TY - JOUR A1 - Morgner, Frank A1 - Bennemann, Mark A1 - Cywiński, Piotr J. A1 - Kollosche, Matthias A1 - Górski, Krzysztof A1 - Pietraszkiewicz, Marek A1 - Geßner, André A1 - Löhmannsröben, Hans-Gerd T1 - Elastic FRET sensors for contactless pressure measurement JF - RSC Advances : an international journal to further the chemical sciences N2 - Contactless pressure monitoring based on Forster resonance energy transfer between donor/acceptor pairs immobilized within elastomers is demonstrated. The donor/acceptor energy transfer is employed by dispersing terbium(III) tris[(2-hydroxybenzoyl)-2-aminoethyl] amine complex (LLC, donor) and CdSe/ZnS quantum dots (QD655, acceptor) in styrene-ethylene/buthylene-styrene (SEBS) and poly(dimethylsiloxane) (PDMS). The continuous monitoring of QD luminescence showed a reversible intensity change as the pressure signal is alternated between two stable states indicating a pressure sensitivity of 6350 cps kPa(-1). Time-resolved measurements show the pressure impact on the FRET signal due to an increase of decay time (270 ms up to 420 ms) for the donor signal and parallel drop of decay time (170 mu s to 155 mu s) for the acceptor signal as the net pressure applied. The LLC/QD655 sensors enable a contactless readout as well as space resolved monitoring to enable miniaturization towards smaller integrated stretchable opto-electronics. Elastic FRET sensors can potentially lead to developing profitable analysis systems capable to outdo conventional wired electronic systems (inductive, capacitive, ultrasonic and photoelectric sensors) especially for point-of-care diagnostics, biological monitoring required for wearable electronics. Y1 - 2017 U6 - https://doi.org/10.1039/c7ra06379b SN - 2046-2069 VL - 7 SP - 50578 EP - 50583 PB - RSC Publishing CY - Cambridge ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Belyakov, Alexander V. A1 - Sigolaev, Yurii F. A1 - Khramov, Alexander N. A1 - Kleinpeter, Erich T1 - Molecular Structure and Conformational Analysis of 1-Phenyl-1-X-1-Silacyclohexanes (X = F, Cl) by Electron Diffraction, Low-Temperature NMR, and Quantum Chemical Calculations JF - The journal of organic chemistry N2 - The molecular structure and conformational preferences of 1-phenyl-1-X-1-silacyclohexanes C5H10Si(Ph,X) (X = F (3), Cl (4)) were studied by gas-phase electron diffraction, low-temperature NMR spectroscopy, and high-level quantum chemical calculations. In the gas phase only three (3) and two (4) stable conformers differing in the axial or equatorial location of the phenyl group and the angle of rotation about the Si-C-ph bond (axi and axo denote the Ph group lying in or out of the X-Si-C-ph plane) contribute to the equilibrium. In 3 the ratio Ph-eq:Ph-axo:Ph-axi is 40(12):55(24):5 and 64:20:16 by experiment and theory, respectively. In 4 the ratio Ph-eq:Ph-axo is 79(15):21(15) and 71:29 by experiment and theory (M06-2X calculations), respectively. The gas-phase electron diffraction parameters are in good agreement with those obtained from theory at the M06-2X/aug-ccPVTZ and MP2/aug-cc-pVTZ levels. Unlike the case for M06-2X, MP2 calculations indicate that 3-Ph-eq conformer lies 0.5 kcal/mol higher than the 3-Ph-axo, conformer. As follows from QTAIM analysis, the phenyl group is more stable when it is located in the axial position but produces destabilization of the silacyclohexane ring: By low temperature NMR spectroscopy the six-membered ring interconversion could be frozen, at 103 K and the present conformational equilibria of 3 and 4 could be determined. The ratio of the conformers is 3-Ph-eq:3-Ph-ax = (75-77):(23-25) and 4-Ph-eq:4-Ph-ax = 82:18. Y1 - 2017 U6 - https://doi.org/10.1021/acs.joc.6b02538 SN - 0022-3263 VL - 82 IS - 1 SP - 461 EP - 470 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Hildebrand, Viet A1 - Laschewsky, Andre A1 - Päch, Michael A1 - Müller-Buschbaum, Peter A1 - Papadakis, Christine M. T1 - Effect of the zwitterion structure on the thermo-responsive behaviour of poly(sulfobetaine methacrylates) JF - Polymer Chemistry N2 - A series of new sulfobetaine methacrylates, including nitrogen-containing saturated heterocycles, was synthesised by systematically varying the substituents of the zwitterionic group. Radical polymerisation via the RAFT (reversible addition–fragmentation chain transfer) method in trifluoroethanol proceeded smoothly and was well controlled, yielding polymers with predictable molar masses. Molar mass analysis and control of the end-group fidelity were facilitated by end-group labeling with a fluorescent