TY - JOUR A1 - Strauch, Peter A1 - Neumann, Mike A1 - Kelling, Alexandra A1 - Schilde, Uwe T1 - Bis(1,2-dithiosquarato)nickelates(II): Synthesis, Structure, EPR and Thermal Behavior JF - Acta chimica Slovenica N2 - 1,2-Dithiosquaratonickelates are available by direct synthesis from metal salts with dipotassium-1,2-dithiosquarate and the appropriate counter cations. The synthesis and characterization, including mass spectrometry, of a series 1,2-dithiosquaratonickelates(II), [Ni(dtsq)(2)](2-), with several "onium" cations is reported and the X-ray structures of two diamagnetic complexes, (HexPh(3)P)(2)[Ni(dtsq)(2)] and (BuPh3P)(2)[Ni(dtsq)(2)] with sterically demanding counter ions are presented. The diamagnetic nickel complexes have been doped as host lattices with traces of Cu(II) to measure EPR for additional structural information. The thermal behavior of this series is studied by thermogravimetry and differential thermal analysis (TG/DTA). The thermolysis in air as well as under nitrogen atmosphere of these complexes results in nickel oxide nano-particles in all cases, which are characterized by X-ray powder diffraction. KW - 1,2-Dithiosquarate,1,2-Dithiosquaratonickelate KW - X-ray structure KW - TG/DTA KW - Nickel oxide KW - EPR spectroscopy Y1 - 2015 SN - 1318-0207 SN - 1580-3155 VL - 62 IS - 2 SP - 288 EP - 296 PB - Drustvo CY - Ljubljana ER - TY - JOUR A1 - Kroener, Dominik T1 - Laser-driven electron dynamics for circular dichroism in mass spectrometry: from onephoton excitations to multiphoton ionization JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - The distinction of enantiomers is a key aspect of chemical analysis. In mass spectrometry the distinction of enantiomers has been achieved by ionizing the sample with circularly polarized laser pulses and comparing the ion yields for light of opposite handedness. While resonant excitation conditions are expected to be most efficient, they are not required for the detection of a circular dichroism (CD) in the ion yield. However, the prediction of the size and sign of the circular dichroism becomes challenging if non-resonant multiphoton excitations are used to ionize the sample. Employing femtosecond laser pulses to drive electron wavepacket dynamics based on ab initio calculations, we attempt to reveal underlying mechanisms that determine the CD under non-resonant excitation conditions. Simulations were done for (R)-1,2-propylene oxide, using time-dependent configuration interaction singles with perturbative doubles (TD-CIS(D)) and the aug-cc-pVTZ basis set. Interactions between the electric field and the electric dipole and quadrupole as well as between the magnetic field and the magnetic dipole were explicitly accounted for. The ion yield was determined by treating states above the ionization potential as either stationary or non-stationary with energy-dependent lifetimes based on an approved heuristic approach. The observed population dynamics do not allow for a simple interpretation, because of highly non-linear interactions. Still, the various transition pathways are governed by resonant enantiospecific n-photon excitation, with preferably high transition dipole moments, which eventually dominate the CD in the ionized population. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp02193f SN - 1463-9076 SN - 1463-9084 VL - 17 IS - 29 SP - 19643 EP - 19655 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Niedl, Robert Raimund A1 - Beta, Carsten T1 - Hydrogel-driven paper-based microfluidics JF - LAB on a chip : miniaturisation for chemistry and biology N2 - Paper-based microfluidics provide an inexpensive, easy to use technology for point-of-care diagnostics in developing countries. Here, we combine paper-based microfluidic devices with responsive hydrogels to add an entire new class of functions to these versatile low-cost fluidic systems. The hydrogels serve as fluid reservoirs. In response to an external stimulus, e.g. an increase in temperature, the hydrogels collapse and release fluid into the structured paper substrate. In this way, chemicals that are either stored on the paper substrate or inside the hydrogel pads can be dissolved, premixed, and brought to reaction to fulfill specific analytic tasks. We demonstrate that multi-step sequences of chemical reactions can be implemented in a paper-based system and operated without the need for external precision pumps. We exemplify this technology by integrating an antibody-based E. coli test on a small and easy to use paper device. Y1 - 2015 U6 - https://doi.org/10.1039/c5lc00276a SN - 1473-0197 SN - 1473-0189 VL - 11 IS - 15 SP - 2452 EP - 2459 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Kathrein, Christine C. A1 - Bai, Wubin A1 - Currivan-Incorvia, Jean Anne A1 - Liontos, George A1 - Ntetsikas, Konstantinos A1 - Avgeropoulos, Apostolos A1 - Böker, Alexander A1 - Tsarkova, Larisa A1 - Ross, Caroline A. T1 - Combining Graphoepitaxy and Electric Fields toward Uniaxial Alignment of Solvent-Annealed Polystyrene-b-Poly(dimethylsiloxane) Block Copolymers JF - Chemistry of materials : a publication of the American Chemical Society N2 - We report a combined directing effect of the simultaneously applied graphoepitaxy and electric field on the self-assembly of cylinder forming polystyrene-b-poly(dimethylsiloxane) block copolymer in thin films. A correlation length of up to 20 mu m of uniaxial ordered striped patterns is an order of magnitude greater than that produced by either graphoepitaxy or electric field alignment alone and is achieved at reduced annealing times. The angle between the electric field direction and the topographic guides as well as the dimensions of the trenches affected both the quality of the ordering and the direction of the orientation of cylindrical domains: parallel or perpendicular to the topographic features. We quantified the interplay between the electric field and the geometry of the topographic structures by constructing the phase diagram of microdomain orientation. This combined approach allows the fabrication of highly ordered block copolymer structures using macroscopically prepatterned photolithographic substrates. Y1 - 2015 U6 - https://doi.org/10.1021/acs.chemmater.5b03354 SN - 0897-4756 SN - 1520-5002 VL - 27 IS - 19 SP - 6890 EP - 6898 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Liedel, Clemens A1 - Lewin, Christian A1 - Tsarkova, Larisa A1 - Böker, Alexander T1 - Reversible Switching of Block Copolymer Nanopatterns by Orthogonal Electric Fields JF - Small N2 - It is demonstrated that the orientation of striped patterns can be reversibly switched between two perpendicular in-plane orientations upon exposure to electric fields. The results on thin films of symmetric polystyrene-block-poly(2-vinyl pyridine) polymer in the intermediate segregation regime disclose two types of reorientation mechanisms from perpendicular to parallel relative to the electric field orientation. Domains orient via grain rotation and via formation of defects such as stretched undulations and temporal phase transitions. The contribution of additional fields to the structural evolution is also addressed to elucidate the generality of the observed phenomena. In particular solvent effects are considered. This study reveals the stabilization of the meta-stable in-plane oriented lamella due to sequential swelling and quenching of the film. Further, the reorientation behavior of lamella domains blended with selective nanoparticles is addressed, which affect the interfacial tensions of the blocks and hence introduce another internal field to the studied system. Switching the orientation of aligned block copolymer patterns between two orthogonal directions may open new applications of nanomaterials as switchable electric nanowires or optical gratings. KW - alignments KW - block copolymers KW - electric fields KW - reorientation KW - solvent vapor annealing KW - polymers Y1 - 2015 U6 - https://doi.org/10.1002/smll.201502259 SN - 1613-6810 SN - 1613-6829 VL - 11 IS - 45 SP - 6058 EP - 6064 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Pester, Christian W. A1 - Schmidt, Kristin A1 - Ruppel, Markus A1 - Schoberth, Heiko G. A1 - Böker, Alexander T1 - Electric-Field-Induced Order-Order Transition from Hexagonally Perforated Lamellae to Lamellae JF - Macromolecules : a publication of the American Chemical Society N2 - Block copolymers form a variety of microphase morphologies due to their ability to phase separate. The hexagonally perforated lamellar (HPL) morphology represents an unusually long-lived, nonequilibrium transient structure between lamellar and cylindrical phases. We present a detailed study of a concentrated, HPL-forming poly(styrene-b-isoprene) diblock copolymer solution in toluene in the presence of an electric field. We will show that this phase is readily aligned by a moderate electric field and provide experimental evidence for an electric-field-induced order order transition toward the lamellar phase under sufficiently strong fields. This process is shown to be fully reversible as lamellar perforations reconnect immediately upon secession of the external stimulus, recovering highly aligned perforated lamellae. Y1 - 2015 U6 - https://doi.org/10.1021/acs.macromol.5b01336 SN - 0024-9297 SN - 1520-5835 VL - 48 IS - 17 SP - 6206 EP - 6213 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Vukicevic, Radovan A1 - Neffe, Axel T. A1 - Luetzow, Karola A1 - Pierce, Benjamin F. A1 - Lendlein, Andreas T1 - Conditional Ultrasound Sensitivity of Poly[(N-isopropylacrylamide)-co-(vinyl imidazole)] Microgels for Controlled Lipase Release JF - Macromolecular rapid communications N2 - Triggering the release of cargo from a polymer network by ultrasonication as an external, non-invasive stimulus can be an interesting concept for on-demand release. Here, it is shown that, in pH-and thermosensitive microgels, the ultrasound sensitivity of the polymer network depends on the external conditions. Crosslinked poly[(N-isopropylacrylamide)-co-(vinyl imidazole)] microgels showed a volume phase transition temperature (VPTT) of 25-50 degrees C, which increases with decreasing pH. Above the VPTT the polymer chains