@article{RottkeSchulzRichauetal.2016, author = {Rottke, Falko O. and Schulz, Burkhard and Richau, Klaus and Kratz, Karl and Lendlein, Andreas}, title = {An ellipsometric approach towards the description of inhomogeneous polymer-based Langmuir layers}, series = {Beilstein journal of nanotechnology}, volume = {7}, journal = {Beilstein journal of nanotechnology}, publisher = {Beilstein-Institut zur F{\~A}\Prderung der Chemischen Wissenschaften}, address = {Frankfurt, Main}, issn = {2190-4286}, doi = {10.3762/bjnano.7.107}, pages = {1156 -- 1165}, year = {2016}, abstract = {The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewster angle microscopy (BAM) and imaging ellipsometry (IE) is presented for the characterization of ultrathin films at the air-water interface. First, the methodology is demonstrated for a vertically nonmoving Langmuir layer of star-shaped, 4-arm poly(omega-pentadecalactone) (PPDL-D4). Using nulling-based ellipsometric mapping, PPDL-D4-based inhomogeneously structured morphologies with a vertical dimension in the lower nm range could be mapped. In addition to the identification of these structures, the differentiation between a monolayer and bare water was possible. Second, the potential and limitations of this method were verified by applying it to more versatile Langmuir layers of telechelic poly[(rac-lactide)-co-glycolide]-diol (PLGA). All ellipsometric maps were converted into thickness maps by introduction of the refractive index that was derived from independent ellipsometric experiments, and the result was additionally evaluated in terms of the root mean square roughness, R-q. Thereby, a three-dimensional view into the layers was enabled and morphological inhomogeneity could be quantified.}, language = {en} } @article{RumschoettelKosmellaPrietzeletal.2016, author = {Rumsch{\"o}ttel, Jens and Kosmella, Sabine and Prietzel, Claudia Christina and Appelhans, Dietmar and Koetz, Joachim}, title = {Change in size, morphology and stability of DNA polyplexes with hyperbranched poly(ethyleneimines) containing bulky maltose units}, series = {Colloids and surfaces : an international journal devoted to fundamental and applied research on colloid and interfacial phenomena in relation to systems of biological origin ; B, Biointerfaces}, volume = {138}, journal = {Colloids and surfaces : an international journal devoted to fundamental and applied research on colloid and interfacial phenomena in relation to systems of biological origin ; B, Biointerfaces}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-7765}, doi = {10.1016/j.colsurfb.2015.11.061}, pages = {78 -- 85}, year = {2016}, abstract = {Polyplexes between Salmon DNA and non-modified hyperbranched poly(ethyleneimines) of varying molar mass, i.e., PEI(5 k) with 5000 g/mol and PEI(25 k) with 25,000 g/mol, and modified PEI(5 k) with maltose units (PEI-Mal) were investigated in dependence on the molar N/P ratio by using dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (mu-DSC), scanning-transmission electron microscopy (STEM), and cryo-scanning electron microscopy (cryo-SEM). A reloading of the polyplexes can be observed by adding the unmodified PEI samples of different molar mass. In excess of PEI a morphological transition from core-shell particles (at N/P 8) to loosely packed onion-like polyplexes (at N/P 40) is observed. The shift of the DSC melting peak from 88 degrees C to 76 degrees C indicates a destabilization of the DNA double helix due to the complexation with the unmodified PEI. Experiments with the maltose-modified PEI show a reloading already at a lower N/P ratio. Due to the presence of the sugar units in the periphery of the polycation electrostatic interactions between DNA become weaker, but cooperative H-bonding forces are reinforced. The resulting less-toxic, more compact polyplexes in excess of the PEI-Mal with two melting points and well distributed DNA segments are of special interest for extended gene delivery experiments. (C) 2015 Elsevier B.V. All rights reserved.}, language = {en} } @article{RyabchunRaguzinStumpeetal.2016, author = {Ryabchun, Alexander and Raguzin, Ivan and Stumpe, Joachim and Shibaev, Valery and Bobrovsky, Alexey}, title = {Cholesteric Polymer Scaffolds Filled with Azobenzene-Containing Nematic Mixture with Phototunable Optical Properties}, series = {Scientific reports}, volume = {8}, journal = {Scientific reports}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.6b09642}, pages = {27227 -- 27235}, year = {2016}, abstract = {The past two decades witnessed tremendous progress in the field of creation of different types of responsive materials. Cholesteric polymer networks present a very promising class of smart materials due to the combination of the unique optical properties of cholesteric mesophase and high mechanical properties of polymer networks. In the present work we demonstrate the possibility of fast and reversible photocontrol of the optical properties of cholesteric polymer networks. Several cholesteric photopolymerizable mixtures are prepared, and porous cholesteric network films with different helix pitches are produced by polymerization of these mixtures. An effective and simple method of the introduction of photochromic azobenzene-containing nematic mixture capable of isothermal photoinducing the nematic isotropic phase transition into the porous polymer matrix is developed, It is found that cross-linking density and degree of polymer network filling with a photochromic nematic mixture strongly influence the photo-optical behavior of the obtained composite films. In particular, the densely cross-linked films are characterized by a decrease in selective light reflection bandwidth, whereas weakly cross-linked systems display two processes: the shift of selective light reflection peak and decrease of its width. It is noteworthy that the obtained cholesteric materials are shown to be very promising for the variety applications in optoelectronics and photonics.}, language = {en} } @article{SchildeKellingUmbreenetal.2016, author = {Schilde, Uwe and Kelling, Alexandra and Umbreen, Sumaira and Linker, Torsten}, title = {Crystal structures of three bicyclic carbohydrate derivatives}, series = {Acta crystallographica Section E ; Crystallographic communications}, volume = {72}, journal = {Acta crystallographica Section E ; Crystallographic communications}, number = {12}, publisher = {IUCR}, address = {Chester}, issn = {2056-9890}, doi = {10.1107/S2056989016018727}, pages = {1839 -- 1844}, year = {2016}, abstract = {The title compounds, [(1R,3R,4R,5R,6S)-4,5-bis(acetyloxy)-7-oxo-2-oxabicyclo- [4.2.0]octan-3-yl]methyl acetate, C14H18O8, (I), [(1S,4R,5S,6R)-5-acetyloxy-7- hydroxyimino-2-oxobicyclo[4.2.0]octan-4-yl acetate, C11H15NO6, (II), and [(3aR,5R,6R,7R,7aS)-6,7-bis(acetyloxy)-2-oxooctahydropyrano[3,2-b]pyrrol-5- yl]methyl acetate, C14H19NO8, (III), are stable bicyclic carbohydrate derivatives. They can easily be synthesized in a few steps from commercially available glycals. As a result of the ring strain from the four-membered rings in (I) and (II), the conformations of the carbohydrates deviate strongly from the ideal chair form. Compound (II) occurs in the boat form. In the five-membered lactam (III), on the other hand, the carbohydrate adopts an almost ideal chair conformation. As a result of the distortion of the sugar rings, the configurations of the three bicyclic carbohydrate derivatives could not be determined from their NMR coupling constants. From our three crystal structure determinations, we were able to establish for the first time the absolute configurations of all new stereocenters of the carbohydrate rings.}, language = {en} } @misc{SchildeKellingUmbreenetal.2016, author = {Schilde, Uwe and Kelling, Alexandra and Umbreen, Sumaira and Linker, Torsten}, title = {Crystal structures of three bicyclic carbohydrate derivatives}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-100833}, pages = {6}, year = {2016}, abstract = {The title compounds, [(1R,3R,4R,5R,6S)-4,5-bis­(acet­yloxy)-7-oxo-2-oxabi­cyclo[4.2.0]octan-3-yl]methyl acetate, C14H18O8, (I), [(1S,4R,5S,6R)-5-acet­yloxy-7-hy­droxy­imino-2-oxobi­cyclo­[4.2.0]octan-4-yl acetate, C11H15NO6, (II), and [(3aR,5R,6R,7R,7aS)-6,7-bis­(acet­yloxy)-2-oxo­octa­hydro­pyrano[3,2-b]pyrrol-5-yl]methyl acetate, C14H19NO8, (III), are stable bicyclic carbohydrate derivatives. They can easily be synthesized in a few steps from commercially available glycals. As a result of the ring strain from the four-membered rings in (I) and (II), the conformations of the carbohydrates deviate strongly from the ideal chair form. Compound (II) occurs in the boat form. In the five-membered lactam (III), on the other hand, the carbohydrate adopts an almost ideal chair conformation. As a result of the distortion of the sugar rings, the configurations of the three bicyclic carbohydrate derivatives could not be determined from their NMR coupling constants. From our three crystal structure determinations, we were able to establish for the first time the absolute configurations of all new stereocenters of the carbohydrate rings.}, language = {en} } @article{SchildeKellingUmbreenetal.2016, author = {Schilde, Uwe and Kelling, Alexandra and Umbreen, Sumaira and Linker, Torsten}, title = {Crystal structures of three bicyclic carbohydrate derivatives}, series = {Acta crystallographica, Section E, Crystallographic communications}, volume = {72}, journal = {Acta crystallographica, Section E, Crystallographic communications}, publisher = {International Union of Crystallography}, address = {Chester}, issn = {2056-9890}, doi = {10.1107/S2056989016018727}, pages = {1839 -- +}, year = {2016}, abstract = {The title compounds, [(1R,3R,4R,5R,6S)-4,5-bis(acetyloxy)-7-oxo-2-oxabicyclo-[4.2.0]octan-3-yl]methyl acetate, C14H18O8, (I), [(1S,4R,5S,6R)-5-acetyloxy-7-hydroxyimino-2-oxobicyclo[4.2.0] octan-4-yl acetate, C11H15NO6, (II), and [(3aR, 5R, 6R, 7R, 7aS)-6,7-bis(acetyloxy)-2-oxooctahydropyrano[3,2-b]pyrrol-5-yl] methyl acetate, C14H19NO8, (III), are stable bicyclic carbohydrate derivatives. They can easily be synthesized in a few steps from commercially available glycals. As a result of the ring strain from the four-membered rings in (I) and (II), the conformations of the carbohydrates deviate strongly from the ideal chair form. Compound (II) occurs in the boat form. In the five-membered lactam (III), on the other hand, the carbohydrate adopts an almost ideal chair conformation. As a result of the distortion of the sugar rings, the configurations of the three bicyclic carbohydrate derivatives could not be determined from their NMR coupling constants. From our three crystal structure determinations, we were able to establish for the first time the absolute configurations of all new stereocenters of the carbohydrate rings.