dye. The polymers showed distinct thermo-responsive behaviour of the UCST (upper critical solution temperature) type in an aqueous solution, which could not be simply correlated to their molecular structure via an incremental analysis of the hydrophilic and hydrophobic elements incorporated within them. Increasing the spacer length separating the ammonium and the sulfonate groups of the zwitterion moiety from three to four carbons increased the phase transition temperatures markedly, whereas increasing the length of the spacer separating the ammonium group and the carboxylate ester group on the backbone from two to three carbons provoked the opposite effect. Moreover, the phase transition temperatures of the analogous polyzwitterions decreased in the order dimethylammonio > morpholinio > piperidinio alkanesulfonates. In addition to the basic effect of the polymers’ precise molecular structure, the concentration and the molar mass dependence of the phase transition temperatures were studied. Furthermore, we investigated the influence of added low molar mass salts on the aqueous-phase behaviour for sodium chloride and sodium bromide as well as sodium and ammonium sulfate. The strong effects evolved in a complex way with the salt concentration. The strength of these effects depended on the nature of the anion added, increasing in the order sulfate < chloride < bromide, thus following the empirical Hofmeister series. In contrast, no significant differences were observed when changing the cation, i.e. when adding sodium or ammonium sulfate. Y1 - 2016 U6 - https://doi.org/10.1039/c6py01220e SN - 1759-9954 SN - 1759-9962 VL - 8 SP - 310 EP - 322 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Hoogenboom, Richard A1 - Schlaad, Helmut T1 - Thermoresponsive poly(2-oxazoline)s, polypeptoids, and polypeptides JF - Polymer Chemistry N2 - This review covers the recent advances in the emerging field of thermoresponsive polyamides or polymeric amides, i.e., poly(2-oxazoline)s, polypeptoids, and polypeptides, with a specific focus on structure-thermoresponsive property relationships, self-assembly, and applications. Y1 - 2016 U6 - https://doi.org/10.1039/c6py01320a SN - 1759-9954 SN - 1759-9962 VL - 8 IS - 1 SP - 24 EP - 40 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schürmann, Robin Mathis A1 - Bald, Ilko T1 - Real-time monitoring of plasmon induced dissociative electron transfer to the potential DNA radiosensitizer 8-bromoadenine JF - Nanoscale N2 - The excitation of localized surface plasmons in noble metal nanoparticles (NPs) results in different nanoscale effects such as electric field enhancement, the generation of hot electrons and a temperature increase close to the NP surface. These effects are typically exploited in diverse fields such as surface-enhanced Raman scattering (SERS), NP catalysis and photothermal therapy (PTT). Halogenated nucleobases are applied as radiosensitizers in conventional radiation cancer therapy due to their high reactivity towards secondary electrons. Here, we use SERS to study the transformation of 8-bromoadenine ((8Br)A) into adenine on the surface of Au and AgNPs upon irradiation with a low-power continuous wave laser at 532, 633 and 785 nm, respectively. The dissociation of (8Br)A is ascribed to a hot-electron transfer reaction and the underlying kinetics are carefully explored. The reaction proceeds within seconds or even milliseconds. Similar dissociation reactions might also occur with other electrophilic molecules, which must be considered in the interpretation of respective SERS spectra. Furthermore, we suggest that hot-electron transfer induced dissociation of radiosensitizers such as (8Br)A can be applied in the future in PTT to enhance the damage of tumor tissue upon irradiation. Y1 - 2017 U6 - https://doi.org/10.1039/c6nr08695k SN - 2040-3364 SN - 2040-3372 VL - 9 SP - 1951 EP - 1955 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Lorenz, U. A1 - Saalfrank, Peter T1 - A novel system-bath Hamiltonian for vibration-phonon coupling BT - Formulation, and application to the relaxation of Si-H and Si-D bending modes of H/D:Si(100)-(2 x 1) JF - Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature N2 - We present a rigorous method to set up a system-bath Hamiltonian for the coupling of adsorbate vibrations (the system) to surface phonons (the bath). The Hamiltonian is straightforward to derive and exact up to second order in the environment coordinates, thus capable of treating one- and two-phonon contributions to vibration-phonon coupling. The