TY - JOUR A1 - Mazurek-Budzyńska, Magdalena A1 - Behl, Marc A1 - Razzaq, Muhammad Yasar A1 - Nöchel, Ulrich A1 - Rokicki, Gabriel A1 - Lendlein, Andreas T1 - Hydrolytic stability of aliphatic poly(carbonate-urea-urethane)s: Influence of hydrocarbon chain length in soft segment JF - Polymer Degradation and Stability N2 - Poly(carbonate-urethane)s (PCUs) exhibit improved resistance to hydrolytic degradation and in vivo stress cracking compared to poly(ester-urethane)s and their degradation leads to lower inflammation of the surrounding tissues. Therefore, PCUs are promising implant materials and are considered for devices such as artificial heart or spine implants. In this work, the hydrolytic stability of different poly(carbonate-urethane-urea)s (PCUUs) was studied under variation of the length of hydrocarbon chain (6, 9, 10, and 12 methylene units) between the carbonate linkages in the precursors. PCUUs were synthesized from isophorone diisocyanate and oligo(alkylene carbonate) diols using the moisture-cure method. The changes of sample weight, thermal and mechanical properties, morphology, as well as the degradation products after immersion in a buffer solution (PBS, pH = 7.4) for up to 10 weeks at 37 degrees C were monitored and analyzed. In addition, mechanical properties after 20 weeks (in PBS, 37 degrees C) were investigated. The gel content was determined based on swelling experiments in chloroform. Based on the DSC analysis, slight increases of melting transitions of PCUUs were observed, which were attributed to structure reorganization related to annealing at 37 degrees C rather than to the degradation of the PCUU. Tensile strength after 20 weeks of all investigated samples remained in the range of 29-39 MPa, whereas the elongation at break e(m) decreased only slightly and remained in the range between 670 and 800%. Based on the characterization of degradation products after up to 10 weeks of immersion it was assessed that oligomers are mainly consisting of hard segments containing urea linkages, which could be assigned to hindered-urea dissociation mechanism. The investigations confirmed good resistance of PCUUs to hydrolysis. Only minor changes in the crystallinity, as well as thermal and mechanical properties were observed and depended on hydrocarbon chain length in soft segment of PCUUs. (C) 2019 Published by Elsevier Ltd. KW - Poly(carbonate-urea-urethane)s KW - Hydrolytic stability KW - Degradation Y1 - 2019 SN - 0141-3910 SN - 1873-2321 VL - 161 SP - 283 EP - 297 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Rothe, Martin A1 - Zhao, Yuhang A1 - Kewes, Günter A1 - Kochovski, Zdravko A1 - Sigle, Wilfried A1 - van Aken, Peter A. A1 - Koch, Christoph A1 - Ballauff, Matthias A1 - Lu, Yan A1 - Benson, Oliver T1 - Silver nanowires with optimized silica coating as versatile plasmonic resonators JF - Scientific reports N2 - Metal nanoparticles are the most frequently used nanostructures in plasmonics. However, besides nanoparticles, metal nanowires feature several advantages for applications. Their elongation offers a larger interaction volume, their resonances can reach higher quality factors, and their mode structure provides better coupling into integrated hybrid dielectric-plasmonic circuits. It is crucial though, to control the distance of the wire to a supporting substrate, to another metal layer or to active materials with sub-nanometer precision. A dielectric coating can be utilized for distance control, but it must not degrade the plasmonic properties. In this paper, we introduce a controlled synthesis and coating approach for silver nanowires to fulfill these demands. We synthesize and characterize silver nanowires of around 70 nm in diameter. These nanowires are coated with nm-sized silica shells using a modified Stober method to achieve a homogeneous and smooth surface quality. We use transmission electron microscopy, dark-field microscopy and electron-energy loss spectroscopy to study morphology and plasmonic resonances of individual nanowires and quantify the influence of the silica coating. Thorough numerical simulations support the experimental findings showing that the coating does not deteriorate the plasmonic properties and thus introduce silver nanowires as usable building blocks for integrated