are collapsed, while below VPTT they are extended. Only in the case of maximum observed swelling, where the polymer chains are expanded, the microgels are mechanically fragmented through ultrasonication. In contrast, when the polymer chains are partially collapsed it is not possible to manipulate the microgels by ultrasound. Additionally, the ultrasound-induced on-demand release of wheat germ lipase from the microgels could be demonstrated successfully. The principle of conditional ultrasound sensitivity is likely to be general and can be used for selection of matrix-cargo combinations. KW - ultrasound KW - polymers KW - microgels KW - lipase release KW - controlled release KW - thermoresponsive polymers KW - biomaterials Y1 - 2015 U6 - https://doi.org/10.1002/marc.201500311 SN - 1022-1336 SN - 1521-3927 VL - 36 IS - 21 SP - 1891 EP - 1896 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Federico, Stefania A1 - Pierce, Benjamin F. A1 - Piluso, Susanna A1 - Wischke, Christian A1 - Lendlein, Andreas A1 - Neffe, Axel T. T1 - Design of Decorin-Based Peptides That Bind to CollagenI and their Potential as Adhesion Moieties in Biomaterials JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - Mimicking the binding epitopes of protein-protein interactions by using small peptides is important for generating modular biomimetic systems. A strategy is described for the design of such bioactive peptides without accessible structural data for the targeted interaction, and the effect of incorporating such adhesion peptides in complex biomaterial systems is demonstrated. The highly repetitive structure of decorin was analyzed to identify peptides that are representative of the inner and outer surface, and it was shown that only peptides based on the inner surface of decorin bind to collagen. The peptide with the highest binding affinity for collagenI, LHERHLNNN, served to slow down the diffusion of a conjugated dye in a collagen gel, while its dimer could physically crosslink collagen, thereby enhancing the elastic modulus of the gel by one order of magnitude. These results show the potential of the identified peptides for the design of biomaterials for applications in regenerative medicine. KW - biomaterials KW - collagen KW - gels KW - peptides KW - protein-protein interactions Y1 - 2015 U6 - https://doi.org/10.1002/anie.201505227 SN - 1433-7851 SN - 1521-3773 VL - 54 IS - 37 SP - 10980 EP - 10984 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Neffe, Axel T. A1 - Lendlein, Andreas T1 - Going Beyond Compromises in Multifunctionality of Biomaterials JF - Advanced healthcare materials Y1 - 2015 U6 - https://doi.org/10.1002/adhm.201400724 SN - 2192-2640 SN - 2192-2659 VL - 4 IS - 5 SP - 642 EP - 645 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Mondal, Suvendu Sekhar A1 - Behrens, Karsten A1 - Matthes, Philipp R. A1 - Schönfeld, Fabian A1 - Nitsch, Jörn A1 - Steffen, Andreas A1 - Primus, Philipp-Alexander A1 - Kumke, Michael Uwe A1 - Müller-Buschbaum, Klaus A1 - Holdt, Hans-Jürgen T1 - White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ JF - Journal of materials chemistry : C, Materials for optical and electronic devices N2 - Co-doping of the MOF 3∞[Zn(2-methylimidazolate-4-amide-5-imidate)] (IFP-1 = Imidazolate Framework Potsdam-1) with luminescent Eu3+ and Tb3+ ions presents an approach to utilize the porosity of the MOF for the intercalation of luminescence centers and for tuning of the chromaticity to the emission of white light of the quality of a three color emitter. Organic based fluorescence processes of the MOF backbone as well as metal based luminescence of the dopants are combined to one homogenous single source emitter while retaining the MOF's porosity. The lanthanide ions Eu3+ and Tb3+ were doped in situ into IFP-1 upon formation of the MOF by intercalation into the micropores of the growing framework without a structure directing effect. Furthermore, the color point is temperature sensitive, so that a cold white light with a higher blue content is observed at 77 K and a warmer white light at room temperature (RT) due to the reduction of the organic emission at higher temperatures. The study further illustrates the dependence of the amount of luminescent ions on porosity and sorption properties of the MOF and proves the intercalation of luminescence centers into the pore system by low-temperature site selective photoluminescence spectroscopy, SEM and EDX. It also covers an investigation of the border of homogenous uptake within the MOF pores and the formation of secondary phases of lanthanide formates on the surface of the MOF. Crossing the border from a homogenous co-doping to a two-phase composite system can be beneficially used to adjust the character and warmth of the white light. This study also describes two-color emitters of the formula Ln@IFP-1a–d (Ln: Eu, Tb) by doping with just one lanthanide Eu3+ or Tb3+. Y1 - 2015 U6 - https://doi.org/10.1039/C4TC02919D SN - 2050-7534 SN - 2050-7526 VL - 18 IS - 3 SP - 4623 EP - 4631 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Mondal, Suvendu Sekhar A1 - Behrens, Karsten A1 - Matthes, Philipp R. A1 - Schönfeld, Fabian A1 - Nitsch, Jörn A1 - Steffen, Andreas A1 - Primus, Philipp-Alexander A1 - Kumke, Michael Uwe A1 - Müller-Buschbaum, Klaus A1 - Holdt, Hans-Jürgen T1 - White light emission of IFP-1 by in situ co-doping of the MOF pore system with Eu3+ and Tb3+ JF - Journal of materials chemistry : C, Materials for optical and electronic devices Y1 - 2015 U6 - https://doi.org/10.1039/c4tc02919d SN - 2050-7526 SN - 2050-7534 VL - 3 IS - 18 SP - 4623 EP - 4631 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Mondal, Suvendu Sekhar A1 - Thomas, Arne A1 - Holdt, Hans-Jürgen T1 - In situ synthesis of amide-imidate-imidazolate ligand and formation of metal-organic frameworks: Application for gas storage JF - Microporous and mesoporous materials : zeolites, clays, carbons and related materials N2 - In this review article, we highlight the synthesis, structures and gas-sorption properties of a series of nine isostructural IFPs (IFP = Imidazolate Framework Potsdam) and two H-bonded networks. IFPs were synthesized by in situ partial hydrolysis of a 4,5-dicyanoimidazole under solvothermal conditions and hence an imidazolate-4-amide-5-imidate linker (C5H3N4O2) was generated, forming the metal -amide-imidate-imidazolateframeworks [M(C5H3N4O2)-R]. Varying R in the 2-substitued linker (R = Me, Cl, Br, Et, OMe and OEt) and metal centre (M2+ = zinc and cobalt) allowed the variation in channel diameter (4.2-03 angstrom) and a fine-tuning of the polarity and functionality of the channel walls of IFPs. Furthermore, we show that using ethyl or alkoxy substituted IFPs the flexible groups act as molecular gates for guest molecules. This allows highly selective CO2 sorption over Ny and CH4 gases. Moreover, during the synthesis of methoxy substituted IFPs (IFP-7 and -8), an imidazolate-4,5-diamide-2-olate linker (C5H4N4O3) formed in situ leads to the formation of a molecular building block (MBB) with a M-6 octahedron inscribed in a M-8 cube (M Zn2+ and Co2+). The MBBs connect by amide amide hydrogen bonds to a 3D robust supramolecular networks [Zn-14(C5H4N4O3)(12)(O) (OH)(2) (DMF)(4) denoted as 1 and 2, respectively, DMF = N,N'-dimethylformamide], which can be activated for N-2, CO2, CH4, and H-2 gas-sorption. (C) 2015 Elsevier Inc. All rights reserved. KW - Flexible linker KW - Gas sorption KW - Gate-effects KW - Hydrogen-bonding KW - Solvothermal synthesis Y1 - 2015 U6 - https://doi.org/10.1016/j.micromeso.2015.01.049 SN - 1387-1811 SN - 1873-3093 VL - 216 SP - 2 EP - 12 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Mondal, Suvendu Sekhar A1 - Behrens, Karsten A1 - Kelling, Alexandra A1 - Nabein, Hans-Peter A1 - Schilde, Uwe A1 - Holdt, Hans-Jürgen T1 - Two Cd-II/Co-II-Imidazolate Coordination Polymers: Syntheses, Crystal Structures, Stabilities, and Luminescent/Magnetic Properties JF - Zeitschrift für anorganische und allgemeine Chemie N2 - Cadmium(II) based 2D coordination polymer [Cd(L1)(2)(DMF)(2)] (1) (L1 = 4,5-dicyano-2-methylimidazolate, DMF = N,N'-dimethylformamide) and 2D cobalt(II)-imidazolate framework [Co(L3)(4)] (2) (L3 = 4,5-diamide-2-ethoxyimidazolate) were synthesized under solvothermal reaction conditions. The materials were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction measurement (PXRD) and single-crystal X-ray diffraction. Compound 1 has hexacoordinate Cd-II ions and forms a zigzag chain-like coordination polymer structure, whereas compound 2 exhibits a 2D square grid type structure. The thermal stability analysis reveals that 2 showed an exceptional thermal stability up to 360 degrees C. Also, 2 maintained its fully crystalline integrity in boiling water as confirmed by PXRD. The solid state luminescent property of 1 was not observed at room temperature. Compound 2 showed an independent high spin central Co-II atom. KW - Cobalt KW - Cadmium KW - Coordination polymers KW - Crystal structures KW - Imidazole Y1 - 2015 U6 - https://doi.org/10.1002/zaac.201500526 SN - 0044-2313 SN - 1521-3749 VL - 641 IS - 11 SP - 1991 EP - 1997 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Hentrich, Doreen A1 - Junginger, Mathias A1 - Bruns, Michael A1 - Börner, Hans Gerhard A1 - Brandt, Jessica A1 - Brezesinski, Gerald A1 - Taubert, Andreas T1 - Interface-controlled calcium phosphate mineralization BT - effect of oligo(aspartic acid)-rich interfaces JF - CrystEngComm N2 - The phase behavior of an amphiphilic block copolymer based on a poly(aspartic acid) hydrophilic block and a poly(n-butyl acrylate) hydrophobic block was investigated at the air–water and air–buffer interface. The polymer forms stable monomolecular films on both subphases. At low pH, the isotherms exhibit a plateau. Compression–expansion experiments and infrared reflection absorption spectroscopy suggest that the plateau is likely due to the formation of polymer bi- or multilayers. At high pH the films remain intact upon compression and no multilayer formation is observed. Furthermore, the mineralization of calcium phosphate beneath the monolayer was studied at different pH. The pH of the subphase and thus the polymer charge strongly affects the phase behavior of the film and the mineral formation. After 4 h of mineralization at low pH, atomic force microscopy shows smooth mineral films with a low roughness. With increasing pH the mineral films become inhomogeneous and the roughness increases. Transmission electron microscopy confirms this: at low pH a few small but uniform particles form whereas particles grown at higher pH are larger and highly agglomerated. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirm the formation of calcium phosphate. The levels of mineralization are higher in samples grown at high pH. Y1 - 2015 U6 - https://doi.org/10.1039/C4CE02274B SN - 1466-8033 IS - 17 SP - 6901 EP - 6913 PB - Royal Society of Chemistry CY - London ER - TY - JOUR A1 - Kirchhecker, Sarah A1 - Tröger-Müller, Steffen A1 - Bake, Sebastian A1 - Antonietti, Markus A1 - Taubert, Andreas A1 - Esposito, Davido T1 - Renewable pyridinium ionic liquids from the continuous hydrothermal decarboxylation of furfural-amino acid derived pyridinium zwitterions JF - Green chemistry N2 - Fully renewable pyridinium ionic liquids were synthesised via the hydrothermal decarboxylation of pyridinium zwitterions derived from furfural and amino acids in flow. The functionality of the resulting ionic liquid (IL) can be tuned by choice of different amino acids as well as different natural carboxylic acids as the counterions. A representative member of this new class of ionic liquids was successfully used for the synthesis of ionogels and as a solvent for the Heck coupling. Y1 - 2015 U6 - https://doi.org/10.1039/c5gc00913h SN - 1463-9262 SN - 1463-9270 VL - 8 IS - 17 SP - 4151 EP - 4156 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Leroux, Fabrice A1 - Rabu, Pierre A1 - Sommerdijk, Nico A. J. M. A1 - Taubert, Andreas T1 - Two-Dimensional Hybrid Materials: Transferring Technology from Biology to Society JF - European journal of inorganic chemistry : a journal of ChemPubSoc Europe N2 - Hybrid materials are at the forefront of modern research and technology; hence a large number of publications on hybrid materials has already appeared in the scientific literature. This essay focuses on the specifics and peculiarities of hybrid materials based on two-dimensional (2D) building blocks and confinements, for two reasons: (1) 2D materials have a very broad field of application, but they also illustrate many of the scientific challenges the community faces, both on a fundamental and an application level; (2) all authors of this essay are involved in research on 2D materials, but their perspective and vision of how the field will develop in the future and how it is possible to benefit from these new developments are rooted in very different scientific subfields. The current article will thus present a personal, yet quite broad, account of how hybrid materials, specifically 2D hybrid materials, will provide means to aid modern societies in fields as different as healthcare and energy. Y1 - 2015 U6 - https://doi.org/10.1002/ejic.201500153 SN - 1434-1948 SN - 1099-0682 IS - 7 SP - 1089 EP - 1095 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Hentrich, Doreen A1 - Junginger, Mathias A1 - Bruns, Michael A1 - Boerner, Hans G. A1 - Brandt, Jessica A1 - Brezesinski, Gerald A1 - Taubert, Andreas T1 - Interface-controlled calcium phosphate mineralization: effect of oligo(aspartic acid)-rich interfaces JF - CrystEngComm N2 - The phase behavior of an amphiphilic block copolymer based on a poly(aspartic acid) hydrophilic block and a poly(n-butyl acrylate) hydrophobic block was investigated at the air-water and air-buffer interface. The polymer forms stable monomolecular films on both subphases. At low pH, the isotherms exhibit a plateau. Compression-expansion experiments and infrared reflection absorption spectroscopy suggest that the plateau is likely due to the formation of polymer bi- or multilayers. At high pH the films remain intact upon compression and no multilayer formation is observed. Furthermore, the mineralization of calcium phosphate beneath the monolayer was studied at different pH. The pH of the subphase and thus the polymer charge strongly affects the phase behavior of the film and the mineral formation. After 4 h of mineralization at low pH, atomic force microscopy shows smooth mineral films with a low roughness. With increasing pH the mineral films become inhomogeneous and the roughness increases. Transmission electron microscopy confirms this: at low pH a few small but uniform particles form whereas particles grown at higher pH are larger and highly agglomerated. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirm the formation of calcium phosphate. The levels of mineralization are higher in samples grown at high pH. Y1 - 2015 U6 - https://doi.org/10.1039/c4ce02274b SN - 1466-8033 VL - 17 IS - 36 SP - 6901 EP - 6913 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Kirchhecker, Sarah A1 - Tröger-Müller, Steffen A1 - Bake, Sebastian A1 - Antonietti, Markus A1 - Taubert, Andreas A1 - Esposito, Davide T1 - Renewable pyridinium ionic liquids from the continuous hydrothermal decarboxylation of furfural-amino acid derived pyridinium zwitterions JF - Green chemistry : an international journal and green chemistry resource N2 - Fully renewable pyridinium ionic liquids were synthesised via the hydrothermal decarboxylation of pyridinium zwitterions derived from furfural and amino acids in flow. The functionality of the resulting ionic liquid (IL) can be tuned by choice of different amino acids as well as different natural carboxylic acids as the counter-ions. A representative member of this new class of ionic liquids was successfully used for the synthesis of ionogels and as a solvent for the Heck coupling. Y1 - 2015 U6 - https://doi.org/10.1039/c5gc00913h SN - 1463-9262 SN - 1463-9270 VL - 17 IS - 8 SP - 4151 EP - 4156 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Mai, Tobias A1 - Boye, Susanne A1 - Yuan, Jiayin A1 - Völkel, Antje A1 - Gräwert, Marlies A1 - Günter, Christina A1 - Lederer, Albena A1 - Taubert, Andreas T1 - Poly(ethylene oxide)-based block copolymers with very high molecular weights for biomimetic calcium phosphate mineralization JF - RSC Advances : an international journal to further the chemical sciences N2 - The present article is among the first reports on the effects of poly(ampholyte)s and poly(betaine)s on the biomimetic formation of calcium phosphate. We have synthesized a series of di- and triblock copolymers based on a non-ionic poly(ethylene oxide) block and several charged methacrylate monomers, 2-(trimethylammonium)ethyl methacrylate chloride, 2-((3-cyanopropyl)-dimethylammonium)ethyl methacrylate chloride, 3-sulfopropyl methacrylate potassium salt, and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide. The resulting copolymers are either positively charged, ampholytic, or betaine block copolymers. All the polymers have very high molecular weights of over 106 g mol−1. All polymers are water-soluble and show a strong effect on the precipitation and dissolution of calcium phosphate. The strongest effects are observed with triblock copolymers based on a large poly(ethylene oxide) middle block (nominal Mn = 100 000 g mol−1). Surprisingly, the data show that there is a need for positive charges in the polymers to exert tight control over mineralization and dissolution, but that the exact position of the charge in the polymer is of minor importance for both calcium phosphate precipitation and dissolution. Y1 - 2015 U6 - https://doi.org/10.1039/c5ra20035k SN - 2046-2069 IS - 5 SP - 103494 EP - 103505 PB - RSC Publishing CY - London ER - TY - JOUR A1 - Ehlert, Christopher A1 - Kröner, Dominik A1 - Saalfrank, Peter T1 - A combined quantum chemical/molecular dynamics study of X-ray photoelectron spectra of polyvinyl alcohol using oligomer models JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - X-ray photoelectron spectroscopy (XPS) is a powerful tool for probing the local chemical environment of atoms near surfaces. When applied to soft matter, such as polymers, XPS spectra are frequently shifted and broadened due to thermal atom motion and by interchain interactions. We present a combined quantum mechanical QM/molecular dynamics (MD) simulation of X-ray photoelectron spectra of polyvinyl alcohol (PVA) using oligomer models in order to account for and quantify these effects on the XPS (C1s) signal. In our study, molecular dynamics at finite temperature were performed with a classical forcefield and by ab initio MD (AIMD) using the Car-Parrinello method. Snapshots along, the trajectories represent possible conformers and/or neighbouring environments, with different C1s ionization potentials for individual C atoms leading to broadened XPS peaks. The latter are determined by Delta-Kohn Sham calculations. We also examine the experimental practice of gauging XPS (C1s) signals of alkylic C-atoms in C-containing polymers to the C1s signal of polyethylene. We find that (i) the experimental XPS (C1s) spectra of PVA (position and width) can be roughly represented by single-strand models, (ii) interchain interactions lead to red-shifts of the XPS peaks by about 0.6 eV, and (iii) AIMD simulations match the findings from classical MD semi-quantitatively. Further, (iv) the gauging procedure of XPS (C1s) signals to the values of PE, introduces errors of about 0.5 eV. (C) 2014 Elsevier B.V. All rights reserved. KW - Simulation of polymer XPS KW - Delta-Kohn Sham method KW - Thermal broadening effects KW - Interchain interactions KW - Classical MD KW - Poly vinyl alcohol Y1 - 2015 U6 - https://doi.org/10.1016/j.elspec.2014.12.007 SN - 0368-2048 SN - 1873-2526 VL - 199 SP - 38 EP - 45 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Banerjee, Shiladitya A1 - Stueker, Tony A1 - Saalfrank, Peter T1 - Vibrationally resolved optical spectra of modified diamondoids obtained from time-dependent correlation function methods JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Optical properties of modified diamondoids have been studied theoretically using vibrationally resolved electronic absorption, emission and resonance Raman spectra. A time-dependent correlation function approach has been used for electronic two-state models, comprising a ground state (g) and a bright, excited state (e), the latter determined from linear-response, time-dependent density functional theory (TD-DFT). The harmonic and Condon approximations were adopted. In most cases origin shifts, frequency alteration and Duschinsky rotation in excited states were considered. For other cases where no excited state geometry optimization and normal mode analysis were possible or desired, a short-time approximation was used. The optical properties and spectra have been computed for (i) a set of recently synthesized sp(2)/sp(3) hybrid species with CQC double-bond connected saturated diamondoid subunits, (ii) functionalized (mostly by thiol or thione groups) diamondoids and (iii) urotropine and other C-substituted diamondoids. The ultimate goal is to tailor optical and electronic features of diamondoids by electronic blending, functionalization and substitution, based on a molecular-level understanding of the ongoing photophysics. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp02615f SN - 1463-9076 SN - 1463-9084 VL - 17 IS - 29 SP - 19656 EP - 19669 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schulze, Michael A1 - Utecht, Manuel Martin A1 - Moldt, Thomas A1 - Przyrembel, Daniel A1 - Gahl, Cornelius A1 - Weinelt, Martin A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10(-18) cm(2) for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp03093e SN - 1463-9076 SN - 1463-9084 VL - 17 IS - 27 SP - 18079 EP - 18086 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Lorenz, Ulf A1 - Saalfrank, Peter T1 - Measures for the non-Markovianity of a harmonic oscillator coupled to a discrete bath derived from numerically exact references JF - The European physical journal : D, Atomic, molecular, optical and plasma physics N2 - System-bath problems in physics and chemistry are often described by Markovian master equations. However, the Markov approximation, i.e., neglect of bath memory effects is not always justified, and different measures of non-Markovianity have been suggested in the literature to judge the validity of this approximation. Here we calculate several computable measures of non-Markovianity for the non-trivial problem of a harmonic oscillator coupled to a large number of bath oscillators. The Multi Configurational Time Dependent Hart ree nietliod is used to provide a numerically converged solution of the system-bath Schrodinger equation, from which the appropriate quantities can be calculated. In particular, we consider measures based on trace-distances and quantum discord for a variety of initial states. These quantities have proven useful in the case of two-level and other small model systems Tpically encountered in quantum optics; but are less straightforward to interpret for the more complex model systems that are relevant for chemical physics. Y1 - 2015 U6 - https://doi.org/10.1140/epjd/e2014-50727-8 SN - 1434-6060 SN - 1434-6079 VL - 69 IS - 2 PB - Springer CY - New York ER - TY - JOUR A1 - Matis, Jochen Rene A1 - Schoenborn, Jan Boyke A1 - Saalfrank, Peter T1 - A multi-reference study of the byproduct formation for a ring-closed dithienylethene photoswitch JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Photodriven molecular switches are sometimes hindered in their performance by forming byproducts which act as dead ends in sequences of switching cycles, leading to rapid fatigue effects. Understanding the reaction pathways to unwanted byproducts is a prerequisite for preventing them. This article presents a study of the photochemical reaction pathways for byproduct formation in the photochromic switch 1,2-bis-(3-thienyl)-ethene. Specifically, using single-and multi-reference methods the post-deexcitation reaction towards the byproduct in the electronic ground state S-0 when starting from the S-1-S-0 conical intersection (CoIn), is considered in detail. We find an unusual low-energy pathway, which offers the possibility for the formation of a dyotropic byproduct. Several high-energy pathways can be excluded with high probability. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp00987a SN - 1463-9076 SN - 1463-9084 VL - 17 IS - 21 SP - 14088 EP - 14095 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schulze, Michael A1 - Utecht, Manuel Martin A1 - Hebert, Andreas A1 - Rück-Braun, Karola A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Reversible Photoswitching of the Interfacial Nonlinear Optical Response JF - The journal of physical chemistry letters N2 - Incorporating photochromic molecules into organic/inorganic hybrid materials may lead to photoresponsive systems. In such systems, the second-order nonlinear properties can be controlled via external stimulation with light at an appropriate wavelength. By creating photochromic molecular switches containing self-assembled monolayers on Si(111), we can demonstrate efficient reversible switching, which is accompanied by a pronounced modulation of the nonlinear optical (NLO) response of the system. The concept of utilizing functionalized photoswitchable Si surfaces could be a way for the generation of two-dimensional NLO switching materials, which are promising for applications in photonic and optoelectronic devices. Y1 - 2015 U6 - https://doi.org/10.1021/jz502477m SN - 1948-7185 VL - 6 IS - 3 SP - 505 EP - 509 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Floss, Gereon A1 - Saalfrank, Peter T1 - The Photoinduced E -> Z Isomerization of Bisazobenzenes: A Surface Hopping Molecular Dynamics Study JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - The photoinduced E -> Z isomerization of azobenzene is a prototypical example of molecular switching. On the way toward rigid molecular rods such as those for opto-mechanical applications, multiazobenzene structures have been suggested in which several switching units are linked together within the same molecule (Bleger et al., J. Phys. Chem. B 2011, 115, 9930-9940). Large differences in the switching efficiency of multiazobenzenes have been observed, depending on whether the switching units are electronically decoupled or not. In this paper we study, on a time-resolved molecular level, the E -> Z isomerization of the simplest multiazobenzene, bisazobenzene (BAB). Two isomers (ortho- and para-BAB), differing only in the connectivity of two azo groups on a shared phenyl ring will be considered.To do so, nonadiabatic semiclassical dynamics after photo-excitation of the isomers are studied by employing an "on-the-fly", fewest switches surface hopping approach. States and couplings are calculated by Configuration Interaction (CI) based on a semiempirical (AM1) Hamiltonian (Persico and co-workers, Chem. Eur. J. 2004, 10, 2327-2341). In the case of para-BAB, computed quantum yields for photoswitching are drastically reduced compared to pristine azobenzene, due to electronic coupling of both switching units. A reason for this (apart from altered absorption spectra and reduced photochromicity) is the drastically reduced lifetimes of electronically excited states which are transiently populated. In contrast for meta-connected species, electronic subsystems are largely decoupled, and computed quantum yields are slightly higher than that for pristine azobenzene because of new isomerization channels. In this case we can also distinguish between single- and double-switch events and we find a cooperative effect: The isomerization of a single azo group is facilitated if the other azo group is already in the Z-configuration. Y1 - 2015 U6 - https://doi.org/10.1021/acs.jpca.5b02933 SN - 1089-5639 VL - 119 IS - 20 SP - 5026 EP - 5037 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Martinez-Mesa, Aliezer A1 - Saalfrank, Peter T1 - Semiclassical modelling of finite-pulse effects on non-adiabatic photodynamics via initial condition filtering: The predissociation of NaI as a test case JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Femtosecond-laser pulse driven non-adiabatic spectroscopy and dynamics in molecular and condensed phase systems continue to be a challenge for theoretical modelling. One of the main obstacles is the "curse of dimensionality" encountered in non-adiabatic, exact wavepacket propagation. A possible route towards treating complex molecular systems is via semiclassical surface-hopping schemes, in particular if they account not only for non-adiabatic post-excitation dynamics but also for the initial optical excitation. One such approach, based on initial condition filtering, will be put forward in what follows. As a simple test case which can be compared with exact wavepacket dynamics, we investigate the influence of the different parameters determining the shape of a laser pulse (e.g., its finite width and a possible chirp) on the predissociation dynamics of a NaI molecule, upon photoexcitation of the A(0(+)) state. The finite-pulse effects are mapped into the initial conditions for semiclassical surface-hopping simulations. The simulated surface-hopping diabatic populations are in qualitative agreement with the quantum mechanical results, especially concerning the subpicosend photoinduced dynamics, the main deviations being the relative delay of the non-adiabatic transitions in the semiclassical picture. Likewise, these differences in the time-dependent electronic populations calculated via the semiclassical and the quantum methods are found to have a mild influence on the overall probability density distribution. As a result, the branching ratios between the bound and the dissociative reaction channels and the time-evolution of the molecular wavepacket predicted by the semiclassical method agree with those computed using quantum wavepacket propagation. Implications for more challenging molecular systems are given. (C) 2015 AIP Publishing LLC. Y1 - 2015 U6 - https://doi.org/10.1063/1.4919780 SN - 0021-9606 SN - 1089-7690 VL - 142 IS - 19 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Wirth, Jonas A1 - Hatter, Nino A1 - Drost, Robert A1 - Umbach, Tobias R. A1 - Barja, Sara A1 - Zastrow, Matthias A1 - Rück-Braun, Karola A1 - Pascual, Jose