}, language = {en} } @article{SchmidtAudoerschKunz2016, author = {Schmidt, Bernd and Audoersch, Stephan and Kunz, Oliver}, title = {Stereoselective Synthesis of 2Z,4E-Configured Dienoates through Tethered Ring Closing Metathesis}, series = {Synthesis}, volume = {48}, journal = {Synthesis}, publisher = {Thieme}, address = {Stuttgart}, issn = {0039-7881}, doi = {10.1055/s-0035-1562536}, pages = {4509 -- 4518}, year = {2016}, language = {en} } @article{SchmidtRiemer2016, author = {Schmidt, Bernd and Riemer, Martin}, title = {Microwave-Promoted Deprenylation: Prenyl Ether as a Thermolabile Phenol Protecting Group}, series = {Synthesis}, volume = {48}, journal = {Synthesis}, publisher = {Thieme}, address = {Stuttgart}, issn = {0039-7881}, doi = {10.1055/s-0035-1561366}, pages = {1399 -- 1406}, year = {2016}, abstract = {para-Substituted aryl prenyl ethers undergo a deprenylation reaction upon microwave irradiation. This offers the opportunity to use a prenyl ether as a thermolabile protecting group in the synthesis of natural products with a chromone structure, which proceeds via a tandem deprenylation/6-endo-cyclization sequence.}, language = {en} } @article{SchmidtRiemer2016, author = {Schmidt, Bernd and Riemer, Martin}, title = {Synthesis of Allyl- and Prenylcoumarins via Microwave-Promoted Tandem Claisen Rearrangement/Wittig Olefination}, series = {Synthesis}, volume = {48}, journal = {Synthesis}, publisher = {Thieme}, address = {Stuttgart}, issn = {0039-7881}, doi = {10.1055/s-0035-1560501}, pages = {141 -- 149}, year = {2016}, abstract = {Allyl, dimethylallyl, crotyl, and prenyl ethers of various aromatic ortho-hydroxy carbonyl compounds undergo a tandem sequence of Claisen rearrangement, carbonyl olefination, and cyclization upon microwave irradiation in the presence of a stabilized ylide. The products are multiply substituted 6- or 8-allylated or prenylated coumarins (2H-chromen-2-ones).}, language = {en} } @article{SchmidtWolfBrunner2016, author = {Schmidt, Bernd and Wolf, Felix and Brunner, Heiko}, title = {Styrylsulfonates and -Sulfonamides through Pd-Catalysed Matsuda-Heck Reactions of Vinylsulfonic Acid Derivatives and Arenediazonium Salts}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201600469}, pages = {2972 -- 2982}, year = {2016}, abstract = {Arene diazonium salts undergo Matsuda-Heck reactions with vinylsulfonates and -sulfonamides to give styrylsulfonic acid derivatives in high to excellent yields and with high to excellent selectivities. By quantifying the evolution of nitrogen over time in a gas-meter apparatus, the reactivities of ethylvinylsulfonate and the benchmark olefin methyl acrylate were compared for an electron-rich and an -deficient arene diazonium salt. Tertiary sulfonamides react in Matsuda-Heck couplings with high conversions, but require long reaction times, which prevents the determination of kinetic data through the measurement of nitrogen evolution. Secondary sulfonamides were found to be unreactive. From these results, the following order of reactivity could be deduced: H2C=CHCO2Me > H2C=CHSO2OEt > H2C=CHSO2N(Me)Bn >> H2C=CHSO2NHBn. Through the Matsuda-Heck coupling of 5-indolyldiazonium salt and a tertiary vinylsulfonamide, the synthesis of the C-5-substituted indole part of the antimigraine drug naratriptan was accomplished in high yield.}, language = {en} } @article{SchmidtWolfEhlert2016, author = {Schmidt, Bernd and Wolf, Felix and Ehlert, Christopher}, title = {Systematic Investigation into the Matsuda-Heck Reaction of alpha-Methylene Lactones: How Conformational Constraints Direct the beta-H-Elimination Step}, series = {The journal of organic chemistry}, volume = {81}, journal = {The journal of organic chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.6b02207}, pages = {11235 -- 11249}, year = {2016}, abstract = {alpha-Methylene-gamma-butyrolactone and alpha-methylene-gamma-valerolactone undergo Pd-catalyzed Matsuda-Heck couplings with arene diazonium salts to alpha-benzyl butenolides or pentenolides, respectively, or to alpha-benzylidene lactones. The observed regioselectivity is strongly ring size dependent, with six-membered rings giving exclusively alpha-benzyl pentenolides, whereas the five-membered alpha-methylene lactone reacts to mixtures of regioisomers with a high proportion of (E)-alpha-benzylidene-gamma-butyrolactones. DFT calculations suggest that the reasons for these differences are not thermodynamic but kinetic in nature. The relative energies of the conformers of the Pd sigma-complexes resulting from insertion into the Pd-aryl bond were correlated with the dihedral angles between Pd and endo-beta-H. This correlation revealed that in the case of the six-membered lactone an energetically favorable conformer adopts a nearly synperiplanar Pd/endo-beta-H arrangement, whereas for the analogous Pd sigma-complex of the five-membered lactone the smallest Pd/endo-beta-H dihedral angle is observed for a conformer with a comparatively high potential energy. The optimized conditions for Matsuda-Heck arylations of exo-methylene lactones were eventually applied to the synthesis of the natural product anemarcoumarin A.}, language = {en} } @article{SchmidtLorenz2016, author = {Schmidt, Burkhard and Lorenz, Ulf}, title = {WavePacket}, series = {Computer physics communications : an international journal devoted to computational physics and computer programs in physics}, volume = {213}, journal = {Computer physics communications : an international journal devoted to computational physics and computer programs in physics}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0010-4655}, doi = {10.1016/j.cpc.2016.12.007}, pages = {223 -- 234}, year = {2016}, abstract = {WavePacket is an open-source program package for the numerical simulation of quantum-mechanical dynamics. It can be used to solve time-independent or time-dependent linear Schr{\"o}dinger and Liouville-von Neumann-equations in one or more dimensions. Also coupled equations can be treated, which allows to simulate molecular quantum dynamics beyond the Born-Oppenheimer approximation. Optionally accounting for the interaction with external electric fields within the semiclassical dipole approximation, WavePacket can be used to simulate experiments involving tailored light pulses in photo-induced physics or chemistry. The graphical capabilities allow visualization of quantum dynamics 'on the fly', including Wigner phase space representations. Being easy to use and highly versatile, WavePacket is well suited for the teaching of quantum mechanics as well as for research projects in atomic, molecular and optical physics or in physical or theoretical chemistry. The present Part I deals with the description of closed quantum systems in terms of Schr{\"o}dinger equations. The emphasis is on discrete variable representations for spatial discretization as well as various techniques for temporal discretization. The upcoming Part II will focus on open quantum systems and dimension reduction; it also describes the codes for optimal control of quantum dynamics. The present work introduces the MATLAB version of WavePacket 5.2.1 which is hosted at the Sourceforge platform, where extensive Wiki-documentation as well as worked-out demonstration examples can be found.}, language = {en} } @misc{SchneiderWeigertLesnyaketal.2016, author = {Schneider, Ralf and Weigert, Florian and Lesnyak, Vladimir and Leubner, Susanne and Lorenz, Tommy and Behnke, Thomas and Dubavik, Aliaksei and Joswig, Jan-Ole and Resch-Genger, Ute and Gaponik, Nikolai and Eychm{\"u}ller, Alexander}, title = {pH and concentration dependence of the optical properties of thiol-capped CdTe nanocrystals in water and D2O}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395143}, pages = {10}, year = {2016}, abstract = {The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which - together with alloyed CdxHg1-xTe - are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D2O and compared to the results from previous dilution studies with a set of thiol-capped Cd1-xHgxTe SC NCs in D2O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H2O compared to D2O, underlining also the role of hydrogen bonding and solvent molecules.}, language = {en} } @article{SchneiderWeigertLesnyaketal.2016, author = {Schneider, Rudolf and Weigert, F. and Lesnyak, V. and Leubner, S. and Lorenz, T. and Behnke, Thomas and Dubavik, A. and Joswig, J. -O. and Resch-Genger, U. and Gaponik, N. and Eychmueller, A.}, title = {pH and concentration dependence of the optical properties of thiol-capped CdTe nanocrystals in water and D2O}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {18}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c6cp03123d}, pages = {19083 -- 19092}, year = {2016}, abstract = {The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which - together with alloyed CdxHg1\&\#8722;xTe - are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D2O and compared to the results from previous dilution studies with a set of thiol-capped Cd1\&\#8722;xHgxTe SC NCs in D2O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H2O compared to D2O, underlining also the role of hydrogen bonding and solvent molecules.}, language = {en} } @article{ScholzFlossSaalfranketal.2016, author = {Scholz, Robert and Floss, Gereon and Saalfrank, Peter and F{\"u}chsel, Gernot and Loncaric, Ivor and Juaristi, J. I.}, title = {Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion}, series = {Physical review : B, Condensed matter and materials physics}, volume = {94}, journal = {Physical review : B, Condensed matter and materials physics}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.94.165447}, pages = {17}, year = {2016}, abstract = {A Langevin model accounting for all six molecular degrees of freedom is applied to femtosecond-laser induced, hot-electron driven dynamics of Ru(0001)(2 x 2): CO. In our molecular dynamics with electronic friction approach, a recently developed potential energy surface based on gradient-corrected density functional theory accounting for van der Waals interactions is adopted. Electronic friction due to the coupling of molecular degrees of freedom to electron-hole pairs in the metal are included via a local density friction approximation, and surface phonons by a generalized Langevin oscillator model. The action of ultrashort laser pulses enters through a substrate-mediated, hot-electron mechanism via a time-dependent electronic temperature (derived from a two-temperature model), causing random forces acting on the molecule. The model is applied to laser induced lateral diffusion of CO on the surface, "hot adsorbate" formation, and laser induced desorption. Reaction probabilities are strongly enhanced compared to purely thermal processes, both for diffusion and desorption. Reaction yields depend in a characteristic (nonlinear) fashion on the applied laser fluence, as well as branching ratios for various reaction channels. Computed two-pulse correlation traces for desorption and other indicators suggest that aside from electron-hole pairs, phonons play a non-negligible role for laser induced dynamics in this system, acting on a surprisingly short time scale. Our simulations on precomputed potentials allow for good statistics and the treatment of long-time dynamics (300 ps), giving insight into this system which hitherto has not been reached. We find generally good agreement with experimental data where available and make predictions in addition. A recently proposed laser induced population of physisorbed precursor states could not be observed with the present low-coverage model.