construction of the Hamiltonian uses orthogonal coordinates for system and bath modes, is based on an embedded cluster approach, and generalizes previous Hamiltonians of a similar type, but avoids several (additional) approximations. While the parametrization of the full Hamiltonian is in principle feasible by a first principles quantum mechanical treatment, here we adopt in the spirit of a QM/MM model a combination of density functional theory (“QM”, for the system) and a semiempirical forcefield (“MM”, for the bath). We apply the Hamiltonian to a fully H-covered Si(100)-(2 × 1) surface, using Fermi’s Golden Rule to obtain vibrational relaxation rates of various H–Si bending modes of this system. As in earlier work it is found that the relaxation is dominated by two-phonon contributions because of an energy gap between the Si–H bending modes and the Si phonon bands. We obtain vibrational lifetimes (of the first excited state) on the order of 2 ps at K. The lifetimes depend only little on the type of bending mode (symmetric vs. antisymmetric, parallel vs. perpendicular to the Si2H2 dimers). They decrease by a factor of about two when heating the surface to 300 K. We also study isotope effects by replacing adsorbed H atoms by deuterium, D. The Si–D bending modes are shifted into the Si phonon band of the solid, opening up one-phonon decay channels and reducing the lifetimes to few hundred fs. Y1 - 2016 U6 - https://doi.org/10.1016/j.chemphys.2016.06.004 SN - 0301-0104 SN - 1873-4421 VL - 482 SP - 69 EP - 80 PB - Elsevier Science CY - Amsterdam ER - TY - JOUR A1 - von Klitzing, Regine A1 - Stehl, Dimitrij A1 - Pogrzeba, Tobias A1 - Schomaäcker, Reinhard A1 - Minullina, Renata A1 - Panchal, Abhishek A1 - Konnova, Svetlana A1 - Fakhrullin, Rawil A1 - Koetz, Joachim A1 - Moehwald, Helmuth A1 - Lvov, Yuri T1 - Halloysites Stabilized Emulsions for Hydroformylation of Long Chain Olefins JF - Advanced materials interfaces N2 - Halloysites as tubular alumosilicates are introduced as inexpensive natural nanoparticles to form and stabilize oil-water emulsions. This stabilized emulsion is shown to enable efficient interfacial catalytic reactions. Yield, selectivity, and product separation can be tremendously enhanced, e.g., for the hydroformylation reaction of dodecene to tridecanal. In perspective, this type of formulation may be used for oil spill dispersions. The key elements of the described formulations are clay nanotubes (halloysites) which are highly anisometric, can be filled by helper molecules, and are abundantly available in thousands of tons, making this technology scalable for industrial applications. Y1 - 2016 U6 - https://doi.org/10.1002/admi.201600435 SN - 2196-7350 VL - 4 IS - 1 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Goulet-Hanssens, Alexis A1 - Utecht, Manuel A1 - Mutruc, Dragos A1 - Titov, Evgenii A1 - Schwarz, Jutta A1 - Grubert, Lutz A1 - Bleger, David A1 - Saalfrank, Peter A1 - Hecht, Stefan T1 - Electrocatalytic Z -> E Isomerization of Azobenzenes JF - Journal of the American Chemical Society N2 - A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo)switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z -> E) by the same wavelength of light, which normally triggers E -> Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways. Y1 - 2017 U6 - https://doi.org/10.1021/jacs.6b10822 SN - 0002-7863 VL - 139 IS - 1 SP - 335 EP - 341 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Behrendt, Felix Nicolas A1 - Schlaad, Helmut T1 - Metathesis polymerization of cystine-based macrocycles JF - Polymer Chemistry N2 - Macrocycles based on L-cystine were synthesized by ring-closing metathesis (RCM) and subsequently polymerized by entropy-driven ring-opening metathesis polymerization (ED-ROMP). Monomer conversion reached similar to 80% in equilibrium and the produced poly (ester-amine-disulfide-alkene)s exhibited apparent molar masses (M-w(app)) of up to 80 kDa and dispersities (D) of similar to 2. The polymers can be further functionalized with acid anhydrides and degraded by reductive cleavage of the main-chain disulfide. Y1 - 2016 U6 - https://doi.org/10.1039/c6py01864e SN - 1759-9954 SN - 1759-9962 VL - 8 IS - 2 SP - 366 EP - 369 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Ehlert, Christopher A1 - Klamroth, Tillmann T1 - The quest for best suited references for configuration interaction singles calculations of core excited states JF - Journal of computational chemistry : organic, inorganic, physical, biological N2 - Near edge X-ray absorption fine