@article{WangRazzaqRudolphetal.2018, author = {Wang, Li and Razzaq, Muhammad Yasar and Rudolph, Tobias and Heuchel, Matthias and N{\"o}chel, Ulrich and Mansfeld, Ulrich and Jiang, Yi and Gould, Oliver E. C. and Behl, Marc and Kratz, Karl and Lendlein, Andreas}, title = {Reprogrammable, magnetically controlled polymeric nanocomposite actuators}, series = {Material horizons}, volume = {5}, journal = {Material horizons}, number = {5}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2051-6347}, doi = {10.1039/c8mh00266e}, pages = {861 -- 867}, year = {2018}, abstract = {Soft robots and devices with the advanced capability to perform adaptive motions similar to that of human beings often have stimuli-sensitive polymeric materials as the key actuating component. The external signals triggering the smart polymers' actuations can be transmitted either via a direct physical connection between actuator and controlling unit (tethered) or remotely without a connecting wire. However, the vast majority of such polymeric actuator materials are limited to one specific type of motion as their geometrical information is chemically fixed. Here, we present magnetically driven nanocomposite actuators, which can be reversibly reprogrammed to different actuation geometries by a solely physical procedure. Our approach is based on nanocomposite materials comprising spatially segregated crystallizable actuation and geometry determining units. Upon exposure to a specific magnetic field strength the actuators' geometric memory is erased by the melting of the geometry determining units allowing the implementation of a new actuator shape. The actuation performance of the nanocomposites can be tuned and the technical significance was demonstrated in a multi-cyclic experiment with several hundreds of repetitive free-standing shape shifts without losing performance.}, language = {en} } @article{YangHuDingetal.2018, author = {Yang, Guang and Hu, Rongting and Ding, Hong-ming and Kochovski, Zdravko and Mei, Shilin and Lu, Yan and Ma, Yu-qiang and Chen, Guosong and Jiang, Ming}, title = {CO2-switchable response of protein microtubules}, series = {Materials chemistry frontiers}, volume = {2}, journal = {Materials chemistry frontiers}, number = {9}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2052-1537}, doi = {10.1039/c8qm00245b}, pages = {1642 -- 1646}, year = {2018}, abstract = {Recently, we proposed a small molecular inducing ligand strategy to assemble proteins into highly-ordered structures via dual non-covalent interactions, i.e. carbohydrate-protein interaction and dimerization of Rhodamine B. Using this approach, artificial protein microtubules were successfully constructed. In this study, we find that these microtubules exhibit a perfect CO2 responsiveness; assembly and disassembly of these microtubules were nicely controlled by the alternative passage of CO2 and N-2. Upon the injection of CO2, a negative net-charged SBA turns into a neutral or positive net-charged SBA, which elongated, to some extent, the effective distance between SBA and Rhodamine B, resulting in the disassociation of the Rhodamine B dimer. Further experimental and simulation results reveal that the CO2-responsive mechanism differs from that of solubility change of the previously reported CO2-responsive synthetic materials.}, language = {en} } @article{HoangHaubitzKumke2018, author = {Hoang, Hoa T. and Haubitz, Toni and Kumke, Michael Uwe}, title = {Photophysics of "Floppy" Dyadsas Potential Biomembrane Probes}, series = {Journal of fluorescence}, volume = {28}, journal = {Journal of fluorescence}, number = {5}, publisher = {Springer}, address = {New York}, issn = {1053-0509}, doi = {10.1007/s10895-018-2286-4}, pages = {1225 -- 1237}, year = {2018}, abstract = {In the study a dyad (C6 probe), constructed of two dyes with highly different hydrophobicities, was investigated by steady-state and time-resolved spectroscopic techniques in chloroform, methanol, and in phospholipid vesicles, respectively. The dyad was built on two dyes: the lipophilic benzo[a]pyrene (BaP) and the hydrophilic sulforhodamine B (SRB). The dyes were linked via a short, but flexible alkyl chain (six C-atoms). Based on their spectroscopic properties, BaP and SRB showed a very efficient non-radiative resonance energy transfer in solution. Incorporation into a lipid bilayer limited the relative flexibility (degree of freedom) between donor and acceptor and was used for the investigation of fundamental photophysical aspects (especially of FRET) as well as to elucidate the potential of the dyad to probe the interface of vesicles (or cells). The location of the two dyes in vesicles and their respective accessibility for interactions with dye-specific antibodies was investigated. Based on the alteration of the anisotropy, on the rotational correlation time as well as on the diffusion coefficient the incorporation of the C6 probe into the vesicles was evaluated. Especially the limitation in the relative movements of the two dyes was considered and used to differentiate between potential parameters, that influence the energy transfer in the dyad. Transient absorption spectroscopy (TAS) and pulsed-interleave single molecule fluorescence experiments were performed to better understand the intramolecular interactions in the dyad. Finally, in a showcase for a biosensing application of the dyads, the binding of an SRB-specific antibody was investigated when the dyad was incorporated in vesicles.}, language = {en} } @article{SchulzeWehrholdHille2018, author = {Schulze, Sven and Wehrhold, Michel and Hille, Carsten}, title = {Femtosecond-Pulsed laser written and etched fiber bragg gratings for fiber-optical biosensing}, series = {Sensors}, volume = {18}, journal = {Sensors}, number = {9}, publisher = {MDPI}, address = {Basel}, issn = {1424-8220}, doi = {10.3390/s18092844}, pages = {20}, year = {2018}, abstract = {We present the development of a label-free, highly sensitive fiber-optical biosensor for online detection and quantification of biomolecules. Here, the advantages of etched fiber Bragg gratings (eFBG) were used, since they induce a narrowband Bragg wavelength peak in the reflection operation mode. The gratings were fabricated point-by-point via a nonlinear absorption process of a highly focused femtosecond-pulsed laser, without the need of prior coating removal or specific fiber doping. The sensitivity of the Bragg wavelength peak to the surrounding refractive index (SRI), as needed for biochemical sensing, was realized by fiber cladding removal using hydrofluoric acid etching. For evaluation of biosensing capabilities, eFBG fibers were biofunctionalized with a single-stranded DNA aptamer specific for binding the C-reactive protein (CRP). Thus, the CRP-sensitive eFBG fiber-optical biosensor showed a very low limit of detection of 0.82 pg/L, with a dynamic range of CRP detection from approximately 0.8 pg/L to 1.2 mu g/L. The biosensor showed a high specificity to CRP even in the presence of interfering substances. These results suggest that the proposed biosensor is capable for quantification of CRP from trace amounts of clinical samples. In addition, the adaption of this eFBG fiber-optical biosensor for detection of other relevant analytes can be easily realized.}, language = {en} } @article{PereiraZehbeGuenteretal.2018, author = {Pereira, Rui F. P. and Zehbe, Kerstin and G{\"u}nter, Christina and dos Santos, Tiago and Nunes, Silvia C. and Almeida Paz, Filipe A. and Silva, Maria M. and Granja, Pedro L. and Taubert, Andreas and de Zea Bermudez, Ver{\´o}nica}, title = {Ionic liquid-assisted synthesis of mesoporous silk fibroin/silica hybrids for biomedical applications}, series = {ACS Omega}, volume = {3}, journal = {ACS Omega}, number = {9}, publisher = {American Chemical Society}, address = {Washington}, issn = {2470-1343}, doi = {10.1021/acsomega.8b02051}, pages = {10811 -- 10822}, year = {2018}, abstract = {New mesoporous silk fibroin (SF)/silica hybrids were processed via a one-pot soft and energy-efficient sol-gel chemistry and self-assembly from a silica precursor, an acidic or basic catalyst, and the ionic liquid 1-butyl-3-methylimidazolium chloride, acting as both solvent and mesoporosity-inducer. The as-prepared materials were obtained as slightly transparent-opaque, amorphous monoliths, easily transformed into powders, and stable up to ca. 300 degrees C. Structural data suggest the formation of a hexagonal mesostructure with low range order and apparent surface areas, pore volumes, and pore radii of 205-263 m(2) g(-1), 0.16-0.19 cm(3) g(-1), and 1.2-1.6 nm, respectively. In all samples, the dominating conformation of the SF chains is the beta-sheet. Cytotoxicity/bioactivity resazurin assays and fluorescence microscopy demonstrate the high viability of MC3T3 pre-osteoblasts to indirect (>= 99 +/- 9\%) and direct (78 +/- 2 to 99 +/- 13\%) contact with the SF/silica materials. Considering their properties and further improvements, these systems are promising candidates to be explored in bone tissue engineering. They also offer excellent prospects as electrolytes for solid-state electrochemical devices, in particular for fuel cells.}, language = {en} } @article{HaubitzTsushimaSteudtneretal.2018, author = {Haubitz, Toni and Tsushima, Satoru and Steudtner, Robin and Drobot, Bj{\"o}rn and Geipel, Gerhard and Stumpf, Thorsten and Kumke, Michael Uwe}, title = {Ultrafast Transient Absorption Spectroscopy of UO(2)(2+)and [UO2Cl](+)}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {122}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {35}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.8b05567}, pages = {6970 -- 6977}, year = {2018}, abstract = {For the only water coordinated "free" uranyl (VI) aquo ion in perchlorate solution we identified and assigned several different excited states and showed that the (3)Delta state is the luminescent triplet state from transient absorption spectroscopy. With additional data from other spectroscopic methods (TRLFS, UV/vis) we generated a detailed Jablonski diagram and determined rate constants for several state transitions, like the inner conversion rate constant from the (3)Phi state to the (3)Delta state transition to be 0.35 ps(-1). In contrast to luminescence measurements, it was possible to observe the highly quenched uranyl(VI) ion in highly concentrated chloride solution by TAS and we were able to propose a dynamic quenching mechanism, where chloride complexation is followed by the charge transfer from the excited state uranyl(VI) to chloride. This proposed quenching route is supported by TD-DFT calculations.}, language = {en} } @article{SenfRuprechtKishanietal.2018, author = {Senf, Deborah and Ruprecht, Colin and Kishani, Saina and Matic, Aleksandar and Toriz, Guillermo and Gatenholm, Paul and Wagberg, Lars and Pfrengle, Fabian}, title = {Tailormade polysaccharides with defined branching patterns}, series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, volume = {57}, journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, number = {37}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1433-7851}, doi = {10.1002/anie.201806871}, pages = {11987 -- 11992}, year = {2018}, abstract = {The heterogeneous nature of non-cellulosic polysaccharides, such as arabinoxylan, makes it difficult to correlate molecular structure with macroscopic properties. To study the impact of specific structural features of the polysaccharides on crystallinity or affinity to other cell wall components, collections of polysaccharides with defined repeating units are required. Herein, a chemoenzymatic approach to artificial arabinoxylan polysaccharides with systematically altered branching patterns is described. The polysaccharides were obtained by glycosynthase-catalyzed polymerization of glycosyl fluorides derived from arabinoxylan oligosaccharides. X-ray diffraction and adsorption experiments on cellulosic surfaces revealed that the physicochemical properties of the synthetic polysaccharides strongly depend on the specific nature of their substitution patterns. The artificial polysaccharides allow structure-property relationship studies that are not accessible by other means.}, language = {en} } @article{UchidaBinetAroraetal.2018, author = {Uchida, Ryusuke and Binet, Silvia and Arora, Neha and Jacopin, Gwenole and Alotaibi, Mohammad Hayal and Taubert, Andreas and Zakeeruddin, Shaik Mohammed and Dar, M. Ibrahim and Graetzel, Michael}, title = {Insights about the Absence of Rb Cation from the 3D Perovskite Lattice}, series = {Small}, volume = {14}, journal = {Small}, number = {36}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1613-6810}, doi = {10.1002/smll.201802033}, pages = {7}, year = {2018}, abstract = {Efficiencies >20\% are obtained from the perovskite solar cells (PSCs) employing Cs+ and Rb+ based perovskite compositions; therefore, it is important to understand the effect of these inorganic cations specifically Rb+ on the properties of perovskite structures. Here the influence of Cs+ and Rb+ is elucidated on the structural, morphological, and photophysical properties of perovskite structures and the photovoltaic performances of resulting PSCs. Structural, photoluminescence (PL), and external quantum efficiency studies establish the incorporation of Cs+ (x < 10\%) but amply rule out the possibility of Rb-incorporation into the MAPbI(3) (MA = CH3NH3+) lattice. Moreover, morphological studies and time-resolved PL show that both Cs+ and Rb+ detrimentally affect the surface coverage of MAPbI(3) layers and charge-carrier dynamics, respectively, by influencing nucleation density and by inducing nonradiative recombination. In addition, differential scanning calorimetry shows that the transition from orthorhombic to tetragonal phase occurring around 160 K requires more thermal energy for the Cs-containing MAPbI(3) systems compared to the pristine MAPbI(3). Investigation including mixed halide (I/Br) and mixed cation A-cation based compositions further confirms the absence of Rb+ from the 3D-perovskite lattice. The fundamental insights gained through this work will be of great significance to further understand highly promising perovskite compositions.}, language = {en} } @article{VacogneWeiTaueretal.2018, author = {Vacogne, Charlotte Dominique and Wei, Chunxiang and Tauer, Klaus and Schlaad, Helmut}, title = {Self-assembly of alpha-helical polypeptides into microscopic and enantiomorphic spirals}, series = {Journal of the american chemical society}, volume = {140}, journal = {Journal of the american chemical society}, number = {36}, publisher = {American Chemical Society}, address = {Washington}, issn = {0002-7863}, doi = {10.1021/jacs.8b06503}, pages = {11387 -- 11394}, year = {2018}, abstract = {Helical structures are ubiquitous in biological materials and often serve a structural purpose. Bioinspired helical materials can be challenging to synthesize and rarely reach the degree of hierarchy of their natural counterparts. Here we report the first example of particles synthesized by direct emulsification of polypeptides found to display spiral morphologies in the dry state. The polypeptides were alpha-helical homo- and copolypeptides of gamma-benzyl glutamate and allylglycine. The chirality of the spirals was controlled by the chirality of the alpha-helices. Notably, right-handed alpha-helical polypeptides (rich in 1, residues) produced clockwise spirals, whereas left-handed alpha-helical polypeptides (rich in D residues) produced the enantiomorphs, i.e., counterclockwise spirals. The disruption of the alpha-helical conformation by the introduction of chiral defects led to less regular spirals and in some cases their suppression. A hypothesis for the transmission of helicity and chirality from a molecular to a higher hierarchical level, involving fibril bundling of coiled alpha-helices, is proposed.