}, language = {en} } @misc{SchulzeKoetz2016, author = {Schulze, Nicole and Koetz, Joachim}, title = {Kinetically Controlled Growth of Gold Nanotriangles in a Vesicular Template Phase by Adding a Strongly Alternating Polyampholyte}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98380}, pages = {22}, year = {2016}, abstract = {This paper is focused on the temperature dependent synthesis of gold nanotriangles in a vesicular template phase, containing phosphatidylcholin and AOT, by adding the strongly alternating polyampholyte PalPhBisCarb. UV-vis absorption spectra in combination with TEM micrographs show that flat gold nanoplatelets are formed predominantly in presence of the polyampholyte at 45 °C. The formation of triangular and hexagonal nanoplatelets can be directly influenced by the kinetic approach, i.e., by varying the polyampholyte dosage rate at 45 °C. Corresponding zeta potential measurements indicate that a temperature dependent adsorption of the polyampholyte on the {111} faces will induce the symmetry breaking effect, which is responsible for the kinetically controlled hindered vertical and preferred lateral growth of the nanoplatelets.}, language = {en} } @article{SchulzePrietzelKoetz2016, author = {Schulze, Nicole and Prietzel, Claudia Christina and Koetz, Joachim}, title = {Polyampholyte-mediated synthesis of anisotropic gold nanoplatelets}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {294}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-016-3890-y}, pages = {1297 -- 1304}, year = {2016}, abstract = {This paper focused on the synthesis of triangular nanoplatelets in the presence of a tubular network structure. The tubular network structure is formed by adding a strongly alternating polyampholyte, i.e., PalPhBisCarb, to a mixed vesicle system with a negatively charged bilayer containing phosphatidylcholin and AOT. Using the tubular network as a reducing agent in a one-step procedure, triangular and hexagonal nanoplatelets are formed. One can show that the nanoplatelet yield is enhanced by increasing the temperature and decreasing the reaction time. The platelet edge length can be decreased by heating the system up to 100 A degrees C. Due to specific interactions between PalPhBisCarb and the AOT/phospholipid bilayer, stacking and welding effects lead to the formation of ordered platelet structures. The reaction pathway to flat gold nanotriangles is discussed with regard to the twin plane growth model of gold nanoplates.}, language = {en} } @article{SchwarzeSchneiderRiemeretal.2016, author = {Schwarze, Thomas and Schneider, Radu and Riemer, Janine and Holdt, Hans-J{\"u}rgen}, title = {A Highly K+-Selective Fluorescent Probe - Tuning the K+-Complex Stability and the K+/Na+ Selectivity by Varying the Lariat-Alkoxy Unit of a Phenylaza[18]crown-6 Ionophore}, series = {Chemistry : an Asian journal ; an ACES journal}, volume = {11}, journal = {Chemistry : an Asian journal ; an ACES journal}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1861-4728}, doi = {10.1002/asia.201500956}, pages = {241 -- 247}, year = {2016}, abstract = {A desirable goal is to synthesize easily accessible and highly K+/Na+-selective fluoroionophores to monitor physiological K+ levels in vitro and in vivo. Therefore, highly K+/Na+-selective ionophores have to be developed. Herein, we obtained in a sequence of only four synthetic steps a set of K+-responsive fluorescent probes 4, 5 and 6. In a systematic study, we investigated the influence of the alkoxy substitution in ortho position of the aniline moiety in -conjugated aniline-1,2,3-triazole-coumarin-fluoroionophores 4, 5 and 6 [R=MeO (4), EtO (5) and iPrO (6)] towards the K+-complex stability and K+/Na+ selectivity. The highest K+-complex stability showed fluoroionophore 4 with a dissociation constant K-d of 19mm, but the K-d value increases to 31mm in combined K+/Na+ solutions, indicating a poor K+/Na+ selectivity. By contrast, 6 showed even in the presence of competitive Na+ ions equal K-d values (K-d(K+)=45mm and K-d(K+/Na+)=45mm) and equal K+-induced fluorescence enhancement factors (FEFs=2.3). Thus, the fluorescent probe 6 showed an outstanding K+/Na+ selectivity and is a suitable fluorescent tool to measure physiological K+ levels in the range of 10-80mm in vitro. Further, the isopropoxy-substituted N-phenylaza[18]crown-6 ionophore in 6 is a highly K+-selective building block with a feasible synthetic route.}, language = {en} } @article{SchoenbornSaalfrankKlamroth2016, author = {Sch{\"o}nborn, Jan Boyke and Saalfrank, Peter and Klamroth, Tillmann}, title = {Controlling the high frequency response of H-2 by ultra-short tailored laser pulses: A time-dependent configuration interaction study}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {144}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4940316}, pages = {9}, year = {2016}, abstract = {We combine the stochastic pulse optimization (SPO) scheme with the time-dependent configuration interaction singles method in order to control the high frequency response of a simple molecular model system to a tailored femtosecond laser pulse. For this purpose, we use H-2 treated in the fixed nuclei approximation. The SPO scheme, as similar genetic algorithms, is especially suited to control highly non-linear processes, which we consider here in the context of high harmonic generation. Here, we will demonstrate that SPO can be used to realize a "non-harmonic" response of H2 to a laser pulse. Specifically, we will show how adding low intensity side frequencies to the dominant carrier frequency of the laser pulse and stochastically optimizing their contribution can create a high-frequency spectral signal of significant intensity, not harmonic to the carrier frequency. At the same time, it is possible to suppress the harmonic signals in the same spectral region, although the carrier frequency is kept dominant during the optimization. (C) 2016 AIP Publishing LLC.}, language = {en} } @article{SchoeneKratzSchulzetal.2016, author = {Sch{\"o}ne, Anne-Christin and Kratz, Karl and Schulz, Burkhard and Lendlein, Andreas}, title = {The relevance of hydrophobic segments in multiblock copolyesterurethanes for their enzymatic degradation at the air-water interface}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {102}, journal = {Polymer : the international journal for the science and technology of polymers}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-3861}, doi = {10.1016/j.polymer.2016.09.001}, pages = {92 -- 98}, year = {2016}, abstract = {The interplay of an enzyme with a multiblock copolymer PDLCL containing two segments of different hydrophilicity and degradability is explored in thin films at the air-water interface. The enzymatic degradation was studied in homogenous Langmuir monolayers, which are formed when containing more than 40 wt\% oligo(epsilon-caprolactone) (OCL). Enzymatic degradation rates were significantly reduced with increasing content of hydrophobic oligo(omega-pentadecalactone) (OPDL). The apparent deceleration of the enzymatic process is caused by smaller portion of water-soluble degradation fragments formed from degradable OCL fragments. Beside the film degradation, a second competing process occurs after adding lipase from Pseudomonas cepacia into the subphase, namely the enrichment of the lipase molecules in the polymeric monolayer. The incorporation of the lipase into the Langmuir film is experimentally revealed by concurrent surface area enlargement and by Brewster angle microscopy (BAM). Aside from the ability to provide information about the degradation behavior of polymers, the Langmuir monolayer degradation (LMD) approach enables to investigate polymer-enzyme interactions for non-degradable polymers. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{SchoeneKratzSchulzetal.2016, author = {Sch{\"o}ne, Anne-Christin and Kratz, Karl and Schulz, Burkhard and Lendlein, Andreas}, title = {Polymer architecture versus chemical structure as adjusting tools for the enzymatic degradation of oligo(epsilon-caprolactone) based films at the air-water interface}, series = {Polymer Degradation and Stability}, volume = {131}, journal = {Polymer Degradation and Stability}, publisher = {Elsevier}, address = {Oxford}, issn = {0141-3910}, doi = {10.1016/j.polymdegradstab.2016.07.010}, pages = {114 -- 121}, year = {2016}, abstract = {The enzymatic degradation of oligo(epsilon-caprolactone) (OCL) based films at the air-water interface is investigated by Langmuir monolayer degradation (LMD) experiments to elucidate the influence of the molecular architecture and of the chemical structure on the chain scission process. For that purpose, the interactions of 2D monolayers of two star-shaped poly(epsilon-caprolactone)s (PCLs) and three linear OCL based copolyesterurethanes (P(OCL-U)) with the lipase from Pseudomonas cepacia are evaluated in comparison to linear OCL. While the architecture of star-shaped PCL Langmuir layers slightly influences their degradability compared to OCL films, significantly retarded degradations are observed for P(OCL-U) films containing urethane junction units derived from 2, 2 (4), 4-trimethyl hexamethylene diisocyanate (TMDI), hexamethylene diisocyanate (HDI) or lysine ethyl ester diisocyanate (LDI). The enzymatic degradation of the OCL based 2D structures is related to the presence of hydrophilic groups within the macromolecules rather than to the packing density of the film or to the molecular weight. The results reveal that the LMD technique allows the parallel analysis of both the film/enzyme interactions and the degradation process on the molecular level. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{SchoeneSchulzLendlein2016, author = {Sch{\"o}ne, Anne-Christin and Schulz, Burkhard and Lendlein, Andreas}, title = {Stimuli Responsive and Multifunctional Polymers: Progress in Materials and Applications}, series = {Macromolecular rapid communications}, volume = {37}, journal = {Macromolecular rapid communications}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201600650}, pages = {1856 -- 1859}, year = {2016}, language = {en} } @article{SchueringsNevskyiEliaschetal.2016, author = {Sch{\"u}rings, Marco-Philipp and Nevskyi, Oleksii and Eliasch, Kamill and Michel, Ann-Katrin and Liu, Bing and Pich, Andrij and B{\"o}ker, Alexander and von Plessen, Gero and W{\"o}ll, Dominik}, title = {Diffusive Motion of Linear Microgel Assemblies in Solution}, series = {Polymers}, volume = {8}, journal = {Polymers}, publisher = {MDPI}, address = {Basel}, issn = {2073-4360}, doi = {10.3390/polym8120413}, pages = {14}, year = {2016}, abstract = {Due to the ability of microgels to rapidly contract and expand in response to external stimuli, assemblies of interconnected microgels are promising for actuation applications, e.g., as contracting fibers for artificial muscles. Among the properties determining the suitability of microgel assemblies for actuation are mechanical parameters such as bending stiffness and mobility. Here, we study the properties of linear, one-dimensional chains of poly(N-vinylcaprolactam) microgels dispersed in water. They were fabricated by utilizing wrinkled surfaces as templates and UV-cross-linking the microgels. We image the shapes of the chains on surfaces and in solution using atomic force microscopy (AFM) and fluorescence microscopy, respectively. In solution, the chains are observed to execute translational and rotational diffusive motions. Evaluation of the motions yields translational and rotational diffusion coefficients and, from the translational diffusion coefficient, the chain mobility. The microgel chains show no perceptible bending, which yields a lower limit on their bending stiffness.