The scavenging reaction of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH.) or galvinoxyl radical (GO.) by a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H), was significantly accelerated by the presence of Mg(ClO4)2 in de-aerated methanol (MeOH). Such an acceleration indicates that the radical-scavenging reaction of 1H in MeOH proceeds via an electron transfer from 1H to the radical, followed by a proton transfer, rather than the one-step hydrogen atom transfer which has been observed in acetonitrile (MeCN). A significant negative shift of the one-electron oxidation potential of 1H in MeOH (0.63 V vs. SCE), due to strong solvation as compared to that in MeCN (0.97 V vs. SCE), may result in change of the radical-scavenging mechanisms between protic and aprotic media.

No abstract

A kinetic study of a hydrogen-transfer reaction from (+)-catechin (1) to galvinoxyl radical (G•) has been performed using UV−vis spectroscopy in the presence of Mg(ClO4)2 in deaerated acetonitrile (MeCN). The rate constants of hydrogen transfer from 1 to G• determined from the decay of the absorbance at 428 nm due to G• increase significantly with an increase in the concentration of Mg2+. The kinetics of hydrogen transfer from 1 to cumylperoxyl radical has also been examined in propionitrile (EtCN) at low temperature with use of ESR. The decay rate of cumylperoxyl radical in the presence of 1 was also accelerated by the presence of scandium triflate [Sc(OTf)3 (OTf = OSO2CF3)]. These results indicate that the hydrogen-transfer reaction of (+)-catechin proceeds via electron transfer from 1 to oxyl radicals followed by proton transfer rather than via a one-step hydrogen atom transfer. The coordination of metal ions to the one-electron reduced anions may stabilize the product, resulting in the acceleration of electron transfer.

No abstract

Planar catechin analogues having various alkyl side chain lengths were synthesized, and their remarkable antioxidative abilities and alpha-glucosidase inhibitory activities are shown.

No abstract

Poly(ADP-ribose) glycohydrolase (Parg) is the main enzyme of poly(ADP-ribose) degradation. To understand its structure-and-function relationship, we purified Parg from rat testis 9,740-fold using an improved affinity column; the purified product was a 60 kDa protein. Based on the determined sequences of three peptide fragments, degenerated primers were synthesized and a Parg cDNA comprising 3,974 nucleotides, encoding a 109 kDa protein, was isolated. The 60 kDa Parg purified from rat testes corresponded to the C-terminal half of the 109 kDa deduced peptide. When recombinant rat Parg was expressed as a glutathione S-transferase fusion protein in Escherichia coli, Parg activity was observed for the full-length and C-terminal half proteins but not in for the N-terminal half protein. Taken together, these data indicate that the catalytic domain of Parg is located in the C-terminal half. Further, we newly identified the presence of a potential nuclear export signal in the N-terminal half in addition to the previously reported nuclear localization signals in rat and other mammalian Pargs. Northern blot analysis showed the ubiquitous expression of a single 4.0 kb Parg mRNA in various rat tissues. The findings suggest that the 60 kDa Parg is produced by post-transcriptional processing.

Hydrogen transfer from artepillin C to cumylperoxyl radical proceeds via one-step hydrogen atom transfer rather than via electron transfer, the rate constant of which is comparable to that of (+)-catechin, indicating that artepillin C can act as an efficient antioxidant.