structure (NEXAFS) simulations based on the conventional configuration interaction singles (CIS) lead to excitation energies, which are systematically blue shifted. Using a (restricted) open shell core hole reference instead of the Hartree Fock (HF) ground state orbitals improves (Decleva et al., Chem. Phys., 1992, 168, 51) excitation energies and the shape of the spectra significantly. In this work, we systematically vary the underlying SCF approaches, that is, based on HF or density functional theory, to identify best suited reference orbitals using a series of small test molecules. We compare the energies of the K edges and NEXAFS spectra to experimental data. The main improvement compared to conventional CIS, that is, using HF ground state orbitals, is due to the electrostatic influence of the core hole. Different SCF approaches, density functionals, or the use of fractional occupations lead only to comparably small changes. Furthermore, to account for bigger systems, we adapt the core-valence separation for our approach. We demonstrate that the good quality of the spectrum is not influenced by this approximation when used together with the non-separated ground state wave function. Simultaneously, the computational demands are reduced remarkably. (C) 2016 Wiley Periodicals, Inc. KW - core excited states KW - configuration interaction KW - near edge X-ray absorption fine structure Y1 - 2016 U6 - https://doi.org/10.1002/jcc.24531 SN - 0192-8651 SN - 1096-987X VL - 38 SP - 116 EP - 126 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Lippold, Holger A1 - Eidner, Sascha A1 - Kumke, Michael Uwe A1 - Lippmann-Pipke, Johanna T1 - Dynamics of metal-humate complexation equilibria as revealed by isotope exchange studies - a matter of concentration and time JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Complexation with dissolved humic matter can be crucial in controlling the mobility of toxic or radioactive contaminant metals. For speciation and transport modelling, a dynamic equilibrium process is commonly assumed, where association and dissociation run permanently. This is, however, questionable in view of reported observations of a growing resistance to dissociation over time. In this study, the isotope exchange principle was employed to gain direct insight into the dynamics of the complexation equilibrium, including kinetic inertisation phenomena. Terbium(III), an analogue of trivalent actinides, was used as a representative of higher-valent metals. Isotherms of binding to (flocculated) humic acid, determined by means of Tb-160 as a radiotracer, were found to be identical regardless of whether the radioisotope was introduced together with the bulk of stable Tb-159 or subsequently after pre-equilibration for up to 3 months. Consequently, there is a permanent exchange of free and humic-bound Tb since all available binding sites are occupied in the plateau region of the isotherm. The existence of a dynamic equilibrium was thus evidenced. There was no indication of an inertisation under these experimental conditions. If the small amount of Tb-160 was introduced prior to saturation with Tb-159, the expected partial desorption of Tb-160 occurred at much lower rates than observed for the equilibration process in the reverse procedure. In addition, the rates decreased with time of pre-equilibration. Inertisation phenomena are thus confined to the stronger sites of humic molecules (occupied at low metal concentrations). Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium. Since, however, metal-humic interaction remains reversible, exchange of metals between humic carriers and mineral surfaces cannot be neglected on the long time scale to be considered in predictive transport models. KW - Humic substances KW - Metal complexation KW - Kinetics KW - Reversibility KW - Isotope exchange KW - Dynamic equilibrium Y1 - 2016 U6 - https://doi.org/10.1016/j.gca.2016.10.019 SN - 0016-7037 SN - 1872-9533 VL - 197 SP - 62 EP - 70 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Michalik-Onichimowska, Aleksandra A1 - Beitz, Toralf A1 - Panne, Ulrich A1 - Löhmannsröben, Hans-Gerd A1 - Riedel, Jens T1 - Microsecond mid-infrared laser pulses for atmospheric pressure laser ablation/ionization of liquid samples JF - Sensors and actuators : B, Chemical N2 - In many laser based ionization techniques with a subsequent drift time separation, the laser pulse generating the ions is considered as the start time to. Therefore, an accurate temporal definition of this event is crucial for the resolution of the