TY - JOUR A1 - Adelsberger, Joseph A1 - Metwalli, Ezzeldin A1 - Diethert, Alexander A1 - Grillo, Isabelle A1 - Bivigou Koumba, Achille Mayelle A1 - Laschewsky, André A1 - Müller-Buschbaum, Peter A1 - Papadakis, Christine M. T1 - Kinetics of collapse transition and cluster formation in a thermoresponsive micellar solution of P(S-b-NIPAM-b-S) induced by a temperature jump JF - Macromolecular rapid communications N2 - Structural changes at the intra- as well as intermicellar level were induced by the LCST-type collapse transition of poly(N-isopropyl acrylamide) in ABA triblock copolymer micelles in water. The distinct process kinetics was followed in situ and in real-time using time-resolved small-angle neutron scattering (SANS), while a micellar solution of a triblock copolymer, consisting of two short deuterated polystyrene endblocks and a long thermoresponsive poly(N-isopropyl acrylamide) middle block, was heated rapidly above its cloud point. A very fast collapse together with a multistep aggregation behavior is observed. The findings of the transition occurring at several size and time levels may have implications for the design and application of such thermoresponsive self-assembled systems. KW - polymer physics KW - thermoresponsive polymers KW - small-angle neutron scattering KW - time-resolved measurements Y1 - 2012 U6 - https://doi.org/10.1002/marc.201100631 SN - 1022-1336 VL - 33 IS - 3 SP - 254 EP - 259 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Ali, Mostafa A1 - Homann, Thomas A1 - Kreisel, Janka A1 - Khalil, Mahmoud A1 - Puhlmann, Ralf A1 - Kruse, Hans-Peter A1 - Rawel, Harshadrai Manilal T1 - Characterization and modeling of the interactions between coffee storage proteins and phenolic compounds JF - Journal of agricultural and food chemistry : a publication of the American Chemical Society N2 - This study addresses the interactions of coffee storage proteins with coffee-specific phenolic compounds. Protein profiles, of Coffea arabica and Coffea canephora (var robusta) were compared. Major Phenolic compounds were extracted and analyzed with appropriate methods. The polyphenol-protein interactions during protein extraction have been addressed by different analytical setups [reversed-phase high-performance liquid chromatography (RP-HPLC), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS), and Trolox equivalent antioxidant capacity (TEAC) assays], with focus directed toward identification of covalent adduct formation. The results indicate that C. arabica proteins are more susceptible to these interactions and the polyphenol oxidase activity seems to be a crucial factor for the formation of these addition products. A tentative allocation of the modification type and site in the protein has been attempted. Thus, the first available in silico modeling of modified coffee proteins is reported. The extent of these modifications may contribute to the structure and function of "coffee melanoidins" and are discussed in the context of coffee flavor formation. KW - Coffee beans KW - storage proteins KW - phenolic compounds KW - antioxidants KW - protein-phenol interactions KW - modeling Y1 - 2012 U6 - https://doi.org/10.1021/jf303372a SN - 0021-8561 VL - 60 IS - 46 SP - 11601 EP - 11608 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Ast, Sandra A1 - Rutledge, Peter J. A1 - Todd, Matthew H. T1 - Reversing the triazole topology in a cyclam-triazole-dye ligand gives a 10-fold brighter signal response to Zn2+ in aqueous solution JF - European journal of inorganic chemistry : a journal of ChemPubSoc Europe N2 - The fluorescence response of a set of cyclam-triazole-dye ligands is controlled by the appended dye, but simple reversal of the triazole topology affords a novel probe for Zn2+ with a longer fluorescence lifetime and higher fluorescence quantum yield upon Zn2+ binding ( = 2.0 ns, Phi(f) = 0.76). KW - Sensors KW - Zinc KW - Click chemistry KW - Fluorescence KW - Electrochemistry Y1 - 2012 U6 - https://doi.org/10.1002/ejic.201201072 SN - 1434-1948 IS - 34 SP - 5611 EP - 5615 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Awad, Duha Jawad A1 - Koch, Andreas A1 - Mickler, Wulfhard A1 - Schilde, Uwe A1 - Strauch, Peter T1 - EPR spectroscopy of 4, 4 '-Bis(tert-butyl)-2, 2 '-bipyridine-1, 2-dithiolatocuprates(II) in host lattices with different coordination geometries JF - Zeitschrift für anorganische und allgemeine Chemie N2 - A series of new heteroleptic MN2S2 transition metal complexes with M = Cu2+ for EPR measurements and as diamagnetic hosts Ni2+, Zn2+, and Pd2+ were synthesized and characterized. The ligands are N2 = 4, 4'-bis(tert-butyl)-2, 2'-bipyridine (tBu2bpy) and S2 =1, 2-dithiooxalate, (dto), 1, 2-dithiosquarate, (dtsq), maleonitrile-1, 2-dithiolate, or 1, 2-dicyanoethene-1, 2-dithiolate, (mnt). The CuII complexes were studied by EPR in solution and as powders, diamagnetically diluted in the isostructural planar [NiII(tBu2bpy)(S2)] or[PdII(tBu2bpy)(S2)] as well as in tetrahedrally coordinated[ZnII(tBu2bpy)(S2)] host structures to put steric stress on the coordination geometry of the central CuN2S2 unit. The spin density contributions