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961.
962.
963.
Simaan AJ Boillot ML Carrasco R Cano J Girerd JJ Mattioli TA Ensling J Spiering H Gütlich P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(6):1779-1793
As a functional model of the catechol dioxygenases, [(TPA)Fe(Cat)]BPh4 (TPA = tris(2-pyridylmethyl)amine and Cat = catecholate dianion) exhibits the purple-blue coloration indicative of some charge transfer within the ground state. In contrast to a number of high-spin bioinspired systems, it was previously shown that, in the solid state, [(TPA)Fe(Cat)]BPh4 undergoes a two-step S = 1/2 = S = 5/2 spin-crossover. Therefore, the electronic and vibrational characteristics of this compound were investigated in the solid state by UV/Vis absorption and resonance Raman spectroscopies over the temperature range of the transition. This allowed the charge-transfer transitions of the low-spin (LS) form to be identified. In addition, the vibrational progression observed in the NIR absorption of the LS form was assigned to a five-membered chelate ring mode. The X-ray crystal structure solved at two different temperatures, shows the presence of highly distorted pseudo-octahedral ferric complexes that occupy two nonequivalent crystalline sites. The variation of the molecular parameters as a function of temperature strongly suggests that the two-step transition proceeds by a successive transition of the species in the two nonequivalent sites. The thermal dependence of the high-spin fraction of metal ions determined by M?ssbauer experiments is consistent with the magnetic data, except for slight deviations in the high temperature range. The optimized geometries, the electronic transitions, vibrational frequencies, and thermodynamic functions were calculated with the B3LYP density functional method for the doublet and the sextet states. The finding of a ground state that possesses a significant mixture of Fe(III)-catecholate and FeII-semiquinonate configurations is discussed with regard to the set of experimental and theoretical data. 相似文献
964.
We recently characterized rimocidin B (3b) and CE-108B (4b) as two polyene amides with improved pharmacological properties, produced by genetically modified Streptomyces diastaticus var. 108. In this work, genetic and biochemical analysis of the producer strain show that the two amides are derived from the parental polyenes rimocidin (3a) and CE-108 (4a) by a post-PKS modification of the free side chain carboxylic acid. This modification is mediated by an amidotransferase activity operating after the biosynthesis of rimocidin (3a) and CE-108 (4a) are completed. Two polyenes, intermediates of the biosynthetic pathway of rimocidin (3a) and CE-108 (4a), were also isolated and shown to have some improved pharmacological properties compared with the final products. 相似文献
965.
966.
Mario Schubert Hartmut Oschkinat Peter Schmieder 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,153(2):186
Amino acid type-selective experiments can help to remove ambiguities in automated assignment procedures for 15N/13C-labeled proteins. Here we present five triple-resonance experiments that yield amino acid type-selective 1H–15N correlations for aromatic amino acids. Four of the novel experiments are based on the MUSIC coherence transfer scheme that replaces the initial INEPT transfer and is selective for CH2. The MUSIC sequence is combined with selective excitation pulses to create experiments for Trp (W-HSQC) as well as Phe, Tyr, and His (FYH-HSQC). In addition, an experiment selective for Trp H1–N1 is presented. The new experiments are recorded as two-dimensional experiments and their performance is demonstrated with the application to a protein domain of 115 amino acids. 相似文献
967.
968.
Hartmut Haug 《Zeitschrift für Physik A Hadrons and Nuclei》1966,194(5):482-506
An equation for the intensities and frequencies of laser modes is given for general optical transitions between bands. The models of transitions with and without anyK-selection rule are treated as special cases. With the assumption that the emission band for transitions withK-selection is inhomogeneously broadened a mutual influence of two laser modes is found which is similar to that of a conventional laser with an inhomogeneous line. For the model of no selection rule the intensity of one laser mode is calculated for a given inversion. The lack of a selection rule produces a homogenisation. It is shown that this effect highly favours the single mode operation for running modes. 相似文献
969.
Hartmut Lindel 《Mathematische Annalen》1980,250(2):99-108
Ohne Zusammenfassung 相似文献
970.