experiments. In this contribution, the laser induced plume dynamics of liquids evaporating into atmospheric pressure are visualized for two distinctively different laser pulse widths, Delta t = 6 nanoseconds and Delta tau = 280 microseconds. For ns-pulses the expansion of the generated vapour against atmospheric pressure is found to lead to turbulences inside the gas phase. This results in spatial and temporal broadening of the nascent clouds. A more equilibrated expansion, without artificial smearing of the temporal resolution can, in contrast, be observed to follow mu s-pulse excitation. This leads to the counterintuitive finding that longer laser pulses results in an increased temporal vapour formation definition. To examine if this fume expansion also eventually results in a better definition of ion formation, the nascent vapour plumes were expanded into a linear drift tube ion mobility spectrometer (IMS). This time resolved detection of ion formation corroborates the temporal broadening caused by collisional impeding of the supersonic expansion at atmospheric pressure and the overall better defined ion formation by evaporation with long laser pulses. A direct comparison of the observed results strongly suggests the coexistence of two individual ion formation mechanisms that can be specifically addressed by the use of appropriate laser sources. KW - Laser ablation KW - Ion mobility spectrometry KW - Pulse duration KW - Plume KW - Ionization Y1 - 2016 U6 - https://doi.org/10.1016/j.snb.2016.06.155 SN - 0925-4005 VL - 238 SP - 298 EP - 305 PB - Elsevier CY - Lausanne ER - TY - JOUR A1 - Rackwitz, Jenny A1 - Ranković, Miloš Lj. A1 - Milosavljević, Aleksandar R. A1 - Bald, Ilko T1 - A novel setup for the determination of absolute cross sections for low-energy electron induced strand breaks in oligonucleotides BT - the effect of the radiosensitizer 5-fluorouracil* JF - The European physical journal : D, Atomic, molecular, optical and plasma physics N2 - Low-energy electrons (LEEs) play an important role in DNA radiation damage. Here we present a method to quantify LEE induced strand breakage in well-defined oligonucleotide single strands in terms of absolute cross sections. An LEE irradiation setup covering electron energies <500 eV is constructed and optimized to irradiate DNA origami triangles carrying well-defined oligonucleotide target strands. Measurements are presented for 10.0 and 5.5 eV for different oligonucleotide targets. The determination of absolute strand break cross sections is performed by atomic force microscopy analysis. An accurate fluence determination ensures small margins of error of the determined absolute single strand break cross sections sigma SSB. In this way, the influence of sequence modification with the radiosensitive 5-Fluorouracil (U-5F) is studied using an absolute and relative data analysis. We demonstrate an increase in the strand break yields of U-5F containing oligonucleotides by a factor of 1.5 to 1.6 compared with non-modified oligonucleotide sequences when irradiated with 10 eV electrons. Y1 - 2017 U6 - https://doi.org/10.1140/epjd/e2016-70608-4 SN - 1434-6060 SN - 1434-6079 VL - 71 PB - Springer CY - New York ER - TY - JOUR A1 - Kelly, Mary Allison A1 - Roland, Steffen A1 - Zhang, Qianqian A1 - Lee, Youngmin A1 - Kabius, Bernd A1 - Wang, Qing A1 - Gomez, Enrique D. A1 - Neher, Dieter A1 - You, Wei T1 - Incorporating Fluorine Substitution into Conjugated Polymers for Solar Cells BT - three Different Means, Same Results JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Fluorinating conjugated polymers is a proven strategy for creating high performance materials in polymer solar cells, yet few studies have investigated the importance of the fluorination method. We compare the performance of three fluorinated systems: a poly(benzodithieno-dithienyltriazole) (PBnDT-XTAZ) random copolymer where 50% of the acceptor units are difluorinated, PBnDT-mFTAZ where every acceptor unit is monofluorinated, and a 1:1 physical blend of the difluorinated and nonfluorinated polymer. All systems have the same degree of fluorination (50%) yet via different methods (chemically vs physically, random vs regular). We show that these three systems have equivalent photovoltaic behavior:,similar to 5.2% efficiency with a short-circuit current (J(sc)) at,similar to 11 mA cm(-2), an open-circuit voltage (v(oc)) at 0.77 V, and a fill factor (FF) of similar to 60%. Further investigation of these three systems demonstrates that the charge generation, charge extraction, and charge