Nakanishi Ikuo, Shoji Yoshimi, Ohkubo Kei, Fukuhara Kiyoshi, Ozawa Toshihiko, Matsumoto Ken-Ichiro, Fukuzumi Shunichi
Quantitative RedOx Sensing Group, Department of Basic Medical Sciences for Radiation Damages, National Institute of Radiological Sciences (NIRS), Quantum Medical Science Directorate, National Institutes for Quantum and Radiological Science and Technology (QST), Inage-ku, Chiba 263-8555, Japan.
Institute for Advanced Co-Creation Studies, Open and Transdisciplinary Research Initiatives, Osaka University, Suita, Osaka 565-0871, Japan.
J Clin Biochem Nutr. 2021 Mar;68(2):116-122. doi: 10.3164/jcbn.20-147. Epub 2021 Jan 16.
The effects of reaction environments on the radical-scavenging mechanisms of ascorbic acid (AscH) were investigated using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) as a reactivity model of reactive oxygen species. Water-insoluble DPPH was solubilized by β-cyclodextrin (β-CD) in water. The DPPH-scavenging rate of AscH in methanol (MeOH) was much slower than that in phosphate buffer (0.05 M, pH 7.0). An organic soluble 5,6-isopropylidene-l-ascorbic acid (iAscH) scavenged DPPH much slower in acetonitrile (MeCN) than in MeOH. In MeOH, Mg(ClO) significantly decelerated the DPPH-scavenging reaction by AscH and iAscH, while no effect of Mg(ClO) was observed in MeCN. On the other hand, Mg(ClO) significantly accelerated the reaction between AscH and β-CD-solubilized DPPH (DPPH/β-CD) in phosphate buffer (0.05 M, pH 6.5), although the addition of 0.05 M Mg(ClO) to the AscH-DPPH/β-CD system in phosphate buffer (0.05 M, pH 7.0) resulted in the change in pH of the phosphate buffer to be 6.5. Thus, the DPPH-scavenging reaction by iAscH in MeCN may proceed via a one-step hydrogen-atom transfer, while an electron-transfer pathway is involved in the reaction between AscH and DPPH/β-CD in phosphate buffer solution. These results demonstrate that the DPPH-scavenging mechanism of AscH are affected by the reaction environments.
以2,2-二苯基-1-苦基肼自由基（DPPH）作为活性氧的反应模型，研究了反应环境对抗坏血酸（AscH）自由基清除机制的影响。水不溶性的DPPH通过β-环糊精（β-CD）在水中增溶。AscH在甲醇（MeOH）中的DPPH清除率比在磷酸盐缓冲液（0.05 M，pH 7.0）中慢得多。有机可溶性的5,6-异亚丙基-L-抗坏血酸（iAscH）在乙腈（MeCN）中清除DPPH的速度比在MeOH中慢得多。在MeOH中，Mg(ClO)显著减缓了AscH和iAscH的DPPH清除反应，而在MeCN中未观察到Mg(ClO)的影响。另一方面，Mg(ClO)显著加速了AscH与β-CD增溶的DPPH（DPPH/β-CD）在磷酸盐缓冲液（0.05 M，pH 6.5）中的反应，尽管向磷酸盐缓冲液（0.05 M，pH 7.0）中的AscH-DPPH/β-CD体系中加入0.05 M Mg(ClO)导致磷酸盐缓冲液的pH变为6.5。因此，iAscH在MeCN中的DPPH清除反应可能通过一步氢原子转移进行，而AscH与磷酸盐缓冲溶液中的DPPH/β-CD之间的反应涉及电子转移途径。这些结果表明，AscH的DPPH清除机制受反应环境的影响。