hybrid plasmonic systems. Y1 - 2019 U6 - https://doi.org/10.1038/s41598-019-40380-5 SN - 2045-2322 VL - 9 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Is the term "Carbene" justified for remote N-heterocyclic carbenes (r-NHCs) and abnormal N-heterocyclic carbenes (aNHCs/MICs)? JF - Tetrahedron N2 - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of typical N-heterocyclic carbenes NHCs, r-NHCs, a-NHCs and MICs have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. Prior to that both structures and 13C chemical shifts were calculated and in case of isolated carbenes the computed δ(13C)/ppm values compared (as a quality criterion for obtained structures) with the experimental ones. The TSNMRS values of the studied carbenes, which are in mesomeric equilibrium with zwitterionic (ylide/betaine/mesoionic) resonance contributors, are employed to qualify and quantify the present electronic structure and if the term carbene is still justified to denote the compounds studied. The results, thus obtained from spatial magnetic properties (TSNMRS), are compared with the geometry of the compounds, the corresponding WIBERG's bond index values, and the 13C chemical shifts especially of the carbene electron-deficient centre. KW - Carbene or zwitterions KW - Ylide KW - Mesomeric equilibrium of carbene/zwitterion KW - Through-space NMR shieldings (TSNMRS) KW - NICS Y1 - 2019 U6 - https://doi.org/10.1016/j.tet.2019.02.005 SN - 0040-4020 VL - 75 IS - 11 SP - 1548 EP - 1554 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Zaitsev-Doyle, John J. A1 - Puchert, Anke A1 - Pfeifer, Yannik A1 - Yan, Hao A1 - Yorke, Briony A. A1 - Müller-Werkmeister, Henrike A1 - Uetrecht, Charlotte A1 - Rehbein, Julia A1 - Huse, Nils A1 - Pearson, Arwen R. A1 - Sans, Marta T1 - Synthesis and characterisation of alpha-carboxynitrobenzyl photocaged l-aspartates for applications in time-resolved structural biology JF - RSC Advances N2 - We report a new synthetic route to a series of a-carboxynitrobenzyl photocaged L-aspartates for application in time-resolved structural biology. The resulting compounds were characterised in terms of UV/Vis absorption properties, aqueous solubility and stability, and photocleavage rates (tau = ms to ms) and quantum yields (phi = 0.05 to 0.14). Y1 - 2019 U6 - https://doi.org/10.1039/c9ra00968j SN - 2046-2069 VL - 9 IS - 15 SP - 8695 EP - 8699 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Jetzschmann, Katharina J. A1 - Tank, Steffen A1 - Jagerszki, Gyula A1 - Gyurcsanyi, Robert E. A1 - Wollenberger, Ulla A1 - Scheller, Frieder W. T1 - Bio-Electrosynthesis of Vectorially Imprinted Polymer Nanofilms for Cytochrome P450cam JF - ChemElectroChem N2 - A new approach for synthesizing a vectorially imprinted polymer (VIP) is presented for the microbial cytochrome P450cam enzyme. A surface attached binding motif of a natural reaction partner of the target protein, putidaredoxin (Pdx), is the anchor to the underlying transducer. The 15 amino acid peptide anchor, which stems from the largest continuous amino acid chain within the binding site of Pdx was modified: (i) internal cysteines were replaced by serines to prevent disulfide bond formation; (ii) 2 ethylene glycol units were attached to the N-terminus as a spacer region; and (iii) an N-terminal cysteine was added to allow the immobilization on the gold electrode surface. Immobilization on GCE was achieved via an N-(1-pyrenyl)maleimide (NPM) cross-linker. In this way oriented immobilization of P450cam was accomplished by binding it to a peptide-modified gold or glassy carbon electrode (GCE) prior to the electrosynthesis of a polymer nanofilm around the immobilized target. This VIP nanofilm enabled reversible oriented docking of P450cam as it is indicated by the catalytic oxygen reduction via direct electron transfer between the enzyme and the underlying electrode. Catalysis of oxygen reduction by P450cam bound to the VIP-modified GCE was used to measure rebinding to the VIP. The mild coupling of an oxidoreductase with the electrode may be appropriate for realizing electrode-driven substrate conversion by instable P450 enzymes without the need of NADPH co-factor. KW - cytochrome P450 KW - direct electron transfer KW - electropolymerization KW - molecularly imprinted polymers KW - protein imprinting Y1 - 2019 U6 - https://doi.org/10.1002/celc.201801851 SN - 2196-0216 VL - 6 IS - 6 SP - 1818 EP - 1823 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Vogel, Stefanie A1 - Ebel, Kenny A1 - Schürmann, Robin Mathis A1 - Heck, Christian A1 - Meiling, Till A1 - Milosavljevic, Aleksandar R. A1 - Giuliani, Alexandre A1 - Bald, Ilko T1 - Vacuum-UV and Low-Energy Electron-Induced DNA Strand Breaks BT - Influence of the DNA Sequence and Substrate JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - DNA is effectively damaged by radiation, which can on the one hand lead to cancer and is on the other hand directly exploited in the treatment of tumor tissue. DNA strand breaks are already induced by photons having an energy below the ionization energy of DNA. At high photon energies, most of the DNA strand breaks are induced by low-energy secondary electrons. In the present study we quantified photon and electron induced DNA strand breaks in four different 12mer oligonucleotides. They are irradiated directly with 8.44 eV vacuum ultraviolet (VUV) photons and 8.8 eV low energy electrons (LEE). By using Si instead of VUV transparent CaF2 as a substrate the VUV exposure leads to an additional release of LEEs, which have a maximum energy of 3.6 eV and can significantly enhance strand break cross sections. Atomic force microscopy is used to visualize strand breaks on DNA origami platforms and to determine absolute values for the strand break cross sections. Upon irradiation with 8.44 eV photons all the investigated sequences show very similar strand break cross sections in the range of 1.7-2.3x10(-16) cm(2). The strand break cross sections for LEE irradiation at 8.8 eV are one to two orders of magnitude larger than the ones for VUV photons, and a slight sequence dependence is observed. The sequence dependence is even more pronounced for LEEs with energies <3.6 eV. The present results help to assess DNA damage by photons and electrons close to the ionization threshold. KW - DNA origami KW - DNA radiation damage KW - DNA strand breaks KW - low-energy electrons KW - vacuum-UV radiation Y1 - 2019 U6 - https://doi.org/10.1002/cphc.201801152 SN - 1439-4235 SN - 1439-7641 VL - 20 IS - 6 SP - 823 EP - 830 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Mehr, Fatemeh Naderi A1 - Grigoriev, Dmitry A1 - Puretskiy, Nikolay A1 - Böker, Alexander T1 - Mono-patchy zwitterionic microcolloids as building blocks for pH-controlled self-assembly JF - Soft matter N2 - A directional molecular interaction between microcolloids can be achieved through pre-defined sites on their surface, patches, which might make them follow each other in a controlled way and assemble into target structures of more complexity. In this article, we report the successful generation and characterization of mono-patchy melamine-formaldehyde microparticles with oppositely charged patches made of poly(methyl vinyl ether-alt-maleic acid) or polyethyleneimine via microcontact printing. The study of their self-aggregation behavior in solution shows that by change of pH, particle dimers are formed via attractive electrostatic force between the patchy and non-patchy surface of the particles, which reaches its optimum at a specific pH. Y1 - 2019 U6 - https://doi.org/10.1039/c8sm02151a SN - 1744-683X SN - 1744-6848 VL - 15 IS - 11 SP - 2430 EP - 2438 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Heiden, Sophia A1 - Usvyat, Denis A1 - Saalfrank, Peter T1 - Theoretical Surface Science Beyond Gradient-Corrected Density Functional Theory BT - Water at alpha-Al2O3(0001) as a Case Study JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - The quantum chemical description of the adsorption, vibrations, and reactions of molecules at periodic solid surfaces is frequently based on a methodological "standard model": density functional theory (DFT) in the generalized gradient approximation (GGA), using plane wave bases and three-dimensional supercells. Although the computationally efficient GGA functionals can be very successful, cases are known where they do not perform so well. Most importantly, activation energies for chemical reactions are typically underestimated, with the consequence of computed reaction rates being too large. In this work, we consider a well-studied model