Ignacio A1 - Saalfrank, Peter A1 - Franke, Katharina J. T1 - Diarylethene Molecules on a Ag(111) Surface: Stability and Electron-Induced Switching JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Diarylethene derivatives are photochromic molecular switches, undergoing a ring-opening/-closing reaction by illumination with light. The symmetry of the closed form is determined by the WoodWard Hoffinann rules according to which the reaction proceeds by corirotatory rotation -in that case. Here, we show by a cOrnbined approach of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations that the Open isomer of 4,4'-(4,4'-(perfluorocydopent-1-ene-1,2-diyl)bis(5-methyl-thiophent-4,2,4-dipyridine) (PDTE) retains its open form upon adsorption on a Ag(111) surface. It caribe switched into a closed form, which we identify as the digrotatOly cydization product, by controlled manipulation 'With the STM tip, Evidence of an electric-field dependent switching-process 'is interpreted on the basis of a Simple electroStatic Model, which suggests that the reaction proceedS via an "upright" intermediate state. This pathway thus strongly differs from the switching reaction in solution. Y1 - 2015 U6 - https://doi.org/10.1021/jp5122036 SN - 1932-7447 VL - 119 IS - 9 SP - 4874 EP - 4883 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Chandran, Sivasurender A1 - Dold, Stefanie A1 - Buvignier, Amaury A1 - Krannig, Kai-Steffen A1 - Schlaad, Helmut A1 - Reiter, Günter A1 - Reiter, Renate T1 - Tuning Morphologies of Langmuir Polymer Films Through Controlled Relaxations of Non-Equilibrium States JF - Langmuir N2 - Langmuir polymers films (LPFs) frequently form non-equilibrium states which are manifested in a decay of the surface pressure with time when the system is allowed to relax. Monitoring and manipulating the temporal evolution of these relaxations experimentally helps to shed light on the associated molecular reorganization processes. We present a systematic study based on different compression protocols and show how these reorganization processes impact the morphology of LPFs of poly(gamma-benzyl-L-glutamate) (PBLG); visualized by means of atomic force microscopy. Upon continuous compression, a fibrillar morphology was formed with a surface decorated by squeezed-out islands. By contrast, stepwise compression promoted the formation of a fibrillar network with a bimodal distribution of fibril diameters, caused by merging of fibrils. Finally, isobaric compression induced in-plane compaction of the monolayer. We correlate these morphological observations with the kinetics of the corresponding relaxations, described best by a sum of two exponential functions with different time scales representing two molecular processes. We discuss the observed kinetics and the resulting morphologies in the context of nucleation and growth, characteristic for first-order phase transitions. Our results demonstrate that the preparation conditions of LPFs have tremendous impact on ordering of the molecules and hence various macroscopic properties of such films. Y1 - 2015 U6 - https://doi.org/10.1021/acs.langmuir.5b01212 SN - 0743-7463 VL - 31 IS - 23 SP - 6426 EP - 6435 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Mai, Tobias A1 - Boye, Susanne A1 - Yuan, Jiayin A1 - Voelkel, Antje A1 - Graewert, Marlies A1 - Günter, Christina A1 - Lederer, Albena A1 - Taubert, Andreas T1 - Poly(ethylene oxide)-based block copolymers with very high molecular weights for biomimetic calcium phosphate mineralization JF - RSC Advances N2 - The present article is among the first reports on the effects of poly(ampholyte)s and poly(betaine) s on the biomimetic formation of calcium phosphate. We have synthesized a series of di- and triblock copolymers based on a non-ionic poly(ethylene oxide) block and several charged methacrylate monomers, 2-(trimethylammonium) ethyl methacrylate chloride, 2-((3-cyanopropyl)-dimethylammonium)ethyl methacrylate chloride, 3-sulfopropyl methacrylate potassium salt, and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide. The resulting copolymers are either positively charged, ampholytic, or betaine block copolymers. All the polymers have very high molecular weights of over 10(6) g mol(-1). All polymers are water-soluble and show a strong effect on the precipitation and dissolution of calcium phosphate. The strongest effects are observed with triblock copolymers based on a large poly(ethylene oxide) middle block (nominal M-n = 100 000 g mol(-1)). Surprisingly, the data show that there is a need for positive charges in the polymers to exert tight control over mineralization and dissolution, but that the exact position of the charge in the polymer is of minor importance for both calcium phosphate precipitation and dissolution. Y1 - 2015 U6 - https://doi.org/10.1039/c5ra20035k SN - 2046-2069 VL - 5 IS - 125 SP - 103494 EP - 103505 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Behrens, Karsten A1 - Mondal, Suvendu Selchar A1 - Nöske, Robert A1 - Baburin, Igor A. A1 - Leoni, Stefano A1 - Günter, Christina A1 - Weber, Jens A1 - Holdt, Hans-Jürgen T1 - Microwave-Assisted Synthesis of Defects Metal-Imidazolate-Amide-Imidate Frameworks and Improved CO2 Capture JF - Inorganic chemistry N2 - In this work, we report three isostructural 3D frameworks, named IFP-11 (R = Cl), IFP-12 (R = Br), and IFP-13 (R = Et) (IFP = Imidazolate Framework Potsdam) based on a cobalt(II) center and the chelating linker 2-substituted imidazolate-4-amide-5-imidate. These chelating ligands were generated in situ by partial hydrolysis of 2-substituted 4,5-dicyanoimidazoles under microwave (MW)-assisted conditions in DMF. Structure determination of these IFPs was investigated by IR spectroscopy and a combination of powder X-ray diffraction (PXRD) with structure modeling. The structural models were initially built up from the single-crystal X-ray structure determination of IFP-5 (a cobalt center and 2-methylimidazolate-4-amide-5-imidate linker based framework) and were optimized by using density functional theory calculations. Substitution on position 2 of the linker (R = Cl, Br, and Et) in the isostructural IFP-11, -12, and -13 allowed variation of the potential pore window in 1D hexagonal channels (3.8 to 1.7 angstrom A). The potential of the materials to undergo specific interactions with CO2 was measured by the isosteric heat adsorption. Further, we resynthesized zinc based IFPs, namely IFP-1 = Me), IFP-2 (R = Cl), IFP-3 (R = Br), and IFP-4 (R = Et), and cobalt based IFP-5 under MW-assisted conditions with higher yield. The transition from a nucleation phase to the pure crystalline material of IFP-1 in MW-assisted synthesis depends on reaction time. IFP-1, -3, and -5, which are synthesized by MW-assisted conditions, showed an enhancement of N-2 and CO2, compared to the analogous conventional electrical (CE) heating method based materials due to crystal defects. Y1 - 2015 U6 - https://doi.org/10.1021/acs.inorgchem.5b01952 SN - 0020-1669 SN - 1520-510X VL - 54 IS - 20 SP - 10073 EP - 10080 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schulze, Michael A1 - Utecht, Manuel Martin A1 - Moldt, Thomas A1 - Przyrembel, Daniel A1 - Gahl, Cornelius A1 - Weinelt, Martin A1 - Saalfrank, Peter A1 - Tegeder, Petra T1 - Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10−18 cm2 for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. Y1 - 2015 U6 - https://doi.org/10.1039/c5cp03093e SN - 1463-9076 SN - 1463-9084 VL - 27 IS - 17 SP - 18079 EP - 18086 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Matis, Jochen René A1 - Schönborn, Jan Boyke A1 - Saalfrank, Peter T1 - A multi-reference study of the byproduct formation for a ring-closed dithienylethene photoswitch JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - Photodriven molecular switches are sometimes hindered in their performance by forming byproducts which act as dead ends in sequences of switching cycles, leading to rapid fatigue effects. Understanding the reaction pathways to unwanted byproducts is a prerequisite for preventing them. This article presents a study of the photochemical reaction pathways for byproduct formation in the photochromic switch 1,2-bis-(3-thienyl)-ethene. Specifically, using single- and multi-reference methods the post-deexcitation reaction towards the byproduct in the electronic ground state S0 when starting from the S1–S0 conical intersection (CoIn), is considered in detail. We find an unusual low-energy pathway, which offers the possibility for the formation of a dyotropic byproduct. Several high-energy pathways can be excluded with high probability. Y1 - 2015 U6 - https://doi.org/10.1039/C5CP00987A SN - 1463-9076 SN - 1463-9084 IS - 17 SP - 14088 EP - 14095 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Eisold, Ursula A1 - Sellrie, Frank A1 - Schenk, Jörg A. A1 - Lenz, Christine A1 - Stöcklein, Walter F. M. A1 - Kumke, Michael Uwe T1 - Bright or dark immune complexes of anti-TAMRA antibodies for adapted fluorescence-based bioanalysis JF - Analytical & bioanalytical chemistry N2 - Fluorescence labels, for example fluorescein or rhodamin derivatives, are widely used in bioanalysis applications including lateral-flow assays, PCR, and fluorescence microscopy. Depending on the layout of the particular application, fluorescence quenching or enhancement may be desired as the detection principle. Especially for multiplexed applications or high-brightness requirements, a tunable fluorescence probe can be beneficial. The alterations in the photophysics of rhodamine derivatives upon binding to two different anti-TAMRA antibodies were investigated by absorption and fluorescence-spectroscopy techniques, especially determining the fluorescence decay time and steady-state and time-resolved fluorescence anisotropy. Two monoclonal anti-TAMRA antibodies were generated by the hybridoma technique. Although surface-plasmon-resonance measurements clearly proved the high affinity of both antibodies towards 5-TAMRA, the observed effects on the fluorescence of rhodamine derivatives were very different. Depending on the anti-TAMRA antibody either a strong fluorescence quenching (G71-DC7) or a distinct fluorescence