@misc{oai:repo.qst.go.jp:00064495,
 author = {Kawashima, Tomonori and Nakanishi, Ikuo and Imai, Kohei and Ohkubo, Kei and Fukuhara, Kiyoshi and Fukuzumi, Shunichi and Matsumoto, Kenichiro and 川島 知憲 and 中西 郁夫 and 今井 耕平 and 松本 謙一郎},
 month = {Feb},
 note = {It is known that there are three mechanisms for the radical-scavenging reactions of phenolic compounds, such as tocopherol and (+)-catechin, i.e., one-step hydrogen-atom transfer (HAT) from the phenolic OH group to radicals, electron transfer from phenolic compounds to radicals followed by proton transfer (ET-PT), and sequential proton-loss electron transfer (SPLET). The scavenging reaction of galvinoxyl radical, used as a reactive oxygen-centered radical model, by catechin was reported to proceed via ET-PT.  Although, three mechanisms of radical scavenging are known to be controlled by solvents, there are few reports on the solvent effect on the radical-scavenging mechanisms of catechins.  We report herein the kinetics and mechanism of the radical-scavenging reaction by (+)-catechin and (–)-epicatechin in various solvents.  
    The UV-vis absorption change was monitored after mixing of deaerated acetonitrile (MeCN) solutions of galvinoxyl radical (GO•), as a stable model of reactive oxygen species, and (+)-catechin using the stopped-flow technique.  The radical-scavenging rate constants (k) of (+)-catechin and (-)-epicatechin were determined to be 6.1 x 10 and 1.1 x 102 M-1 s-1, respectively.  No effect of acetic acid (CH3COOH) on the GO-scavenging reaction by catechins indicates that these scavenging reactions proceed via ET-PT.  In methanol (MeOH), the pseudo-first order rate constant (kobs) for (+)-catechin increased with increasing concentration of (+)-catechin and reached a constant value.  In the case of (-)-epicatechin, the kobs value was increased linearly with an increase in concentration of (-)-epicatechin.  When CH3COOH was added to the reaction solutions in order to inhibit the deprotonation of catechins in MeOH, the k values of catechins were significantly decreased.  The effect of CH3COOH on the k values was also observed in ethanol (EtOH).  These results suggest that the GO•-scavenging reaction by catechins may proceed via the SPLET mechanism in protic media, such as MeOH and EtOH., 第19回日本学術振興会先端研究拠点事業セミナー：Winter School in Fukuoka 2012},
 title = {Solvent effects on the galvinoxyl radical-scavenging dynamics of catechins},
 year = {2012}
}