}, language = {en} } @article{TanLiuSiemensmeyeretal.2018, author = {Tan, Li and Liu, Bing and Siemensmeyer, Konrad and Glebe, Ulrich and B{\"o}ker, Alexander}, title = {Synthesis of thermo-responsive nanocomposites of superparamagnetic cobalt nanoparticlesipoly(N-isopropylacrylamide)}, series = {Journal of colloid and interface science}, volume = {526}, journal = {Journal of colloid and interface science}, publisher = {Elsevier}, address = {San Diego}, issn = {0021-9797}, doi = {10.1016/j.jcis.2018.04.074}, pages = {124 -- 134}, year = {2018}, abstract = {Novel nanocomposites of superparamagnetic cobalt nanoparticles (Co NPs) and poly(N-isopropylacrylamide) (PNIPAM) were fabricated through surface-initiated atom-transfer radical polymerization (SI-ATRP). We firstly synthesized a functional ATRP initiator, containing an amine (as anchoring group) and a 2-bromopropionate group (SI-ATRP initiator). Oleic acid- and trioctylphosphine oxide-coated Co NPs were then modified with the initiator via ligand exchange. The process is facile and rapid for efficient surface functionalization and afterwards the Co NPs can be dispersed into polar solvent DMF without aggregation. Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and dynamic light scattering measurements confirmed the success of ligand exchange. The following polymerization of NIPAM was conducted on the surface of Co NPs. Temperature-dependent dynamic light scattering study showed the responsive behavior of PNIPAM-coated Co NPs. The combination of superparamagnetic and thermo-responsive properties in these hybrid nanoparticles is promising for future applications e.g. in biomedicine. (C) 2018 Elsevier Inc. All rights reserved.}, language = {en} } @article{CherstvyNagelBetaetal.2018, author = {Cherstvy, Andrey G. and Nagel, Oliver and Beta, Carsten and Metzler, Ralf}, title = {Non-Gaussianity, population heterogeneity, and transient superdiffusion in the spreading dynamics of amoeboid cells}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {20}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {35}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c8cp04254c}, pages = {23034 -- 23054}, year = {2018}, abstract = {What is the underlying diffusion process governing the spreading dynamics and search strategies employed by amoeboid cells? Based on the statistical analysis of experimental single-cell tracking data of the two-dimensional motion of the Dictyostelium discoideum amoeboid cells, we quantify their diffusive behaviour based on a number of standard and complementary statistical indicators. We compute the ensemble- and time-averaged mean-squared displacements (MSDs) of the diffusing amoebae cells and observe a pronounced spread of short-time diffusion coefficients and anomalous MSD-scaling exponents for individual cells. The distribution functions of the cell displacements, the long-tailed distribution of instantaneous speeds, and the velocity autocorrelations are also computed. In particular, we observe a systematic superdiffusive short-time behaviour for the ensemble- and time-averaged MSDs of the amoeboid cells. Also, a clear anti-correlation of scaling exponents and generalised diffusivity values for different cells is detected. Most significantly, we demonstrate that the distribution function of the cell displacements has a strongly non-Gaussian shape andusing a rescaled spatio-temporal variablethe cell-displacement data collapse onto a universal master curve. The current analysis of single-cell motions can be implemented for quantifying diffusive behaviours in other living-matter systems, in particular, when effects of active transport, non-Gaussian displacements, and heterogeneity of the population are involved in the dynamics.}, language = {en} } @article{FudickarLinker2018, author = {Fudickar, Werner and Linker, Torsten}, title = {Release of Singlet Oxygen from Aromatic Endoperoxides by Chemical Triggers}, series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, volume = {57}, journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, number = {39}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1433-7851}, doi = {10.1002/anie.201806881}, pages = {12971 -- 12975}, year = {2018}, abstract = {The generation of reactive singlet oxygen under mild conditions is of current interest in chemistry, biology, and medicine. We were able to release oxygen from dipyridylanthracene endoperoxides (EPOs) by using a simple chemical trigger at low temperature. Protonation and methylation of such EPOs strongly accelerated these reactions. Furthermore, the methyl pyridinium derivatives are water soluble and therefore serve as oxygen carriers in aqueous media. Methylation of the EPO of the ortho isomer affords the parent form directly without increasing the temperature under very mild conditions. This exceptional behavior is ascribed to the close contact between the nitrogen atom and the peroxo group. Singlet oxygen is released upon this reaction, and can be used to oxygenate an acceptor such as tetramethylethylene in the dark with no heating. Thus, a new chemical source of singlet oxygen has been found, which is triggered by a simple stimulus.}, language = {en} } @article{FranzToebbensSteckhanetal.2018, author = {Franz, Alexandra and T{\"o}bbens, Daniel M. and Steckhan, Julia and Schorr, Susan}, title = {Determination of the miscibility gap in the solid solutions series of methylammonium lead iodide/chloride}, series = {Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials}, volume = {74}, journal = {Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials}, publisher = {International Union of Crystallography}, address = {Chester}, issn = {2052-5206}, doi = {10.1107/S2052520618010764}, pages = {445 -- 449}, year = {2018}, abstract = {Perovskites are widely known for their enormous possibility of elemental substitution, which leads to a large variety of physical properties. Hybrid perovskites such as CH3NH3PbI3 (MAPbI(3)) and CH3NH3PbCl3 (MAPbCl(3)) are perovskites with an A([XII])B([VI)X(-)([II)(])structure, where A is an organic molecule, B is a lead(II) cation and X is a halide anion of iodine or chlorine. Whereas MAPbCl(3) crystallizes in the cubic space group Pm (3) over barm, MAPbI(3) is in the tetragonal space group I4/mcm. The substitution of I by Cl leads to an increased tolerance against humidity but is challenging or even impossible due to their large difference in ionic radii. Here, the influence of an increasing Cl content in the reaction solution on the miscibility of the solid solution members is examined systematically. Powders were synthesized by two different routes depending on the I:Cl ratio. High-resolution synchrotron X-ray data are used to establish values for the limits of the miscibility gap which are 3.1 (1.1) mol\% MAPbCl(3) in MAPI(3) and 1.0 (1) mol\% MAPbI(3) in MAPCl. The establishment of relations between average pseudo-cubic lattice parameters for both phases allows a determination of the degree of substitution from the observed lattice parameters.}, language = {en} } @article{FredeSchreinerZrenneretal.2018, author = {Frede, Katja and Schreiner, Monika and Zrenner, R. and Graefe, Jan and Baldermann, Susanne}, title = {Carotenoid biosynthesis of pak choi (Brassica rapa ssp chinensis) sprouts grown under different light-emitting diodes during the diurnal course}, series = {Photochemical \& photobiological sciences}, volume = {17}, journal = {Photochemical \& photobiological sciences}, number = {10}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1474-905X}, doi = {10.1039/c8pp00136g}, pages = {1289 -- 1300}, year = {2018}, abstract = {Light-emitting diodes (LEDs) are considered the future of greenhouse lighting. This study investigates the carotenoid concentrations of pak choi sprouts after growth under blue, red and white LEDs at six different time points. Furthermore, the diurnal changes of RNA transcripts of key genes of the carotenoid biosynthesis pathway as well as of the carotenoid cleavage dioxygenase 4 (CCD4) gene and of the transcription factor genes elongated hypocotyl 5 (HY5) and circadian clock associated 1 (CCA1) were investigated. The carotenoid concentrations were steady throughout the day, but showed a small maximum in the afternoon. An average total carotenoid concentration of 536 +/- 29 ng mg(-1) DM produced under white LEDs was measured, which is comparable to previously described field-grown levels. The carotenoid concentrations were slightly lower under blue or red LEDs. Moreover, the diurnal RNA transcript rhythms of most of the carotenoid biosynthesis genes showed an increase during the light period, which can be correlated to the carotenoid maxima in the afternoon. Blue LEDs caused the highest transcriptional induction of biosynthetic genes as well as of CCD4, thereby indicating an increased flux through the pathway. In addition, the highest levels of HY5 transcripts and CCA1 transcripts were determined under blue LEDs.}, language = {en} } @article{ErlerRiebeBeitzetal.2018, author = {Erler, Alexander and Riebe, Daniel and Beitz, Toralf and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Grothusheitkamp, Daniela and Kunz, T. and Methner, Frank-J{\"u}rgen}, title = {Detection of volatile organic compounds in the headspace above mold fungi by GC-soft X-radiation-based APCI-MS}, series = {Journal of mass spectrometr}, volume = {53}, journal = {Journal of mass spectrometr}, number = {10}, publisher = {Wiley}, address = {Hoboken}, issn = {1076-5174}, doi = {10.1002/jms.4210}, pages = {911 -- 920}, year = {2018}, abstract = {Mold fungi on malting barley grains cause major economic loss in malting and brewery facilities. Possible proxies for their detection are volatile and semivolatile metabolites. Among those substances, characteristic marker compounds have to be identified for a confident detection of mold fungi in varying surroundings. The analytical determination is usually performed through passive sampling with solid phase microextraction, gas chromatographic separation, and detection by electron ionization mass spectrometry (EI-MS), which often does not allow a confident determination due to the absence of molecular ions. An alternative is GC-APCI-MS, generally, allowing the determination of protonated molecular ions. Commercial atmospheric pressure chemical ionization (APCI) sources are based on corona discharges, which are often unspecific due to the occurrence of several side reactions and produce complex product ion spectra. To overcome this issue, an APCI source based on soft X-radiation is used here. This source facilitates a more specific ionization by proton transfer reactions only. In the first part, the APCI source is characterized with representative volatile fungus metabolites. Depending on the proton affinity of the metabolites, the limits of detection are up to 2 orders of magnitude below those of EI-MS. In the second part, the volatile metabolites of the mold fungus species Aspergillus, Alternaria, Fusarium, and Penicillium are investigated. In total, 86 compounds were found with GC-EI/APCI-MS. The metabolites identified belong to the substance classes of alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, terpenes, and sesquiterpenes. In addition to substances unspecific for the individual fungus species, characteristic patterns of metabolites, allowing their confident discrimination, were found for each of the 4 fungus species. Sixty-seven of the 86 metabolites are detected by X-ray-based APCI-MS alone. The discrimination of the fungus species based on these metabolites alone was possible. Therefore, APCI-MS in combination with collision induced dissociation alone could be used as a supervision method for the detection of mold fungi.}, language = {en} } @article{PloetzMegowNiehausetal.2018, author = {Pl{\"o}tz, Per-Arno and Megow, J{\"o}rg and Niehaus, Thomas and K{\"u}hn, Oliver}, title = {All-DFTB Approach to the Parametrization of the System-Bath Hamiltonian Describing Exciton-Vibrational Dynamics of Molecular Assemblies}, series = {Journal of chemical theory and computation}, volume = {14}, journal = {Journal of chemical theory and computation}, number = {10}, publisher = {American Chemical Society}, address = {Washington}, issn = {1549-9618}, doi = {10.1021/acs.jctc.8b00493}, pages = {5001 -- 5010}, year = {2018}, abstract = {Spectral density functions are central to the simulation of complex many body systems. Their determination requires making approximations not only to the dynamics but also to the underlying electronic structure theory. Here, blending different methods bears the danger of an inconsistent description. To solve this issue we propose an all-DFTB approach to determine spectral densities for the description of Frenkel excitons in molecular assemblies. The protocol is illustrated for a model of a PTCDI crystal, which involves the calculation of monomeric excitation energies and Coulomb couplings between monomer transitions, as well as their spectral distributions due to thermal fluctuations of the nuclei. Using dynamically defined normal modes, a mapping onto the standard harmonic oscillator spectral densities is achieved.}, language = {en} } @article{TanLiuSiemensmeyeretal.2018, author = {Tan, Li and Liu, Bing and Siemensmeyer, Konrad and Glebe, Ulrich and B{\"o}ker, Alexander}, title = {Synthesis of Polystyrene-Coated Superparamagnetic and Ferromagnetic Cobalt Nanoparticles}, series = {Polymers}, volume = {10}, journal = {Polymers}, number = {10}, publisher = {MDPI}, address = {Basel}, issn = {2073-4360}, doi = {10.3390/polym10101053}, pages = {18}, year = {2018}, abstract = {Polystyrene-coated cobalt nanoparticles (NPs) were synthesized through a dual-stage thermolysis of cobalt carbonyl (Co-2(CO)(8)). The amine end-functionalized polystyrene surfactants with varying molecular weight were prepared via atom-transfer radical polymerization technique. By changing the concentration of these polymeric surfactants, Co NPs with different size, size distribution, and magnetic properties were obtained. Transmission electron microscopy characterization showed that the size of Co NPs stabilized with lower molecular weight polystyrene surfactants (M-n = 2300 g/mol) varied from 12-22 nm, while the size of Co NPs coated with polystyrene of middle (M-n = 4500 g/mol) and higher molecular weight (M-n = 10,500 g/mol) showed little change around 20 nm. Magnetic measurements revealed that the small cobalt particles were superparamagnetic, while larger particles were ferromagnetic and self-assembled into 1-D chain structures. Thermogravimetric analysis revealed that the grafting density of polystyrene with lower molecular weight is high. To the best of our knowledge, this is the first study to obtain both superparamagnetic and ferromagnetic Co NPs by changing the molecular weight and concentration of polystyrene through the dual-stage decomposition method.