}, language = {en} } @misc{SchuermannBald2016, author = {Sch{\"u}rmann, Robin Mathis and Bald, Ilko}, title = {Real-time monitoring of plasmon induced dissociative electron transfer to the potential DNA radiosensitizer 8-bromoadenine}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395113}, pages = {5}, year = {2016}, abstract = {The excitation of localized surface plasmons in noble metal nanoparticles (NPs) results in different nanoscale effects such as electric field enhancement, the generation of hot electrons and a temperature increase close to the NP surface. These effects are typically exploited in diverse fields such as surface-enhanced Raman scattering (SERS), NP catalysis and photothermal therapy (PTT). Halogenated nucleobases are applied as radiosensitizers in conventional radiation cancer therapy due to their high reactivity towards secondary electrons. Here, we use SERS to study the transformation of 8-bromoadenine (8BrA) into adenine on the surface of Au and AgNPs upon irradiation with a low-power continuous wave laser at 532, 633 and 785 nm, respectively. The dissociation of 8BrA is ascribed to a hot-electron transfer reaction and the underlying kinetics are carefully explored. The reaction proceeds within seconds or even milliseconds. Similar dissociation reactions might also occur with other electrophilic molecules, which must be considered in the interpretation of respective SERS spectra. Furthermore, we suggest that hot-electron transfer induced dissociation of radiosensitizers such as 8BrA can be applied in the future in PTT to enhance the damage of tumor tissue upon irradiation.}, language = {en} } @article{SchuermannBald2016, author = {Sch{\"u}rmann, Robin Mathis and Bald, Ilko}, title = {Decomposition of DNA Nucleobases by Laser Irradiation of Gold Nanoparticles Monitored by Surface-Enhanced Raman Scattering}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {120}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b10564}, pages = {3001 -- 3009}, year = {2016}, abstract = {Different approaches have been proposed to treat cancer cells using gold nanoparticles (AuNPs) in combination with radiation ranging from infrared lasers to high-energy ion beams. Here we study the decomposition of the DNA/RNA nucleobases thymine (T) and uracil (U) and the well-known radiosensitizer 5-bromouracil (BrU) in close vicinity to AuNPs, which are irradiated with a nanosecond pulsed laser (532 nm) matching the surface plasmon resonance of the AuNPs. The induced damage of nucleobases is analyzed by UV-vis absorption spectroscopy and surface-enhanced Raman scattering (SERS). A clear DNA damage is observed upon laser irradiation. SERS spectra indicate the fragmentation of the aromatic ring system of T and U as the dominant form of damage, whereas with BrU mainly the cleavage of the Br-C bond and formation of Br- ions is observed. This is accompanied by a partial transformation of BrU into U. The observed damage is at least partly ascribed to the intermediate formation of low energy electrons from the laser-excited AuNPs and subsequent dissociative electron attachment to T, U, and BrU. These reactions represent basic DNA damage pathways occurring on the one hand in plasmon-assisted cancer therapy and on the other hand in conventional cancer radiation therapy using AuNPs as sensitizing agents.}, language = {en} } @article{SechiFreitasWuennemannetal.2016, author = {Sechi, Antonio and Freitas, Joana M. G. and W{\"u}nnemann, Patrick and T{\"o}pel, Alexander and Paschoalin, Rafaella Takehara and Ullmann, Sabrina and Schr{\"o}der, Ricarda and Aydin, G{\"u}lcan and R{\"u}tten, Stephan and B{\"o}ker, Alexander and Zenke, Martin and Pich, Andrij}, title = {Surface-Grafted Nanogel Arrays Direct Cell Adhesion and Motility}, series = {Advanced materials interfaces}, volume = {3}, journal = {Advanced materials interfaces}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {2196-7350}, doi = {10.1002/admi.201600455}, pages = {13}, year = {2016}, abstract = {It has long been appreciated that material chemistry and topology profoundly affect cell adhesion and migration. Here, aqueous poly(N- isopropyl acrylamide) nanogels are designed, synthesized and printed in form of colloidal arrays on glass substrates using wrinkled polydimethylsiloxane templates. Using low-temperature plasma treatment, nanogels are chemically grafted onto glass supports thus leading to highly stable nanogel layers in cell culture media. Liquid cell atomic force microscopy investigations show that surface-grafted nanogels retain their swelling behavior in aqueous media and that extracellular matrix protein coating do not alter their stability and topography. It is demonstrated that surface-grafted nanogels could serve as novel substrates for the analysis of cell adhesion and migration. Nanogels influence size, speed, and dynamics of focal adhesions and cell motility forcing cells to move along highly directional trajectories. Moreover, modulation of nanogel state or spacing serves as an effective tool for regulation of cell motility. It is suggested that nanogel arrays deposited on solid surfaces could be used to provide a precise and tunable system to understand and control cell migration. Additionally, such nanogel arrays will contribute to the development of implantable systems aimed at supporting and enhancing cell migration during, for instance, wound healing and tissue regeneration.}, language = {en} } @article{SeckerVoelkelTierschetal.2016, author = {Secker, Christian and Voelkel, Antje and Tiersch, Brigitte and Koetz, Joachim and Schlaad, Helmut}, title = {Thermo-Induced Aggregation and Crystallization of Block Copolypeptoids in Water}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {49}, journal = {Macromolecules : a publication of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.5b02481}, pages = {979 -- 985}, year = {2016}, abstract = {Block copolypeptoids comprising a thermosensitive, crystallizable poly(N-(n-propyl)glycine) block and a watersoluble poly(N-methylglycine) block, P70My (y = 23, 42, 76, 153, and 290), were synthesized bY ring-opening polymerization of the corresponding N-alkylglycine N-carboxyanhydrides (NCAs) and examined according to their thermo-induced aggregation and crystallization in water by turbidimetty, micro-differential scanning calorimetry (micro-DSC); cryogenic scanning electron microscopy (cryo-SEM), analytical ultracentrifugation (AUC), and static light scattering (SLS). At a temperature above the cloud point temperature, the initially formed micellar aggregates started to crystallize and grow into larger complex assemblies of about 100-500 nm, exhibiting flower-like (P70M23), ellipsoidal (P70M42 and P70M72) or irregular shapes (P70M153 and.P70M290).}, language = {en} } @article{SengeFlanaganRyanetal.2016, author = {Senge, Mathias O. and Flanagan, Keith J. and Ryan, Aoife A. and Ryppa, Claudia and Donath, Mandy and Twamley, Brendan}, title = {Conformational and structural studies of meso monosubstituted metalloporphyrins-Edge-on molecular interactions of porphyrins in crystals}, series = {Tetrahedron}, volume = {72}, journal = {Tetrahedron}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.11.008}, pages = {105 -- 115}, year = {2016}, abstract = {A series of meso monosubstituted metalloporphyrins were synthesized to assess the structural chemistry of porphyrins with only one substituent. The structures of four nickel(II) and zinc(II) complexes with either alkyl or aryl residues indicate primarily planar macrocycles. This gives rise to a different type of pi-interactions in the crystal and the formation of dimeric, trimeric or tetrameric porphyrin units that function as building blocks for the overall crystal structure. Notably, some structures exhibit a unique edge-on packing of porphyrins, while the molecules of (5-n-butylporphyrinato)nickel(II) forms an unusual bilayer type structure where rows of two porphyrin macrocycles are separated by the alkyl residues arranged in a head-to-head fashion. This adds to the canon of intermolecular porphyrin packing arrangements and is of relevance for the preparation of ordered nanoscopic porphyrin devices. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{SoliveresManningPratietal.2016, author = {Soliveres, Santiago and Manning, Peter and Prati, Daniel and Gossner, Martin M. and Alt, Fabian and Arndt, Hartmut and Baumgartner, Vanessa and Binkenstein, Julia and Birkhofer, Klaus and Blaser, Stefan and Bluethgen, Nico and Boch, Steffen and Boehm, Stefan and Boerschig, Carmen and Buscot, Francois and Diekoetter, Tim and Heinze, Johannes and Hoelzel, Norbert and Jung, Kirsten and Klaus, Valentin H. and Klein, Alexandra-Maria and Kleinebecker, Till and Klemmer, Sandra and Krauss, Jochen and Lange, Markus and Morris, E. Kathryn and Mueller, Joerg and Oelmann, Yvonne and Overmann, J{\"o}rg and Pasalic, Esther and Renner, Swen C. and Rillig, Matthias C. and Schaefer, H. Martin and Schloter, Michael and Schmitt, Barbara and Schoening, Ingo and Schrumpf, Marion and Sikorski, Johannes and Socher, Stephanie A. and Solly, Emily F. and Sonnemann, Ilja and Sorkau, Elisabeth and Steckel, Juliane and Steffan-Dewenter, Ingolf and Stempfhuber, Barbara and Tschapka, Marco and Tuerke, Manfred and Venter, Paul and Weiner, Christiane N. and Weisser, Wolfgang W. and Werner, Michael and Westphal, Catrin and Wilcke, Wolfgang and Wolters, Volkmar and Wubet, Tesfaye and Wurst, Susanne and Fischer, Markus and Allan, Eric}, title = {Locally rare species influence grassland ecosystem multifunctionality}, series = {Philosophical transactions of the Royal Society of London : B, Biological sciences}, volume = {371}, journal = {Philosophical transactions of the Royal Society of London : B, Biological sciences}, publisher = {Royal Society}, address = {London}, issn = {0962-8436}, doi = {10.1098/rstb.2015.0269}, pages = {3175 -- 3185}, year = {2016}, abstract = {Species diversity promotes the delivery of multiple ecosystem functions (multifunctionality). However, the relative functional importance of rare and common species in driving the biodiversity multifunctionality relationship remains unknown. We studied the relationship between the diversity of rare and common species (according to their local abundances and across nine different trophic groups), and multifunctionality indices derived from 14 ecosystem functions on 150 grasslands across a land use intensity (LUI) gradient. The diversity of above- and below-ground rare species had opposite effects, with rare above-ground species being associated with high levels of multifunctionality, probably because their effects on different functions did not trade off against each other. Conversely, common species were only related to average, not high, levels of multifunctionality, and their functional effects declined with LUI. Apart from the community level effects of diversity, we found significant positive associations between the abundance of individual species and multifunctionality in 6\% of the species tested. Species specific functional effects were best predicted by their response to LUI: species that declined in abundance with land use intensification were those associated with higher levels of multifunctionality. Our results highlight the importance of rare species for ecosystem multifunctionality and help guiding future conservation priorities.