. Furthermore a porous Cu(II)-coordinated polyNHC network can be generated. Supercritical drying generates polymer networks with high permanent surface areas and porosities which can be applied for different catalytic reactions. The catalytic properties were demonstrated for example in the activation of CO2 or in the deoxygenation of sulfoxides to the corresponding sulfides.
Herein, we report the synthesis of two phenylaza-[18]crown-6 lariat ethers with a coumarin fluorophore (1 and 2) and we reveal that compound 1 is an excellent probe for K+ ions under simulated physiological conditions. The presence of a 2-methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat-free phenylaza-[18] crown-6 ether analogues. Probe 1 shows a high K+/Na+ selectivity and a 2.5-fold fluorescence enhancement was observed in the presence of 100 mm K+ ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8% per 1 mm K+ within the range 1-10 mm K+. The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K+ ions on both the extracellular and intracellular levels.
Acetanilides can be deacetylated and diazotized in situ, and subsequently used in Pd-catalyzed coupling reactions without isolation of the diazonium intermediate. Heck reactions, Suzuki cross-coupling reactions, and a Pd-catalyzed [2+2+1]cycloaddition have been investigated as terminating CC bond-forming steps of this one-flask sequence. The sequence does not require the exchange of solvents or removal of by-products between the individual steps, but proceeds by addition of reagents and catalysts in due course.
A conformational study of N-acetyl glucosamine derivatives utilizing residual dipolar couplings
(2013)
Two new 3-hydroxyisoflavanones, (S)-3,4',5-trihydroxy-2',7-dimethoxy-3'-prenylisoflavanone (trivial name kenusanone F 7-methyl ether) and (S)-3,5-dihydroxy-2',7-dimethoxy-2 '',2 ''-dimethylpyrano[5 '',6 '':3',4']isoflavanone (trivial name sophoronol-7-methyl ether) along with two known compounds (dalbergin and formononetin) were isolated from the stem bark of Dalbergia melanoxylon. The structures were elucidated using spectroscopic techniques. Kenusanone F 7-methyl ether showed activity against Mycobacterium tuberculosis, whereas both of the new compounds were inactive against the malaria parasite Plasmodium falciparum at 10 mu g/ml. Docking studies showed that the new compounds kenusanone F 7-methyl ether and sophoronol-7-methyl ether have high affinity for the M. tuberculosis drug target INHA.
A series of 5-unsubstituted and 5-substituted 2-alkylidene-4-oxothiazolidine-S-oxides were synthesized by the sulfur-oxidation with m-CPBA. The stereochemistry of 5-substituted sulfoxides was determined by means of NMR spectroscopy and DFT theoretical calculations. It was found that the thermodynamically less stable anti-isomer was initially formed in the course of the oxidation, but it underwent epimerization to the mixture enriched in the more stable syn-isomer, during the work-up process. The higher stability of syn-isomers is ascribed to the stronger hyperconjugative sigma(C-H)->sigma*(S-O) interaction versus the weaker sigma(C-C)->sigma*(S-O) delocalization in their anti-counterparts and to the existence of intramolecular 1,5-CH center dot center dot center dot C hydrogen bonds.
User-friendly protocols for the protecting group-free synthesis of 2,2'-biphenols via Suzuki-Miyaura coupling of o-halophenols and o-boronophenol are presented. The reactions proceed in water in the presence of simple additives such as K2CO3, KOH, KF, or TBAF and with commercially available Pd/C as precatalyst. Expensive or laboriously synthesized ligands or other additives are not required. In the case of bromophenols, efficient rate acceleration and short reaction times were accomplished by microwave irradiation.
The first Si-H-containing azasilaheterocycle, 1,3-dimethyl-3-silapiperidine 1, was synthesized, and its molecular structure and conformational properties were studied by gas-phase electron diffraction (GED), low temperature NMR, IR and Raman spectroscopy and quantum chemical calculations. The compound exists as a mixture of two conformers possessing the chair conformation with the equatorial NMe group and differing by axial or equatorial position of the SiMe group. In the gas phase, the SiMeax conformer predominates (GED: ax/eq = 65(7):35(7)%,Delta G = 0.36(18) kcal/mol; IR: ax/eq = 62(5):38(5)%,Delta G = 0.16(7) kcal/mol). In solution, at 143 k the SiMeeq conformer predominates' in the frozen equilibrium (NMR: ax/eq = 31.5(1.5):68.5(1.5)%, Delta G = -0.22(2) kcal/mol). Thermodynamic parameters of the ring inversion are determined (Delta G(double dagger) = 8.9-9.0 kcal/mol, Delta H-double dagger = 9.6 kcal/mol, Delta S-double dagger = 2.1 eu). High-level quantum chemical calculations :(MP2, G2, CCSD(T)) nicely reproduce the experimental geometry and the predominance of the axial conformer in the gas phase.
The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of already synthesized dehydro[n]annulenes of various ring size (from C-12 to C-20) have been computed, visualized as Isochemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to present (anti)aromaticity. For this purpose the thus quantified ring current effect of the macro cycles on proximate protons in proton NMR spectra was employed.
This paper focuses on two different strategies to incorporate gold nanoparticles (AuNPs) into the matrix of polyacrylamide (PAAm) hydrogels. Poly(ethyleneimine) (PEI) is used as both reducing and stabilizing agent for the formation of AuNPs. In addition, the influence of an ionic liquid (IL) (i.e., 1-ethyl-3-methylimidazolium ethylsulfate) on the stability of the nanoparticles and their immobilization in the hydrogel is investigated The results show that AuNPs surrounded by a shell containing PEI and IL, synthesized according to the one-pot approach, are much better immobilized within the PAAm hydrogel. Hereby, the IL is responsible for structural changes in the hydrogel as well as the improved stabilization and embedding of the AuNPs into the polymer gel matrix.