}, language = {en} } @article{WolffFrischmannSchulzeetal.2018, author = {Wolff, Christian Michael and Frischmann, Peter D. and Schulze, Marcus and Bohn, Bernhard J. and Wein, Robin and Livadas, Panajotis and Carlson, Michael T. and J{\"a}ckel, Frank and Feldmann, Jochen and W{\"u}rthner, Frank and Stolarczyk, Jacek K.}, title = {All-in-one visible-light-driven water splitting by combining nanoparticulate and molecular co-catalysts on CdS nanorods}, series = {Nature Energy}, volume = {3}, journal = {Nature Energy}, number = {10}, publisher = {Nature Publ. Group}, address = {London}, issn = {2058-7546}, doi = {10.1038/s41560-018-0229-6}, pages = {862 -- 869}, year = {2018}, abstract = {Full water splitting into hydrogen and oxygen on semiconductor nanocrystals is a challenging task; overpotentials must be overcome for both half-reactions and different catalytic sites are needed to facilitate them. Additionally, efficient charge separation and prevention of back reactions are necessary. Here, we report simultaneous H-2 and O-2 evolution by CdS nanorods decorated with nanoparticulate reduction and molecular oxidation co-catalysts. The process proceeds entirely without sacrificial agents and relies on the nanorod morphology of CdS to spatially separate the reduction and oxidation sites. Hydrogen is generated on Pt nanoparticles grown at the nanorod tips, while Ru(tpy)(bpy)Cl-2-based oxidation catalysts are anchored through dithiocarbamate bonds onto the sides of the nanorod. O-2 generation from water was verified by O-18 isotope labelling experiments, and time-resolved spectroscopic results confirmed efficient charge separation and ultrafast electron and hole transfer to the reaction sites. The system demonstrates that combining nanoparticulate and molecular catalysts on anisotropic nanocrystals provides an effective pathway for visible-light-driven photocatalytic water splitting.}, language = {en} } @article{QiZhangKochovskietal.2018, author = {Qi, Wenjing and Zhang, Yufei and Kochovski, Zdravko and Wang, Jue and Lu, Yan and Chen, Guosong and Jiang, Ming}, title = {Self-assembly of Human Galectin-1 via dual supramolecular interactions and its inhibition of T-cell agglutination and apoptosis}, series = {Nano Research}, volume = {11}, journal = {Nano Research}, number = {10}, publisher = {Tsinghua Univ Press}, address = {Beijing}, issn = {1998-0124}, doi = {10.1007/s12274-018-2169-7}, pages = {5566 -- 5572}, year = {2018}, abstract = {Recently, we proposed a new strategy to construct artificial plant protein assemblies, which were induced by adding a small molecule, based on dual supramolecular interactions. In this paper, we further explored this method by employing Human Galectin-1 (Gal-1) as a building block to form self-assembled microribbons. Two non-covalent interactions, including lactose-lectin binding and dimerization of Rhodamine B (RhB), induced by the small molecule ligand addition, were involved in the crosslinking of the animal protein, resulting in the formation of assemblies. By using transmission electron microscopy (TEM), cryo-electron microscopy (cryo-EM), and three-dimensional (3D) tomographic analysis, we arrived at a possible mechanistic model for the microribbon formation. Furthermore, the morphology of protein assemblies could be fine-timed by varying the incubation time, the protein/ligand ratio, and the chemical structures of ligands. Interestingly, the formation of protein microribbons successfully inhibited Gal-1 induced T-cell agglutination and apoptosis. This is because the multivalent and dynamic interactions in protein assemblies compete with the binding between Gal-1 and the glycans on cell surfaces, which suppresses the function of Gal-1 in promotion of tumor progression and metastasis.}, language = {en} } @article{DuyduBasaranAydinetal.2018, author = {Duydu, Yalcin and Basaran, Nursen and Aydin, Sevtap and Ustundag, Aylin and Yalcin, Can {\"O}zg{\"u}r and Anlar, Hatice Gul and Bacanli, Merve and Aydos, Kaan and Atabekoglu, Cem Somer and Golka, Klaus and Ickstadt, Katja and Schwerdtle, Tanja and Werner, Matthias and Meyer, S{\"o}ren and Bolt, Hermann M.}, title = {Evaluation of FSH, LH, testosterone levels and semen parameters in male boron workers under extreme exposure conditions}, series = {Archives of toxicology : official journal of EUROTOX}, volume = {92}, journal = {Archives of toxicology : official journal of EUROTOX}, number = {10}, publisher = {Springer}, address = {Heidelberg}, issn = {0340-5761}, doi = {10.1007/s00204-018-2296-7}, pages = {3051 -- 3059}, year = {2018}, abstract = {Boric acid and sodium borates are currently classified in the EU-CLP regulation as "toxic to reproduction" under "Category 1B", with hazard statement of H360FD. However, so far field studies on male reproduction in China and in Turkey could not confirm such boron-associated toxic effects. As validation by another independent study is still required, the present study has investigated possible boron-associated effects on male reproduction in workers (n = 212) under different boron exposure conditions. The mean daily boron exposure (DBE) and blood boron concentration of workers in the extreme exposure group (n = 98) were 47.17 +/- 17.47 (7.95-106.8) mg B/day and 570.6 +/- 160.1 (402.6-1100) ng B/g blood, respectively. Nevertheless, boron-associated adverse effects on semen parameters, as well as on FSH, LH and total testosterone levels were not seen, even within the extreme exposure group. With this study, a total body of evidence has accumulated that allows to conclude that male reproductive effects are not relevant to humans, under any feasible and realistic conditions of exposure to inorganic boron compounds.}, language = {en} } @article{GoldhahnSchubertSchlaadetal.2018, author = {Goldhahn, Christian and Schubert, Jonas and Schlaad, Helmut and Ferri, James K. and Fery, Andreas and Chanana, Munish}, title = {Synthesis of Metal@Protein@Polymer Nanoparticles with Distinct Interfacial and Phase Transfer Behavior}, series = {Chemistry of materials : a publication of the American Chemical Society}, volume = {30}, journal = {Chemistry of materials : a publication of the American Chemical Society}, number = {19}, publisher = {American Chemical Society}, address = {Washington}, issn = {0897-4756}, doi = {10.1021/acs.chemmater.8b02314}, pages = {6717 -- 6727}, year = {2018}, abstract = {In this study, we present a novel and facile method for the synthesis of multiresponsive plasmonic nanoparticles with an interesting interfacial behavior. We used thiol-initiated photopolymerization technique to graft poly(N-isopropylacrylamide) onto the surface of protein-coated gold nanoparticles. The combination of the protein bovine serum albumin with the thermoresponsive polymer leads to smart hybrid nanoparticles, which show a stimuli-responsive behavior of their aggregation and a precisely controllable phase transfer behavior. Three interconnected stimuli, namely, temperature, ionic strength, and pH, were identified as property tuning switches. The aggregation was completely reversible and was quantified by determining Smoluchowski's instability ratios with time-resolved dynamic light scattering. The tunable hydrophobicity via the three stimuli was used to study interfacial activity and phase transfer behavior of the nanoparticles at an octanol/water interface. Depending on the type of coating (i.e., protein or protein/polymer) as well as the three external stimuli, the nanoparticles either remained in the aqueous phase (aggregated or nonaggregated), accumulated at the oil/water interface, wet the glass wall between the glass vial and the octanol phase, or even crossed the oil/water interface. Such smart and interfacially active nanoparticles with external triggers that are capable of crossing oil/water interfaces under physiological conditions open up new avenues for a variety of applications ranging from the development of drug-delivery nanosystems across biological barriers to the preparation of new catalytic materials.}, language = {en} } @article{EhlertGuehrSaalfrank2018, author = {Ehlert, Christopher and G{\"u}hr, Markus and Saalfrank, Peter}, title = {An efficient first principles method for molecular pump-probe NEXAFS spectra}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {149}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {14}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5050488}, pages = {13}, year = {2018}, abstract = {Pump-probe near edge X-ray absorption fine structure (PP-NEXAFS) spectra of molecules offer insight into valence-excited states, even if optically dark. In PP-NEXAFS spectroscopy, the molecule is "pumped" by UV or visible light enforcing a valence excitation, followed by an X-ray "probe" exciting core electrons into (now) partially empty valence orbitals. Calculations of PP-NEXAFS have so far been done by costly, correlated wavefunction methods which are not easily applicable to medium-sized or large molecules. Here we propose an efficient, first principles method based on density functional theory in combination with the transition potential and Delta SCF methodology (TP-DFT/Delta SCF) to compute molecular ground state and PP-NEXAFS spectra. We apply the method to n ->pi* pump/O-K-edge NEXAFS probe spectroscopy of thymine (for which both experimental and other theoretical data exist) and to n -> pi* or pi -> pi* pump/N-K-edge NEXAFS probe spectroscopies of trans-and cis-azobenzene. Published by AIP Publishing.}, language = {en} } @article{SunGlebeCharanetal.2018, author = {Sun, Zhiyong and Glebe, Ulrich and Charan, Himanshu and B{\"o}ker, Alexander and Wu, Changzhu}, title = {Enzyme-Polymer Conjugates as Robust Pickering Interfacial Biocatalysts for Efficient Biotransformations and One-Pot Cascade Reactions}, series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, volume = {57}, journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, number = {42}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1433-7851}, doi = {10.1002/anie.201806049}, pages = {13810 -- 13814}, year = {2018}, abstract = {Despite the rapid development of Pickering interfacial catalysis (PIC) at liquid-liquid interfaces with chemocatalysts, the use of unstable biocatalysts at emulsion interfaces remains a technical challenge. Herein, we present a Pickering interfacial biocatalysis (PIB) platform based on robust and recyclable enzyme-polymer conjugates that act as both catalytic sites and stabilizers at the interface of Pickering emulsions. The conjugates were prepared by growing poly(N-isopropylacrylamide) on a fragile enzyme, benzaldehyde lyase, under physiological conditions. The mild in situ conjugation process preserved the enzyme structure, and the conjugates were used to emulsify a water-organic two-phase system into a stable Pickering emulsion, leading to a significantly larger interfacial area and a 270-fold improvement in catalytic performance as compared to the unemulsified two-phase system. The PIB system could be reused multiple times. Conjugates of other enzymes were also fabricated and applied for cascade reactions.}, language = {en} } @article{TurriniKroepflJensenetal.2018, author = {Turrini, Nikolaus G. and Kroepfl, Nina and Jensen, Kenneth Bendix and Reiter, Tamara C. and Francesconi, Kevin A. and Schwerdtle, Tanja and Kroutil, Wolfgang and Kuehnelt, Doris}, title = {Biosynthesis and isolation of selenoneine from genetically modified fission yeast}, series = {Metallomics : integrated biometal science}, volume = {10}, journal = {Metallomics : integrated biometal science}, number = {10}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1756-5901}, doi = {10.1039/c8mt00200b}, pages = {1532 -- 1538}, year = {2018}, abstract = {Selenoneine, a naturally occurring form of selenium, is the selenium analogue of ergothioneine, a sulfur species with health relevance not only as a purported antioxidant but likely also beyond. Selenoneine has been speculated to exhibit similar effects. To study selenoneine's health properties as well as its metabolic transformation, the pure compound is required. Chemical synthesis of selenoneine, however, is challenging and biosynthetic approaches have been sought. We herein report the biosynthesis and isolation of selenoneine from genetically modified fission yeast Schizosaccharomyces pombe grown in a medium containing sodium selenate. After cell lysis and extraction with methanol, selenoneine was purified by three consecutive preparative reversed-phase HPLC steps. The product obtained at the mg level was characterised by high resolution mass spectrometry, NMR and HPLC/ICPMS. Biosynthesis was found to be a promising alternative to chemical synthesis, and should be suitable for upscaling to produce higher amounts of this important selenium species in the future.}, language = {en} } @article{TadjoungWaffoYesildagCasertaetal.2018, author = {Tadjoung Waffo, Armel Franklin and Yesildag, Cigdem and Caserta, Giorgio and Katz, Sagie and Zebger, Ingo and Lensen, Marga C. and Wollenberger, Ulla and Scheller, Frieder W. and Altintas, Zeynep}, title = {Fully electrochemical MIP sensor for artemisinin}, series = {Sensors and actuators : B, Chemical}, volume = {275}, journal = {Sensors and actuators : B, Chemical}, publisher = {Elsevier}, address = {Lausanne}, issn = {0925-4005}, doi = {10.1016/j.snb.2018.08.018}, pages = {163 -- 173}, year = {2018}, abstract = {This study aims to develop a rapid, sensitive and cost-effective biomimetic electrochemical sensor for artemisinin determination in plant extracts and for pharmacokinetic studies. A novel molecularly imprinted polymer (MIP)based electrochemical sensor was developed by electropolymerization of o-phenylenediamine (o-PD) in the presence of artemisinin on gold wire surface for sensitive detection of artemisinin. The experimental parameters, including selection of functional monomer, polymerization conditions, template extraction after polymerization, influence of pH and buffer were all optimized. Every step of imprinted film synthesis were evaluated by employing voltammetry techniques, surface-enhanced infrared absorption spectroscopy (SEIRAS) and atomic force microscopy (AFM). The specificity was further evaluated by investigating non-specific artemisinin binding on non-imprinted polymer (NIP) surfaces and an imprinting factor of 6.8 was achieved. The artemisinin imprinted polymers using o-PD as functional monomer have provided highly stable and effective binding cavities for artemisinin. Cross-reactivity studies with drug molecules showed that the MIPs are highly specific for artemisinin. The influence of matrix effect was further investigated both in artificial plant matrix and diluted human serum. The results revealed a high affinity of artemisinin-MIP with dissociation constant of 7.3 x 10(-9) M and with a detection limit of 0.01 mu M and 0.02 mu M in buffer and plant matrix, respectively.