@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{ZengFrascaRumschoetteletal.2016, author = {Zeng, Ting and Frasca, Stefano and Rumsch{\"o}ttel, Jens and Koetz, Joachim and Leimk{\"u}hler, Silke and Wollenberger, Ursula}, title = {Role of Conductive Nanoparticles in the Direct Unmediated Bioelectrocatalysis of Immobilized Sulfite Oxidase}, series = {Electroanalysis : an international journal devoted to fundamental and practical aspects of electroanalysis}, volume = {28}, journal = {Electroanalysis : an international journal devoted to fundamental and practical aspects of electroanalysis}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1040-0397}, doi = {10.1002/elan.201600246}, pages = {2303 -- 2310}, year = {2016}, language = {en} } @article{HolertYuecelJagmannetal.2016, author = {Holert, Johannes and Y{\"u}cel, Onur and Jagmann, Nina and Prestel, Andreas and M{\"o}ller, Heiko Michael and Philipp, Bodo}, title = {Identification of bypass reactions leading to the formation of one central steroid degradation intermediate in metabolism of different bile salts in Pseudomonas sp strain Chol1}, series = {Environmental microbiology}, volume = {18}, journal = {Environmental microbiology}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {1462-2912}, doi = {10.1111/1462-2920.13192}, pages = {3373 -- 3389}, year = {2016}, language = {en} } @article{PoghosyanArsenyanShahinyanetal.2016, author = {Poghosyan, Armen H. and Arsenyan, Levon H. and Shahinyan, Aram A. and Koetz, Joachim}, title = {Polyethyleneimine loaded inverse SDS micelle in pentanol/toluene media}, series = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, volume = {506}, journal = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2016.07.018}, pages = {402 -- 408}, year = {2016}, abstract = {An atomic scale molecular dynamics simulation (100 ns) was carried out to reveal the conformational features of a cationic polyelectrolyte, i.e., hyperbranched polyethyleneimine (PEI), inside of water-in-oil microemulsion droplets stabilized by the anionic sodium dodecyl sulfate surfactant (SDS) layer. Simulations show that the polymer reorients very quickly and is localized at the headgroup region, i.e., the polymer nitrogens are close to SDS sulfur atoms. In spite of the availability of surface roughness caused by the polymer, we track a stable inverse micelle during the production run. In overall, the obtained parameters are well compared with experimental findings. (C) 2016 Elsevier B.V. All rights reserved.}, language = {en} } @article{WeilerMenzelPertschetal.2016, author = {Weiler, Markus and Menzel, Christoph and Pertsch, Thomas and Alaee, Rasoul and Rockstuhl, Carsten and Pacholski, Claudia}, title = {Bottom-Up Fabrication of Hybrid Plasmonic Sensors: Gold-Capped Hydrogel Microspheres Embedded in Periodic Metal Hole Arrays}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {8}, journal = {Polymer : the international journal for the science and technology of polymers}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.6b08636}, pages = {26392 -- 26399}, year = {2016}, abstract = {The high potential of bottom-up fabrication strategies for realizing sophisticated optical sensors combining the high sensitivity of a surface plasmon resonance with the exceptional properties of stimuli-responsive hydrogel is demonstrated. The sensor is composed of a periodic hole array in a gold film whose holes are filled with gold-capped poly(N-isoproyl-acrylamide) (polyNIPAM) microspheres. The production of this sensor relies on a pure chemical approach enabling simple, time-efficient, and cost-efficient preparation of sensor platforms covering areas of cm(2). The transmission spectrum of this plasmonic sensor shows a strong interaction between propagating surface plasmon polaritons at the metal film surface and localized surface plasmon resonance of the gold cap on top of the polyNIPAM microspheres. Computer simulations support this experimental observation. These interactions lead to distinct changes in the transmission spectrum, which allow for the simultaneous, sensitive optical detection of refractive index changes in the surrounding medium and the swelling state of the embedded polyNIPAM microsphere under the gold cap. The volume of the polyNIPAM microsphere located underneath the gold cap can be changed by certain stimuli such as temperature, pH, ionic strength, and distinct molecules bound to the hydrogel matrix facilitating the detection of analytes which do not change the refractive index of the surrounding medium significantly.}, language = {en} } @article{KuleszaTitovDalyetal.2016, author = {Kulesza, Alexander Jan and Titov, Evgenii and Daly, Steven and Wlodarczyk, Radoslaw and Megow, J{\"o}rg and Saalfrank, Peter and Choi, Chang Min and MacAleese, Luke and Antoine, Rodolphe and Dugourd, Philippe}, title = {Excited States of Xanthene Analogues: Photofragmentation and Calculations by CC2 and Time-Dependent Density Functional Theory}, series = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, volume = {17}, journal = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1439-4235}, doi = {10.1002/cphc.201600650}, pages = {3129 -- 3138}, year = {2016}, abstract = {Action spectroscopy has emerged as an analytical tool to probe excited states in the gas phase. Although comparison of gas-phase absorption properties with quantum-chemical calculations is, in principle, straightforward, popular methods often fail to describe many molecules of interest-such as xanthene analogues. We, therefore, face their nano-and picosecond laser-induced photofragmentation with excited-state computations by using the CC2 method and time-dependent density functional theory (TDDFT). Whereas the extracted absorption maxima agree with CC2 predictions, the TDDFT excitation energies are blueshifted. Lowering the amount of Hartree-Fock exchange in the DFT functional can reduce this shift but at the cost of changing the nature of the excited state. Additional bandwidth observed in the photofragmentation spectra is rationalized in terms of multiphoton processes. Observed fragmentation from higher-lying excited states conforms to intense excited-to-excited state transitions calculated with CC2. The CC2 method is thus suitable for the comparison with photofragmentation in xanthene analogues.