system: water or water fragments adsorbed on an Al-terminated alpha-Al2O3(0001) surface as a test bed for studying the performance of electronic structure methods, both from DFT and wave function theory. On the DFT side, we employ two GGA exchange correlation functionals: PW91 and PBE with and without dispersion corrections, whose results are then compared to those of hybrid functionals B3LYP and HSE06. Further, we follow a periodic wave function approach in the form of local second-order Moller-Plesset perturbation theory, LMP2, on a Hartree-Fock reference. En route, we address issues arising from the choice of the basis set. The key findings of our study are as follows: (i) DFT-GGA adsorption energies are in reasonable agreement with both hybrid-DFT and LMP2 values. In particular, the deviations between the relative energies, corresponding to different adsorption structures, are in the range of the error due to missing dispersion corrections or the basis set error. (ii) Harmonic DFT-GGA vibrational frequencies for oxygen hydrogen stretch modes are by several tens of wavenumbers red-shifted compared to corresponding hybrid-DFT values. The latter are in much better agreement with recent experimental data. (iii) The activation energy for a hydrogen diffusion reaction is grossly underestimated by GGA compared to hybrid-DFT or LMP2, which in turn are quite comparable. Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpcc.9b00407 SN - 1932-7447 VL - 123 IS - 11 SP - 6675 EP - 6684 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schimka, Selina A1 - Klier, Dennis Tobias A1 - de Guerenu, Anna Lopez A1 - Bastian, Philipp A1 - Lomadze, Nino A1 - Kumke, Michael Uwe A1 - Santer, Svetlana T1 - Photo-isomerization of azobenzene containing surfactants induced by near-infrared light using upconversion nanoparticles as mediator JF - Journal of physics : Condensed matter N2 - Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of an appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in darkness, or can be accelerated by exposure to illumination with a longer wavelength typically in a blue/green range. We present the application of lanthanide doped UCNPs to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm-3(+) or Er-3(+) as activator ions, the UCNPs provide emissions in the spectral range of 450 nm < lambda(em) < 480 nm (for Tm-3(+), three and four photon induced emission) or 525 nm < lambda(em) < 545 nm (for Er-3(+), two photon induced emission), respectively. Especially for UCNPs containing Tm-3(+) a good overlap of the emissions with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (lambda(ex) = 976 nm) in the presence of the Tm-3(+)-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13 times compared to thermally induced isomerization. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g. CHCl3) in contrast to water, which shows a distinct absorption in the NIR. KW - upconversion nanoparticles KW - azobenzene containing surfactants KW - kinetic of cis-trans isomerization Y1 - 2019 U6 - https://doi.org/10.1088/1361-648X/aafcfa SN - 0953-8984 SN - 1361-648X VL - 31 IS - 12 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Quan, Ting A1 - Goubard-Bretesche, Nicolas A1 - Haerk, Eneli A1 - Kochovski, Zdravko A1 - Mei, Shilin A1 - Pinna, Nicola A1 - Ballauff, Matthias A1 - Lu, Yan T1 - Highly Dispersible Hexagonal Carbon-MoS2-Carbon Nanoplates with Hollow Sandwich Structures for Supercapacitors JF - Chemistry - a European journal N2 - MoS2, a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon-MoS2-carbon was successfully synthesized through an L-cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS2 flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m(2) g(-1), a total pore volume of 0.677 cm(3) g(-1), and fairly small mesopores (approximate to 5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g(-1) (0.12 F cm(-2)) at a constant current density of 0.1 Ag-1; thus suggesting that hollow carbon-MoS2 carbon nanoplates are promising candidate materials for supercapacitors. KW - carbon KW - chalcogens KW - electrochemistry KW - nanostructures KW - supercapacitors Y1 - 2019 U6 - https://doi.org/10.1002/chem.201806060 SN - 0947-6539 SN - 1521-3765 VL - 25 IS - 18 SP - 4757 EP - 4766 PB - Wiley-VCH CY - Weinheim ER -