}, language = {en} } @article{BuechnerJohnMertensetal.2018, author = {B{\"u}chner, D{\"o}rthe and John, Leonard and Mertens, Monique and Wessig, Pablo}, title = {Detection of dsDNA with [1,3]Dioxolo[4,5-f]benzodioxol (DBD) Dyes}, series = {Chemistry - a European journal}, volume = {24}, journal = {Chemistry - a European journal}, number = {60}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201804057}, pages = {16183 -- 16190}, year = {2018}, abstract = {DBD fluorescent dyes have proven to be useful in numerous applications. To widen the range of biological applications, we propose three different types of DBD molecules that have been modified in such a way that DNA interaction becomes probable. After the successful synthesis of all three compounds, we tested their fluorescent properties and their DNA binding abilities. Two of the three probes exhibit an interaction with dsDNA with subsequent fluorescence enhancement. The determined binding constants of the two new DNA dyes are comparable to other minorgroove-binding dyes. Their large Stokes shifts and their long fluorescent lifetimes are outstanding features of these dyes.}, language = {en} } @article{SchulzMehrabiMuellerWerkmeisteretal.2018, author = {Schulz, Eike C. and Mehrabi, Pedram and M{\"u}ller-Werkmeister, Henrike and Tellkamp, Friedjof and Jha, Ajay and Stuart, William and Persch, Elke and De Gasparo, Raoul and Diederich, Fran{\c{c}}ois and Pai, Emil F. and Miller, R. J. Dwayne}, title = {The hit-and-return system enables efficient time-resolved serial synchrotron crystallography}, series = {Nature methods : techniques for life scientists and chemists}, volume = {15}, journal = {Nature methods : techniques for life scientists and chemists}, number = {11}, publisher = {Nature Publishing Group (London)}, address = {London}, issn = {1548-7091}, doi = {10.1038/s41592-018-0180-2}, pages = {901 -- 904}, year = {2018}, abstract = {We present a 'hit-and-return' (HARE) method for time-resolved serial synchrotron crystallography with time resolution from milliseconds to seconds or longer. Timing delays are set mechanically, using the regular pattern in fixed-target crystallography chips and a translation stage system. Optical pump-probe experiments to capture intermediate structures of fluoroacetate dehalogenase binding to its ligand demonstrated that data can be collected at short (30 ms), medium (752 ms) and long (2,052 ms) intervals.}, language = {en} } @article{RiemerCoswigShipmanetal.2018, author = {Riemer, Nastja and Coswig, Christin and Shipman, Michael and Schmidt, Bernd}, title = {Palladium-catalyzed cross-coupling of arenediazonium salts with organoindium or organobismuth reagents}, series = {Synlett : accounts and rapid communications in synthetic organic chemistry}, volume = {29}, journal = {Synlett : accounts and rapid communications in synthetic organic chemistry}, number = {18}, publisher = {Georg Thieme Verlag KG}, address = {Stuttgart}, issn = {0936-5214}, doi = {10.1055/s-0037-1611001}, pages = {2427 -- 2431}, year = {2018}, abstract = {Arylindium and isolated triarylbismuth compounds generated in situ react as nucleophiles with arenediazonium salts in palladium-catalyzed cross-coupling reactions to give substituted biphenyls.}, language = {en} } @article{HardyBertinTorresRendonetal.2018, author = {Hardy, John G. and Bertin, Annabelle and Torres-Rendon, Jose Guillermo and Leal-Egana, Aldo and Humenik, Martin and Bauer, Felix and Walther, Andreas and C{\"o}lfen, Helmut and Schlaad, Helmut and Scheibel, Thomas R.}, title = {Facile photochemical modification of silk protein-based biomaterials}, series = {Macromolecular bioscience}, volume = {18}, journal = {Macromolecular bioscience}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-5187}, doi = {10.1002/mabi.201800216}, pages = {6}, year = {2018}, abstract = {Silk protein-based materials show promise for application as biomaterials for tissue engineering. The simple and rapid photochemical modification of silk protein-based materials composed of either Bombyx mori silkworm silk or engineered spider silk proteins (eADF4(C16)) is reported. Radicals formed on the silk-based materials initiate the polymerization of monomers (acrylic acid, methacrylic acid, or allylamine) which functionalize the surface of the silk materials with poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(allylamine) (PAAm). To demonstrate potential applications of this type of modification, the polymer-modified silks are mineralized. The PAA- and PMAA-functionalized silks are mineralized with calcium carbonate, whereas the PAAm-functionalized silks are mineralized with silica, both of which provide a coating on the materials that may be useful for bone tissue engineering, which will be the subject of future investigations.}, language = {en} } @article{ZhengBaiTaoetal.2018, author = {Zheng, Botuo and Bai, Tianwen and Tao, Xinfeng and Schlaad, Helmut and Ling, Jun}, title = {Identifying the Hydrolysis of Carbonyl Sulfide as a Side Reaction Impeding the Polymerization of N-Substituted Glycine N-Thiocarboxyanhydride}, series = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences}, volume = {19}, journal = {Biomacromolecules : an interdisciplinary journal focused at the interface of polymer science and the biological sciences}, number = {11}, publisher = {American Chemical Society}, address = {Washington}, issn = {1525-7797}, doi = {10.1021/acs.biomac.8b01119}, pages = {4263 -- 4269}, year = {2018}, abstract = {Polypeptoids are noticeable biological materials due to their versatile properties and various applications in drug delivery, surface modification, self-assembly, etc. N-Substituted glycine N-thiocarboxyanhydrides (NNTAs) are more stable monomers than the corresponding N-carboxyanhydrides (NNCAs) and enable one to prepare polypeptoids via ring-opening polymerization even in the presence of water. However, larger amounts of water (>10,000 ppm) cause inhibition of the polymerization. Herein, we discover that during polymerization hydrogen sulfide evolves from the hydrolysis of carbonyl sulfide, which is the byproduct of ring-opening reaction, and reacts with NNTA to produce cyclic oligopeptoids. The capture of N-ethylethanethioic acid as an intermediate product confirms the reaction mechanism together with density functional theory quantum computational results. By bubbling the polymerization solution with argon, the side reaction can be suppressed to allow the synthesis of polysarcosine with high molar mass (M-n = 11,200 g/mol, D = 1.25) even in the presence of similar to 10,000 ppm of water.}, language = {en} } @article{KutlugHassRecketal.2018, author = {Kutlug, Oezg{\"u}r and Hass, Roland and Reck, Stephan and Hartwig, Andreas}, title = {Inline characterization of dispersion formation of a solvent-borne acrylic copolymer by Photon Density Wave spectroscopy}, series = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, volume = {556}, 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.2018.08.011}, pages = {113 -- 119}, year = {2018}, abstract = {Most investigations on phase inversion (PI) of resins upon addition of water have been carried out by dynamic light scattering (DLS), torque, and viscosity measurements. The main problem, however, is analytic discontinuity due to sample removal and a changing matrix due to dilution during the preparation of the aqueous resin dispersions. This work presents Photon Density Wave (PDW) spectroscopy as a tool for the inline characterization of the acetone process for an acrylic copolymer with high acrylic acid (AA) content. PDW spectroscopy revealed different trends for optical properties compared to torque during water feed. Also the absence of PI due to dissolution of copolymer in the solvent/water mixture is observed by PDW spectroscopy. PI for the investigated copolymer did not occour during water feed but during removal of solvent. Different feeding rates of water gave similar trends while a change in temperature and degree of AA neutralization led to changes in optical properties and torque. Thermal processing showed that the optical properties of mixtures prior and after removal of solvent were completely different caused by changes of solubility.}, language = {en} } @article{BurekKrauseSchwotzeretal.2018, author = {Burek, Katja and Krause, Felix and Schwotzer, Matthias and Nefedov, Alexei and S{\"u}ssmuth, Julia and Haubitz, Toni and Kumke, Michael Uwe and Thissen, Peter}, title = {Hydrophobic Properties of Calcium-Silicate Hydrates Doped with Rare-Earth Elements}, series = {ACS sustainable chemistry \& engineering}, volume = {6}, journal = {ACS sustainable chemistry \& engineering}, number = {11}, publisher = {American Chemical Society}, address = {Washington}, issn = {2168-0485}, doi = {10.1021/acssuschemeng.8b03244}, pages = {14669 -- 14678}, year = {2018}, abstract = {In this study, the apparent relationship between the transport process and the surface chemistry of the Calcium-Silicate Hydrate (CSH) phases was investigated. For this purpose, a method was developed to synthesize ultrathin CSH phases to be used as a model substrate with the specific modification of their structure by introducing europium (Eu(III)). The structural and chemical changes during this Eu(III)-doping were observed by means of infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and time-resolved laser fluorescence spectroscopy (TRLFS). These alterations of the CSH phases led to significant changes in the surface chemistry and consequently to considerable variations in the interaction with water, as evidenced by measurements of the contact angles on the modified model substrates. Our results provide the basis for a more profound molecular understanding of reactive transport processes in cement-based systems. Furthermore, these results broaden the perspective of improving the stability of cement-based materials, which are subjected to the impact of aggressive aqueous environments through targeted modifications of the CSH phases.}, language = {en} } @article{HaenselBartaRietzeetal.2018, author = {H{\"a}nsel, Marc and Barta, Christoph and Rietze, Clemens and Utecht, Manuel Martin and Rueck-Braun, Karola and Saalfrank, Peter and Tegeder, Petra}, title = {Two-Dimensional Nonlinear Optical Switching Materials}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {122}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {44}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.8b08212}, pages = {25555 -- 25564}, year = {2018}, abstract = {Combining photochromism and nonlinear optical (NLO) properties of molecular switches-functionalized self-assembled monolayers (SAMs) represents a promising concept toward novel photonic and optoelectronic devices. Using second harmonic generation, density functional theory, and correlated wave function methods, we studied the switching abilities as well as the NLO contrasts between different molecular states of various fulgimide-containing SAMs on Si(111). Controlled variations of the linker systems as well as of the fulgimides enabled us to demonstrate very efficient reversible photoinduced ring-opening/closure reactions between the open and closed forms of the fulgimides. Thus, effective cross sections on the order of 10(-18) cm(-2) are observed. Moreover, the reversible switching is accompanied by pronounced NLO contrasts up to 32\%. Further molecular engineering of the photochromic switches and the linker systems may even increase the NLO contrast upon switching.}, language = {en} } @article{XiongWlodarczykSaalfrank2018, author = {Xiong, Tao and Wlodarczyk, Radoslaw and Saalfrank, Peter}, title = {Vibrationally resolved absorption and fluorescence spectra of perylene and N-substituted derivatives from autocorrelation function approaches}, series = {Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature}, volume = {515}, journal = {Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2018.06.011}, pages = {728 -- 736}, year = {2018}, abstract = {Vibrationally resolved absorption and emission (fluorescence) spectra of perylene and its N-derivatives in gas phase and in solution (acetonitrile) were simulated using a time-dependent approach based on correlation functions determined by density functional theory. By systematically varying the number and position of N atoms, it is shown that the presence of nitrogen heteroatoms has a negligible effect on the molecular structure and geometric distortions upon electronic transitions, while spectral properties change: in particular the number of N atoms is important while their position is less decisive. Thus, the N-substitution can be used to fine-tune the optical properties of perylene-based molecules.}, language = {en} } @article{UtechtGaebelKlamroth2018, author = {Utecht, Manuel Martin and Gaebel, Tina and Klamroth, Tillmann}, title = {Desorption induced by low energy charge carriers on Si(111)-7 x 7}, series = {Journal of computational chemistry : organic, inorganic, physical, biological}, volume = {39}, journal = {Journal of computational chemistry : organic, inorganic, physical, biological}, number = {30}, publisher = {Wiley}, address = {Hoboken}, issn = {0192-8651}, doi = {10.1002/jcc.25607}, pages = {2517 -- 2525}, year = {2018}, abstract = {We use clusters for the modeling of local ion resonances caused by low energy charge carriers in STM-induced desorption of benzene derivates from Si(111)-7 x 7. We perform Born-Oppenheimer molecular dynamics for the charged systems assuming vertical transitions to the charged states at zero temperature, to rationalize the low temperature activation energies, which are found in experiment for chlorobenzene. Our calculations suggest very similar low temperature activation energies for toluene and benzene. For the cationic resonance transitions to physisorption are found even at 0 K, while the anion remains chemisorbed during the propagations. Further, we also extend our previous static quantum chemical investigations to toluene and benzene. In addition, an in depth analysis of the ionization potentials and electron affinities, which are used to estimate resonance energies, is given.}, language = {en} } @article{TanLiuGlebeetal.2018, author = {Tan, Li and Liu, Bing and Glebe, Ulrich and B{\"o}ker, Alexander}, title = {Magnetic Field-Induced Assembly of Superparamagnetic Cobalt Nanoparticles on Substrates and at Liquid-Air Interface}, series = {Langmuir}, volume = {34}, journal = {Langmuir}, number = {46}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.8b02673}, pages = {13993 -- 14002}, year = {2018}, abstract = {Superparamagnetic cobalt nanoparticles (Co NPs) are an interesting material for self-assembly processes because of their magnetic properties. We investigated the magnetic field-induced assembly of superparamagnetic cobalt nanoparticles and compared three different approaches, namely, the assembly on solid substrates, at water-air, and ethylene glycol-air interfaces. Oleic acid- and trioctylphosphine oxide-coated Co NPs were synthesized via a thermolysis of cobalt carbonyl and dispersed into either hexane or toluene. The Co NP dispersion was dropped onto different substrates (e.g., transmission electron microscopy (TEM) grid, silicon wafer) and onto liquid surfaces. Transmission electron microscopy (TEM), scanning force microscopy, optical microscopy, as well as scanning electron microscopy showed that superparamagnetic Co NPs assembled into one-dimensional chains in an external magnetic field. By varying the concentration of the Co NP dispersion (1-5 mg/mL) and the strength of the magnetic field (4-54 mT), the morphology of the chains changed. Short, thin, and flexible chain structures were obtained at low NP concentration and low strength of magnetic field, whereas they became long, thick and straight when the NP concentration and the magnetic field strength increased. In comparison, the assembly of Co NPs from hexane dispersion at ethylene glycol-air interface showed the most regular and homogeneous alignment, since a more efficient spreading could be achieved on ethylene glycol than on water and solid substrates.