}, language = {en} } @phdthesis{Stahlhut2016, author = {Stahlhut, Frank}, title = {Entwicklung neuer triphiler, fluorkohlenstofffreier Blockcopolymere und Untersuchung ihrer Eigenschaften f{\"u}r Multikompartiment-Mizellen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-96299}, school = {Universit{\"a}t Potsdam}, pages = {iv, 191}, year = {2016}, abstract = {Neue Systeme f{\"u}r triphile, fluorkohlenstofffreie Blockcopolymere in Form von Acrylat-basierten thermoresponsiven Blockcopolymeren sowie Acrylat- bzw. Styrol-basierten Terblock-Polyelektrolyten mit unterschiedlich chaotropen Kationen des jeweiligen polyanionischen Blocks wurden entwickelt. Multikompartiment-Mizellen, mizellare Aggregate mit ultrastrukturiertem hydrophobem Mizellkern die biologischen Strukturen wie dem Humanalbumin nachempfunden sind, sollten bei der Selbstorganisation in w{\"a}ssriger Umgebung entstehen. Durch Verwendung apolarer und polarer Kohlenwasserstoff-Dom{\"a}nen anstelle von fluorophilen Fluorkohlenstoff-Dom{\"a}nen sollte erstmals anhand solcher triphilen Systeme nachgewiesen werden, ob diese in der Lage zur selektiven Aufnahme hydrophober Substanzen in unterschiedliche Dom{\"a}nen des Mizellkerns sind. Mit Hilfe von sequentieller RAFT-Polymerisation wurden diese neuen triphilen Systeme hergestellt, die {\"u}ber einen permanent hydrophilen, eine permanent stark hydrophoben und einen dritten Block verf{\"u}gen, der durch externe Einfl{\"u}sse, speziell die Induzierung eines thermischen Coil-to-globule-{\"U}bergangs bzw. die Zugabe von organischen, hydrophoben Gegenionen von einem wasserl{\"o}slichen in einen polar-hydrophoben Block umgewandelt werden kann. Als RAFT-Agens wurde 4-(Trimethylsilyl)benzyl(3-(trimethylsilyl)-propyl)-trithiocarbonat mit zwei unterschiedlichen TMS-Endgruppen verwendet, das kontrollierte Reaktions-bedingungen sowie die molekulare Charakterisierung der komplexen Copolymere erm{\"o}glichte. Die beiden Grundtypen der linearen tern{\"a}ren Blockcopolymere wurden jeweils in zwei 2 Modell-Systeme, die geringf{\"u}gig in ihren chemischen Eigenschaften sowie in dem Blockl{\"a}ngenverh{\"a}ltnis von hydrophilen und hydrophoben Polymersegmenten variierten, realisiert und unterschiedliche Permutation der Bl{\"o}cke aufwiesen. Als ersten Polymertyp wurden amphiphile thermoresponsive Blockcopolymere verwendet. Modell-System 1 bestand aus dem permanent hydrophoben Block Poly(1,3-Bis(butylthio)-prop-2-yl-acrylat), permanent hydrophilen Block Poly(Oligo(ethylenglykol)monomethyletheracrylat) und den thermoresponsiven Block Poly(N,N'-Diethylacrylamid), dessen Homopolymer eine LCST-Phasen{\"u}bergang (LCST, engl.: lower critical solution temperature) bei ca. 36°C aufweist. Das Modell-System 2 bestand aus dem permanent hydrophilen Block Poly(2-(Methylsulfinyl)ethylacrylat), dem permanent hydrophoben Block Poly(2-Ethylhexylacrylat) und wiederum Poly(N,N'-Diethylacrylamid). Im tern{\"a}ren Blockcopolymer erh{\"o}hte sich, je nach Blocksequenz und relativen Blockl{\"a}ngen, der LCST-{\"U}bergang auf 50 - 65°C. Bei der Untersuchung der Selbstorganisation f{\"u}r die Polymer-Systeme dieses Typs wurde die Temperatur variiert, um verschieden mizellare {\"U}berstrukturen in w{\"a}ssriger Umgebung zu erzeugen bzw. oberhalb des LCST-{\"U}bergangs Multikompartiment-Mizellen nachzuweisen. Die Unterschiede in der Hydrophilie bzw. den sterischen Anspr{\"u}che der gew{\"a}hlten hydrophilen Bl{\"o}cke sowie die Variation der jeweiligen Blocksequenzen erm{\"o}glichte dar{\"u}ber hinaus die Bildung verschiedenster Morphologien mizellarer Aggregate. Der zweite Typ basierte auf ein Terblock-Polyelektrolyt-System mit Polyacrylaten bzw. Polystyrolen als Polymerr{\"u}ckgrat. Polymere ionische Fl{\"u}ssigkeiten wurden als Vorlage der Entwicklung zweier Modell-Systeme genommen. Eines der beiden Systeme bestand aus dem permanent hydrophilen Block Poly(Oligo(ethylenglykol)monomethyletheracrylat, dem permanent hydrophoben Block Poly(2-Ethylhexylacrylat) sowie dem Polyanion-Block Poly(3-Sulfopropylacrylat). Die Hydrophobie des Polyanion-Blocks variierte durch Verwendung großer organischer Gegenionen, n{\"a}mlich Tetrabutylammonium, Tetraphenylphosphonium und Tetraphenylstibonium. Analog wurde in einem weiteren System aus dem permanent hydrophilen Block Poly(4-Vinylbenzyltetrakis(ethylenoxy)methylether), dem permanent hydrophoben Block Poly(para-Methylstyrol) und Poly(4-Styrolsulfonat) mit den entsprechenden Gegenionen gebildet. Aufgrund unterschiedlicher Kettensteifigkeit in beiden Modell-Systemen sollte es bei der Selbstorganisation der mizellarer Aggregate zu unterschiedlichen {\"U}berstrukturen kommen. Mittels DSC-Messungen konnte nachgewiesen werden, dass f{\"u}r alle Modell-Systeme die Bl{\"o}cke in Volumen-Phase miteinander inkompatibel waren, was eine Voraussetzung f{\"u}r Multikompartimentierung von mizellaren Aggregaten ist. Die Gr{\"o}ße mizellarer Aggregate sowie der Einfluss externer Einfl{\"u}sse wie der Ver{\"a}nderung der Temperatur bzw. der Hydrophobie und Gr{\"o}ße von Gegenionen auf den hydrodynamischen Durchmesser mittels DLS-Untersuchungen wurden f{\"u}r alle Modell-Systeme untersucht. Die Ergebnisse zu den thermoresponsiven tern{\"a}ren Blockcopolymeren belegten , dass sich oberhalb der Phasen{\"u}bergangstemperatur des thermoresponsiven Blocks die Struktur der mizellaren Aggregate {\"a}nderte, indem der p(DEAm)-Block scheinbar kollabierte und so zusammen mit den permanent hydrophoben Block den jeweiligen Mizellkern bildete. Nach gewisser Equilibrierungszeit konnten bei Raumtemperatur dir urspr{\"u}nglichen mizellaren Strukturen regeneriert werden. Hingegen konnte f{\"u}r die Terblock-Polyelektrolyt-Systeme bei Verwendung der unterschiedlich hydrophoben Gegenionen kein signifikanter Unterschied in der Gr{\"o}ße der mizellaren Aggregate beobachtet werden. Zur Abbildung der mizellaren Aggregate mittels kryogene Transmissionselektronenmikroskopie (cryo-TEM) der mizellaren Aggregate war mit Poly(1,3-Bis(butylthio)-prop-2-yl-acrylat) ein Modell-System so konzipiert, dass ein erh{\"o}hter Elektronendichtekontrast durch Schwefel-Atome die Visualisierung ultrastrukturierter hydrophober Mizellkerne erm{\"o}glichte. Dieser Effekt sollte in den Terblock-Polyelektrolyt-Systemen auch durch die Gegenionen Tetraphenylphosphonium und Tetraphenylstibonium nachgestellt werden. W{\"a}hrend bei den thermoresponsiven Systemen auch oberhalb des Phasen{\"u}bergangs kein Hinweis auf Ultrastrukturierung beobachtet wurde, waren f{\"u}r die Polyelektrolyt-Systeme, insbesondere im Fall von Tetraphenylstibonium als Gegenion {\"U}berstrukturen zu erkennen. Der Nachweis der Bildung von Multikompartiment-Mizellen war f{\"u}r beide Polymertypen mit dieser abbildenden Methode nicht m{\"o}glich. Die Unterschiede in der Elektronendichte einzelner Bl{\"o}cke m{\"u}sste m{\"o}glicherweise weiter erh{\"o}ht werden um Aussagen diesbez{\"u}glich zu treffen. Die Untersuchung von ortsspezifischen Solubilisierungsexperimenten mit solvatochromen Fluoreszenzfarbstoffen mittels „steady-state"-Fluoreszenzspektroskopie durch Vergleich der Solubilisierungsorte der Terblockcopolymere bzw. -Polyelektrolyte mit den jeweiligen Solubilisierungsorten von Homopolymer- und Diblock-Vorstufen sollten den qualitativen Nachweis der Multikompartimentierung erbringen. Aufgrund der geringen Mengen an Farbstoff, die f{\"u}r die Solubilisierungsexperimente eingesetzt wurden zeigten DLS-Untersuchungen keine st{\"o}renden Effekte der Sonden auf die Gr{\"o}ße der mizellaren Aggregate. Jedoch erschwerten Quench-Effekte im Falle der Polyelektrolyt Modell-Systeme eine klare Interpretation der Daten. Im Falle der Modell-Systeme der thermoresponsiven Blockcopolymere waren dagegen deutliche solvatochrome Effekte zwischen der Solubilisierung in den mizellaren Aggregaten unterhalb und oberhalb des Phasen{\"u}bergangs zu erkennen. Dies k{\"o}nnte ein Hinweis auf Multikompartimentierung oberhalb des LCST-{\"U}bergangs sein. Ohne die Informationen einer Strukturanalyse wie z.B. der R{\"o}ntgen- oder Neutronenkleinwinkelstreuung (SAXS oder SANS), kann nicht abschließend gekl{\"a}rt werden, ob die Solubilisierung in mizellaren hydrophoben Dom{\"a}nen des kollabierten Poly(N,N'-Diethylacrylamid) erfolgt oder in einer Mischform von mizellaren Aggregaten mit gemittelter Polarit{\"a}t.}, language = {de} } @phdthesis{Steeples2016, author = {Steeples, Elliot}, title = {Amino acid-derived imidazolium salts: platform molecules for N-Heterocyclic carbene metal complexes and organosilica materials}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-101861}, school = {Universit{\"a}t Potsdam}, pages = {139}, year = {2016}, abstract = {In the interest of producing functional catalysts from sustainable building-blocks, 1, 3-dicarboxylate imidazolium salts derived from amino acids were successfully modified to be suitable as N-Heterocyclic carbene (NHC) ligands within metal complexes. Complexes of Ag(I), Pd(II), and Ir(I) were successfully produced using known procedures using ligands derived from glycine, alanine, β-alanine and phenylalanine. The complexes were characterized in solid state using X-Ray crystallography, which allowed for the steric and electronic comparison of these ligands to well-known NHC ligands within analogous metal complexes. The palladium complexes were tested as catalysts for aqueous-phase Suzuki-Miyaura cross-coupling. Water-solubility could be induced via ester hydrolysis of the N-bound groups in the presence of base. The mono-NHC-Pd complexes were seen to be highly active in the coupling of aryl bromides with phenylboronic acid; the active catalyst of which was determined to be mostly Pd(0) nanoparticles. Kinetic studies determined that reaction proceeds quickly in the coupling of bromoacetophenone, for both pre-hydrolyzed and in-situ hydrolysis catalyst dissolution. The catalyst could also be recycled for an extra run by simply re-using the aqueous layer. The imidazolium salts were also used to produce organosilica hybrid materials. This was attempted via two methods: by post-grafting onto a commercial organosilica, and co-condensation of the corresponding organosilane. The co-condensation technique harbours potential for the production of solid-support catalysts.