transfer state are essentially identical for the three studied systems. Transmission electron microscopy shows no significant differences in the morphologies. All these data illustrate that it is possible to improve performance not only via regular or random fluorination but also by physical addition via a ternary blend. Thus, our results demonstrate the versatility of incorporating fluorine in the active layer of polymer solar cells to enhance device performance. Y1 - 2017 U6 - https://doi.org/10.1021/acs.jpcc.6b10993 SN - 1932-7447 VL - 121 IS - 4 SP - 2059 EP - 2068 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schmidt, Bernd A1 - Audörsch, Stephan T1 - Stereoselective Total Syntheses of Polyacetylene Plant Metabolites via Ester-Tethered Ring Closing Metathesis JF - The journal of organic chemistry N2 - Total syntheses of five naturally occurring polyacetylenes from three different plants are described. These natural products have in common an E,Z-configured conjugated diene linked to a di-or triyne chain. As the key method to stereoselectively establish the E,Z-diene part, an ester-tethered ring-closing metathesis/base-induced eliminative ring opening sequence was used. The results presented herein do not only showcase the utility of this tethered RCM variant but have also prompted us to suggest that the originally assigned absolute configurations of chiral polyacetylenes from Atractylodes macrocephala should be revised or at least reconsidered. Y1 - 2017 U6 - https://doi.org/10.1021/acs.joc.6b02987 SN - 0022-3263 VL - 82 IS - 3 SP - 1743 EP - 1760 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schweighöfer, F. A1 - Moreno, J. A1 - Bobone, Sara A1 - Chiantia, Salvatore A1 - Herrmann, A. A1 - Hecht, S. A1 - Wachtveitl, Josef T1 - Connectivity pattern modifies excited state relaxation dynamics of fluorophore-photoswitch molecular dyads JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - In order to modulate the emission of BODIPY fluorophores, they were connected to a diarylethene (DAE) photoswitch via phenylene-ethynylene linkers of different lengths and orientations. The latter allowed for modulation of the electronic coupling in the prepared four BODIPY-DAE dyads, which were compared also to appropriate BODIPY and DAE model compounds by steady state as well as time-resolved spectroscopies. In their open isomers, all dyads show comparable luminescence behavior indicative of an unperturbed BODIPY fluorophore. In strong contrast, in the closed isomers the BODIPY emission is efficiently quenched but the deactivation mechanism depends on the nature of the linker. The most promising dyad was rendered water-soluble by means of micellar encapsulation and aqueous suspensions were investigated by fluorescence spectroscopy and microscopy. Our results (i) illustrate that the electronic communication between the BODIPY and DAE units can indeed be fine-tuned by the nature of the linker to achieve fluorescence modulation while maintaining photoswitchability and (ii) highlight potential applications to image and control biological processes with high spatio-temporal resolution. Y1 - 2016 U6 - https://doi.org/10.1039/c6cp07112k SN - 1463-9076 SN - 1463-9084 VL - 19 SP - 4010 EP - 4018 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Reschke, Stefan A1 - Mebs, Stefan A1 - Sigfridsson-Clauss, Kajsa G. V. A1 - Kositzki, Ramona A1 - Leimkühler, Silke A1 - Haumann, Michael T1 - Protonation and Sulfido versus Oxo Ligation Changes at the Molybdenum Cofactor in Xanthine Dehydrogenase (XDH) Variants Studied by X-ray Absorption Spectroscopy JF - Inorganic chemistry N2 - Enzymes of the xanthine oxidase family are among the best characterized mononuclear molybdenum enzymes. Open questions about their mechanism of transfer of an oxygen atom to the substrate remain. The enzymes share a molybdenum cofactor (Moco) with the metal ion binding a molybdopterin (MPT) molecule via its dithiolene function and terminal sulfur and oxygen groups. For xanthine dehydrogenase (XDH) from the bacterium Rhodobacter capsulatus, we used X-ray absorption spectroscopy to determine the Mo site structure, its changes in a pH range of 5-10, and the influence of amino acids (Glu730 and Gln179) close to Moco in wild-type (WT), Q179A, and E730A variants, complemented by enzyme kinetics and quantum chemical studies. Oxidized WT and Q179A revealed a similar Mo (VI) ion with each one MPT, Mo=O, Mo-O-, and Mo=S ligand, and a weak Mo-O(E730) bond at alkaline pH. Protonation of an oxo to a hydroxo (OH) ligand (pK similar to 6.8) causes