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51.
Comparison of Electrochemical Oxidation of Flavonols and Calculated Proton Affinity and Electron Transfer Enthalpy in Water
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Flavonols, a class of flavonoids, are present in flowers, fruits and vegetables. They are jointly responsible for antioxidant activity as free radical acceptors. The redox behaviour of myricetin, quercetin, isorhamnetin, fisetin, morin and kaempferol is investigated using cyclic and differential pulse voltammetry. Quantum chemical calculations of proton affinities and electron transfer enthalpies were performed to identify possible reactive sites and radical species to compare them with measured oxidation potentials of the flavonols. Regarding to their chemical structure, these flavonols showed an oxidation order: myricetin > quercetin > isorhamnetin > fisetin > morin > kaempferol. 相似文献
52.
C,C‐ and N,C‐Coupled Dimers of 2‐Aminotetraphenylporphyrins: Regiocontrolled Synthesis,Spectroscopic Properties,and Quantum‐Chemical Calculations
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Dr. Torsten Bruhn Dipl.‐Chem. Franziska Witterauf Dr. Daniel C. G. Götz Carina T. Grimmer Dipl.‐Chem. Max Würtemberger Prof. Dr. Udo Radius Prof. Dr. Gerhard Bringmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3998-4006
β,β′‐Bisporphyrins are intrinsically chiral porphyrin dimers with fascinating properties. The configurational stability at their axes can be directed by variation of the central metal atoms. Herein, we present a regioselective functionalization of the monomeric 2‐amino‐tetraphenyl‐porphyrin as a versatile substrate for dimerization by oxidative coupling. By simple variation of the reaction conditions (solvent and oxidant), the oxidation selectively gave either the axially chiral C,C‐coupled diaminobisporphyrin in high yields or, under Ullmann conditions, the twofold N,C‐linked achiral dimer, also in good yields. A generalized mechanism for the coupling reaction is proposed based on DFT calculations. The axially chiral β,β′‐coupled porphyrin dimers were isolated as racemic mixtures, but can be resolved by HPLC on a chiral phase. TDDFT and coupled‐cluster calculations were used to explain the spectroscopic properties of the aminoporphyrins and their dimers and to elucidate the absolute configurations of the C,C‐coupled bisporphyrins. 相似文献
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Miriam R. B. Porzberg Laust Moesgaard Catrine Johansson Udo Oppermann Jacob Kongsted Jasmin Mecinovi 《Molecules (Basel, Switzerland)》2022,27(3)
Epigenetic readout of the combinatorial posttranslational modification comprised of trimethyllysine and asymmetric dimethylarginine (H3K4me3R8me2a) takes place via biomolecular recognition of tandem Tudor-domain-containing protein Spindlin1. Through comparative thermodynamic data and molecular dynamics simulations, we sought to explore the binding scope of asymmetric dimethylarginine mimics by Spindlin1. Herein, we provide evidence that the biomolecular recognition of H3K4me2R8me2a is not significantly affected when R8me2a is replaced by dimethylarginine analogues, implying that the binding of K4me3 provides the major binding contribution. High-energy water molecules inside both aromatic cages of the ligand binding sites contribute to the reader–histone association upon displacement by histone peptide, with the K4me3 hydration site being lower in free energy due to a flip of Trp151. 相似文献
55.
FUNDAMENTALS OF TRANSMISSION FLUCTUATION SPECTROMETRY WITH VARIABLE SPATIAL AVERAGING 总被引:4,自引:0,他引:4
JianqiShen UlrichRiebel MarcusBreitenstein UdoKraeuter 《中国颗粒学报》2003,1(6):242-246
Transmission signal of radiation in suspension of particles performed with a high spatial and temporal resolution shows significant fluctuations,which are related to the physical properties of the particles and the process of spatial and temporal averaging.Exploiting this connection,it is possible to calculate the particle size distribution (PSD) and particle concentration.This paper provides an approach of transmission fluctuation spectrometry (TFS) with variable spatial averaging,The transmission fluctuations are expressed in terms of the expectancy of transmission square (ETS) and are obtained as a spectrum,which is a function of the variable beam diameter.The reversal point and the depth of the spectrum contain the information of particle size and particle concentration,respectively. 相似文献
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Francis R. Costa Sudip Pradhan Udo Wagenknecht Anil K. Bhowmick Gert Heinrich 《Journal of Polymer Science.Polymer Physics》2010,48(22):2302-2311
In elastomer/organo clay nanocomposites, the morphological characteristics, and hence the mechanical properties, of the vulcanizates are strongly influenced by the organic modifier and the vulcanization process. When the elastomer itself undergoes strain‐induced crystallization, both the organic modifier and the dispersed filler particles could significantly influence the crystallization process. These phenomena are very common in case of natural rubber‐based vulcanizates. In this study, the similar effects have been demonstrated with carboxylated nitrile rubber (XNBR) and organically modified layered double hydroxide (O‐LDH)‐based nanocomposites. The effect of size of the organic modifier was obviously visible on the interlayer distance of O‐LDH and also on the morphological reorganization of the dispersed O‐LDH particles during vulcanization process. The strain‐induced crystallization of the XNBR was found to be strongly dependent on the morphological change that occurs during vulcanization process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010 相似文献
58.
Francis E. Burstall Udo Hertrich-Jeromin Wayne Rossman 《Comptes Rendus Mathematique》2010,348(11-12):661-664
We propose a Lie geometric point of view on flat fronts in hyperbolic space as special Ω-surfaces and discuss the Lie geometric deformation of flat fronts. 相似文献
59.
Udo Mayer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1972,84(4):176-176
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