}, language = {en} } @article{YalcinkayaBresselLindneretal.2018, author = {Yalcinkaya, Hacer and Bressel, Katharina and Lindner, Peter and Gradzielski, Michael}, title = {Controlled formation of vesicles with added styrene and their fixation by polymerization}, series = {Journal of colloid and interface science}, volume = {531}, journal = {Journal of colloid and interface science}, publisher = {Elsevier}, address = {San Diego}, issn = {0021-9797}, doi = {10.1016/j.jcis.2018.07.097}, pages = {672 -- 680}, year = {2018}, abstract = {Hypothesis: An effective way for fixating vesicle structures is the insertion of monomers and cross-linking agents into their bilayer, and their subsequent polymerization can lead to the formation of polymeric nanocapsules. Particularly attractive here are vesicle systems that form spontaneously well-defined small vesicles, as obtaining such small nanocapsules with sizes below 100 nm is still challenging. Experiments: A spontaneously forming well-defined vesicle system composed of the surfactants TDMAO (tetradecyldimethylamine oxide), Pluronic L35, and LiPFOS (lithium perfluorooctylsulfonate) mixture was used as template for fixation by polymerization. Therefore, styrene monomer was incorporated into the vesicle bilayer and ultimately these structures were fixated by UV induced radical polymerization. Structural alteration of the vesicles upon loading with monomer and the cross-linker as well as the effect of subsequent polymerization in the membrane were investigated in detail by turbidity measurements, dynamic and static light scattering, (DLS, SLS), and small angle neutron scattering (SANS). Findings: The analysis showed the changes on vesicle structures due to the monomer loading, and that these structures can become permanently fixed by the polymerization process. The potential of this approach to produce well-defined nanocapsules starting from a self-assembled system and following polymerization is critically evaluated. (C) 2018 Elsevier Inc. All rights reserved.}, language = {en} } @article{PengBehlZhangetal.2018, author = {Peng, Xingzhou and Behl, Marc and Zhang, Pengfei and Mazurek-Budzynska, Magdalena and Feng, Yakai and Lendlein, Andreas}, title = {Synthesis of Well-Defined Dihydroxy Telechelics by (Co)polymerization of Morpholine-2,5-Diones Catalyzed by Sn(IV) Alkoxide}, series = {Macromolecular bioscience}, volume = {18}, journal = {Macromolecular bioscience}, number = {12}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-5187}, doi = {10.1002/mabi.201800257}, pages = {11}, year = {2018}, abstract = {Well-defined dihydroxy telechelic oligodepsipeptides (oDPs), which have a high application potential as building blocks for scaffold materials for tissue engineering applications or particulate carrier systems for drug delivery applications are synthesized by ring-opening polymerization (ROP) of morpholine-2,5-diones (MDs) catalyzed by 1,1,6,6-tetra-n-butyl-1,6-distanna-2,5,7,10-tetraoxacyclodecane (Sn(IV) alkoxide). In contrast to ROP catalyzed by Sn(Oct)(2), the usage of Sn(IV) alkoxide leads to oDPs, with less side products and well-defined end groups, which is crucial for potential pharmaceutical applications. A slightly faster reaction of the ROP catalyzed by Sn(IV) alkoxide compared to the ROP initiated by Sn(Oct)(2)/EG is found. Copolymerization of different MDs resulted in amorphous copolymers with T(g)s between 44 and 54 degrees C depending on the molar comonomer ratios in the range from 25\% to 75\%. Based on the well-defined telechelic character of the Sn(IV) alkoxide synthesized oDPs as determined by matrix-assisted laser desorption/ionization time of flight measurements, they resemble interesting building blocks for subsequent postfunctionalization or multifunctional materials based on multiblock copolymer systems whereas the amorphous oDP-based copolymers are interesting building blocks for matrices of drug delivery systems.}, language = {en} } @article{HermannsSchmidt2018, author = {Hermanns, Jolanda and Schmidt, Bernd}, title = {Developing and Applying Stepped Supporting Tools in Organic Chemistry To Promote Students' Self-Regulated Learning}, series = {Journal of chemical education}, volume = {96}, journal = {Journal of chemical education}, number = {1}, publisher = {American Chemical Society}, address = {Washington}, issn = {0021-9584}, doi = {10.1021/acs.jchemed.8b00565}, pages = {47 -- 52}, year = {2018}, abstract = {Stepped supporting tools were developed and used in the university seminar Organic Chemistry taken by nonmajor chemistry students, which supported self-regulated learning. These supporting tools were also used for accompanying homework, which included a QR code that led to additional supporting tools. The application of stepped supporting tools in the seminars was evaluated by a four-item Likert scale. The students assessed the tools as a helpful instrument for solving tasks in chemistry.}, language = {en} } @article{NoackSchanzenbachKoetzetal.2018, author = {Noack, Sebastian and Schanzenbach, Dirk and Koetz, Joachim and Schlaad, Helmut}, title = {Polylactide-based amphiphilic block copolymers}, series = {Macromolecular rapid communications}, volume = {40}, journal = {Macromolecular rapid communications}, number = {1}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201800639}, pages = {6}, year = {2018}, abstract = {The aqueous self-assembly behavior of a series of poly(ethylene glycol)-poly(l-/d-lactide) block copolymers and corresponding stereocomplexes is examined by differential scanning calorimetry, dynamic light scattering, and transmission electron microscopy. Block copolymers assemble into spherical micelles and worm-like aggregates at room temperature, whereby the fraction of the latter seemingly increases with decreasing lactide weight fraction or hydrophobicity. The formation of the worm-like aggregates arises from the crystallization of the polylactide by which the spherical micelles become colloidally unstable and fuse epitaxically with other micelles. The self-assembly behavior of the stereocomplex aggregates is found to be different from that of the block copolymers, resulting in rather irregular-shaped clusters of spherical micelles and pearl-necklace-like structures.}, language = {en} } @misc{HeckMichaeliBaldetal.2018, author = {Heck, Christian and Michaeli, Yael and Bald, Ilko and Ebenstein, Yuval}, title = {Analytical epigenetics}, series = {Current Opinion in Biotechnology}, volume = {55}, journal = {Current Opinion in Biotechnology}, publisher = {Elsevier}, address = {London}, issn = {0958-1669}, doi = {10.1016/j.copbio.2018.09.006}, pages = {151 -- 158}, year = {2018}, abstract = {The field of epigenetics describes the relationship between genotype and phenotype, by regulating gene expression without changing the canonical base sequence of DNA. It deals with molecular genomic information that is encoded by a rich repertoire of chemical modifications and molecular interactions. This regulation involves DNA, RNA and proteins that are enzymatically tagged with small molecular groups that alter their physical and chemical properties. It is now clear that epigenetic alterations are involved in development and disease, and thus, are the focus of intensive research. The ability to record epigenetic changes and quantify them in rare medical samples is critical for next generation diagnostics. Optical detection offers the ultimate single-molecule sensitivity and the potential for spectral multiplexing. Here we review recent progress in ultrasensitive optical detection of DNA and histone modifications.}, language = {en} } @article{JiangMansfeldFangetal.2018, author = {Jiang, Yi and Mansfeld, Ulrich and Fang, Liang and Kratz, Karl and Lendlein, Andreas}, title = {Temperature-induced evolution of microstructures on poly[ethylene-co-(vinyl acetate)] substrates switches their underwater wettability}, series = {Materials \& design}, volume = {163}, journal = {Materials \& design}, publisher = {Elsevier}, address = {Oxford}, issn = {0264-1275}, doi = {10.1016/j.matdes.2018.12.002}, pages = {10}, year = {2018}, abstract = {Material surfaces with tailored aerophobicity are crucial for applications where gas bubble wettability has to be controlled, e.g., gas storage and transport, electrodes, bioreactors or medical devices. Here, we present switchable underwater aerophobicity of hydrophobic polymeric substrates, which respond to heat with multilevel micro-and nanotopographical changes. The cross-linked poly[ethylene-co-(vinyl acetate)] substrates possess arrays of microcylinders with a nanorough top surface. It is hypothesized that the specific micro-/nanotopography of the surface allows trapping of a water film at the micro interspace and in this way generates the aerophobic behavior. The structured substrates were programmed to a temporarily stable, nanoscale flat substrate showing aerophilic behavior. Upon heating, the topographical changes caused a switch in contact angle from aerophilic to aerophobic for approaching air bubbles. In this way, the initial adhesion of air bubbles to the programmed flat substrate could be turned into repellence for the recovered substrate surface. The temperature at which the repellence of air bubbles starts can be adjusted from 58 +/- 3 degrees C to 73 +/- 3 degrees C by varying the deformation temperature applied during the temperature-memory programming procedure. The presented actively switching polymeric substrates are attractive candidates for applications, where an on-demand gas bubble repellence is advantageous. (c) 2018 Helmholtz-Zentrum Geesthacht, Zentrum fur Material- und Kustenforschung. Published by Elsevier Ltd.}, language = {en} } @article{XuAngiolettiUbertiLuetal.2018, author = {Xu, Xiao and Angioletti-Uberti, Stefano and Lu, Yan and Dzubiella, Joachim and Ballauff, Matthias}, title = {Interaction of Proteins with Polyelectrolytes}, series = {Langmuir}, volume = {35}, journal = {Langmuir}, number = {16}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.8b01802}, pages = {5373 -- 5391}, year = {2018}, abstract = {We discuss recent investigations of the interaction of polyelectrolytes with proteins. In particular, we review our recent studies on the interaction of simple proteins such as human serum albumin (HSA) and lysozyme with linear polyelectrolytes, charged dendrimers, charged networks, and polyelectrolyte brushes. In all cases discussed here, we combined experimental work with molecular dynamics (MD) simulations and mean-field theories. In particular, isothermal titration calorimetry (ITC) has been employed to obtain the respective binding constants K-b and the Gibbs free energy of binding. MD simulations with explicit counterions but implicit water demonstrate that counterion release is the main driving force for the binding of proteins to strongly charged polyelectrolytes: patches of positive charges located on the surface of the protein become multivalent counterions of the polyelectrolyte, thereby releasing a number of counterions condensed on the polyelectrolyte. The binding Gibbs free energy due to counterion release is predicted to scale with the logarithm of the salt concentration in the system, which is verified by both simulations and experiment. In several cases, namely, for the interaction of proteins with linear polyelectrolytes and highly charged hydrophilic dendrimers, the binding constant could be calculated from simulations to very good approximation. This finding demonstrated that in these cases explicit hydration effects do not contribute to the Gibbs free energy of binding. The Gibbs free energy can also be used to predict the kinetics of protein uptake by microgels for a given system by applying dynamic density functional theory. The entire discussion demonstrates that the direct comparison of theory with experiments can lead to a full understanding of the interaction of proteins with charged polymers. Possible implications for applications, such as drug design, are discussed.}, language = {en} } @article{LuetzowHommesSchattmannNeffeetal.2018, author = {L{\"u}tzow, Karola and Hommes-Schattmann, Paul J. and Neffe, Axel T. and Ahmad, Bilal and Williams, Gareth R. and Lendlein, Andreas}, title = {Perfluorophenyl azide functionalization of electrospun poly(para-dioxanone)}, series = {Polymers for advanced technologies}, volume = {30}, journal = {Polymers for advanced technologies}, number = {5}, publisher = {Wiley}, address = {Hoboken}, issn = {1042-7147}, doi = {10.1002/pat.4331}, pages = {1165 -- 1172}, year = {2018}, abstract = {Strategies to surface-functionalize scaffolds by covalent binding of biologically active compounds are of fundamental interest to control the interactions between scaffolds and biomolecules or cells. Poly(para-dioxanone) (PPDO) is a clinically established polymer that has shown potential as temporary implant, eg, for the reconstruction of the inferior vena cava, as a nonwoven fiber mesh. However, PPDO lacks suitable chemical groups for covalent functionalization. Furthermore, PPDO is highly sensitive to hydrolysis, reflected by short in vivo half-life times and degradation during storage. Establishing a method for covalent functionalization without degradation of this hydrolyzable polymer is therefore important to enable the surface tailoring for tissue engineering applications. It was hypothesized that treatment of PPDO with an N-hydroxysuccinimide ester group bearing perfluorophenyl azide (PFPA) under UV irradiation would allow efficient surface functionalization of the scaffold. X-ray photoelectron spectroscopy and attenuated total reflectance Fourier-transformed infrared spectroscopy investigation revealed the successful binding, while a gel permeation chromatography study showed that degradation did not occur under these conditions. Coupling of a rhodamine dye to the N-hydroxysuccinimide esters on the surface of a PFPA-functionalized scaffold via its amine linker showed a homogenous staining of the PPDO in laser confocal microscopy. The PFPA method is therefore applicable even to the surface functionalization of hydrolytically labile polymers, and it was demonstrated that PFPA chemistry may serve as a versatile tool for the (bio-)functionalization of PPDO scaffolds.