for different geometries calculated from experimental parameters are compared with the electronic situation in the frontier orbital, namely in the semi-occupied molecular orbital (SOMO) of the copper complex, derived from quantum chemical calculations on different levels (EHT and DFT). One of the hosts, [NiII(tBu2bpy)(mnt)], is characterized by X-ray structure analysis to prove the coordination geometry. The complex crystallizes in a square-planar coordination mode in the monoclinic space group P21/a with Z = 4 and the unit cell parameters a = 10.4508(10) angstrom, b = 18.266(2) angstrom, c = 12.6566(12) angstrom, beta = 112.095(7)degrees. Oxidation and reductions potentials of one of the host complexes, [Ni(tBu2bpy)(mnt)], were obtained by cyclovoltammetric measurements. KW - 1 KW - 2-Dithiosquarate KW - 1 KW - 2-Dithiooxalate KW - 1 KW - 2-Dicyanoethene-1 KW - 2-dithiolate KW - 4 KW - 4'-Bis(tert-butyl)-2 KW - 2'-bipyridine KW - X-ray structure KW - EPR KW - Copper KW - Nickel KW - Zinc Y1 - 2012 U6 - https://doi.org/10.1002/zaac.201100517 SN - 0044-2313 VL - 638 IS - 6 SP - 965 EP - 975 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Balci, Kubilay A1 - Yapar, G. A1 - Akkaya, Y. A1 - Akyuz, S. A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - A conformational analysis and vibrational spectroscopic investigation on 1,2-bis(o-carboxyphenoxy) ethane molecule JF - Vibrational spectroscopy : an international journal devoted to applications of infrared and raman spectroscopy N2 - The minima on the potential energy surface of 1,2-bis(o-carboxyphenoxy)ethane (CPE) molecule in its electronic ground state were searched by a molecular dynamics simulation performed with MM2 force field. For each of the found minimum-energy conformers, the corresponding equilibrium geometry, charge distribution, HOMO-LUMO energy gap, force field, vibrational normal modes and associated IR and Raman spectral data were determined by means of the density functional theory (DFT) based electronic structure calculations carried out by using B3LYP method and various Pople-style basis sets. The obtained theoretical data confirmed the significant effects of the intra- and inter-molecular hydrogen bonding interactions on the conformational structure, force field, and group vibrations of the molecule. The same data have also revealed that two of the determined stable conformers, both of which exhibit pseudo-crown structure, are considerably more favorable in energy to the others and accordingly provide the major contribution to the experimental spectra of CPE. In the light of the improved vibrational spectral data obtained within the "SQM FF" methodology and "Dual Scale Factors" approach for the monomer and dimer forms of these two conformers, a reliable assignment of the fundamental bands observed in the experimental room-temperature IR and Raman spectra of the molecule was given, and the sensitivities of its group vibrations to conformation, substitution and dimerization were discussed. KW - Glycol podands KW - Salicylic acid KW - IR and Raman spectra KW - SQM FF KW - Dual Scale Factors Y1 - 2012 U6 - https://doi.org/10.1016/j.vibspec.2011.11.011 SN - 0924-2031 VL - 58 IS - 1-2 SP - 27 EP - 43 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Baranac-Stojanovic, Marija A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Density Functional Calculations of the Anisotropic Effects of Borazine and 1,3,2,4-Diazadiboretidine JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - On the basis of the nucleus-independent chemical shift (NICS) concept, the anisotropic effects of two inorganic rings, namely, borazine and planar 1,3,2,4-diazadiboretidine, are quantitatively calculated and visualized as isochemical shielding surfaces (ICSSs). Dissection of magnetic shielding values along the three Cartesian axes into contributions from s and p bonds by the natural chemical shieldingnatural bond orbital (NCSNBO) method revealed that their appearance is not a simple reflection of the extent of (anti)aromaticity. KW - anisotropic effects KW - aromaticity KW - B,N heterocycles KW - density functional calculations KW - NMR spectroscopy Y1 - 2012 U6 - https://doi.org/10.1002/cphc.201200732 SN - 1439-4235 VL - 13 IS - 17 SP - 3803 EP - 3811 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Baranac-Stojanovic, Marija A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Is the conventional interpretation of the anisotropic effects of C=C double bonds and aromatic rings in NMR spectra in terms of the p-electron shielding/deshielding contributions correct? JF - Chemistry - a European journal N2 - Based on the nucleus-independent chemical shift (NICS) concept, isotropic magnetic shielding values have been computed along the three Cartesian axes for ethene, cyclobutadiene, benzene, naphthalene, and benzocyclobutadiene, starting from the molecular/ring center up to 10 angstrom away. These through-space NMR spectroscopic shielding (TSNMRS) values, which reflect the anisotropic effects, have been broken down into contributions from localized- and canonical molecular orbitals (LMOs and CMOs); these