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Dmytro Neshchadin Dr. Rebecca Levinn Georg Gescheidt Prof. Dr. Stephen N. Batchelor Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):7008-7016
Polyphenols occur naturally in a vast variety of plants. One of their predominant properties is their antioxidant activity. To provide a deeper understanding of the antioxidant mechanism, 1H CIDNP spectroscopy (CIDNP=chemically induced dynamic nuclear polarization) is used to study model hydrogen abstraction reactions with four catechin‐based polyphenols: catechin (CA), gallocatechin (GC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). The experiments involve photoinduced hydrogen‐atom transfer to a hydrogen abstractor (e.g., excited isopropylthioxanthone) followed under steady‐state conditions and in a time‐resolved fashion (resolution 500 ns–1 ms). It is found that hydrogen abstraction is an essentially stochastic process with a slight preference for the B rings in the catechin‐based polyphenols. Remarkably, analogous reactivity patterns could be followed in the “real systems”, green tea and red wine. We also show that CIDNP can be used as a semiquantitative tool to assess chemical reactivity. 相似文献
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Wolfgang QuappVladlen Melnikov Georg Ch. Mellau 《Journal of Molecular Spectroscopy》2002,211(2):189-197
High-resolution measurements have been made on the infrared emission spectrum of the doubly substituted HCN isotopomer, H13C15N, at temperatures on the order of 1370 K. The measurements cover the region 400-850 cm−1 with a resolution (1/MOPD) of 0.006 cm−1. We could assign hot bands with upper levels up to the 0 1111 0 state. The assignments have been verified for states up to v2=5 by fitting with earlier room temperature absorption measurements of overtone and hot bands. All the measurements for H13C15N have been combined in a single least-squares fit that includes approximately 8670 rovibrational lines which have a root-mean-square deviation on the order of 0.000 33 cm−1. The spectroscopic constants for the bending states v2=1,…,11 are reported, as well as those for some combination states involving the two stretching modes. 相似文献
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This review covers the research on brown algal pheromones from the first structural characterisation of an active principle in 1971 to the recent detailed insight into their biosynthesis. Development of analytical methods and bioassays that lead to the identification of a structural variety of different fatty acid-derived pheromones are reported. Special emphasis is focused on the inactivation of initially released pheromones through pericyclic reactions. The impact of pheromone-research on the defensive chemistry of brown algae and diatoms is discussed. 121 references are cited. 相似文献
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An efficient synthesis of 13-epi-7-O-(triethylsilyl)baccatin III from 13-deoxybaccatin III is described. Oxidation of 13-deoxy-7-O-(triethylsilyl)baccatin III with tert-butyl peroxide, followed by reduction with SmI(2), produced 13-epi-7-O-(triethylsilyl)baccatin III in good overall yield. The preparation of 13-oxo-7-O-(triethylsilyl)baccatin III from 13-epi-7-O-(triethylsilyl)baccatin III using tetrapropylammonium perruthenate and N-methylmorpholine N-oxide is also reported. 相似文献
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Squalene-hopene cyclase (SHC) catalyzes the conversion of squalene into pentacyclic compounds. It is the prokaryotic counterpart of the eukaryotic oxidosqualene cyclase (OSC) that catalyzes the steroid scaffold formation. Because of clear sequence homology, SHC can serve as a model for OSC, which is an attractive target for anticholesteremic drugs. We have established the crystal structure of SHC complexed with Ro48-8071, a potent inhibitor of OSC and therefore of cholesterol biosynthesis. Ro48-8071 is bound in the active-center cavity of SHC and extends into the channel that connects the cavity with the membrane. The binding site of Ro48-8071 is largely identical with the expected site of squalene; it differs from a previous model based on photoaffinity labeling. The knowledge of the inhibitor binding mode in SHC is likely to help develop more potent inhibitors for OSC. 相似文献