}, language = {en} } @article{CzarneckiWessig2018, author = {Czarnecki, Maciej and Wessig, Pablo}, title = {Scaling Up UV-Mediated Intramolecular Photodehydro-Diels-Alder Reactions Using a Homemade High-Performance Annular Continuous-Flow Reactor}, series = {Organic Process Research \& Development}, volume = {22}, journal = {Organic Process Research \& Development}, number = {12}, publisher = {American Chemical Society}, address = {Washington}, issn = {1083-6160}, doi = {10.1021/acs.oprd.8b00353}, pages = {1823 -- 1827}, year = {2018}, abstract = {Here we present a self-made annular continuous-flow reactor that can be used in the UV/vis range in an internal numbering-up manner. As a model reaction, we chose a powerful batch-scale-limited benzoannelation method, namely, an intramolecular photodehydro-Diels-Alder (IMPDDA) reaction. The scale-up potential of this particular photochemical benchmark reaction toward the preparation of macrocylic (1,7)naphthalenophanes by variation of selected flow parameters is presented.}, language = {en} } @article{HoangMertensWessigetal.2018, author = {Hoang, Hoa T. and Mertens, Monique and Wessig, Pablo and Sellrie, Frank and Schenk, J{\"o}rg A. and Kumke, Michael Uwe}, title = {Antibody Binding at the Liposome-Water Interface}, series = {ACS Omega}, volume = {3}, journal = {ACS Omega}, number = {12}, publisher = {American Chemical Society}, address = {Washington}, issn = {2470-1343}, doi = {10.1021/acsomega.8b03016}, pages = {18109 -- 18116}, year = {2018}, abstract = {Different signal amplification strategies to improve the detection sensitivity of immunoassays have been applied which utilize enzymatic reactions, nanomaterials, or liposomes. The latter are very attractive materials for signal amplification because liposomes can be loaded with a large amount of signaling molecules, leading to a high sensitivity. In addition, liposomes can be used as a cell-like "bioscaffold" to directly test recognition schemes aiming at cell-related processes. This study demonstrates an easy and fast approach to link the novel hydrophobic optical probe based on [1,3]dioxolo[4,5-f]-[1,3]benzodioxole (DBD dye mm239) with tunable optical properties to hydrophilic recognition elements (e.g., antibodies) using liposomes for signal amplification and as carrier of the hydrophobic dye. The fluorescence properties of mm239 (e.g., long fluorescence lifetime, large Stokes shift, high photostability, and high quantum yield), its high hydrophobicity for efficient anchoring in liposomes, and a maleimide bioreactive group were applied in a unique combination to build a concept for the coupling of antibodies or other protein markers to liposomes (coupling to membranes can be envisaged). The concept further allowed us to avoid multiple dye labeling of the antibody. Here, anti-TAMRA-antibody (DC7-Ab) was attached to the liposomes. In proof-of-concept, steady-state as well as time-resolved fluorescence measurements (e.g., fluorescence depolarization) in combination with single molecule detection (fluorescence correlation spectroscopy, FCS) were used to analyze the binding interaction between DC7-Ab and liposomes as well as the binding of the antigen rhodamine 6G (R6G) to the antibody. Here, the Forster resonance energy transfer (FRET) between mm239 and R6G was monitored. In addition to ensemble FRET data, single-molecule FRET (PIE-FRET) experiments using pulsed interleaved excitation were used to characterize in detail the binding on a single-molecule level to avoid averaging out effects.}, language = {en} } @article{SunDongOsenbergetal.2018, author = {Sun, Fu and Dong, Kang and Osenberg, Markus and Hilger, Andre and Risse, Sebastian and Lu, Yan and Kamm, Paul H. and Klaus, Manuela and Markoetter, Henning and Garcia-Moreno, Francisco and Arlt, Tobias and Manke, Ingo}, title = {Visualizing the morphological and compositional evolution of the interface of InLi-anode|thio-LISION electrolyte in an all-solid-state Li-S cell by in operando synchrotron X-ray tomography and energy dispersive diffraction}, series = {Journal of materials chemistry : A, Materials for energy and sustainability}, volume = {6}, journal = {Journal of materials chemistry : A, Materials for energy and sustainability}, number = {45}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2050-7488}, doi = {10.1039/c8ta08821g}, pages = {22489 -- 22496}, year = {2018}, abstract = {Dynamic and direct visualization of interfacial evolution is helpful in gaining fundamental knowledge of all-solid-state-lithium battery working/degradation mechanisms and clarifying future research directions for constructing next-generation batteries. Herein, in situ and in operando synchrotron X-ray tomography and energy dispersive diffraction were simultaneously employed to record the morphological and compositional evolution of the interface of InLi-anode|sulfide-solid-electrolyte during battery cycling. Compelling morphological evidence of interfacial degradation during all-solid-state-lithium battery operation has been directly visualized by tomographic measurement. The accompanying energy dispersive diffraction results agree well with the observed morphological deterioration and the recorded electrochemical performance. It is concluded from the current investigation that a fundamental understanding of the phenomena occurring at the solid-solid electrode|electrolyte interface during all-solid-state-lithium battery cycling is critical for future progress in cell performance improvement and may determine its final commercial viability.}, language = {en} } @article{ZivanovicKochovskiArenzetal.2018, author = {Zivanovic, Vesna and Kochovski, Zdravko and Arenz, Christoph and Lu, Yan and Kneipp, Janina}, title = {SERS and Cryo-EM Directly Reveal Different Liposome Structures during Interaction with Gold Nanoparticles}, series = {The journal of physical chemistry letters}, volume = {9}, journal = {The journal of physical chemistry letters}, number = {23}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/acs.jpclett.8b03191}, pages = {6767 -- 6772}, year = {2018}, abstract = {The combination of gold nanoparticles with liposomes is important for nano- and biotechnology. Here, we present direct, label-free characterization of liposome structure and composition at the site of its interaction with citrate-stabilized gold nanoparticles by surface-enhanced Raman scattering (SERS) and cryogenic electron microscopy (cryo-EM). Evidenced by the vibrational spectra and cryo-EM, the gold nanoparticles destroy the bilayer structure of interacting liposomes in the presence of a high amount of citrate, while at lower citrate concentration the nanoparticles interact with the surface of the intact liposomes. The spectra of phosphatidylcholine and phosphatidylcholine/sphingomyelin liposomes show that at the site of interaction the lipid chains are in the gel phase. The SERS spectra indicate that cholesterol has strong effects on the contacts of the vesicles with the nanoparticles. By combining cryo-EM and SERS, the structure and properties of lipid nanoparticle composites could be tailored for the development of drug delivery systems.}, language = {en} } @article{SchultzeSchmidt2018, author = {Schultze, Christiane and Schmidt, Bernd}, title = {Ring-closing-metathesis-based synthesis of annellated coumarins from 8-allylcoumarins}, series = {Beilstein journal of organic chemistry}, volume = {14}, journal = {Beilstein journal of organic chemistry}, publisher = {Beilstein-Institut zur F{\"o}rderung der Chemischen Wissenschaften}, address = {Frankfurt, Main}, issn = {1860-5397}, doi = {10.3762/bjoc.14.278}, pages = {2991 -- 2998}, year = {2018}, abstract = {8-Allylcoumarins are conveniently accessible through a microwave-promoted tandem Claisen rearrangement/Wittig olefination/cyclization sequence. They serve as a versatile platform for the annellation of five- to seven-membered rings using ring-closing olefin metathesis (RCM). Furano-, pyrano-, oxepino- and azepinocoumarins were synthesized from the same set of precursors using Ru-catalyzed double bond isomerizations and RCM in a defined order. One class of products, pyrano[2,3-f]chromene-2,8-diones, were inaccessible through direct RCM of an acrylate, but became available from the analogous allyl ether via an assisted tandem catalytic RCM/allylic oxidation sequence.}, language = {en} } @article{NguyenLeeAudoerschetal.2018, author = {Nguyen, Hiep N. and Lee, Hyeunjoo and Aud{\"o}rsch, Stephan and Reznichenko, Alexander L. and Nawara-Hultzsch, Agnieszka J. and Schmidt, Bernd and Hultzsch, Kai C.}, title = {Asymmetric Intra- and Intermolecular Hydroamination Catalyzed by 3,3′-Bis(trisarylsilyl)- and 3,3′-Bis(arylalkylsilyl)-Substituted Binaphtholate Rare-Earth-Metal Complexes}, series = {Organometallics}, volume = {37}, journal = {Organometallics}, number = {23}, publisher = {American Chemical Society}, address = {Washington}, issn = {0276-7333}, doi = {10.1021/acs.organomet.8b00510}, pages = {4358 -- 4379}, year = {2018}, abstract = {The series of novel 3,3′-bis(trisarylsilyl)- and 3,3′-bis(arylalkylsilyl)-substituted binaphtholate rare-earth-metal complexes 2a-i (SiR3 = Si(o-biphenylene)Ph (a), SiCyPh2 (b), Si-t-BuPh2 (c), Si(i-Pr)3 (d), SiCy2Ph (e), Si(2-tolyl)Ph2 (f), Si(4-t-Bu-C6H4)3 (g), Si(4-MeO-C6H4)Ph2 (h), SiBnPh2 (i)) have been prepared via arene elimination from [Ln(o-C6H4CH2NMe2)3] (Ln = Y, Lu) and the corresponding 3,3′-bis(silyl)-substituted binaphthol. The complexes exhibit high catalytic activity in the hydroamination/cyclization of aminoalkenes, with activities exceeding 1000 h-1 for (R)-2f-Ln, (R)-2g-Ln, and (R)-2h-Ln in the cyclization of 2,2-diphenylpent-4-enylamine (3a) at 25 °C, while the rigid dibenzosilole-substituted complexes (R)-2a-Ln and the triisopropylsilyl-substituted complexes (R)-2d-Ln exhibited the lowest activity in the range of 150-270 h-1. Catalysts (R)-2b-Lu, (R)-2c-Lu, (R)-2f-Lu, and (R)-2i-Lu provide the highest selectivities for the majority of the substrates, while the yttrium congeners are usually less selective. The highest enantioselectivities of 96\% ee were observed using (R)-2a-Lu and (R)-2c-Lu in the cyclization of (4E)-2,2,5-triphenylpent-4-enylamine (9). The reactions show apparently zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, with some reactions exhibiting a slightly accelerated rate at high conversion due to a shift in the equilibrium between a less active, higher coordinate catalyst species in favor of a more active, lower coordinate species as a result of weaker binding of the hydroamination product in comparison to the aminoalkene substrate. The shift in equilibrium from the higher to the lower coordinate species is also entropically favored at elevated temperatures, which results in an unusual increase in selectivity in the cyclization of 2,2-dimethylpent-4-enylamine (3d), presumably due to a higher selectivity of the lower coordinate catalyst species. All binaphtholate yttrium complexes, except (R)-2a-Y, are catalytically active in the intermolecular hydroamination of benzylamines with terminal alkenes. The highest selectivity of 66\% ee was observed for the reaction of benzylamine with 4-phenyl-1-butene using (R)-2h-Y at 110 °C.}, language = {en} } @article{ParamonovKlamrothLuetal.2018, author = {Paramonov, Guennaddi K. and Klamroth, Tillmann and Lu, H. Z. and Bandrauk, Andre D.}, title = {Quantum dynamics, isotope effects, and power spectra of H-2(+) and HD+ excited to the continuum by strong one-cycle laser pulses: Three-dimensional non-Born-Oppenheimer simulations}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {98}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {6}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.98.063431}, pages = {16}, year = {2018}, abstract = {Non-Born-Oppenheimer quantum dynamics of H-2(+) and HD+ excited by single one-cycle laser pulses linearly polarized along the molecular (z) axis have been studied within a three-dimensional model, including the internuclear distance R and electron coordinates z and rho, by means of the numerical solution of the time-dependent Schrodinger equation on the timescale of about 200 fs. Laser carrier frequencies corresponding to the wavelengths of lambda(l) = 400 and 50 nm have been used and the amplitudes of the pulses have been chosen such that the energies of H-2(+) and HD+ are above the dissociation threshold after the ends of the laser pulses. It is shown that excitation of H-2(+) and HD+ above the dissociation threshold is accompanied by formation of vibrationally "hot" and "cold" ensembles of molecules. Dissociation of vibrationally "hot" molecules does not prevent the appearance of post-laser-pulse electronic oscillations, parallel z oscillations, and transversal rho oscillations. Moreover, dissociation of "hot" molecules does not influence characteristic frequencies of electronic z and rho oscillations. The main difference between the laser-induced quantum dynamics of homonuclear H-2(+) and its heteronuclear isotope HD+ is that fast post-laser-pulse electronic z oscillations in H-2(+) are regularly shaped with the period of tau(shp) approximate to 30 fs corresponding to nuclear oscillations in H-2(+), while electronic z oscillations in HD+ arise as "echo pulses" of its initial excitation and appear with the period of tau(echo) approximate to 80 fs corresponding to nuclear motion in HD+. Accordingly, corresponding power spectra of nuclear motion contain strong low-frequency harmonics at omega(shp) = 2 pi/tau(shp) in H2(+) and omega(echo) = 2 pi/tau(echo) in HD+. Power spectra related to both electronic and nuclear motion have been calculated in the acceleration form. Both higher- and lower-order harmonics are generated at the laser wavelength lambda(l) = 400 nm, while only lower-order harmonics are well pronounced at lambda(l) = 50 nm. It is also shown that a rationalized harmonic order, defined in terms of the frequency of the laser-induced electronic z oscillations, agrees with the concept of inversion symmetry for electronic motion in diatomic molecules.}, language = {en} } @article{BalderasValadezEstevezEspinozaSalazarKurietal.2018, author = {Balderas-Valadez, Ruth Fabiola and Estevez-Espinoza, J. O. and Salazar-Kuri, U. and Pacholski, Claudia and Mochan, Wolf Luis and Agarwal, Vivechana}, title = {Fabrication of ordered tubular porous silicon structures by colloidal lithography and metal assisted chemical etching}, series = {Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces}, volume = {462}, journal = {Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0169-4332}, doi = {10.1016/j.apsusc.2018.08.120}, pages = {783 -- 790}, year = {2018}, abstract = {Fabrication of well-ordered porous silicon tubular structures using colloidal lithography and metal assisted chemical etching is reported. A continuous hexagonal hole/particle gold pattern was designed over monocrystalline silicon through deposition of polyNIPAM microspheres, followed by the surface decoration with gold nanoparticles and thermal treatment. An etching reaction with HF, ethanol and H2O2 dissolved the silicon in contact with the metal nanoparticles (NP), creating a porous tubular array in the "off-metal area". The morphological characterization revealed the formation of a cylindrical hollow porous tubular shape with external and internal diameter of approx. 