}, 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{FangYanNoecheletal.2016, author = {Fang, Liang and Yan, Wan and N{\"o}chel, Ulrich and Kratz, Karl and Lendlein, Andreas}, title = {Programming structural functions in phase-segregated polymers by implementing a defined thermomechanical history}, 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.2016.08.105}, pages = {54 -- 62}, year = {2016}, abstract = {Unwanted shrinkage behaviors or failure in structural functions such as mechanical strength or deformability of polymeric products related to their thermomechanical history are a major challenge in production of plastics. Here, we address the question whether we can turn this challenge into an opportunity by creating defined thermomechanical histories in polymers, represented by a specific morphology and nanostructure, to equip polymeric shaped bodies with desired functions, e.g. a temperature-memory, by hot, warm or cold deformation into multiblock copolymers having two partially overlapping melting transitions. A copolyesterurethane named PDLCL, consisting of poly(epsilon-caprolactone) (PCL) and poly(omega-pentadecalactone) (PPDL) crystalline domains, exhibiting a pronounced phase-segregated morphology and partially overlapping melting transitions was selected for this study. Different types of PCL and PPDL crystals as well as distinct degrees of orientation in both amorphous and crystalline domains were obtained after deformation at 20 or 40 degrees C and to a lower extent at 60 degrees C. The generated non-isotropic structures were stable at ambient temperature and represent the different stresses stored. Stress-free heating experiments showed that the relaxation in both amorphous and crystalline phases occurred predominantly with melting of PCL crystals. When the switching temperature, which was similar to the applied deformation temperature (temperature-memory), was exceeded in stress-free heating experiments, the implemented thermomechanical history could be reversed. In contrast, during constant-strain heating to 60 degrees C the generated structural features remained almost unchanged. These findings provide insights about the structure function relation in multiblock copolymers with two crystalline phases exhibiting a temperature-memory effect by implementation of specific thermomechanical histories, which might be a general principle for tailoring other functions like mechanical strength or deformability in polymers. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{WagnerLazarSchnakenbergetal.2016, author = {Wagner, Tom and Lazar, Jaroslav and Schnakenberg, Uwe and B{\"o}ker, Alexander}, title = {In situ Electrothemical Impedance Spectroscopy of Electrostatically Driven Selective Gold Nanoparticle Adsorption on Block Copolymer Lamellae}, series = {Trials}, volume = {8}, journal = {Trials}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.6b07708}, pages = {27282 -- 27290}, year = {2016}, abstract = {Electrostatic attraction between charged nano particles and oppositely charged nanopatterned polymeric films enables tailored structuring of functional nanoscopic surfaces. The bottom-up fabrication of organic/inorganic composites for example bears promising potential toward cheap fabrication of catalysts, optical sensors, and the manufacture of miniaturized electric circuitry. However, only little is known about the time-dependent adsorption behavior and the electronic or ionic charge transfer in the film bulk and at interfaces during nanoparticle assembly via electrostatic interactions. In situ electrochemical impedance spectroscopy (EIS) in combination with a microfluidic system for fast and reproducible liquid delivery was thus applied to monitor the selective deposition of negatively charged gold nanoparticles on top of positively charged poly(2-vinylpyridinium) (qP2VP) domains of phase separated lamellar poly(styrene)-block-poly(2-vinylpyridinium) (PS-b-qP2VP) diblock copolymer thin films. The acquired impedance data delivered information with respect to interfacial charge alteration, ionic diffusion, and the charge dependent nanoparticle adsorption kinetics, considering this yet unexplored system. We demonstrate that the selective adsorption of negatively charged gold nanoparticles (AuNPs) on positively charged qP2VP domains of lamellar PS-b-qP2VP thin films can indeed be tracked by EIS. Moreover, we show that the nanoparticle adsorption kinetics and the nanoparticle packing density are functions of the charge density in the qP2VP domains.}, 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{GuietUnmuessigGoebeletal.2016, author = {Guiet, Amandine and Unm{\"u}ssig, Tobias and G{\"o}bel, Caren and Vainio, Ulla and Wollgarten, Markus and Driess, Matthias and Schlaad, Helmut and Polte, J{\"o}rg and Fischer, Anna}, title = {Yolk@Shell Nanoarchitectures with Bimetallic Nanocores - Synthesis and Electrocatalytic Applications}, series = {Earth \& planetary science letters}, volume = {8}, journal = {Earth \& planetary science letters}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.6b06595}, pages = {28019 -- 28029}, year = {2016}, language = {en} } @article{PrinzMatkovicPesicetal.2016, author = {Prinz, Julia and Matkovic, Aleksandar and Pesic, Jelena and Gajic, Rados and Bald, Ilko}, title = {Hybrid Structures for Surface-Enhanced Raman Scattering: DNA Origami/Gold Nanoparticle Dimer/Graphene}, series = {Small}, volume = {12}, journal = {Small}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1613-6810}, doi = {10.1002/smll.201601908}, pages = {5458 -- 5467}, year = {2016}, abstract = {A combination of three innovative materials within one hybrid structure to explore the synergistic interaction of their individual properties is presented. The unique electronic, mechanical, and thermal properties of graphene are combined with the plasmonic properties of gold nanoparticle (AuNP) dimers, which are assembled using DNA origami nanostructures. This novel hybrid structure is characterized by means of correlated atomic force microscopy and surface-enhanced Raman scattering (SERS). It is demonstrated that strong interactions between graphene and AuNPs result in superior SERS performance of the hybrid structure compared to their individual components. This is particularly evident in efficient fluorescence quenching, reduced background, and a decrease of the photobleaching rate up to one order of magnitude. The versatility of DNA origami structures to serve as interface for complex and precise arrangements of nanoparticles and other functional entities provides the basis to further exploit the potential of the here presented DNA origami-AuNP dimer-graphene hybrid structures.}, 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{LiebigThuenemannKoetz2016, author = {Liebig, Ferenc and Th{\"u}nemann, Andreas F. and Koetz, Joachim}, title = {Ostwald Ripening Growth Mechanism of Gold Nanotriangles in Vesicular Template Phases}, series = {Langmuir}, volume = {32}, journal = {Langmuir}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.6b02662}, pages = {10928 -- 10935}, year = {2016}, abstract = {The mechanism of nanotriangle formation in multivesicular vesicles (MMV) is investigated by using time-dependent SAXS measurements in combination with UV-vis spectroscopy, light, and transmission electron microscopy. In the first time period 6.5 nm sized spherical gold nanoparticles are formed inside of the vesicles, which build up soft nanoparticle aggregates. a) In situ SAXS experiments show a linear increase of the volume and molar mass of nanotriangles in the second time period. The volume growth rate of the triangles is 16.1 nm(3)/min, and the growth rate in the vertical direction is only 0.02 nm/min. Therefore, flat nanotriangles with a thickness of 7 nm and a diameter of 23 nm are formed. This process can be described by a diffusion limited Ostwald ripening growth mechanism. TEM micrographs visualize soft coral-like structures with thin nanoplatelets at the periphery of the aggregates, which disaggregate in the third time period into nanotriangles and spherical particles. The 16 times faster growth of nanotriangles in the lateral than that in the vertical direction is related to the adsorption of symmetry breaking components, i.e., AOT and the polyampholyte PalPhBisCarb, on the {111} facets of the gold nanoplatelets in combination with confinement effects of the vesicular template phase.