10504-35-5Relevant articles and documents
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Hamilton,Smith
, p. 5162 (1952)
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Oxidation reactions of thymol: A pulse radiolysis and theoretical study
Venu,Naik,Sarkar,Aravind, Usha K.,Nijamudheen,Aravindakumar
, p. 291 - 299 (2013/03/14)
The reactions of ?OH and O?-, with thymol, a monoterpene phenol and an antioxidant, were studied by pulse radiolysis technique and DFT calculations at B3LYP/6-31+G(d,p) level of theory. Thymol was found to efficiently scavenge OH radicals (k = 8.1 × 109 dm3 mol-1 s-1) to produce reducing adduct radicals, with an absorption maximum at 330 nm and oxidizing phenoxyl radicals, with absorption maxima at 390 and 410 nm. A major part of these adduct radicals was found to undergo water elimination, leading to phenoxyl radicals, and the process was catalyzed by OH- (or Na2HPO4). The rate of reaction of O?- with thymol was found to be comparatively low (k = 1.1 × 109 dm3 mol -1 s-1), producing H abstracted species of thymol as well as phenoxyl radicals. Further, these phenoxyl radicals of thymol were found to be repaired by ascorbate (k = 2.1 × 108 dm3 mol -1 s-1). To support the interpretation of the experimental results, DFT calculations were carried out. The transients (both adducts and H abstracted species) have been optimized in gas phase at B3LYP/6-31+G(d,p) level of calculation. The relative energy values and thermodynamic stability suggests that the ortho adduct (C6-OH adduct) to be most stable in the reaction of thymol with OH radicals, which favors the water elimination. However, theoretical calculations showed that C4 atom in thymol (para position) can also be the reaction center as it is the main contributor of HOMO. The absorption maxima (λmax) calculated from time-dependent density functional theory (TDDFT) for these transient species were close to those obtained experimentally. Finally, the redox potential value of thymol?/ thymol couple (0.98 V vs NHE) obtained by cyclic voltammetry is less than those of physiologically important oxidants, which reveals the antioxidant capacity of thymol, by scavenging these oxidants. The repair of the phenoxyl radicals of thymol with ascorbate together with the redox potential value makes it a potent antioxidant with minimum pro-oxidant effects.
Tannins and related compounds. LXXXIV. Isolation and characterization of five new hydrolyzable tannins from the bark of Mallotus japonicus.
Saijo,Nonaka,Nishioka
, p. 2063 - 2070 (2007/10/02)
A chemical examination of the bark of Mallotus japonicus (Thunb.) Mueller-Arg. (Euphorbiaceae) has led to the isolation of five new hydrolyzable tannins (16-20), together with fourteen known tannins (1-14). On the basis of chemical and spectroscopic evidence, the structures of compounds 16 and 17 were established as 1,2-di-O-galloyl-3,6-(R)-hexahydroxydiphenoyl-beta-D-glucose and 1-O-digalloyl-3,6-(R)-hexahydroxydiphenoyl-beta-D-glucose, respectively, while compounds 18 (mallojaponin) and 19 (mallonin) were shown to be 1-O-galloyl-2,4-elaeocarpusinoyl-3,6-(R)-valoneayl-bet a-D-glucose and 1-O-galloyl-2,4-elaeocarpusinoyl-beta-D-glucose. Compound 20 (mallotusinin) was characterized as a novel ellagitannin which possesses a unique 1,1'-(3,3',4,4'-tetrahydroxy)dibenzofurandicarboxyl group. On the other hand, examination of the leaves revealed the presence of hydrolyzable tannins (8-10, 12-15) all containing a beta-D-glucopyranose core with 1C4-conformation. Furthermore, the orientation of the valoneayl group in mallotinic acid (13) and mallotusinic acid (14), which had remained unclarified, was determined on the basis of 1H-13C shift correlation spectral analysis and chemical correlations.