contributions revealed that the proton NMR spectroscopic chemical shifts of nuclei that are spatially close to the C?C double bond or the aromatic ring should not be explained in terms of the conventionally accepted p-electron shielding/deshielding effects. In fact, these effects followed the predictions only for the antiaromatic cyclobutadiene ring. KW - ab initio calculations KW - anisotropic effects KW - NMR spectroscopy KW - nucleus-independent chemical shift KW - pi interactions Y1 - 2012 U6 - https://doi.org/10.1002/chem.201101882 SN - 0947-6539 VL - 18 IS - 1 SP - 370 EP - 376 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Barth, Johannes A1 - Siegmann, Rebekka A1 - Beuermann, Sabine A1 - Russell, Gregory T. A1 - Buback, Michael T1 - Investigations into chain-length-dependent termination in bulk radical polymerization of 1H, 1H, 2H, 2H-Tridecafluorooctyl methacrylate JF - Macromolecular chemistry and physics N2 - The SP-PLP-EPR technique is used to carry out a detailed investigation of the radical termination kinetics of 1H, 1H, 2H, 2H-tridecafluorooctyl methacrylate (TDFOMA) in bulk at relatively low conversion. Composite-model behavior for chain-length-dependent termination rate coefficients, kti,i, is observed. It is found that for TDFOMA, ic approximate to 60 independent of temperature, and as approximate to 0.65 and al approximate to 0.2 at 80 degrees C and above. However, at lower temperatures the situation is strikingly different, with the significantly higher average values of as = 0.89 +/- 0.15 and al = 0.32 +/- 0.10 being obtained at 50 degrees C and below. This makes TDFOMA the first monomer to be found that exhibits clearly different exponent values, as and al, at lower and higher temperature, and that has both a high as, like an acrylate, and a high ic, like a methacrylate. KW - ESR KW - EPR KW - kinetics (polym KW - ) KW - methacrylates KW - radical polymerization KW - termination Y1 - 2012 U6 - https://doi.org/10.1002/macp.201100479 SN - 1022-1352 VL - 213 IS - 1 SP - 19 EP - 28 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Baumgartner, Jens A1 - Lesevic, Paul A1 - Kumari, Monika A1 - Halbmair, Karin A1 - Bennet, Mathieu A1 - Koernig, Andre A1 - Widdrat, Marc A1 - Andert, Janet A1 - Wollgarten, Markus A1 - Bertinetti, Luca A1 - Strauch, Peter A1 - Hirt, Ann A1 - Faivre, Damien T1 - From magnetotactic bacteria to hollow spirilla-shaped silica containing a magnetic chain JF - RSC Advances N2 - Magnetotactic bacteria produce chains of magnetite nanoparticles, which are called magnetosomes and are used for navigational purposes. We use these cells as a biological template to prepare a hollow hybrid material based on silica and magnetite, and show that the synthetic route is nondestructive as the material conserves the cell morphology as well as the alignment of the magnetic particles. The hybrid material can be resuspended in aqueous solution, and can be shown to orient itself in an external magnetic field. We anticipate that chemical modification of the silica can be used to functionalize the material surface in order to obtain multifunctional materials with specialized applications, e.g. targeted drug delivery. Y1 - 2012 U6 - https://doi.org/10.1039/c2ra20911j SN - 2046-2069 VL - 2 IS - 21 SP - 8007 EP - 8009 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Bouakline, Foudhil A1 - Lüder, Franziska A1 - Martinazzo, Rocco A1 - Saalfrank, Peter T1 - Reduced and exact quantum dynamics of the vibrational relaxation of a molecular system interacting with a finite-dimensional bath JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - We investigate the vibrational relaxation of a Morse oscillator, nonlinearly coupled to a finite-dimensional bath of harmonic oscillators at zero temperature, using two different approaches: Reduced dynamics with the help of the Lindblad formalism of reduced density matrix theory in combination with Fermi's Golden Rule, and exact dynamics (within the chosen model). with the multiconfiguration time-dependent Hartree (MCTDH) method. Two different models have been constructed, the situation where the bath spectrum is exactly resonant with the anharmonic oscillator transition frequencies, and the case for which the subsystem is slightly off-resonant with the environment. At short times, reduced dynamics calculations describe the relaxation process qualitatively well but fail to reproduce recurrences observed with MCTDH for longer times. Lifetimes of all the vibrational levels of the Morse oscillator have been calculated, and both Lindblad and MCTDH. results show the same dependence of the lifetimes on the initial vibrational state quantum number. A prediction, which should be generic for adsorbate systems is a striking, sharp increase of lifetimes of the subsystem vibrational levels close to the dissociation This is contradictory with harmonic/linear extrapolation laws, which predict a monotonic decrease of the lifetime with initial vibrational quantum number. Y1 - 2012 U6 - https://doi.org/10.1021/jp304466u SN - 1089-5639 VL - 116 IS - 46 SP - 11118 EP - 11127 PB - American Chemical Society CY - Washington ER -