enhancement (G71-BE11) upon formation of the immune complex was observed. Additional rhodamine derivatives were used to gain further information on the binding interaction. The data reveal that such haptens as 5-TAMRA could generate different paratopes with equal binding affinities but different binding interactions, which provide the opportunity to adapt bioanalysis methods including immunoassays for optimized detection principles for the same hapten depending on the specific requirements. KW - mAb KW - Fluorescence KW - Anisotropy KW - Exciplex KW - Energy-transfer probe Y1 - 2015 U6 - https://doi.org/10.1007/s00216-015-8538-0 SN - 1618-2642 SN - 1618-2650 VL - 407 IS - 12 SP - 3313 EP - 3323 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Mergel, Olga A1 - Wuennemann, Patrick A1 - Simon, Ulrich A1 - Böker, Alexander A1 - Plamper, Felix A. T1 - Microgel Size Modulation by Electrochemical Switching JF - Chemistry of materials : a publication of the American Chemical Society N2 - In this work we present the first e-microgel, whose size can be adjusted by application of an electrochemical potential, as seen by dynamic light scattering (3D-DLS in dependence of equilibrium potential) and scanning force microscopy (SFM). Hereby, polyelectrolyte microgels with attracted electroactive counterions provide an effective platform for the manipulation of the microgel size by electrochemical means. The reversible switching of guest molecules, namely, hexacyanoferrates, between oxidized ferricyanide [Fe(CN)(6)](3-) and reduced ferrocyanide [Fe(CN)(6)](4-), influences the cationic host microgel, poly(N-isopropylacrylamide-co-methacrylamidopropyltrimethylammonium chloride) P(NIPAM-co-MAPTAC), and hence the swelling properties of the microgel. The combination of thermo- and redox-responsiveness in one particle leads to a novel type of multistimuli responsive material. In addition, the use of hydrodynamic voltammetry detects directly the preferred uptake of ferricyanide and enables the determination of the nominal charge ratio (ncr) between microgel and entrapped counterions at different states of switching. Further, electrochemical impedance spectroscopy allows a more detailed mechanistic insight into the microgel modulation. Y1 - 2015 U6 - https://doi.org/10.1021/acs.chemmater.5b02740 SN - 0897-4756 SN - 1520-5002 VL - 27 IS - 21 SP - 7306 EP - 7312 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Banerjee, Shiladitya A1 - Stüker, Tony A1 - Saalfrank, Peter T1 - Vibrationally resolved optical spectra of modified diamondoids obtained from time-dependent correlation function methods JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies N2 - Optical properties of modified diamondoids have been studied theoretically using vibrationally resolved electronic absorption, emission and resonance Raman spectra. A time-dependent correlation function approach has been used for electronic two-state models, comprising a ground state (g) and a bright, excited state (e), the latter determined from linear-response, time-dependent density functional theory (TD-DFT). The harmonic and Condon approximations were adopted. In most cases origin shifts, frequency alteration and Duschinsky rotation in excited states were considered. For other cases where no excited state geometry optimization and normal mode analysis were possible or desired, a short-time approximation was used. The optical properties and spectra have been computed for (i) a set of recently synthesized sp2/sp3 hybrid species with C[double bond, length as m-dash]C double-bond connected saturated diamondoid subunits, (ii) functionalized (mostly by thiol or thione groups) diamondoids and (iii) urotropine and other C-substituted diamondoids. The ultimate goal is to tailor optical and electronic features of diamondoids by electronic blending, functionalization and substitution, based on a molecular-level understanding of the ongoing photophysics. Y1 - 2015 U6 - https://doi.org/10.1039/C5CP02615F SN - 1463-9084 SN - 1463-9076 VL - 17 IS - 29 SP - 19656 EP - 19669 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Adelsberger, Joseph A1 - Bivigou Koumba, Achille Mayelle A1 - Miasnikova, Anna A1 - Busch, Peter A1 - Laschewsky, André A1 - Müller-Buschbaum, Peter A1 - Papadakis, Christine M. T1 - Polystyrene-block-poly (methoxy diethylene glycol acrylate)-block-polystyrene triblock copolymers in aqueous solution-a SANS study of the temperature-induced switching behavior JF - Colloid and polymer science : official journal of the Kolloid-Gesellschaft N2 - A concentrated solution of a symmetric triblock copolymer with a thermoresponsive poly(methoxy diethylene glycol acrylate) (PMDEGA) middle block and short hydrophobic, fully deuterated polystyrene end blocks is investigated in D2O where it undergoes a lower critical solution temperature-type phase transition at ca. 36 A degrees C. Small-angle neutron scattering (SANS) in a wide temperature range (15-50 A degrees C) is used to characterize the size and inner structure of the micelles as well as the correlation between the micelles and the formation of aggregates by the micelles above the cloud point (CP). A model featuring spherical core-shell micelles, which are correlated by a hard-sphere potential or a sticky hard-sphere potential together with a Guinier form factor describing aggregates formed by the micelles above the CP, fits the SANS curves well in the entire temperature range. The thickness of the thermoresponsive micellar PMDEGA shell as well as the hard-sphere radius increase slightly already below the cloud point. Whereas the thickness of the thermoresponsive micellar shell hardly shrinks when heating through the CP and up to 50 A degrees C, the hard-sphere radius decreases within 3.5 K at the CP. The volume fraction decreases already significantly below the CP, which may be at the origin of the previously observed gel-sol transition far below the CP (Miasnikova et al., Langmuir 28: 4479-4490, 2012). Above the CP, small, and at higher temperatures, large aggregates are formed by the micelles. KW - Hydrogel KW - Thermoresponsive KW - LCST behavior KW - SANS Y1 - 2015 U6 - https://doi.org/10.1007/s00396-015-3535-6 SN - 0303-402X SN - 1435-1536 VL - 293 IS - 5 SP - 1515 EP - 1523 PB - Springer CY - New York ER - TY - JOUR A1 - Zhong, Qi A1 - Metwalli, Ezzeldin A1 - Rawolle, Monika A1 - Kaune, Gunar A1 - Bivigou Koumba, Achille Mayelle A1 - Laschewsky, André A1 - Papadakis, Christine M. A1 - Cubitt, Robert A1 - Müller-Buschbaum, Peter T1 - Rehydration of Thermoresponsive Poly(monomethoxydiethylene glycol acrylate) Films Probed in Situ by Real-Time Neutron Reflectivity JF - Macromolecules : a publication of the American Chemical Society N2 - The rehydration of thermoresponsive poly(monomethoxydiethylene glycol acrylate) (PMDEGA) films exhibiting a lower critical solution temperature (LCST) type demixing phase transition in aqueous environments, induced by a decrease in temperature, is investigated in situ with real-time neutron reflectivity. Two different starting conditions (collapsed versus partially swollen chain conformation) are compared. In one experiment, the temperature is reduced from above the demixing temperature to well below the demixing temperature. In a second experiment, the starting temperature is below the demixing temperature, but within the transition regime, and reduced to the same final temperature. In both cases, the observed rehydration process can be divided into three stages: first condensation of water from the surrounding atmosphere, then absorption of water by the PMDEGA film and evaporation of excess water, and finally, rearrangement of the PMDEGA chains. The final rehydrated film is thicker and contains more absorbed water as compared with the initially swollen film at the same temperature well below the demixing temperature. Y1 - 2015 U6 - https://doi.org/10.1021/acs.macromol.5b00645 SN - 0024-9297 SN - 1520-5835 VL - 48 IS - 11 SP - 3604 EP - 3612 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schmidt, Joachim T1 - Die Arbeit bei irreversibler Druck-Volumen-Änderung BT - Varianten der Berechnung N2 - For the calculation of the work in an irreversible pressure-volume change, we propose approxima-tions, which in contrast to the usual representation in the literature reflect the work performed during expansion and compression symmetrically. The calculations are based on the Reversible-Share-Theorem: Is used the force to overcome for calculating the work, so it captures only the configurational reversible work share. KW - physics KW - physical chemistry KW - thermodynamics KW - irreversible volume-change KW - reversible-share-theorem KW - total work KW - reversible work share KW - irreversible work share Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74931 ER - TY - JOUR A1 - Tong, Yujin A1 - Wirth, Jonas A1 - Kirsch, Harald A1 - Wolf, Martin A1 - Saalfrank, Peter A1 - Campen, Richard Kramer T1 - Optically probing Al-O and O-H vibrations to characterize water adsorption and surface reconstruction on alpha-alumina: An experimental and theoretical study JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Oxide/water interfaces are ubiquitous in a wide variety of applications and the environment. Despite this ubiquity, and attendant decades of study, gaining molecular level insight into water/oxide interaction has proven challenging. In part, this challenge springs from a lack of tools to concurrently characterize changes in surface structure (i.e., water/oxide interaction from the perspective of the solid) and O-H population and local environment (i.e., water/oxide interaction from the water perspective). Here, we demonstrate the application of surface specific vibrational spectroscopy to the characterization of the interaction of the paradigmatic alpha-Al2O3(0001) surface and water. By probing both the interfacial Al-O (surface phonon) and O-H spectral response, we characterize this interaction from both perspectives. Through electronic structure calculation, we assign the interfacial Al-O response and rationalize its changes on surface dehydroxylation and reconstruction. Because our technique is all-optical and