}, 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} } @article{CharanKinzelGlebeetal.2016, author = {Charan, Himanshu and Kinzel, Julia and Glebe, Ulrich and Anand, Deepak and Garakani, Tayebeh Mirzaei and Zhu, Leilei and Bocola, Marco and Schwaneberg, Ulrich and B{\"o}ker, Alexander}, title = {Grafting PNIPAAm from beta-barrel shaped transmembrane nanopores}, series = {Biomaterials : biomaterials reviews online}, volume = {107}, journal = {Biomaterials : biomaterials reviews online}, publisher = {Elsevier}, address = {Oxford}, issn = {0142-9612}, doi = {10.1016/j.biomaterials.2016.08.033}, pages = {115 -- 123}, year = {2016}, abstract = {The research on protein-polymer conjugates by grafting from the surface of proteins has gained significant interest in the last decade. While there are many studies with globular proteins, membrane proteins have remained untouched to the best of our knowledge. In this study, we established the conjugate formation with a class of transmembrane proteins and grow polymer chains from the ferric hydroxamate uptake protein component A (FhuA; a beta-barrel transmembrane protein of Escherichia coli). As the lysine residues of naturally occurring FhuA are distributed over the whole protein, FhuA was reengineered to have up to 11 lysines, distributed symmetrically in a rim on the membrane exposed side (outside) of the protein channel and exclusively above the hydrophobic region. Reengineering of FhuA ensures a polymer growth only on the outside of the beta-barrel and prevents blockage of the channel as a result of the polymerization. A water-soluble initiator for controlled radical polymerization (CRP) was consecutively linked to the lysine residues of FhuA and N-isopropylacrylamide (NIPAAm) polymerized under copper mediated CRP conditions. The conjugate formation was analyzed by using MALDI-ToF mass spectrometry, SDS-PAGE, circular dichroism spectroscopy, analytical ultracentrifugation, dynamic light scattering, transmission electron microscopy and size exclusion chromatography. Such conjugates combine the specific functions of the transmembrane proteins, like maintaining membrane potential gradients or translocation of substrates with the unique properties of synthetic polymers such as temperature and pH stimuli handles. FhuA-PNIPAAm conjugates will serve as functional nanosized building blocks for applications in targeted drug delivery, self-assembly systems, functional membranes and transmembrane protein gated nanoreactors. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{OncakWlodarczykSauer2016, author = {Oncak, Milan and Wlodarczyk, Radoslaw and Sauer, Joachim}, title = {Hydration Structures of MgO, CaO, and SrO (001) Surfaces}, 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.6b07434}, pages = {24762 -- 24769}, year = {2016}, abstract = {Using density functional theory (PBE functional), we show that the degree of surface hydroxylation increases in the MgO, CaO, SrO series, accompanied by an increase in water adsorption energy. Already for water coverage of two monolayers, structures with dissolved M2+. ions are considerably more stable than the intact, nondissolved surface. The dissolved ions above the surface form different patterns including ordered ones (e.g., an infinite stripe) that are preferred for MgO(001) and CaO(001) and disordered ones that are favored for SrO(001). Contrary to previous assignments, an analysis of calculated X-ray photoelectron spectra shows that O(1s) signals arising from OH and H2O groups might coincide in the experimental spectrum.}, 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{RossbergRottkeSchulzetal.2016, author = {Rossberg, Joana and Rottke, Falko O. and Schulz, Burkhard and Lendlein, Andreas}, title = {Enzymatic Degradation of Oligo(epsilon-caprolactone)s End-Capped with Phenylboronic Acid Derivatives at the Air-Water Interface}, series = {Macromolecular rapid communications}, volume = {37}, journal = {Macromolecular rapid communications}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201600471}, pages = {1966 -- 1971}, year = {2016}, abstract = {The influence of terminal functionalization of oligo(epsilon-caprolactone)s (OCL) with phenylboronic acid pinacol ester or phenylboronic acid on the enzymatic degradation behavior at the air-water interface is investigated by the Langmuir monolayer degradation technique. While the unsubstituted OCL immediately degrades after injection of the enzyme lipase from Pseudomonas cepacia, enzyme molecules are incorporated into the films based on end-capped OCL before degradation. This incorporation of enzymes does not inhibit or suppress the film degradation, but retards it significantly. A specific binding of lipase to the polymer monolayer allows studying the enzymatic activity of bound proteins and the influence on the degradation process. The functionalization of a macromolecule with phenyl boronic acid groups is an approach to investigate their interactions with diol-containing biomolecules like sugars and to monitor their specified impact on the enzymatic degradation behavior at the air-water interface.}, language = {en} } @article{ZhangBehlPengetal.2016, author = {Zhang, Pengfei and Behl, Marc and Peng, Xingzhou and Razzaq, Muhammad Yasar and Lendlein, Andreas}, title = {Ultrasonic Cavitation Induced Shape-Memory Effect in Porous Polymer Networks}, series = {Macromolecular rapid communications}, volume = {37}, journal = {Macromolecular rapid communications}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201600439}, pages = {1897 -- 1903}, year = {2016}, abstract = {Inspired by the application of ultrasonic cavitation based mechanical force (CMF) to open small channels in natural soft materials (skin or tissue), it is explored whether an artificial polymer network can be created, in which shape-changes can be induced by CMF. This concept comprises an interconnected macroporous rhodium-phosphine (Rh-P) coordination polymer network, in which a CMF can reversibly dissociate the Rh-P microphases. In this way, the ligand exchange of Rh-P coordination bonds in the polymer network is accelerated, resulting in a topological rearrangement of molecular switches. This rearrangement of molecular switches enables the polymer network to release internal tension under ultrasound exposure, resulting in a CMF-induced shape-memory capability. The interconnected macroporous structure with thin pore walls is essential for allowing the CMF to effectively permeate throughout the polymer network. Potential applications of this CMF-induced shape-memory polymer can be mechanosensors or ultrasound controlled switches.}, 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{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{NaolouLendleinNeffe2016, author = {Naolou, Toufik and Lendlein, Andreas and Neffe, Axel T.