inhibition of XDH at acidic pH, whereas deprotonated xanthine (pK similar to 8.8) is an inhibitor at alkaline pH. A similar acidic pK for the WT and Q179A. variants, as well as the metrical parameters of the Mo site and density functional theory calculations, suggested protonation at the equatorial oxo group. The sulfido was replaced with an oxo ligand in the inactive E730A variant, further showing another oxo and one Mo OH ligand at Mo, which are independent of pH. Our findings suggest a reaction mechanism for XDH in which an initial oxo rather than a hydroxo group and the sulfido ligand are essential for xanthine oxidation. Y1 - 2017 U6 - https://doi.org/10.1021/acs.inorgchem.6b02846 SN - 0020-1669 SN - 1520-510X VL - 56 IS - 4 SP - 2165 EP - 2176 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Plötz, Per-Arno A1 - Megow, Jörg A1 - Niehaus, Thomas A1 - Kühn, Oliver T1 - Spectral densities for Frenkel exciton dynamics in molecular crystals BT - a TD-DFTB approach JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Effects of thermal fluctuations on the electronic excitation energies and intermonomeric Coulomb couplings are investigated for a perylene-tetracarboxylic-diimidecrystal. To this end, time dependent density functional theory based tight binding (TD-DFTB) in the linear response formulation is used in combination with electronic ground state classical molecular dynamics. As a result, a parametrized Frenkel exciton Hamiltonian is obtained, with the effect of exciton-vibrational coupling being described by spectral densities. Employing dynamically defined normal modes, these spectral densities are analyzed in great detail, thus providing insight into the effect of specific intramolecular motions on excitation energies and Coulomb couplings. This distinguishes the present method from approaches using fixed transition densities. The efficiency by which intramolecular contributions to the spectral density can be calculated is a clear advantage of this method as compared with standard TD-DFT. Published by AIP Publishing. Y1 - 2017 U6 - https://doi.org/10.1063/1.4976625 SN - 0021-9606 SN - 1089-7690 VL - 146 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Liebeck, Bernd Michael A1 - Hidalgo, Natalia A1 - Roth, Georg A1 - Popescu, Crisan A1 - Böker, Alexander T1 - Synthesis and characterization of Methyl Cellulose/Keratin Hydrolysate Composite Membranes JF - Polymers / Molecular Diversity Preservation International N2 - It is known that aqueous keratin hydrolysate solutions can be produced from feathers using superheated water as solvent. This method is optimized in this study by varying the time and temperature of the heat treatment in order to obtain a high solute content in the solution. With the dissolved polypeptides, films are produced using methyl cellulose as supporting material. Thereby, novel composite membranes are produced from bio-waste. It is expected that these materials exhibit both protein and polysaccharide properties. The influence of the embedded keratin hydrolysates on the methyl cellulose structure is investigated using Fourier transform infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). Adsorption peaks of both components are present in the spectra of the membranes, while the X-ray analysis shows that the polypeptides are incorporated into the semi-crystalline methyl cellulose structure. This behavior significantly influences the mechanical properties of the composite films as is shown by tensile tests. Since further processing steps, e.g., crosslinking, may involve a heat treatment, thermogravimetric analysis (TGA) is applied to obtain information on the thermal stability of the composite materials. KW - bio-based KW - composite materials KW - methyl cellulose KW - keratin KW - superheated water Y1 - 2017 U6 - https://doi.org/10.3390/polym9030091 SN - 2073-4360 VL - 9 PB - MDPI CY - Basel ER - TY - JOUR A1 - Schmidt, Bernd A1 - Riemer, Martin T1 - Microwave-Promoted Pd-Catalyzed Synthesis of Dibenzofurans from Ortho-Arylphenols JF - Journal of Heterocyclic Chemistry N2 - ortho-Aryl phenols, synthesized via protecting group free Suzuki-Miyaura coupling of ortho-halophenols and arene boronic acids, undergo a cyclization to dibenzofurans via oxidative C-H activation. The reaction proceeds under microwave irradiation in short reaction times using catalytic amounts of Pd(OAc)(2) without additional ligands. Y1 - 2017 U6 - https://doi.org/10.1002/jhet.2704 SN - 0022-152X SN - 1943-5193 VL - 54 IS - 2 SP - 1287 EP - 1297 PB - Wiley CY - Hoboken ER -