900 nm and 400 nm respectively, though it can be tuned to other desired sizes by choosing an appropriate dimension for the microspheres. The porous morphology and optical properties were studied as a function of resistivity of silicon substrates. Compared to two different gold templates on cSi and nontubular porous pillar structures, porous silicon tubular framework revealed a maximum surface enhanced Raman scattering enhancement factor of 10(6) for the detection of 6-mercaptopurine (6-MP). Due to the large surface area available for any surface modification, open nanostructured platforms such as those studied here have potential applications in the field of reflection/photoluminescene and SERS based optical bio-/chemical sensors.}, language = {en} } @phdthesis{Werner2018, author = {Werner, Peter}, title = {Untersuchung stark-streuender Polymersuspensionen mittels optischer Methoden}, school = {Universit{\"a}t Potsdam}, pages = {XVIII, 119, XXXV}, year = {2018}, language = {de} } @article{AbbasVranicHoffmannetal.2018, author = {Abbas, Ioana M. and Vranic, Marija and Hoffmann, Holger and El-Khatib, Ahmed H. and Montes-Bay{\´o}n, Mar{\´i}a and M{\"o}ller, Heiko Michael and Weller, Michael G.}, title = {Investigations of the Copper Peptide Hepcidin-25 by LC-MS/MS and NMR⁺}, series = {International Journal of Molecular Sciences}, volume = {19}, journal = {International Journal of Molecular Sciences}, number = {8}, publisher = {Molecular Diversity Preservation International}, address = {Basel}, issn = {1422-0067}, doi = {10.3390/ijms19082271}, pages = {16}, year = {2018}, abstract = {Hepcidin-25 was identified as themain iron regulator in the human body, and it by binds to the sole iron-exporter ferroportin. Studies showed that the N-terminus of hepcidin is responsible for this interaction, the same N-terminus that encompasses a small copper(II) binding site known as the ATCUN (amino-terminal Cu(II)- and Ni(II)-binding) motif. Interestingly, this copper-binding property is largely ignored in most papers dealing with hepcidin-25. In this context, detailed investigations of the complex formed between hepcidin-25 and copper could reveal insight into its biological role. The present work focuses on metal-bound hepcidin-25 that can be considered the biologically active form. The first part is devoted to the reversed-phase chromatographic separation of copper-bound and copper-free hepcidin-25 achieved by applying basic mobile phases containing 0.1\% ammonia. Further, mass spectrometry (tandemmass spectrometry (MS/MS), high-resolutionmass spectrometry (HRMS)) and nuclear magnetic resonance (NMR) spectroscopy were employed to characterize the copper-peptide. Lastly, a three-dimensional (3D)model of hepcidin-25with bound copper(II) is presented. The identification of metal complexes and potential isoforms and isomers, from which the latter usually are left undetected by mass spectrometry, led to the conclusion that complementary analytical methods are needed to characterize a peptide calibrant or referencematerial comprehensively. Quantitative nuclear magnetic resonance (qNMR), inductively-coupled plasma mass spectrometry (ICP-MS), ion-mobility spectrometry (IMS) and chiral amino acid analysis (AAA) should be considered among others.}, language = {en} } @phdthesis{Riemer2018, author = {Riemer, Nastja}, title = {Diazoniumsalze f{\"u}r die Synthese von Pflanzenschutzmitteln}, school = {Universit{\"a}t Potsdam}, pages = {187}, year = {2018}, language = {de} } @phdthesis{Homeyer2018, author = {Homeyer, Marc S{\"o}ren}, title = {Photometrische Bestimmungen mittels eines modifizierten Sch{\"u}lerphotometers und naturwissenschaftliches Arbeiten im Seminarkurs}, address = {119, A 203}, year = {2018}, language = {de} } @phdthesis{Liebig2018, author = {Liebig, Ferenc}, title = {Synthesis and characterization of superstructures based on gold nanotriangles}, school = {Universit{\"a}t Potsdam}, pages = {136}, year = {2018}, language = {en} } @phdthesis{Schimka2018, author = {Schimka, Selina}, title = {Photoresponsive soft nano-objects}, school = {Universit{\"a}t Potsdam}, pages = {135}, year = {2018}, language = {en} } @phdthesis{TroegerMueller2018, author = {Tr{\"o}ger-M{\"u}ller, Steffen}, title = {Truly sustainable imidazolium ionics}, school = {Universit{\"a}t Potsdam}, pages = {158}, year = {2018}, language = {de} } @phdthesis{Muenzberg2018, author = {M{\"u}nzberg, Marvin}, title = {Inline-Untersuchung der Tr{\"u}bung und Partikelgr{\"o}ße von hochkonzentrierten Dispersionen mit Lichtstreutechniken}, school = {Universit{\"a}t Potsdam}, pages = {85}, year = {2018}, language = {de} } @book{BechmannBald2018, author = {Bechmann, Wolfgang and Bald, Ilko}, title = {Einstieg in die Physikalische Chemie f{\"u}r Naturwissenschaftler}, series = {Studienb{\"u}cher Chemie Lehrbuch}, journal = {Studienb{\"u}cher Chemie Lehrbuch}, edition = {6}, publisher = {Springer}, address = {Berlin}, isbn = {978-3-662-55857-7}, publisher = {Universit{\"a}t Potsdam}, pages = {492}, year = {2018}, abstract = {Mit einer ausgewogenen Stoffauswahl aus den Teilgebieten Chemische Thermodynamik, Reaktionskinetik und Elektrochemie wird der Leser an das Studium der Physikalischen Chemie herangef{\"u}hrt. Das Verst{\"a}ndnis der Theorie wird durch zahlreiche Aufgabenstellungen und die Angabe ihrer L{\"o}sungswege erleichtert. Das Buch gibt dem Studenten dar{\"u}ber hinaus Anregungen f{\"u}r ausgew{\"a}hlte Experimente zu den behandelten Teilgebieten, mit denen sich ein Grundverst{\"a}ndnis physikalisch-chemischer Zusammenh{\"a}nge entwickeln l{\"a}sst.}, language = {de} } @phdthesis{Chen2018, author = {Chen, Guoxiang}, title = {Nanoparticles at solid interfaces}, school = {Universit{\"a}t Potsdam}, pages = {112}, year = {2018}, abstract = {Nanoparticles (NPs) are particles between 1 and 100 nanometers in size. They have attracted enormous research interests owing to their remarkable physicochemical properties and potential applications in the optics, catalysis, sensing, electronics, or optical devices. The thesis investigates systems of NPs attached to planar substrates. In the first part of the results section of the thesis a new method is presented to immobilize NPs. In many NP applications a strong, persistent adhesion to substrates is a key requirement. Up to now this has been achieved with various methods, which are not always the optimum regarding adhesion strength or applicability. We propose a new method which uses capillarity to enhance the binding agents in the contact area between NP and substrate. The adhesion strength resulting from the new approach is investigated in detail and it is shown that the new approach is superior to older methods in several ways. The following section presents the optical visualization of nano-sized objects through a combination of thin film surface distortion and interference enhanced optical reflection microscopy. It is a new, fast and non-destructive technique. It not only reveals the location of NPs as small as 20nm attached to planar surfaces and embedded in a molecularly thin liquid film. It also allows the measurement of the geometry of the surface distortion of the liquid film. Even for small NPs the meniscus reaches out for micrometers, which is the reason why the NPs produce such a pronounced optical footprint. The nucleation and growth of individual bubbles is presented in chapter 5. Nucleation is a ubiquitous natural phenomenon and of great importance in numerous industrial processes. Typically it occurs on very small scales (nanometers) and it is of a random nature (thermodynamics of small systems). Up to now most experimental nucleation studies deal with a large number of individual nucleation processes to cope with its inherently statistical, spatio-temporal character. In contrast, in this thesis the individual O2-bubble formation from single localized platinum NP active site is studied experimentally. The bubble formation is initiated by the catalytic reaction of H2O2 on the Pt surface. It is studied how the bubble nucleation and growth depends on the NP size, the H2O2 concentration and the substrate surface properties. It is observed that in some cases the bubbles move laterally over the substrate surface, driven by the O2-production and the film ablation.}, language = {en} } @phdthesis{Heinke2018, author = {Heinke, David}, title = {Biokompatible superparamagnetische Nanopartikel}, publisher = {Infinite Science Publishing}, address = {L{\"u}beck}, isbn = {978-3-945954-45-4}, pages = {142}, year = {2018}, abstract = {Magnetische Eisenoxidnanopartikel werden bereits seit geraumer Zeit erfolgreich als MRT-Kontrastmittel in der klinischen Bildgebung eingesetzt. Durch Optimierung der magnetischen Eigenschaften der Nanopartikel kann die Aussagekraft von MR-Aufnahmen verbessert und somit der diagnostische Wert einer MR-Anwendung weiter erh{\"o}ht werden. Neben der Verbesserung bestehender Verfahren wird die bildgebende Diagnostik ebenso durch die Entwicklung neuer Verfahren, wie dem Magnetic Particle Imaging, vorangetrieben. Da hierbei das Messsignal von den magnetischen Nanopartikeln selbst erzeugt wird, birgt das MPI einen enormen Vorteil hinsichtlich der Sensitivit{\"a}t bei gleichzeitig hoher zeitlicher und r{\"a}umlicher Aufl{\"o}sung. Da es aktuell jedoch keinen kommerziell vertriebenen in vivo-tauglichen MPI-Tracer gibt, besteht ein dringender Bedarf an geeigneten innovativen Tracermaterialien. Daraus resultierte die Motivation dieser Arbeit biokompatible und superparamagnetische Eisenoxidnanopartikel f{\"u}r den Einsatz als in vivo-Diagnostikum insbesondere im Magnetic Particle Imaging zu entwickeln. Auch wenn der Fokus auf der Tracerentwicklung f{\"u}r das MPI lag, wurde ebenso die MR-Performance bewertet, da geeignete Partikel somit alternativ oder zus{\"a}tzlich als MR-Kontrastmittel mit verbesserten Kontrasteigenschaften eingesetzt werden k{\"o}nnten. Die Synthese der Eisenoxidnanopartikel erfolgte {\"u}ber die partielle Oxidation von gef{\"a}lltem Eisen(II)-hydroxid und Green Rust sowie eine diffusionskontrollierte Kopr{\"a}zipitation in einem Hydrogel. Mit der partiellen Oxidation von Eisen(II)-hydroxid und Green Rust konnten erfolgreich biokompatible und {\"u}ber lange Zeit stabile Eisenoxidnanopartikel synthetisiert werden. Zudem wurden geeignete Methoden zur Formulierung und Sterilisierung etabliert, wodurch zahlreiche Voraussetzungen f{\"u}r eine Anwendung als in vivo-Diagnostikum geschaffen wurden. Weiterhin ist auf Grundlage der MPS-Performance eine hervorragende Eignung dieser Partikel als MPI-Tracer zu erwarten, wodurch die Weiterentwicklung der MPI-Technologie maßgeblich vorangetrieben werden k{\"o}nnte. Die Bestimmung der NMR-Relaxivit{\"a}ten sowie ein initialer in vivo-Versuch zeigten zudem das große Potential der formulierten Nanopartikelsuspensionen als MRT-Kontrastmittel. Die Modifizierung der Partikeloberfl{\"a}che erm{\"o}glicht ferner die Herstellung zielgerichteter Nanopartikel sowie die Markierung von Zellen, wodurch das m{\"o}gliche Anwendungsspektrum maßgeblich erweitert wurde. Im zweiten Teil wurden Partikel durch eine diffusionskontrollierte Kopr{\"a}zipitation im Hydrogel, wobei es sich um eine bioinspirierte Modifikation der klassischen Kopr{\"a}zipitation handelt, synthetisiert, wodurch Partikel mit einer durchschnittlichen Kristallitgr{\"o}ße von 24 nm generiert werden konnten. Die Bestimmung der MPS- und MR-Performance elektrostatisch stabilisierter Partikel ergab vielversprechende Resultate. In Vorbereitung auf die Entwicklung eines in vivo-Diagnostikums wurden die Partikel anschließend erfolgreich sterisch stabilisiert, wodurch der kolloidale Zustand in MilliQ-Wasser {\"u}ber lange Zeit aufrechterhalten werden konnte. Durch Zentrifugation konnten die Partikel zudem erfolgreich in verschiedene Gr{\"o}ßenfraktionen aufgetrennt werden. Dies erm{\"o}glichte die Bestimmung der idealen Aggregatgr{\"o}ße dieses Partikelsystems in Bezug auf die MPS-Performance.}, language = {de} } @phdthesis{Rumschoettel2018, author = {Rumsch{\"o}ttel, Jens}, title = {Charakterisierung von DNA-Polyplexen mit verzweigten reinen und Maltose modifizierten Poly(ethyleniminen) sowie Polyplexen mit Goldnanopartikeln}, school = {Universit{\"a}t Potsdam}, pages = {125}, year = {2018}, language = {de} } @phdthesis{Zhang2018, author = {Zhang, Quanchao}, title = {Shape-memory properties of polymeric micro-scale objects prepared by electrospinning and electrospraying}, school = {Universit{\"a}t Potsdam}, pages = {xvi, 53}, year = {2018}, abstract = {The ongoing trend of miniaturizing multifunctional devices, especially for minimally-invasive medical or sensor applications demands new strategies for designing the required functional polymeric micro-components or micro-devices. Here, polymers, which are capable of active movement, when an external stimulus is applied (e.g. shape-memory polymers), are intensively discussed as promising material candidates for realization of multifunctional micro-components. In this context further research activities are needed to gain a better knowledge about the underlying working principles for functionalization of polymeric micro-scale objects with a shape-memory effect. First reports about electrospun solid microfiber scaffolds, demonstrated a much more pronounced shape-memory effect than their bulk counterparts, indicating the high potential of electrospun micro-objects. Based on these initial findings this thesis was aimed at exploring whether the alteration of the geometry of micro-scale electrospun polymeric objects can serve as suitable parameter to tailor their shape-memory properties. The central hypothesis was that different geometries should result in different degrees of macromolecular chain orientation in the polymeric micro-scale objects, which will influence their mechanical properties as well as thermally-induced shape-memory function. As electrospun micro-scale objects, microfiber scaffolds composed of hollow microfibers with different wall thickness and electrosprayed microparticles as well as their magneto-sensitive nanocomposites all prepared from the same polymer exhibiting pronounced bulk shape-memory properties were investigated. For this work a thermoplastic multiblock copolymer, named PDC, with excellent bulk shape-memory properties, associated with crystallizable oligo(ε-caprolactone) (OCL) switching domains, was chosen for the preparation of electrospun micro-scale objects, while crystallizable oligo(p-dioxanone) (OPDO) segments serve as hard domains in PDC. In the first part of the thesis microfiber scaffolds with different microfiber geometries (solid or hollow with different wall thickness) were discussed. Hollow microfiber based PDC scaffolds were prepared by coaxial electrospinning from a 1, 1, 1, 3, 3, 3 hexafluoro-2-propanol (HFP) solution with a polymer concentration of 13\% w·v-1. Here as a first step core-shell fiber scaffolds consisting of microfibers with a PDC shell and sacrificial poly(ethylene glycol) (PEG) core are generated. The hollow PDC microfibers were achieved after dissolving the PEG core with water. The utilization of a fixed electrospinning setup and the same polymer concentration of the PDC spinning solution could ensure the fabrication of microfibers with almost identical