}, title = {Influence of metal softness on the metal-organic catalyzed polymerization of inorpholin-2,5-diones to oligodepsipeptides}, series = {European polymer journal}, volume = {85}, journal = {European polymer journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0014-3057}, doi = {10.1016/j.eurpolymj.2016.10.011}, pages = {139 -- 149}, year = {2016}, 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{VillatoroZuehlkeRiebeetal.2016, author = {Villatoro, Jos{\´e} Andr{\´e}s and Z{\"u}hlke, Martin and Riebe, Daniel and Beitz, Toralf and Weber, Marcus and Riedel, Jens and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {IR-MALDI ion mobility spectrometry: physical source characterization and application as HPLC detector}, series = {International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry}, volume = {19}, journal = {International journal for ion mobility spectrometry : official publication of the International Society for Ion Mobility Spectrometry}, publisher = {Springer}, address = {Heidelberg}, issn = {1435-6163}, doi = {10.1007/s12127-016-0208-1}, pages = {197 -- 207}, year = {2016}, abstract = {Infrared matrix-assisted laser dispersion and ionization (IR-MALDI) in combination with ion mobility (IM) spectrometry enables the direct analysis of biomolecules in aqueous solution. The release of ions directly from an aqueous solution is based on a phase explosion, induced by the absorption of an IR laser pulse, which disperses the liquid as vapor, nano-and micro-droplets. The ionization process is characterized initially by a broad spatial distribution of the ions, which is a result of complex fluid dynamics and desolvation kinetics. These processes have a profound effect on the shape and width of the peaks in the IM spectra. In this work, the transport of ions by the phase explosion-induced shockwave could be studied independently from the transport by the electric field. The shockwave-induced mean velocities of the ions at different time scales were determined through IM spectrometry and shadowgraphy. The results show a deceleration of the ions from 118 m.s(-1) at a distance of 400 mu m from the liquid surface to 7.1 m.s(-1) at a distance of 10 mm, which is caused by a pile-up effect. Furthermore, the desolvation kinetics were investigated and a first-order desolvation constant of 325 +/- 50 s(-1) was obtained. In the second part, the IR-MALDI-IM spectrometer is used as an HPLC detector for the two-dimensional separation of a pesticide mixture.}, 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} } @article{ZuehlkeRiebeBeitzetal.2016, author = {Z{\"u}hlke, Martin and Riebe, Daniel and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Andreotti, Sandro and Reinert, Knut and Zenichowski, Karl and Diener, Marc}, title = {High-performance liquid chromatography with electrospray ionization ion mobility spectrometry: Characterization, data management, and applications}, series = {Journal of separation science}, volume = {39}, journal = {Journal of separation science}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1615-9306}, doi = {10.1002/jssc.201600749}, pages = {4756 -- 4764}, year = {2016}, abstract = {The combination of high-performance liquid chromatography and electrospray ionization ion mobility spectrometry facilitates the two-dimensional separation of complex mixtures in the retention and drift time plane. The ion mobility spectrometer presented here was optimized for flow rates customarily used in high-performance liquid chromatography between 100 and 1500 mu L/min. The characterization of the system with respect to such parameters as the peak capacity of each time dimension and of the 2D spectrum was carried out based on a separation of a pesticide mixture containing 24 substances. While the total ion current chromatogram is coarsely resolved, exhibiting coelutions for a number of compounds, all substances can be separately detected in the 2D plane due to the orthogonality of the separations in retention and drift dimensions. Another major advantage of the ion mobility detector is the identification of substances based on their characteristic mobilities. Electrospray ionization allows the detection of substances lacking a chromophore. As an example, the separation of a mixture of 18 amino acids is presented. A software built upon the free mass spectrometry package OpenMS was developed for processing the extensive 2D data. The different processing steps are implemented as separate modules which can be arranged in a graphic workflow facilitating automated processing of data.}, language = {en} } @article{RendonEnriquezTauschScherf2016, author = {Rendon-Enriquez, I. N. and Tausch, M. W. and Scherf, Ullrich}, title = {Curricular Innovation Electrochromic Window with conductive Polymers}, series = {Chemie in unserer Zeit}, volume = {50}, journal = {Chemie in unserer Zeit}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0009-2851}, doi = {10.1002/ciuz.201600734}, pages = {400 -- 405}, year = {2016}, abstract = {The construction of a low-cost potentiostat and an electrochemical cell are described. Both have been used for the potentiostatic deposition of conducting polymers on FTO-coated glass. According to a reported procedure from literature an electrochromic window has been prepared and tested. Furthermore a novel window containing an additional electrodeposited polymer layer that shows a more pronounced electrochromism than the literature example is described for the first time. The required chemicals are inexpensive as well as the entire electrochemical equipment.}, language = {de} } @article{HerfurthLaschewskyNoirezetal.2016, author = {Herfurth, Christoph and Laschewsky, Andre and Noirez, Laurence and von Lospichl, Benjamin and Gradzielski, Michael}, title = {Thermoresponsive (star) block copolymers from one-pot sequential RAFT polymerizations and their self-assembly in aqueous solution}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {107}, journal = {Polymer : the international journal for the science and technology of polymers}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-3861}, doi = {10.1016/j.polymer.2016.09.089}, pages = {422 -- 433}, year = {2016}, abstract = {A series of hydrophobically end-capped linear triblock copolymers as well as of three-arm and four-arm star block copolymers was synthesized in a one-pot procedure from N,N-dimethylacrylamide (DMA) and N, N-diethylacrylamide (DEA). The sequential reversible addition-fragmentation chain transfer (RAFT) polymerization of these monomers via the R-approach using bi-, tri- and tetrafunctional chain transfer agents (CrAs) bearing hydrophobic dodecyl moieties proceeded in a well-controlled manner up to almost quantitative conversion. Polymers with molar masses up to 150 kDa, narrow molar mass distribution (PDI <= 1.3) and high end group functionality were obtained, which are thermoresponsive in aqueous solution showing a LCST (lower critical solution temperature) transition. The temperature-dependent associative behavior of the polymers was examined using turbidimetry, static and dynamic light scattering (SLS, DLS), and small angle neutron scattering (SANS) for structural analysis. At 25 degrees C, the polymers form weak transient networks, and rather small hydrophobic domains are already present for polymer concentrations of 5 wt\%. However, when heating above the LCST transition (35-40 degrees C) of the PDEA blocks, the enhanced formation of hydrophobic domains is observed by means of light and neutron scattering. These domains have a size of about 12-15 nm and must be effectively physically cross-linked as they induce high viscosity for the more concentrated samples. SANS shows that these domains are ordered as evidenced by the appearance of a correlation peak. The copolymer architecture affects in particular the extent of ordering as the four-arm star block copolymer shows much more repulsive interactions compared to the analogous copolymers with a lower number of arms. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{ReppertSarhanSteteetal.2016, author = {Reppert, Alexander von and Sarhan, Radwan Mohamed and Stete, Felix and Pudell, Jan-Etienne and Del Fatti, N. and Crut, A. and Koetz, Joachim and Liebig, Ferenc and Prietzel, Claudia Christina and Bargheer, Matias}, title = {Watching the Vibration and Cooling of Ultrathin Gold Nanotriangles by Ultrafast X-ray Diffraction}, 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.6b11651}, pages = {28894 -- 28899}, year = {2016}, abstract = {We study the vibrations of ultrathin gold nanotriangles upon optical excitation of the electron gas by ultrafast X-ray diffraction. We quantitatively measure the strain evolution in these highly asymmetric nano-objects, providing a direct estimation of the amplitude and phase of the excited vibrational motion. The maximal strain value is well reproduced by calculations addressing pump absorption by the nanotriangles and their resulting thermal expansion. The amplitude and phase of the out-of-plane vibration mode with 3.6 ps period dominating the observed oscillations are related to two distinct excitation mechanisms. Electronic and phonon pressures impose stresses with different time dependences. The nanosecond relaxation of the expansion yields a direct temperature sensing of the nano-object. The presence of a thin organic molecular layer at the nanotriangle/substrate interfaces drastically reduces the thermal conductance to the substrate.}, language = {en} } @article{WuGlebeBoeker2016, author = {Wu, Lei and Glebe, Ulrich and B{\"o}ker, Alexander}, title = {Synthesis of Hybrid Silica Nanoparticles Densely Grafted with Thermo and pH Dual-Responsive Brushes via Surface-Initiated ATRP}, 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.6b01792}, pages = {9586 -- 9596}, year = {2016}, 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} } @phdthesis{Fandrich2016, author = {Fandrich, Artur}, title = {Untersuchung des Verhaltens von thermoresponsiven Polymeren auf Elektroden in Interaktion mit biomolekularen Systemen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-396551}, school = {Universit{\"a}t Potsdam}, pages = {111}, year = {2016}, abstract = {Diese Arbeit befasst sich mit der Herstellung und Charakterisierung von thermoresponsiven Filmen auf Goldelektroden durch Fixierung eines bereits synthetisierten thermoresponsiven Polymers. Als Basis f{\"u}r die Entwicklung der responsiven Grenzfl{\"a}che dienten drei unterschiedliche Copolymere (Polymere I, II und III) aus der Gruppe der thermisch schaltbaren Poly(oligo(ethylenglykol)methacrylate). Die turbidimetrischen Messungen der Copolymere in L{\"o}sungen haben gezeigt, dass der Tr{\"u}bungspunkt vom pH-Wert, der Gegenwart von Salzen sowie von der Ionenst{\"a}rke der L{\"o}sung abh{\"a}ngig ist. Nach der Charakterisierung der Polymere in L{\"o}sung wurden Experimente der kovalenten Kopplung der Polymere I bis III an die Oberfl{\"a}che der Gold-Elektroden durchgef{\"u}hrt. W{\"a}hrend bei Polymeren I und II die Ankopplung auf einer Amidverbr{\"u}ckung basierte, wurde bei Polymer III als alternative Methode zur Immobilisierung eine photoinduzierte Anbindung unter gleichzeitiger Vernetzung gew{\"a}hlt. Der Nachweis der erfolgreichen Ankopplung erfolgte bei allen Polymeren elektrochemisch mittels Cyclovoltammetrie und Impedanzspektroskopie in K3/4[Fe(CN)6]-L{\"o}sungen. Wie die Ellipsometrie-Messungen zeigten, waren die erhaltenen Polymer-Filme unterschiedlich dick. Die Ankopplung {\"u}ber Amidverbr{\"u}ckung lieferte d{\"u}nne Filme (10 - 15 nm), w{\"a}hrend der photovernetzte Film deutlich dicker war (70-80 nm) und die darunter liegende Oberfl{\"a}che relativ gut isolierte. Elektrochemische Temperaturexperimente an Polymer-modifizierten Oberfl{\"a}chen in L{\"o}sungen in Gegenwart von K3/4[Fe(CN)6] zeigten, dass auch die immobilisierten Polymere I bis III responsives Temperaturverhalten zeigen. Bei Elektroden mit den immobilisierten Polymeren I und II ist der Temperaturverlauf der Parameterwerte diskontinuierlich - ab einem kritischen Punkt (37 °C f{\"u}r Polymer I und 45 °C f{\"u}r Polymer II) wird zun{\"a}chst langsame Zunahme der Peakstr{\"o}me wird deutlich schneller. Das Temperaturverhalten von Polymer III ist dagegen bis 50 °C kontinuierlich, der Peakstrom sinkt hier durchgehend. Weiterhin wurde mit den auf Polymeren II und III basierten Elektroden deren Anwendung als responsive Matrix f{\"u}r Bioerkennungsreaktionen untersucht. Es wurde die Ankopplung von kleinen Biorezeptoren, TAG-Peptiden, an Polymer II- und Polymer III-modifizierten Elektroden durchgef{\"u}hrt. Das hydrophile FLAG-TAG-Peptid ver{\"a}ndert das Temperaturverhalten des Polymer II-Films unwesentlich, da es die Hydrophilie des Netzwerkes nicht beeinflusst. Weiterhin wurde der Effekt der Ankopplung der ANTI-FLAG-TAG-Antik{\"o}rper an FLAG-TAG-modifizierte Polymer II-Filme untersucht. Es konnte gezeigt werden, dass die Antik{\"o}rper spezifisch an FLAG-TAG-modifiziertes Polymer II binden. Es wurde keine unspezifische Anbindung von ANTI-FLAG-TAG an Polymer II beobachtet. Die Temperaturexperimente haben gezeigt, dass die thermische Restrukturierung des Polymer II-FLAG-TAG-Filmes auch nach der Antik{\"o}rper-Ankopplung noch stattfindet. Der Einfluss der ANTI-FLAG-TAG-Ankopplung ist gering, da der Unterschied in der Hydrophilie zwischen Polymer II und FLAG-TAG bzw. ANTI-FLAG-TAG zu gering ist. F{\"u}r die Untersuchungen mit Polymer III-Elektroden wurde neben dem hydrophilen FLAG-TAG-Peptid das deutlich hydrophobere HA-TAG-Peptid ausgew{\"a}hlt. Wie im Falle der Polymer II Elektrode beeinflusst das gekoppelte FLAG-TAG-Peptid das Temperaturverhalten des Polymer III-Netzwerkes nur geringf{\"u}gig. Die gemessenen Stromwerte sind geringer als bei der Polymer III-Elektrode. Das Temperaturverhalten der FLAG-TAG-Elektrode {\"a}hnelt dem der reinen Polymer III-Elektrode - die Stromwerte sinken kontinuierlich bis die Temperatur von ca. 40 °C erreicht ist, bei der ein Plateau beobachtet wird. Offensichtlich ver{\"a}ndert FLAG-TAG auch in diesem Fall nicht wesentlich die Hydrophilie des Polymer III-Netzwerkes. Das an Polymer III-Elektroden gekoppelte hydrophobe HA-TAG-Peptid beeinflusst dagegen im starken Maße den Quellzustand des Netzwerkes. Die Str{\"o}me f{\"u}r die HA-TAG-Elektroden sind deutlich geringer als die f{\"u}r die FLAG-TAG-Polymer III-Elektroden, was auf geringeren Wassergehalt und dickeren Film zur{\"u}ckzuf{\"u}hren ist. Bereits ab 30 °C erfolgt der Anstieg von Stromwerten, der bei Polymer III- bzw. bei Polymer III-FLAG-TAG-Elektroden nicht beobachtet werden kann. Das gekoppelte hydrophobe HA-TAG-Peptid verdr{\"a}ngt Wasser aus dem Polymer III-Netzwerk, was in der Stauchung des Films bereits bei Raumtemperatur resultiert. Dies f{\"u}hrt dazu, dass der Film im Laufe des Temperaturanstieges kaum noch komprimiert. Die Stromwerte steigen in diesem Fall entsprechend des Anstiegs der temperaturabh{\"a}ngigen Diffusion des Redoxpaares. Diese Untersuchungen zeigen, dass das HA-TAG-Peptid als Ankermolek{\"u}l deutlich besser f{\"u}r eine potentielle Verwendung der Polymer III-Filme f{\"u}r sensorische Zwecke geeignet ist, da es sich deutlich in der Hydrophilie von Polymer III unterscheidet.