}, language = {en} } @article{SteeplesKellingSchildeetal.2016, author = {Steeples, Elliot and Kelling, Alexandra and Schilde, Uwe and Esposito, Davide}, title = {Amino acid-derived N-heterocyclic carbene palladium complexes for aqueous phase Suzuki-Miyaura couplings}, series = {New journal of chemistry}, volume = {40}, journal = {New journal of chemistry}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1144-0546}, doi = {10.1039/c5nj03337c}, pages = {4922 -- 4930}, year = {2016}, abstract = {In this work, three ligands produced from amino acids were synthesized and used to produce five bis- and PEPPSI-type palladium-NHC complexes using a novel synthesis route from sustainable starting materials. Three of these complexes were used as precatalysts in the aqueous-phase Suzuki-Miyaura coupling of various substrates displaying high activity. TEM and mercury poisoning experiments provide evidence for Pd-nanoparticle formation stabilized in water.}, language = {en} } @misc{SteeplesKellingSchildeetal.2016, author = {Steeples, Elliot and Kelling, Alexandra and Schilde, Uwe and Esposito, Davide}, title = {Amino acid-derived N-heterocyclic carbene palladium complexes for aqueous phase Suzuki-Miyaura couplings}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394488}, pages = {4922 -- 4930}, year = {2016}, abstract = {In this work, three ligands produced from amino acids were synthesized and used to produce five bis- and PEPPSI-type palladium-NHC complexes using a novel synthesis route from sustainable starting materials. Three of these complexes were used as precatalysts in the aqueous-phase Suzuki-Miyaura coupling of various substrates displaying high activity. TEM and mercury poisoning experiments provide evidence for Pd-nanoparticle formation stabilized in water.}, language = {en} } @article{StorchMaierWessigetal.2016, author = {Storch, Golo and Maier, Frank and Wessig, Pablo and Trapp, Oliver}, title = {Rotational Barriers of Substituted BIPHEP Ligands: A Comparative Experimental and Theoretical Study}, series = {European journal of organic chemistry}, volume = {22}, journal = {European journal of organic chemistry}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201600836}, pages = {5123 -- 5126}, year = {2016}, abstract = {The interconversion barriers of 14 different 3,3- and 5,5-disubstituted tropos BIPHEP [2,2-bis(diphenylphosphino)-1,1-biphenyl] and BIPHEP(O) [2,2-bis(diphenylphosphoryl)-1,1-biphenyl] ligands were investigated by enantioselective dynamic high performance liquid chromatography (DHPLC) and DFT calculations using the B3LYP/6-31G* and M06-2X/6-31G* levels of theory. The experimentally determined enantiomerization barriers varied from 86.8 to 101.4 kJmol(-1) and were found to be in excellent agreement with the calculated data. The root-mean-square deviations are 7.3 kJmol(-1) for the B3LYP functional and 11.3 kJmol(-1) for the M06-2X method.}, language = {en} } @article{StrauchKossmannKellingetal.2016, author = {Strauch, Peter and Kossmann, Alexander and Kelling, Alexandra and Schilde, Uwe}, title = {EPR on bis(1,2-dithiosquarato)cuprate(II) in the bis(1,2-dithiosquarato)nickelate(II) host lattice - structure and spectroscopy}, series = {Chemical papers}, volume = {70}, journal = {Chemical papers}, publisher = {De Gruyter}, address = {Berlin}, issn = {0366-6352}, doi = {10.1515/chempap-2015-0154}, pages = {61 -- 68}, year = {2016}, abstract = {EPR spectroscopy is a well suited analytical tool to monitor the electronic situation around paramagnetic metal centres as copper(II) and therefore the structural influences on the paramagnetic ion. 1,2-Dithiosquaratometalates are available by direct synthesis from metal salts with dipotassium-1,2-dithiosquarate and the appropriate counter cations. Synthesis and characterisation of bis(benzyltributylammonium)1,2-dithiosquaratonickelate(II), (BzlBu(3)N)(2)[Ni(dtsq)(2)], and bis(benzyltributylammonium)1,2-dithiosquaratocuprate(II), (BzlBu(3)N)(2)[Cu(dtsq)(2)], with benzyltributylammonium as the counter ion is reported and the X-ray structures of two complexes, (BzlBu(3)N)(2)[Ni(dtsq)(2)] and (BzlBu(3)N)(2)[Cu(dtsq)(2)], are presented. Both complexes, crystallising in the monoclinic space group P2(1)/c, are isostructural with only small differences in the coordination sphere due to the different metal ions. The diamagnetic nickel complex is therefore well suited as a host lattice for the paramagnetic Cu(II) complex to measure EPR for additional structural information. (c) 2015 Institute of Chemistry, Slovak Academy of Sciences}, language = {en} } @article{SunRynoZhongetal.2016, author = {Sun, Haitao and Ryno, Sean and Zhong, Cheng and Ravva, Mahesh Kumar and Sun, Zhenrong and K{\"o}rzd{\"o}rfer, Thomas and Bredas, Jean-Luc}, title = {Ionization Energies, Electron Affinities, and Polarization Energies of Organic Molecular Crystals: Quantitative Estimations from a Polarizable Continuum Model (PCM)-Tuned Range-Separated Density Functional Approach}, series = {Journal of chemical theory and computation}, volume = {12}, journal = {Journal of chemical theory and computation}, publisher = {American Chemical Society}, address = {Washington}, issn = {1549-9618}, doi = {10.1021/acs.jctc.6b00225}, pages = {2906 -- 2916}, year = {2016}, abstract = {We propose a new methodology for the first principles description of the electronic properties relevant for charge transport in organic molecular crystals. This methodology, which is based on the combination of a nonempirical, optimally tuned range separated hybrid functional with the polarizable continuum model, is applied to a series of eight representative molecular semiconductor crystals. We show that it provides ionization energies, electron affinities, and transport gaps in very good agreement with experimental values, as well as with the results of many-body perturbation theory-within the GW approximation at a fraction of the computational cost. Hence, this approach represents an easily applicable and computationally efficient tool to estimate the gas-to crystal phase shifts of the frontier-orbital quasiparticle energies in organic electronic materials.}, language = {en} } @article{SunCernochVoelkeletal.2016, author = {Sun, Jing and Cernoch, Peter and V{\"o}lkel, Antje and Wei, Yuhan and Ruokolainen, Janne and Schlaad, Helmut}, title = {Aqueous Self-Assembly of a Protein-Mimetic Ampholytic Block Copolypeptide}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {49}, journal = {Macromolecules : a publication of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.6b00817}, pages = {5494 -- 5501}, year = {2016}, abstract = {This report describes the aggregation behavior of an ABC-type ampholytic block copolypeptide, poly(ethylene oxide)-block-poly(L-lysine)-block-poly(L-glutamate), in aqueous media in dependence of pH. Polypeptide secondary structures and self-assemblies are investigated by circular dichroism (CD), Fourier transform infrared (FT-IR) and NMR spectroscopy, zeta potential measurements, analytical ultracentrifugation (AUC), dynamic/static light scattering (DLS/SLS), and cryogenic transmission electron microscopy (cryoTEM). The polymer chains tend to form vesicles when the hydrophobic polypeptide helix is located at the chain end (acidic pH) and are existing as single chains when it is located in the center and flanked by the two hydrophilic segments (basic pH). Precipitation occurs in the intermediate pH range due to polyion complexation of the charged polypeptide segments.}, language = {en} } @article{TetaliJankowskiLuetzowetal.2016, author = {Tetali, Sarada D. and Jankowski, Vera and Luetzow, Karola and Kratz, Karl and Lendlein, Andreas and Jankowski, Joachim}, title = {Adsorption capacity of poly(ether imide) microparticles to uremic toxins}, series = {Clinical hemorheology and microcirculation : blood flow and vessels}, volume = {61}, journal = {Clinical hemorheology and microcirculation : blood flow and vessels}, publisher = {IOS Press}, address = {Amsterdam}, issn = {1386-0291}, doi = {10.3233/CH-152026}, pages = {657 -- 665}, year = {2016}, abstract = {Uremia is a phenomenon caused by retention of uremic toxins in the plasma due to functional impairment of kidneys in the elimination of urinary waste products. Uremia is presently treated by dialysis techniques like hemofiltration, dialysis or hemodiafiltration. However, these techniques in use are more favorable towards removing hydrophilic than hydrophobic uremic toxins. Hydrophobic uremic toxins, such as hydroxy hipuric acid (OH-HPA), phenylacetic acid (PAA), indoxyl sulfate (IDS) and p-cresylsulfate (pCRS), contribute substantially to the progression of chronic kidney disease (CKD) and cardiovascular disease. Therefore, objective of the present study is to test adsorption capacity of highly porous microparticles prepared from poly(ether imide) (PEI) as an alternative technique for the removal of uremic toxins. Two types of nanoporous, spherically shaped microparticles were prepared from PEI by a spraying/coagulation process. PEI particles were packed into a preparative HPLC column to which a mixture of the four types of uremic toxins was injected and eluted with ethanol. Eluted toxins were quantified by analytical HPLC. PEI particles were able to adsorb all four toxins, with the highest affinity for PAA and pCR. IDS and OH-HPA showed a partially non-reversible binding. In summary, PEI particles are interesting candidates to be explored for future application in CKD.}, language = {en} } @article{ThielkeSeckerSchlaadetal.2016, author = {Thielke, Michael W. and Secker, Christian and Schlaad, Helmut and Theato, Patrick}, title = {Electrospinning of Crystallizable Polypeptoid Fibers}, series = {Macromolecular rapid communications}, volume = {37}, journal = {Macromolecular rapid communications}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201500502}, pages = {100 -- 104}, year = {2016}, abstract = {A unique fabrication process of low molar mass, crystalline polypeptoid fibers is described. Thermoresponsive fiber mats are prepared by electrospinning a homogeneous blend of semicrystalline poly(N-(n-propyl) glycine) (PPGly; 4.1 kDa) with high molar mass poly(ethylene oxide) (PEO). Annealing of these fibers at approximate to 100 degrees C selectively removes the PEO and produces stable crystalline fiber mats of pure PPGly, which are insoluble in aqueous solution but can be redissolved in methanol or ethanol. The formation of water-stable polypeptoid fiber mats is an important step toward their utilization in biomedical applications such as tissue engineering or wound dressing.