outer diameters of 1.4 ± 0.3 µm as determined by scanning electron microscopy (SEM). Different hollow microfiber wall thicknesses of 0.5 ± 0.2 and 0.3 ± 0.2 µm (analyzed by SEM) have been realized by variation of the mass flow rate, while solid microfibers were obtained by coaxial electrospinning without supplying any core solution. Differential scanning calorimetry experiments and tensile tests at ambient temperature revealed an increase in degree of OCL crystallinity form χc,OCL = 34 ± 1\% to 43 ± 1\% and a decrease in elongation of break from 800 ± 40\% to 200 ± 50\% associated with an increase in Young´s modulus and failture stress for PDC hollow microfiber scaffolds when compared with soild fibers. The observed effects were enhanced with decreasing wall thickness of the single hollow fibers. The shape-memory properties of the electrospun PDC scaffolds were quantified by cyclic, thermomechanical tensile tests. Here, scaffolds comprising hollow microfibers exhibited lower shape fixity ratios around Rf = 82 ± 1\% and higher shape recovery ratios of Rr = 67 ± 1\% associated to more pronounced relaxation at constant strain during the first test cycle and a lower switching temperature of Tsw = 33 ± 1 °C than the fibrous meshes consisting of solid microfibers. These findings strongly support the central hypothesis that different fiber geometries (solid or hollow with different wall thickness) in electrospun scaffolds result in different degrees of macromolecular chain orientation in the polymeric micro-scale objects, which can be applied as design parameter for tailoring their mechanical and shape-memory properties. The second part of the thesis deals with electrosprayed particulate PDC micro-scale objects. Almost spherical PDC microparticles with diameters of 3.9 ± 0.9 μm (as determined by SEM) were achieved by electrospraying of HFP solution with a polymer concentration of 2\% w·v-1. In contrast, smaller particles with sizes of 400 ± 100 nm or 1.2 ± 0.3 μm were obtained for the magneto-sensitive composite PDC microparticles containing 23 ± 0.5 wt\% superparamagnetic magnetite nanoparticles (mNPs). All prepared PDC microparticles exhibited a similar overall crystallinity like the PDC bulk material as analyzed by DSC. AFM nanoindentation results revealed no influence of the nanofiller incorporation on the local mechanical properties represented by the reduced modulus determined for pure PDC microparticles and magneto-sensitive composite PDC microparticles with similar diameters around 1.3 µm. It was found that the reduced modulus of the nanocomposite microparticles increased substantially with decreasing particles size from 2.4 ± 0.9 GPa (1.2 µm) to 11.9 ± 3.1 GPa (0.4 µm), which can be related to a higher orientation of the macromolecules at the surface of smaller sized microparticles. The magneto-sensitivity of such nanocomposite microparticles could be demonstrated in two aspects. One was by attracting/collecting the composite micro-objects with an external permanent magnet. The other one was by a inductive heating to 44 ± 1 °C, which is well above the melting transition of the OCL switching domains, when compacted to a 10 x 10 mm2 film with a thickness of 10 µm and exposed to an alternating magnet field with an magnetic field strength of 30 kA·m-1. Both functions are of great relevance for designing next generation drug delivery systems combining targeting and on demand release. By a compression approach shape-memory functionalization of individual microparticles could be realized. Here different programming pressures and compression temperatures were applied. The shape-recovery capability of the programmed PDC microparticles was quantified by online and off-line heating experiments analyzed via microscopy measurement. The obtained shape-memory properties were found to be strongly depending on the applied programming pressure and temperature. The best shape-memory performance with a high shape recovery rate of about Rr = 80±1\% was obtained when a low pressure of 0.2 MPa was applied at 55 °C. Finally, it was demonstrated that PDC microparticles can be utilized as micro building parts for preparation of a macroscopic film with temporary stability by compression of a densely packed array of PDC microparticles at 60 °C followed by subsequent cooling to ambient temperature. This film disintegrates into individual microparticles upon heating to 60 °C. Based on this technology the design of stable macroscopic release systems can be envisioned, which can be easily fixed at the site of treatment (i.e. by suturing) and disintegrate on demand to microparticles facilitating the drug release. In summary, the results of this thesis could confirm the central hypothesis that the variation of the geometry of polymeric micro-objects is a suitable parameter to adjust their shape-memory performance by changing the degree of macromolecular chain orientation in the specimens or by enabling new functions like on demand disintegration. These fundamental findings might be relevant for designing novel miniaturized multifunctional polymer-based devices.}, language = {en} } @phdthesis{Wang2018, author = {Wang, Li}, title = {Reprogrammable, magnetically controlled polymer actuators}, school = {Universit{\"a}t Potsdam}, pages = {xxviii, 107}, year = {2018}, abstract = {Polymeric materials, which can perform reversible shape changes after programming, in response to a thermal or electrical stimulation, can serve as (soft) actuating components in devices like artificial muscles, photonics, robotics or sensors. Such polymeric actuators can be realized with hydrogels, liquid crystalline elastomers, electro-active polymers or shape-memory polymers by controlling with stumuli such as heat, light, electrostatic or magnetic field. If the application conditions do not allow the direct heating or electric stimulation of these smart devices, noncontact triggering will be required. Remotely controlled actuation have been reported for liquid crystalline elastomer composites or shape-memory polymer network composites, when a persistent external stress is applied during inductive heating in an alternating magnetic field. However such composites cannot meet the demands of applications requiring remotely controlled free-standing motions of the actuating components. The current thesis investigates, whether a reprogrammable remotely controlled soft actuator can be realized by magneto-sensitive multiphase shape-memory copolymer network composites containing magnetite nanoparticles as magneto-sensitive multivalent netpoints. A central hypothesis was that a magnetically controlled two-way (reversible bidirectional) shape-memory effect in such nanocomposites can be achieved without application of external stress (freestanding), when the required orientation of the crystallizable actuation domains (ADs) can be ensured by an internal skeleton like structure formed by a second crystallizable phase determing the samples´s geometry, while magneto-sensitive iron oxide nanoparticles covalently integrated in the ADs allow remote temperature control. The polymer matrix of these composites should exhibit a phase-segregated morphology mainly composed of cyrstallizable ADs, whereby a second set of higher melting crystallites can take a skeleton like, geometry determining function (geometry determining domains, GDs) after programming of the composite and in this way the orientation of the ADs is established and maintained during actuation. The working principle for the reversible bidirectional movements in the multiphase shape-memory polymer network composite is related to a melting-induced contraction (MIC) during inductive heating and the crystallization induced elongation (CIE) of the oriented ADs during cooling. Finally, the amount of multivalent magnetosensitive netpoints in such a material should be as low as possible to ensure an adequate overall elasticity of the nanocomposite and at the same time a complete melting of both ADs and GDs via inductive heating, which is mandatory for enabling reprogrammability. At first, surface decorated iron oxide nanoparticles were synthesized and investigated. The coprecipitation method was applied to synthesize magnetic nanoparticles (mNPs) based on magnetite with size of 12±3 nm and in a next step a ring-opening polymerization (ROP) was utilized for covalent surface modification of such mNPs with oligo(ϵ-caprolactone) (OCL) or oligo(ω-pentadecalactone) (OPDL) via the "grafting from" approach. A successful coating of mNPs with OCL and OPDL was confirmed by differential scanning calorimetry (DSC) experiments showing melting peaks at 52±1 °C for mNP-OCL and 89±1 °C for mNP-OPDL. It was further explored whether two-layered surface decorated mNPs, can be prepared via a second surface-initiated ROP of mNP-OCL or mNP-OPDL with ω-pentadecalactone or ϵ-caprolactone. The observation of two distinct melting transitions in DSC experiments as well as the increase in molecular weight of the detached coatings determined by GPC and 1H-NMR indicated a successful synthesis of the twolayered nanoparticles mNP-OCL-OPDL and mNP-OPDL-OCL. In contrast TEM micrographs revealed a reduction of the thickness of the polymeric coating on the nanoparticles after the second ROP, indicating that the applied synthesis and purification required further optimization. For evaluating the impact of the dispersion of mNPs within a polymer matrix on the resulting inductive heating capability of composites, plain mNPs as well as OCL coated magnetite nanoparticles (mNP-OCLs) were physically incorporated into crosslinked poly(ε-caprolactone) (PCL) networks. Inductive heating experiments were performed with both networks cPCL/mNP and cPCL/mNP-OCL in an alternating magnetic field (AMF) with a magnetic field strength of H = 30 kA·m-1. Here a bulk temperature of Tbulk = 74±2 °C was achieved for cPCL/mNP-OCL, which was almost 20 °C higher than the melting transition of the PCL-based polymer matrix. In contrast, the composite with plain mNPs could only reach a Tbulk of 48±2 °C, which is not sufficient for a complete melting of all PCL crystallites as required for actuation. The inductive heating capability of a multiphase copolymer nanocomposite network (designed as soft actuators) containing surface decorated mNPs as covalent netpoints was investigated. Such composite was synthesized from star-shaped OCL and OPDL precursors, as well as mNP-OCLs via reaction with HDI. The weight ratio of OPDL and OCL in the starting reaction mixture was 15/85 (wt\%/wt\%) and the amount of iron oxide in the nanocomposite was 4 wt\%. DSC experiments revealed two well separated melting and crystallization peaks confirming the required phase-segregated morphology in the nanocomposite NC-mNP-OCL. TEM images could illustrate a phase-segregated morphology of the polymer matrix on the microlevel with droplet shaped regions attributed to the OPDL domains dispersed in an OCL matrix. The TEM images could further demonstrate that the nanoparticulate netpoints in NC-mNP-OCL were almost homogeneously dispersed within the OCL domains. The tests of the inductive heating capability of the nanocomposites at a magnetic field strength of Hhigh = 11.2 kA·m-1 revealed a achievable plateau surface temperature of Tsurf = 57±1 °C for NC-mNP-OCL recorded by an infrared video camera. An effective heat generation constant (̅P) can be derived from a multi-scale model for the heat generation, which is proportional to the rate of heat generation per unit volume of the sample. NC-mNP-OCL with homogeneously dispersed mNP-OCLs exhibited a ̅P value of 1.04±0.01 K·s- 1 at Hhigh, while at Hreset = 30.0 kA·m-1 a Tsurf of 88±1 °C (where all OPDL related crystallite are molten) and a ̅P value of 1.93±0.02 K·s-1 was obtained indicating a high magnetic heating capability of the composite. The free-standing magnetically-controlled reversible shape-memory effect (mrSME) was explored with originally straight nanocomposite samples programmed by bending to an angle of 180°. By switching the magnetic field on and off the composite sample was allowed to repetitively heat to 60 °C and cool to the ambient temperature. A pronounced mrSME, characterized by changes in bending angle of Δϐrev = 20±3° could be obtained for a composite sample programmed by bending when a magnetic field strength of Hhigh = 11.2 kA·m-1 was applied in a multi-cyclic magnetic bending experiment with 600 heating-cooling cycles it could be shown that the actuation performance did not change with increasing number of test cycles, demonstrating the accuracy and reproducibility of this soft actuator. The degree of actuation as well as the kinetics of the shape changes during heating could be tuned by variation of the magnetic filed strength between Hlow and Hhigh or the magnetic field exposure time. When Hreset = 30.0 kA·m-1 was applied the programmed geometry was erased and the composite sample returned to it´s originally straight shape. The reprogrammability of the nanocomposite actuators was demonstrated by one and the same test specimen first exhibiting reversible angle changes when programmed by bending, secondly reprogrammed to a concertina, which expands upon inductive heating and contracts during cooling and finally reprogrammed to a clip like shape, which closes during cooling and opens when Hhigh was applied. In a next step the applicability of the presented remote controllable shape-memory polymer actuators was demonstrated by repetitive opening and closing of a multiring device prepared from NC-mNP-OCL, which repetitively opens and closes when a alternating magnetic field (Hhigh = 11.2 kA·m-1) was switched on and off. For investigation of the micro- and nanostructural changes related to the actuation of the developed nanocomposite, AFM and WAXS experiments were conducted with programmed nanocomposite samples under cyclic heating and cooling between 25 °C and 60 °C. In AFM experiments the change in the distance (D) between representative droplet-like structures related to the OPDL geometry determining domains was used to calculate the reversible change in D. Here Drev = 3.5±1\% was found for NC-mNP-OCL which was in good agreement with the results of the magneto-mechanical actuation experiments. Finally, the analysis of azimuthal (radial) WAXS scattering profiles could support the oriented crystallization of the OCL actuation domains at 25 °C. In conclusion, the results of this work successfully demonstrated that shape-memory polymer nanocomposites, containing mNPs as magneto-sensitive multifunctional netpoints in a covalently crosslinked multiphase polymer matrix, exhibit magnetically (remotely) controlled actuations upon repetitive exposure to an alternating magnetic field. Furthermore, the (shape) memory of such a nanocomposite can be erased by exposing it to temperatures above the melting temperature of the geometry forming domains, which allows a reprogramming of the actuator. These findings would be relevant for designing novel reprogrammable remotely controllable soft polymeric actuators.}, language = {en} } @phdthesis{Zimmermann2018, author = {Zimmermann, Diana}, title = {Direkte Arylierung}, school = {Universit{\"a}t Potsdam}, pages = {221}, year = {2018}, language = {de} }