}, language = {de} } @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} } @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} } @misc{BehrendtSchlaad2016, author = {Behrendt, Felix Nicolas and Schlaad, Helmut}, title = {Metathesis polymerization of cystine-based macrocycles}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395080}, pages = {4}, year = {2016}, abstract = {Macrocycles based on L-cystine were synthesized by ring-closing metathesis (RCM) and subsequently polymerized by entropy-driven ring-opening metathesis polymerization (ED-ROMP). Monomer conversion reached ∼80\% in equilibrium and the produced poly(ester-amine-disulfide-alkene)s exhibited apparent molar masses (Mappw) of up to 80 kDa and dispersities (Đ) of ∼2. The polymers can be further functionalized with acid anhydrides and degraded by reductive cleavage of the main-chain disulfide.}, language = {en} } @misc{HoogenboomSchlaad2016, author = {Hoogenboom, Richard and Schlaad, Helmut}, title = {Thermoresponsive poly(2-oxazoline)s, polypeptoids, and polypeptides}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395022}, pages = {17}, year = {2016}, abstract = {This review covers the recent advances in the emerging field of thermoresponsive polyamides or polymeric amides, i.e., poly(2-oxazoline)s, polypeptoids, and polypeptides, with a specific focus on structure-thermoresponsive property relationships, self-assembly, and applications.}, 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} } @misc{RasovicBlagojevicBaranacStojanovicetal.2016, author = {Rasovic, Aleksandar and Blagojevic, Vladimir and Baranac-Stojanovic, Marija and Kleinpeter, Erich and Markovic, Rade and Minic, Dragica M.}, title = {Quantification of the push-pull effect in 2-alkylidene-4-oxothiazolidines by using NMR spectral data and barriers to rotation around the C=C bond}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394523}, pages = {6364 -- 6373}, year = {2016}, abstract = {Information about the strength of donor-acceptor interactions in push-pull alkenes is valuable, as this so-called "push-pull effect" influences their chemical reactivity and dynamic behaviour. In this paper, we discuss the applicability of NMR spectral data and barriers to rotation around the C[double bond, length as m-dash]C double bond to quantify the push-pull effect in biologically important 2-alkylidene-4-oxothiazolidines. While olefinic proton chemical shifts and differences in 13C NMR chemical shifts of the two carbons constituting the C[double bond, length as m-dash]C double bond fail to give the correct trend in the electron withdrawing ability of the substituents attached to the exocyclic carbon of the double bond, barriers to rotation prove to be a reliable quantity in providing information about the extent of donor-acceptor interactions in the push-pull systems studied. In particular all relevant kinetic data, that is the Arrhenius parameters (apparent activation energy Ea and frequency factor A) and activation parameters (ΔS‡, ΔH‡ and ΔG‡), were determined from the data of the experimentally studied configurational isomerization of (E)-9a. These results were compared to previously published related data for other two compounds, (Z)-1b and (2E,5Z)-7, showing that experimentally determined ΔG‡ values are a good indicator of the strength of push-pull character. Theoretical calculations of the rotational barriers of eight selected derivatives excellently correlate with the calculated C[double bond, length as m-dash]C bond lengths and corroborate the applicability of ΔG‡ for estimation of the strength of the push-pull effect in these and related systems.}, language = {en} } @phdthesis{Wei2016, author = {Wei, Chunxiang}, title = {On the role of monomer drops and swelling in aqueous heterophase polymerization}, school = {Universit{\"a}t Potsdam}, pages = {122}, year = {2016}, language = {en} } @misc{WirthKirschWlosczyketal.2016, author = {Wirth, Jonas and Kirsch, Harald and Wlosczyk, Sebastian and Tong, Yujin and Saalfrank, Peter and Kramer Campen, Richard}, title = {Characterization of water dissociation on α-Al2O3(1102)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394497}, pages = {14822 -- 14832}, year = {2016}, abstract = {The interaction of water with α-alumina (i.e. α-Al2O3) surfaces is important in a variety of applications and a useful model for the interaction of water with environmentally abundant aluminosilicate phases. Despite its significance, studies of water interaction with α-Al2O3 surfaces other than the (0001) are extremely limited. Here we characterize the interaction of water (D2O) with a well defined α-Al2O3(1[1 with combining macron]02) surface in UHV both experimentally, using temperature programmed desorption and surface-specific vibrational spectroscopy, and theoretically, using periodic-slab density functional theory calculations. This combined approach makes it possible to demonstrate that water adsorption occurs only at a single well defined surface site (the so-called 1-4 configuration) and that at this site the barrier between the molecularly and dissociatively adsorbed forms is very low: 0.06 eV. A subset of OD stretch vibrations are parallel to this dissociation coordinate, and thus would be expected to be shifted to low frequencies relative to an uncoupled harmonic oscillator. To quantify this effect we solve the vibrational Schr{\"o}dinger equation along the dissociation coordinate and find fundamental frequencies red-shifted by more than 1500 cm-1. Within the context of this model, at moderate temperatures, we further find that some fraction of surface deuterons are likely delocalized: dissociatively and molecularly absorbed states are no longer distinguishable.}, 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} } @misc{WessigHilleKumkeetal.2016, author = {Wessig, Pablo and Hille, Carsten and Kumke, Michael Uwe and Meiling, Till Thomas and Behrends, Nicole and Eisold, Ursula}, title = {Two-photon FRET pairs based on coumarin and DBD dyes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394445}, pages = {33510 -- 33513}, year = {2016}, abstract = {The synthesis and photophysical properties of two new FRET pairs based on coumarin as a donor and DBD dye as an acceptor are described. The introduction of a bromo atom dramatically increases the two-photon excitation (2PE) cross section providing a 2PE-FRET system, which is also suitable for 2PE-FLIM.