}, language = {en} } @article{TitovGranucciGoetzeetal.2016, author = {Titov, Evgenii and Granucci, Giovanni and Goetze, Jan Philipp and Persico, Maurizio and Saalfrank, Peter}, title = {Dynamics of Azobenzene Dimer Photoisomerization: Electronic and Steric Effects}, series = {The journal of physical chemistry letters}, volume = {7}, journal = {The journal of physical chemistry letters}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/acs.jpciett.6b01401}, pages = {3591 -- 3596}, year = {2016}, abstract = {While azobenzenes readily photoswitch in solution, their photoisomerization in densely packed self-assembled monolayers (SAMs) can be suppressed. Reasons for this can be steric hindrance and/or electronic quenching, e.g., by exciton coupling. We address these possibilities by means of nonadiabatic molecular dynamics with trajectory surface hopping calculations, investigating the trans -> cis isomerization of azobenzene after excitation into the pi pi* absorption band. We consider a free monomer, an isolated dimer and a dimer embedded in a SAM-like environment of additional azobenzene molecules, imitating in this way the gradual transition from an unconstrained over an electronically coupled to an electronically coupled and sterically hindered, molecular switch. Our simulations reveal that in comparison to the single molecule the quantum yield of the trans -> cis photoisomerization is similar for the isolated dimer, but greatly reduced in the sterically constrained situation. Other implications of dimerization and steric constraints are also discussed.}, language = {en} } @article{TitovSaalfrank2016, author = {Titov, Evgenii and Saalfrank, Peter}, title = {Exciton Splitting of Adsorbed and Free 4-Nitroazobenzene Dimers: A Quantum Chemical Study}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {120}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.5b10376}, pages = {3055 -- 3070}, year = {2016}, abstract = {Molecular photoswitches such as azobenzenes, which undergo photochemical trans <-> cis isomerizations, are often mounted for possible applications on a surface and/or surrounded by other switches, for example, in self-assembled monolayers. This may suppress the isomerization cross section due to possible steric reasons, or, as recently speculated, by exciton coupling to. neighboring switches, leading to ultrafast electronic quenching (Gahl et al., J. Am. Chem. Soc. 2010, 132, 1831). The presence of exciton coupling has been anticipated from a blue shift of the optical absorption band, compared to molecules in solution. From the theory side the need arises to properly analyze and quantify the change of absorption spectra of interacting and adsorbed switches. In particular, suitable methods should be identified, and effects of intermolecule and molecule surface interactions on spectra should be disentangled. In this paper by means of time-dependent Hartree-Fock. (TD-HF), various flavors of time-dependent density functional theory (TD-DFT), and the correlated wave function based, coupled cluster (CC2) method we investigated the 4-nitroazobenzene molecule as an:example: The low-lying singlet excited states in the isolated trans monomer and dieter as well as their composites with a silicon pentamantane nanocluster, which serves also as a crude model for a silicon surface, were determined. As most important results we found that (i) HF, CC2, range-separated density functionals, or global hybrids with large amount of exact exchange are able to describe exciton (Davydov) splitting properly, while hybrids with small amount of exact exchange fail producing spurious charge transfer. (ii) The exciton splitting in a free dimer would lead to a blue shift of the absorption signal; however, this effect is almost nullified or even overcompensated by the shift arising from van der Waals interactions between the two molecules. (iii) Adsorption on the Si "surface" leads to a further, strong red shift for the present system. (iv) At a next-nearest neighbor distance (of similar to 3.6 angstrom), the exciton splitting is similar to 0.3 eV, with or without "surface", suggesting a rapid quenching of the molecular pi ->pi* excitation. At larger distances, exciton splitting decreases rapidly.}, language = {en} } @phdthesis{Trautmann2016, author = {Trautmann, Michael}, title = {Neue Polystyrolharze mit Sulfoxid-Ankergruppen f{\"u}r die Festphasenextraktion von Platin und Ruthenium aus salzsauren L{\"o}sungen}, school = {Universit{\"a}t Potsdam}, pages = {191}, year = {2016}, language = {de} } @article{TrautweinFredrikssonMoelleretal.2016, author = {Trautwein, Matthias and Fredriksson, Kai and M{\"o}ller, Heiko Michael and Exner, Thomas E.}, title = {Automated assignment of NMR chemical shifts based on a known structure and 4D spectra}, series = {Journal of biomolecular NMR}, volume = {65}, journal = {Journal of biomolecular NMR}, publisher = {Springer}, address = {Dordrecht}, issn = {0925-2738}, doi = {10.1007/s10858-016-0050-0}, pages = {217 -- 236}, year = {2016}, abstract = {Apart from their central role during 3D structure determination of proteins the backbone chemical shift assignment is the basis for a number of applications, like chemical shift perturbation mapping and studies on the dynamics of proteins. This assignment is not a trivial task even if a 3D protein structure is known and needs almost as much effort as the assignment for structure prediction if performed manually. We present here a new algorithm based solely on 4D [H-1, N-15]-HSQC-NOESY-[H-1, N-15]-HSQC spectra which is able to assign a large percentage of chemical shifts (73-82 \%) unambiguously, demonstrated with proteins up to a size of 250 residues. For the remaining residues, a small number of possible assignments is filtered out. This is done by comparing distances in the 3D structure to restraints obtained from the peak volumes in the 4D spectrum. Using dead-end elimination, assignments are removed in which at least one of the restraints is violated. Including additional information from chemical shift predictions, a complete unambiguous assignment was obtained for Ubiquitin and 95 \% of the residues were correctly assigned in the 251 residue-long N-terminal domain of enzyme I. The program including source code is available at https://github.com/thomasexner/4Dassign.}, language = {en} } @article{TritschlerZlotnikovFratzletal.2016, author = {Tritschler, Ulrich and Zlotnikov, Igor and Fratzl, Peter and Schlaad, Helmut and Gruener, Simon and Coelfen, Helmut}, title = {Gas barrier properties of bio-inspired Laponite-LC polymer hybrid films}, series = {PLoS one}, volume = {11}, journal = {PLoS one}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1748-3182}, doi = {10.1088/1748-3190/11/3/035005}, pages = {12}, year = {2016}, abstract = {Bio-inspired Laponite (clay)-liquid crystal (LC) polymer composite materials with high clay fractions (>80\%) and a high level of orientation of the clay platelets, i.e. with structural features similar to the ones found in natural nacre, have been shown to exhibit a promising behavior in the context of reduced oxygen transmission. Key characteristics of these bio-inspired composite materials are their high inorganic content, high level of exfoliation and orientation of the clay platelets, and the use of a LC polymer forming the organic matrix in between the Laponite particles. Each single feature may be beneficial to increase the materials gas barrier property rendering this composite a promising system with advantageous barrier capacities. In this detailed study, Laponite/LC polymer composite coatings with different clay loadings were investigated regarding their oxygen transmission rate. The obtained gas barrier performance was linked to the quality, respective Laponite content and the underlying composite micro-and nanostructure of the coatings. Most efficient oxygen barrier properties were observed for composite coatings with 83\% Laponite loading that exhibit a structure similar to sheet-like nacre. Further on, advantageous mechanical properties of these Laponite/LC polymer composites reported previously give rise to a multifunctional composite system.}, language = {en} } @phdthesis{Taeuber2016, author = {T{\"a}uber, Karoline}, title = {Porous Membranes from Imidazolium- and Pyridinium-based Poly(ionic liquid)s with Targeted Properties}, school = {Universit{\"a}t Potsdam}, pages = {115}, year = {2016}, language = {en} } @misc{ToepferTremblay2016, author = {T{\"o}pfer, Kai and Tremblay, Jean Christophe}, title = {How surface reparation prevents catalytic oxidation of carbon monoxide on atomic gold at defective magnesium oxide surfaces}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394978}, pages = {8}, year = {2016}, abstract = {In this contribution, we study using first principles the co-adsorption and catalytic behaviors of CO and O2 on a single gold atom deposited at defective magnesium oxide surfaces. Using cluster models and point charge embedding within a density functional theory framework, we simulate the CO oxidation reaction for Au1 on differently charged oxygen vacancies of MgO(001) to rationalize its experimentally observed lack of catalytic activity. Our results show that: (1) co-adsorption is weakly supported at F0 and F2+ defects but not at F1+ sites, (2) electron redistribution from the F0 vacancy via the Au1 cluster to the adsorbed molecular oxygen weakens the O2 bond, as required for a sustainable catalytic cycle, (3) a metastable carbonate intermediate can form on defects of the F0 type, (4) only a small activation barrier exists for the highly favorable dissociation of CO2 from F0, and (5) the moderate adsorption energy of the gold atom on the F0 defect cannot prevent insertion of molecular oxygen inside the defect. Due to the lack of protection of the color centers, the surface becomes invariably repaired by the surrounding oxygen and the catalytic cycle is irreversibly broken in the first oxidation step.