interface specific, it is equally applicable to oxide surfaces in vacuum, ambient atmospheres and at the solid/liquid interface. Application of this approach to additional alumina surfaces and other oxides thus seems likely to significantly expand our understanding of how water meets oxide surfaces and thus the wide variety of phenomena this interaction controls. (C) 2015 AIP Publishing LLC. Y1 - 2015 U6 - https://doi.org/10.1063/1.4906346 SN - 0021-9606 SN - 1089-7690 VL - 142 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Lohren, Hanna A1 - Bornhorst, Julia A1 - Galla, Hans-Joachim A1 - Schwerdtle, Tanja T1 - The blood–cerebrospinal fluid barrier BT - First evidence for an active transport of organic mercury compounds out of the brain JF - Metallomics : integrated biometal science N2 - Exposure to organic mercury compounds promotes primarily neurological effects. Although methylmercury is recognized as a potent neurotoxicant, its transfer into the central nervous system (CNS) is not fully evaluated. While methylmercury and thiomersal pass the blood–brain barrier, limited data are available regarding the second brain regulating interface, the blood–cerebrospinal fluid (CSF) barrier. This novel study was designed to investigate the effects of organic as well as inorganic mercury compounds on, and their transfer across, a porcine in vitro model of the blood–CSF barrier for the first time. The barrier system is significantly more sensitive towards organic Hg compounds as compared to inorganic compounds regarding the endpoints cytotoxicity and barrier integrity. Whereas there are low transfer rates from the blood side to the CSF side, our results strongly indicate an active transfer of the organic mercury compounds out of the CSF. These results are the first to demonstrate an efflux of organic mercury compounds regarding the CNS and provide a completely new approach in the understanding of mercury compounds specific transport. Y1 - 2015 U6 - https://doi.org/10.1039/C5MT00171D SN - 1756-5901 SN - 1756-591X VL - 10 IS - 7 SP - 1420 EP - 1430 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Crone, Barbara A1 - Aschner, Michael A. A1 - Schwerdtle, Tanja A1 - Karst, Uwe A1 - Bornhorst, Julia T1 - Elemental bioimaging of Cisplatin in Caenorhabditis elegans by LA-ICP-MS JF - Metallomics N2 - cis-Diamminedichloroplatinum(II) (Cisplatin) is one of the most important and frequently used cytostatic drugs for the treatment of various solid tumors. Herein, a laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) method incorporating a fast and simple sample preparation protocol was developed for the elemental mapping of Cisplatin in the model organism Caenorhabditis elegans (C. elegans). The method allows imaging of the spatially-resolved elemental distribution of platinum in the whole organism with respect to the anatomic structure in L4 stage worms at a lateral resolution of 5 μm. In addition, a dose- and time-dependent Cisplatin uptake was corroborated quantitatively by a total reflection X-ray fluorescence spectroscopy (TXRF) method, and the elemental mapping indicated that Cisplatin is located in the intestine and in the head of the worms. Better understanding of the distribution of Cisplatin in this well-established model organism will be instrumental in deciphering Cisplatin toxicity and pharmacokinetics. Since the cytostatic effect of Cisplatin is based on binding the DNA by forming intra- and interstrand crosslinks, the response of poly(ADP-ribose)metabolism enzyme 1 (pme-1) deletion mutants to Cisplatin was also examined. Loss of pme-1, which is the C. elegans ortholog of human poly(ADP-ribose) polymerase 1 (PARP-1) led to disturbed DNA damage response. With respect to survival and brood size, pme-1 deletion mutants were more sensitive to Cisplatin as compared to wildtype worms, while Cisplatin uptake was indistinguishable. Y1 - 2015 U6 - https://doi.org/10.1039/c5mt00096c SN - 1756-591X SN - 1756-5901 VL - 2015 IS - 7 SP - 1189 EP - 1195 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kirpichenko, Svetlana V. A1 - Kleinpeter, Erich T1 - Stereochemistry of 3-isopropoxy-3-methyl-1,3-oxasilinane-the first 3-silatetrahydropyran with an exo-cyclic RO-Si bond JF - Tetrahedron N2 - Molecular structure and conformational behavior of 3-isopropoxy-3-methyl-3-oxasilinane is studied by low temperature C-13 NMR spectroscopy and theoretical calculations (DFT, MP2). Two conformers, 1-ROax and 1-ROeq, were found experimentally and located on the potential energy surface. LT C-13 NMR spectroscopy gives almost equal population of the two conformers at 98 K with Delta G(98K)degrees=0.02 kcal/mol in favor of 1-ROax and Delta G(98K)(#)=4.5 kcal/mol. The corresponding DFT calculated values (Delta G(98K)degrees=0.03 kcal/mol, Delta G(98K)(#)=5.1 kcal/mol) are in excellent agreement with the experiment. Detailed DFT and MP2 calculations of the solvent effect on the conformational equilibrium were performed and highlighted the leveling out of the two conformers when transferred from gas to solution. (C) 2015 Published by Elsevier Ltd. KW - 1,3-Oxasilinanes KW - Conformational equilibrium KW - Barrier to ring inversion KW - Solvent effects KW - Assignment of stereochemistry Y1 - 2015 U6 - https://doi.org/10.1016/j.tet.2015.07.047 SN - 0040-4020 VL - 71 IS - 38 SP - 6720 EP - 6726 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kirpichenko, Svetlana V. A1 - Kleinpeter, Erich A1 - Shlykov, Sergey A. A1 - Osadchiy, Dmitriy Yu. T1 - Molecular structure and conformational analysis of 3-methyl-3-phenyl-3-silatetrahydropyran. Gas-phase electron diffraction, low temperature NMR and quantum chemical calculations JF - Tetrahedron N2 - The molecular structure and conformational behavior of 3-methyl-3-phenyl-3-silatetrahydropyran 1 was studied by gas-phase electron diffraction (GED-MS), low temperature C-13 NMR spectroscopy (LT NMR) and theoretical calculations. The 1-Ph-eq and 1-Ph-ax conformers were located on the potential energy surface. Rotation about the Si-C-ph bond revealed the phenyl ring orthogonal to the averaged plane of the silatetrahydropyran ring for 1-Ph-eq and a twisted orientation for 1-Ph-ax. Theoretical calculations and GED analysis indicate the predominance of 1-Ph-ax in the gas phase with the ratio of conformers (GED) 1-Ph-eq:1-Ph-ax=38:62 (Delta G degrees(307)=-0.29 kcal/mol). In solution, LT NMR spectroscopy gives almost the opposite ratio Ph-eq:1-Ph-ax=68:32 (Delta G degrees(103)=0.16 kcal/mol). Simulation of solvent effects using the PCM continuum model or by calculation of the solvent-solute complexes allowed us to rationalize the experimentally observed opposite conformational predominance of the conformers of compound 1 in the gas phase and in solution. (C) 2015 Elsevier Ltd. All rights reserved. KW - 3-Silatetrahydropyrans KW - Conformational analysis KW - Low temperature NMR spectroscopy KW - Gas-phase electron diffraction KW - Quantum chemical calculations Y1 - 2015 U6 - https://doi.org/10.1016/j.tet.2015.03.117 SN - 0040-4020 VL - 71 IS - 23 SP - 3810 EP - 3818 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Munzke, Dorit A1 - Böhm, Michael A1 - Reich, Oliver T1 - Gaseous Oxygen Detection Using Hollow-Core Fiber-Based Linear Cavity Ring-Down Spectroscopy JF - Journal of lightwave technology N2 - We demonstrate a method for the calibration-free and quantitative analysis of small volumes of gaseous samples. A 10 m hollow-core photonic bandgap fiber is used as the sample cell (volume = 0.44 mu L) and is placed inside a linear resonator setup. The application of cavity ring-down spectroscopy and in consideration of rather small coupling losses, this leads to an increased effective optical path length of up to 70 m. This implies a volume per optical interaction path length of 6.3 nL.m(-1). We used tunable diode laser spectroscopy at 760 nm and scanned the absorption for oxygen sensing. The optical loss due to sample absorption is obtained by measuring the ring-down time of light propagating inside the cavity. The resultant absorption coefficient shows a discrepancy of only 5.1% comparing to the HITRAN database. This approach is applicable for sensitive measurements if only submicroliter sample volumes are available. KW - Cavity ring-down spectroscopy KW - gas sensing KW - hollow-core photonic bandgap fiber KW - oxygen Y1 - 2015 U6 - https://doi.org/10.1109/JLT.2015.2397177 SN - 0733-8724 SN - 1558-2213 VL - 33 IS - 12 SP - 2524 EP - 2529 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Hass, Roland A1 - Munzke, Dorit A1 - Ruiz, Salome Vargas A1 - Tippmann, Johannes A1 - Reich, Oliver T1 - Optical monitoring of chemical processes in turbid biogenic liquid dispersions by Photon Density Wave spectroscopy JF - Analytical & bioanalytical chemistry N2 - In turbid biogenic liquid material, like blood or milk, quantitative optical analysis is often strongly hindered by multiple light scattering resulting from cells, particles, or droplets. Here, optical attenuation is caused by losses due to absorption as well as scattering of light. Fiber-based Photon Density Wave (PDW) spectroscopy is a very promising method for the precise measurement of the optical properties of such materials. They are expressed as absorption and reduced scattering coefficients (mu (a) and mu (s)', respectively) and are linked to the chemical composition and physical properties of the sample. As a process analytical technology, PDW spectroscopy can sense chemical and/or physical processes within such turbid biogenic liquids, providing new scientific insight and process understanding. Here, for the first time, several bioprocesses are analyzed by PDW spectroscopy and the resulting optical coefficients are discussed with respect to established mechanistic models of the chosen processes. As model systems, enzymatic casein coagulation in milk, temperature-induced starch hydrolysis in beer mash, and oxy- as well as deoxygenation of human donor blood were investigated by PDW spectroscopy. The findings indicate that also for very complex biomaterials (i.e., not well-defined model materials like monodisperse polymer dispersions), obtained optical coefficients allow for the