}, language = {en} } @misc{LiebigSarhanPrietzeletal.2016, author = {Liebig, Ferenc and Sarhan, Radwan Mohamed and Prietzel, Claudia Christina and Reinecke, Antje and Koetz, Joachim}, title = {"Green" gold nanotriangles: synthesis, purification by polyelectrolyte/micelle depletion flocculation and performance in surface-enhanced Raman scattering}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394430}, pages = {33561 -- 33568}, year = {2016}, abstract = {The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs. Negatively charged vesicles containing AOT and phospholipids, in the absence and presence of additional reducing agents (polyampholytes, polyanions or low molecular weight compounds), were used as a template phase to form anisotropic gold nanoparticles. Upon addition of the gold chloride solution, the nucleation process is initiated and both types of particles, i.e., isotropic spherical and anisotropic gold nanotriangles, are formed simultaneously. As it was not possible to produce monodisperse nanotriangles with such a one-step procedure, the anisotropic nanoparticles needed to be separated from the spherical ones. Therefore, a new type of separation procedure using combined polyelectrolyte/micelle depletion flocculation was successfully applied. As a result of the different purification steps, a green colored aqueous dispersion was obtained containing highly purified, well-defined negatively charged flat nanocrystals with a platelet thickness of 10 nm and an edge length of about 175 nm. The NTs produce promising results in surface-enhanced Raman scattering.}, language = {en} } @misc{PacholskiAgarwalBalderasValadez2016, author = {Pacholski, Claudia and Agarwal, Vivechana and Balderas-Valadez, Ruth Fabiola}, title = {Fabrication of porous silicon-based optical sensors using metal-assisted chemical etching}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394426}, pages = {21430 -- 21434}, year = {2016}, abstract = {Optical biosensors based on porous silicon were fabricated by metal assisted chemical etching. Thereby double layered porous silicon structures were obtained consisting of porous pillars with large pores on top of a porous silicon layer with smaller pores. These structures showed a similar sensing performance in comparison to electrochemically produced porous silicon interferometric sensors.}, language = {en} } @misc{EhlertHolzweberLippitzetal.2016, author = {Ehlert, Christopher and Holzweber, Markus and Lippitz, Andreas and Unger, Wolfgang E. S. and Saalfrank, Peter}, title = {A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394417}, pages = {8654 -- 8661}, year = {2016}, abstract = {In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([CnC1im]+[NTf2]- and [C4C1im]+[I]-). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.}, language = {en} } @phdthesis{Ehlert2016, author = {Ehlert, Christopher}, title = {Simulationen von R{\"o}ntgenabsorptionsprozessen zur Charakterisierung von Systemen in kondensierter Phase}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-104844}, school = {Universit{\"a}t Potsdam}, pages = {142}, year = {2016}, abstract = {Die vorgelegte Dissertation pr{\"a}sentiert wissenschaftliche Ergebnisse, die in der Zeit vom Dezember 2012 bis August 2016, erarbeitet wurden. Der zentrale Inhalt der Arbeit ist die Simulation von R{\"o}ntgenabsorptionsprozessen von verschiedenen Systemen in kondensierter Phase. Genauer gesagt, werden Nahkantenabsorptions- (NEXAFS) sowie R{\"o}ntgenphotoelektronenspektren (XPS) berechnet. In beiden F{\"a}llen wird ein R{\"o}ntgenphoton von einem molekularen System absorbiert. Aufgrund der hohen Photonenenergie wird ein stark gebundenes kernnahes Elektron angeregt. Bei der XPS gelangt dieses mit einer zu messenden kinetischen Energie in Kontinuumszust{\"a}nde. In Abh{\"a}ngigkeit der eingestrahlten Photonenenergie und der kinetischen Energie des austreten Elektrons, kann die Bindungsenergie berechnet werden, welche die zentrale Gr{\"o}ße der XPS ist. Im Falle der NEXAFS-Spektroskopie wird das kernnahe Elektron in unbesetzte gebundene Zust{\"a}nde angeregt. Die zentrale Gr{\"o}ße ist die Absorption als Funktion der eingestrahlten Photonenenergie. Das erste Kapitel meiner Arbeit er{\"o}rtert detailliert die experimentellen Methoden sowie die daraus gewonnenen charakteristischen Gr{\"o}ßen. Die experimentellen Spektren zeigen oft viele Resonanzen, deren Interpretation aufgrund fehlender Referenzmaterialien schwierig ist. In solchen F{\"a}llen bietet es sich an, die Spektren mittels quantenchemischer Methoden zu simulieren. Der daf{\"u}r erforderliche mathematisch-physikalische Methodenkatalog wird im zweiten Kapitel der Arbeit er{\"o}rtert. Das erste von mir untersuchte System ist Graphen. In experimentellen Arbeiten wurde die Oberfl{\"a}che mittels Bromplasma modifiziert. Die im Anschluss gemessenen NEXAFS-Spektren unterscheiden sich maßgeblich von den Spektren der unbehandelten Oberfl{\"a}che. Mithilfe periodischer DFT-Rechnungen wurden verschiedene Gitterdefekte sowie bromierte Systeme untersucht und die NEXAFS-Spektren simuliert. Mittels der Simulationen k{\"o}nnen die Beitr{\"a}ge verschiedener Anregungszentren analysiert werden. Die Berechnungen erlauben den Schluss, dass Gitterdefekte maßgeblich f{\"u}r die entstandenen Ver{\"a}nderungen verantwortlich sind. Polyvinylalkohol (PVA) wurde als zweites System behandelt. Hierbei sollte untersucht werden, wie groß der Einfluss der Molekularbewegung auf die Verbreiterung der Peaks im XP-Spektrum ist. Des Weiteren wurde untersucht, wie groß der Einfluss von intermolekularen Wechselwirkungen auf die Peakpositionen und Peakverbreiterung ist. F{\"u}r die Berechnung dieses Systems wurde eine Kombination aus molekulardynamischen und quantenchemischen Methoden verwendet. Als Strukturen dienten Oligomermodelle, die unter dem Einfluss eines (ab initio) Potentials propagiert wurden. Entlang der erstellten Trajektorie wurden Schnappsch{\"u}sse der Geometrien extrahiert und f{\"u}r die Berechnung der XP-Spektren verwendet. Die Spektren werden bereits mithilfe klassischer Molekulardynamik sehr gut reproduziert. Die erhaltenen Peakbreiten sind verglichen mit dem Experiment allerdings zu klein. Die Hauptursache der Peakverbreiterung ist die Molekularbewegung. Intermolekulare Wechselwirkungen verschieben die Peakpositionen um 0.6 eV zu kleineren Anregungsenergien. Im dritten Teil der Arbeit stehen die NEXAFS-Spektren von ionischen Fl{\"u}ssigkeiten (ILs) im Fokus. Die experimentell gefundenen Spektren zeigen eine komplexe Struktur mit vielen Resonanzen. In der Arbeit wurden zwei ILs untersucht. Als Geometrien verwenden wir Clustermodelle, die aus experimentellen Kristallstrukturen extrahiert wurden. Die berechneten Spektren erlauben es, die Resonanzen den Anregungszentren zuzuordnen. Außerdem kann eine erstmals gemessene Doppelresonanz simuliert und erkl{\"a}rt werden. Insgesamt kann die Interpretation der Spektren mithilfe der Simulation signifikant erweitert werden. In allen Systemen wurde zur Berechnung des NEXAFS-Spektrums eine auf Dichtefunktionaltheorie basierende Methode verwendet (die sogenannte Transition-Potential Methode). G{\"a}ngige wellenfunktionsbasierte Methoden, wie die Konfigurationswechselwirkung mit Einfachanregungen (CIS), zeigen eine starke Blauverschiebung, wenn als Referenz eine Hartree-Fock Slaterdeterminante verwendet wird. Wir zeigen, dass die Verwendung von kernnah-angeregten Determinanten sowohl das resultierende Spektrum als auch die Anregungsenergien deutlich verbessert. Des Weiteren werden auch Referenzen aus Dichtefunktionalrechnungen getestet. Zus{\"a}tzlich werden auch Referenzen mit gebrochenen Besetzungszahlen f{\"u}r kernnahe Elektronen verwendet. In der Arbeit werden die Resultate der verschiedenen Referenzen miteinander verglichen. Es zeigt sich, dass Referenzen mit gebrochenen Besetzungszahlen das Spektrum nicht weiter verbessern. Der Einfluss der verwendeten Elektronenstrukturmethode ist eher gering.