}, language = {en} } @phdthesis{Ulaganathan2016, author = {Ulaganathan, Vamseekrishna}, title = {Molecular fundamentals of foam fractionation}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-94263}, school = {Universit{\"a}t Potsdam}, pages = {ix, 136}, year = {2016}, abstract = {Foam fractionation of surfactant and protein solutions is a process dedicated to separate surface active molecules from each other due to their differences in surface activities. The process is based on forming bubbles in a certain mixed solution followed by detachment and rising of bubbles through a certain volume of this solution, and consequently on the formation of a foam layer on top of the solution column. Therefore, systematic analysis of this whole process comprises of at first investigations dedicated to the formation and growth of single bubbles in solutions, which is equivalent to the main principles of the well-known bubble pressure tensiometry. The second stage of the fractionation process includes the detachment of a single bubble from a pore or capillary tip and its rising in a respective aqueous solution. The third and final stage of the process is the formation and stabilization of the foam created by these bubbles, which contains the adsorption layers formed at the growing bubble surface, carried up and gets modified during the bubble rising and finally ends up as part of the foam layer. Bubble pressure tensiometry and bubble profile analysis tensiometry experiments were performed with protein solutions at different bulk concentrations, solution pH and ionic strength in order to describe the process of accumulation of protein and surfactant molecules at the bubble surface. The results obtained from the two complementary methods allow understanding the mechanism of adsorption, which is mainly governed by the diffusional transport of the adsorbing protein molecules to the bubble surface. This mechanism is the same as generally discussed for surfactant molecules. However, interesting peculiarities have been observed for protein adsorption kinetics at sufficiently short adsorption times. First of all, at short adsorption times the surface tension remains constant for a while before it decreases as expected due to the adsorption of proteins at the surface. This time interval is called induction time and it becomes shorter with increasing protein bulk concentration. Moreover, under special conditions, the surface tension does not stay constant but even increases over a certain period of time. This so-called negative surface pressure was observed for BCS and BLG and discussed for the first time in terms of changes in the surface conformation of the adsorbing protein molecules. Usually, a negative surface pressure would correspond to a negative adsorption, which is of course impossible for the studied protein solutions. The phenomenon, which amounts to some mN/m, was rather explained by simultaneous changes in the molar area required by the adsorbed proteins and the non-ideality of entropy of the interfacial layer. It is a transient phenomenon and exists only under dynamic conditions. The experiments dedicated to the local velocity of rising air bubbles in solutions were performed in a broad range of BLG concentration, pH and ionic strength. Additionally, rising bubble experiments were done for surfactant solutions in order to validate the functionality of the instrument. It turns out that the velocity of a rising bubble is much more sensitive to adsorbing molecules than classical dynamic surface tension measurements. At very low BLG or surfactant concentrations, for example, the measured local velocity profile of an air bubble is changing dramatically in time scales of seconds while dynamic surface tensions still do not show any measurable changes at this time scale. The solution's pH and ionic strength are important parameters that govern the measured rising velocity for protein solutions. A general theoretical description of rising bubbles in surfactant and protein solutions is not available at present due to the complex situation of the adsorption process at a bubble surface in a liquid flow field with simultaneous Marangoni effects. However, instead of modelling the complete velocity profile, new theoretical work has been started to evaluate the maximum values in the profile as characteristic parameter for dynamic adsorption layers at the bubble surface more quantitatively. The studies with protein-surfactant mixtures demonstrate in an impressive way that the complexes formed by the two compounds change the surface activity as compared to the original native protein molecules and therefore lead to a completely different retardation behavior of rising bubbles. Changes in the velocity profile can be interpreted qualitatively in terms of increased or decreased surface activity of the formed protein-surfactant complexes. It was also observed that the pH and ionic strength of a protein solution have strong effects on the surface activity of the protein molecules, which however, could be different on the rising bubble velocity and the equilibrium adsorption isotherms. These differences are not fully understood yet but give rise to discussions about the structure of protein adsorption layer under dynamic conditions or in the equilibrium state. The third main stage of the discussed process of fractionation is the formation and characterization of protein foams from BLG solutions at different pH and ionic strength. Of course a minimum BLG concentration is required to form foams. This minimum protein concentration is a function again of solution pH and ionic strength, i.e. of the surface activity of the protein molecules. Although at the isoelectric point, at about pH 5 for BLG, the hydrophobicity and hence the surface activity should be the highest, the concentration and ionic strength effects on the rising velocity profile as well as on the foamability and foam stability do not show a maximum. This is another remarkable argument for the fact that the interfacial structure and behavior of BLG layers under dynamic conditions and at equilibrium are rather different. These differences are probably caused by the time required for BLG molecules to adapt respective conformations once they are adsorbed at the surface. All bubble studies described in this work refer to stages of the foam fractionation process. Experiments with different systems, mainly surfactant and protein solutions, were performed in order to form foams and finally recover a solution representing the foamed material. As foam consists to a large extent of foam lamella - two adsorption layers with a liquid core - the concentration in a foamate taken from foaming experiments should be enriched in the stabilizing molecules. For determining the concentration of the foamate, again the very sensitive bubble rising velocity profile method was applied, which works for any type of surface active materials. This also includes technical surfactants or protein isolates for which an accurate composition is unknown.}, language = {en} } @phdthesis{Vacogne2016, author = {Vacogne, Charlotte D.}, title = {New synthetic routes towards well-defined polypeptides, morphologies and hydrogels}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-396366}, school = {Universit{\"a}t Potsdam}, pages = {xii, 175}, year = {2016}, abstract = {Proteins are natural polypeptides produced by cells; they can be found in both animals and plants, and possess a variety of functions. One of these functions is to provide structural support to the surrounding cells and tissues. For example, collagen (which is found in skin, cartilage, tendons and bones) and keratin (which is found in hair and nails) are structural proteins. When a tissue is damaged, however, the supporting matrix formed by structural proteins cannot always spontaneously regenerate. Tailor-made synthetic polypeptides can be used to help heal and restore tissue formation. Synthetic polypeptides are typically synthesized by the so-called ring opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCA). Such synthetic polypeptides are generally non-sequence-controlled and thus less complex than proteins. As such, synthetic polypeptides are rarely as efficient as proteins in their ability to self-assemble and form hierarchical or structural supramolecular assemblies in water, and thus, often require rational designing. In this doctoral work, two types of amino acids, γ-benzyl-L/D-glutamate (BLG / BDG) and allylglycine (AG), were selected to synthesize a series of (co)polypeptides of different compositions and molar masses. A new and versatile synthetic route to prepare polypeptides was developed, and its mechanism and kinetics were investigated. The polypeptide properties were thoroughly studied and new materials were developed from them. In particular, these polypeptides were able to aggregate (or self-assemble) in solution into microscopic fibres, very similar to those formed by collagen. By doing so, they formed robust physical networks and organogels which could be processed into high water-content, pH-responsive hydrogels. Particles with highly regular and chiral spiral morphologies were also obtained by emulsifying these polypeptides. Such polypeptides and the materials derived from them are, therefore, promising candidates for biomedical applications.}, language = {en} } @article{VacogneSchopfererSchlaad2016, author = {Vacogne, Charlotte D. and Schopferer, Michael and Schlaad, Helmut}, title = {Physical Gelation of alpha-Helical Copolypeptides}, series = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences}, volume = {17}, journal = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences}, publisher = {American Chemical Society}, address = {Washington}, issn = {1525-7797}, doi = {10.1021/acs.biomac.6b00427}, pages = {2384 -- 2391}, year = {2016}, abstract = {Owing to its rod-like alpha-helical secondary structure, the synthetic polypeptide poly(gamma-benzyl-L-glutamate) (PBLG) can form physical and thermoreversible gels in helicogenic solvents such as toluene. The versatility of PBLG can be increased by introducing functionalizable comonomers, such as allylglycine (AG). In this work we examined the secondary structure of PBLG and a series of statistical poly(gamma-benzyl-L-glutamate-co-allylglycine) copolypeptides, varying in composition and chain length, by circular dichroism (CD), Fourier-transform infrared (FTIR) and Raman spectroscopy, and wide-angle X-ray scattering (WAXS). The secondary structure of PBLG and the copolypeptides presented dissimilarities that increased with increasing AG molar fraction, especially when racemic AG units were incorporated. The physical gelation behavior of these copolypeptides was analyzed by temperature-sweep H-1 NMR and rheological measurements. The study revealed that both copolypeptide composition and chain length affected secondary structure, gelation temperature, and gel stiffness.}, language = {en} } @article{VargasRuizSchulreichKostevicetal.2016, author = {Vargas-Ruiz, Salome and Schulreich, Christoph and Kostevic, Angelika and Tiersch, Brigitte and Koetz, Joachim and Kakorin, Sergej and von Klitzing, Regine and Jung, Martin and Hellweg, Thomas and Wellert, Stefan}, title = {Extraction of model contaminants from solid surfaces by environmentally compatible microemulsions}, series = {Journal of colloid and interface science}, volume = {471}, journal = {Journal of colloid and interface science}, publisher = {Elsevier}, address = {San Diego}, issn = {0021-9797}, doi = {10.1016/j.jcis.2016.03.006}, pages = {118 -- 126}, year = {2016}, abstract = {In the present contribution, we evaluate the efficiency of eco-friendly microemulsions to decontaminate solid surfaces by monitoring the extraction of non-toxic simulants of sulfur mustard out of model surfaces. The extraction process of the non-toxic simulants has been monitored by means of spectroscopic and chromatographic techniques. The kinetics of the removal process was analyzed by different empirical models. Based on the analysis of the kinetics, we can assess the influence of the amounts of oil and water and the microemulsion structure on the extraction process. (C) 2016 Elsevier Inc. All rights reserved.}, language = {en} }