assessment of a structure/process relationship and thus for a new analytical access to biogenic liquid material. This is of special relevance as PDW spectroscopy data are obtained without any dilution or calibration, as often found in conventional spectroscopic approaches. KW - Photon Density Wave spectroscopy KW - Enzymatic milk coagulation KW - Beer mashing KW - Human donor blood KW - Process analytical technology KW - Light scattering Y1 - 2015 U6 - https://doi.org/10.1007/s00216-015-8513-9 SN - 1618-2642 SN - 1618-2650 VL - 407 IS - 10 SP - 2791 EP - 2802 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Cui, Qianling A1 - Xia, Bihua A1 - Mitzscherling, Steffen A1 - Masic, Admir A1 - Li, Lidong A1 - Bargheer, Matias A1 - Moehwald, Helmuth T1 - Preparation of gold nanostars and their study in selective catalytic reactions JF - Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects N2 - In this work, gold nanostars (AuNSs) with size around 90 nm were prepared through an easy one-step method. They show excellent catalytic activity and large surface-enhanced Raman scattering (SERS) activity at the same time. Surprisingly, they exhibited different catalytic performance on the reduction of aromatic nitro compounds with different substituents on the para position. To understand such a difference, the SERS spectra were recorded, showing that the molecular orientation of reactants on the gold surface were different. We anticipate that this research will help to understand the relationship of the molecular orientation with the catalytic activity of gold nanoparticles. KW - Nanoparticles KW - Gold KW - Catalytic reaction KW - Surface enhanced Raman scattering (SERS) KW - Molecular orientation Y1 - 2015 U6 - https://doi.org/10.1016/j.colsurfa.2014.10.028 SN - 0927-7757 SN - 1873-4359 VL - 465 SP - 20 EP - 25 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Characterization and quantification of quasi-aromaticity by spatial magnetic properties (TSNMRS) JF - Tetrahedron N2 - The spatial magnetic properties (Through Space NMR Shieldings-TSNMRS) of various types of structures with suggested quasi-aromaticity (a summaring topic: in detail push pull, captodative, chelate, supramolecular aromaticity, etc.) have been computed, are visualized as Isochemical Shielding Surfaces (ICSS) of various size/direction and examined subject to identify and quantify present (partial) aromaticity. While the TSNMRS approach proves really helpful [even in cases of (4n+2) pi-electron cyclic moieties formed via non-covalent polar interactions] quasi-aromaticity suggested for enol forms of 1,3-dicarbonyl compounds via resonance-assisted intramolecular and intermolecular hydrogen bonding cannot be confirmed. (C) 2015 Elsevier Ltd. All rights reserved. KW - Quasi-aromaticity KW - Ring current effect KW - Anisotropy effect KW - Theoretical calculations KW - ICSS KW - TSNMRS Y1 - 2015 U6 - https://doi.org/10.1016/j.tet.2015.06.019 SN - 0040-4020 VL - 71 IS - 33 SP - 5275 EP - 5284 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kirpichenko, Svetlana V. A1 - Chipanina, Nina N. A1 - Oznobikhina, Larisa P. A1 - Kleinpeter, Erich A1 - Shlykov, Sergey A. A1 - Osadchiy, Dmitriy Yu. T1 - Synthesis and Conformational Analysis of 3-Methyl-3-silatetrahydropyran by GED, FTIR, NMR, and Theoretical Calculations: Comparative Analysis of 1-Hetero-3-methyl-3-silacyclohexanes JF - The journal of organic chemistry N2 - 3-Methyl-3-silatetrahydropyran 1 was synthesized and its molecular structure and conformational behavior was studied by gas-phase electron diffraction (GED), FTIR, low temperature H-1 and C-13 NMR spectroscopy, and by theoretical calculations (DFT, MP2). Two conformers; 1-ax and 1-eq; were located on the potential energy Surface. In the gas phase; a slight predominance of the axial conformer was determined, with the ratio 1-ax:1-eq = 54(9):46(9) (from GED) or 53:47 or 61;39 (from IR). In solution, LT NMR spectroscopy at 103 K gives the ratio 1-ax:1-eq = 35:65 (-Delta G(103)degrees = 0.13 kcal/mol). Simulation of solvent effects using the PCM continuum model or by calculation of the corresponding solvent-solute complexes allowed us to rationalize the experimentally observed opposite conformational predominance of the conformers of 3-methyl-3-silatettahydropyran in the gas phase and in solution. Comparative analysis of the effect of heteroatom in 1-hetero-3-methyl-3-silacyclohexanes on the structure, stereoelectronic interactions, and relative energies of the conformers is done. Y1 - 2015 U6 - https://doi.org/10.1021/acs.joc.5b02355 SN - 0022-3263 VL - 80 IS - 24 SP - 12492 EP - 12500 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kolocouris, Antonios A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Stylianakis, Ioannis T1 - 2-Substituted and 2,2-disubstituted adamantane derivatives as models for studying substituent chemical shifts and C-H-ax center dot center dot center dot Y-ax cyclohexane contacts-results from experimental and theoretical NMR spectroscopic chemical shifts and DFT structures JF - Tetrahedron N2 - The complete H-1 and C-13 NMR chemical shifts assignment for various 2-substituted and 2,2-disubstituted adamantane derivatives 1-38 in CDCl3 solution was realized on the basis of NMR experiments combined with chemical structure information and DFT-GIAO (B3LYP/6-31+G(d,p)-GIAO) calculations of chemical shifts in solution. Substituent-induced C-13 NMR chemical shifts (SCS) are discussed. C-H-ax center dot center dot center dot Y-ax contacts are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts will be further investigated in this work on basis of new adamantane derivatives, which are substituted at C-2 to provide models for 1,4-C-H-ax center dot center dot center dot Y-ax and 1,5-C-H-ax center dot center dot center dot Y-ax contacts. The B3LYP/6-31+G(d,p) calculations predicted the presence of NBO hyperconjugative attractive interactions between C-H-ax and Y-ax groups along C-H-ax center dot center dot center dot Y-ax contacts. The H-1 NMR signal separation, Delta delta(gamma-CH2), reflects the strength of the H-bonded C-H-ax center dot center dot center dot Y-ax contact. (C) 2015 Elsevier Ltd. All rights reserved. KW - 2-Substituted adamantane derivatives KW - 2,2-Disubstituted adamantane derivatives KW - H-1 NMR KW - C-13 NMR KW - B3LYP/6-31+G(d,p) calculations KW - GIAO calculations KW - Substituent chemical shifts Y1 - 2015 U6 - https://doi.org/10.1016/j.tet.2015.01.044 SN - 0040-4020 VL - 71 IS - 16 SP - 2463 EP - 2481 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Bauer, Monika A1 - Hartmann, Lutz A1 - Kleinpeter, Erich A1 - Kuschel, Frank A1 - Pithart, Cornelia A1 - Weissflog, Wolfgang T1 - Chiral Dopants Derived from Ephedrine/Pseudoephedrine: Structure and Medium Effects on the Helical Twisting Power JF - Molecular crystals and liquid crystals N2 - Chiral dopants were obtained by acylation of enantiomerically pure ephedrine and pseudoephedrine with promesogenic carbonyl reagents. The products have been investigated with respect to their chiral transfer ability on nematic host matrices characterized by extreme differences of the dielectric anisotropy. It has been found that the medium dependence of the helicity induction nearly disappears at reduced temperatures. Based on variable temperature H-1 NMR studies on monoacylated homologues, the estimated coalescence temperatures and free activation enthalpies for the hindered rotation around C-N bonds could be correlated with the helical twisting power. Measurements by dielectric spectroscopy reveal the correlation between the molar mass of substituents linked to the chiral building block and the dynamic glass transition of corresponding chiral dopants. Furthermore, the effect of intramolecular and intermolecular hydrogen bonds has been studied by ATR-FTIR spectroscopy. KW - ephedrine/pseudoephedrine KW - Chiral dopants KW - ATR-FTIR KW - molecular structure KW - dielectric spectroscopy KW - H-1 NMR Y1 - 2015 U6 - https://doi.org/10.1080/15421406.2014.949592 SN - 1542-1406 SN - 1563-5287 VL - 608 IS - 1 SP - 14 EP - 24 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Kriiger, Stefanie A1 - Koch, Andreas T1 - Anisotropy Effect of Three-Membered Rings in H-1 NMR Spectra: Quantification by TSNMRS and Assignment of the Stereochemistry JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - The spatial magnetic properties (through Space NAIR shieldings, TSNMRSs) of cyclopropane; of the heteroanalogous oxirane, thiirane, and aziridine; and of various substituted dis-, and tris-cyclic analogues have been computed by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSSs) of various size and direction. The TSNMRS values, thus obtained, can be employed to visualize the anisotropy (ring current) effect of I the cyclopropane ring moiety. This approach has been employed to qualify and quantify substituent influences and contributions of appropriate ring heteroatoms O, NH, and S on the anisotropy (ring current) effect of three-mernbered ring moieties, and to assign the stereochemistry of mono-, bis-, and tris cyclic structures containing cyclopropane as a structural element. Characteristic examples are included. Y1 - 2015 U6 - https://doi.org/10.1021/acs.jpca.5b03078 SN - 1089-5639 VL - 119 IS - 18 SP - 4268 EP - 4276 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Michaelis, Marcus A1 - Koch, Andreas T1 - Are para-nitro-pyridine N-oxides quinonoid or benzenoid? An answer given by spatial NICS (TSNMRS) JF - Tetrahedron N2 - The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of a number of substituted para-nitro-pyridine N-oxides have been computed, visualized as Iso-Chemical-Shielding-Surfaces (ICSS) of various size and direction, and were examined subject to the present quinonoid or benzenoid pi-relectron distribution of the six-membered ring. (C) 2015 Elsevier Ltd. All rights reserved. KW - para-Nitro-pyridine N-oxides KW - Quinonoid structure KW - Benzenoid structure KW - Ring current effect KW - Anisotropy effect KW - Theoretical calculations Y1 - 2015 U6 - https://doi.org/10.1016/j.tet.2015.02.043 SN - 0040-4020 VL - 71 IS - 15 SP - 2273 EP - 2279 PB - Elsevier CY - Oxford ER -