}, language = {de} } @phdthesis{Prinz2016, author = {Prinz, Julia}, title = {DNA origami substrates as a versatile tool for surface-enhanced Raman scattering (SERS)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-104089}, school = {Universit{\"a}t Potsdam}, pages = {xviii, 184 Seiten}, year = {2016}, abstract = {Surface-enhanced Raman scattering (SERS) is a promising tool to obtain rich chemical information about analytes at trace levels. However, in order to perform selective experiments on individual molecules, two fundamental requirements have to be fulfilled. On the one hand, areas with high local field enhancement, so-called "hot spots", have to be created by positioning the supporting metal surfaces in close proximity to each other. In most cases hot spots are formed in the gap between adjacent metal nanoparticles (NPs). On the other hand, the analyte has to be positioned directly in the hot spot in order to profit from the highest signal amplification. The use of DNA origami substrates provides both, the arrangement of AuNPs with nm precision as well as the ability to bind analyte molecules at predefined positions. Consequently, the present cumulative doctoral thesis aims at the development of a novel SERS substrate based on a DNA origami template. To this end, two DNA-functionalized gold nanoparticles (AuNPs) are attached to one DNA origami substrate resulting in the formation of a AuNP dimer and thus in a hot spot within the corresponding gap. The obtained structures are characterized by correlated atomic force microscopy (AFM) and SERS imaging which allows for the combination of structural and chemical information. Initially, the proof-of principle is presented which demonstrates the potential of the novel approach. It is shown that the Raman signal of 15 nm AuNPs coated with dye-modified DNA (dye: carboxytetramethylrhodamine (TAMRA)) is significantly higher for AuNP dimers arranged on a DNA origami platform in comparison to single AuNPs. Furthermore, by attaching single TAMRA molecules in the hot spot between two 5 nm AuNPs and optimizing the size of the AuNPs by electroless gold deposition, SERS experiments at the few-molecule level are presented. The initially used DNA origami-AuNPs design is further optimized in many respects. On the one hand, larger AuNPs up to a diameter of 60 nm are used which are additionally treated with a silver enhancement solution to obtain Au-Ag-core-shell NPs. On the other hand, the arrangement of both AuNPs is altered to improve the position of the dye molecule within the hot spot as well as to decrease the gap size between the two particles. With the optimized design the detection of single dye molecules (TAMRA and cyanine 3 (Cy3)) by means of SERS is demonstrated. Quantitatively, enhancement factors up to 10^10 are estimated which is sufficiently high to detect single dye molecules. In the second part, the influence of graphene as an additional component of the SERS substrate is investigated. Graphene is a two-dimensional material with an outstanding combination of electronical, mechanical and optical properties. Here, it is demonstrated that single layer graphene (SLG) replicates the shape of underlying non-modified DNA origami substrates very well, which enables the monitoring of structural alterations by AFM imaging. In this way, it is shown that graphene encapsulation significantly increases the structural stability of bare DNA origami substrates towards mechanical force and prolonged exposure to deionized water. Furthermore, SLG is used to cover DNA origami substrates which are functionalized with a 40 nm AuNP dimer. In this way, a novel kind of hybrid material is created which exhibits several advantages compared to the analogue non-covered SERS substrates. First, the fluorescence background of dye molecules that are located in between the AuNP surface and SLG is efficiently reduced. Second, the photobleaching rate of the incorporated dye molecules is decreased up to one order of magnitude. Third, due to the increased photostability of the investigated dye molecules, the performance of polarization-dependent series measurements on individual structures is enabled. This in turn reveals extensive information about the dye molecules in the hot spot as well as about the strain induced within the graphene lattice. Although SLG can significantly influence the SERS substrate in the aforementioned ways, all those effects are strongly related to the extent of contact with the underlying AuNP dimer.}, language = {en} } @phdthesis{Leiendecker2016, author = {Leiendecker, Mai-Thi}, title = {Physikalische Hydrogele auf Polyurethan-Basis}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-103917}, school = {Universit{\"a}t Potsdam}, pages = {109}, year = {2016}, abstract = {Physical hydrogels have gained recent attention as cell substrates, since viscoelasticity or stress relaxation is a powerful parameter in mechanotransduction, which has long been neglected. We designed multi-functional polyurethanes to form physical hydrogels via a unique tunable gelation mechanism. The anionic polyurethanes spontaneously form aggregates in water that are kept in a soluble state through electrostatic repulsion. Fast subsequent gelation can be triggered by charge shielding which allows the aggregation and network building to proceed. This can be induced by adding either acids or salts, resulting in acidic (pH 4-5) or pH-neutral hydrogels, respectively. Whereas conventional polyurethane-based hydrogels are commonly prepared from toxic isocyanate precursors, the physical hydrogelation mechanism described here does not involve chemically reactive species which is ideal for in situ applications in sensitive environments. Both stiffness and stress relaxation can be tuned independently over a broad range and the gels exhibit excellent stress recovery behavior.}, language = {de} } @phdthesis{Koenig2016, author = {K{\"o}nig, Jana}, title = {Synthese und Charakterisierung von 3d-4f-Komplexen und deren Vorl{\"a}ufer mit 1,2-Dithiooxalat als Ligand}, school = {Universit{\"a}t Potsdam}, pages = {89, LXIX}, year = {2016}, language = {de} }