ONE-ELECTRON REDUCTION OF DISULFIDE LINKAGE IN AQUEOUS-SOLUTION - FORMATION, PROTONATION, AND DECAY KINETICS OF RSSR- RADICAL
ONE-ELECTRON REDUCTION OF DISULFIDE LINKAGE IN AQUEOUS-SOLUTION - FORMATION, PROTONATION, AND DECAY KINETICS OF RSSR- RADICAL
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DOI：
10.1021/ja00778a002
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发表时间：
1972-01-01
影响因子：
15
通讯作者：
HAYON, E
中科院分区：
文献类型：
--
作者：
HOFFMAN, MZ;HAYON, E
The rupture of disulfide linkages by the one-electron transfer agents eaq~ and H atoms in aqueous solution has been studied using the fast-reaction technique of pulse radiolysis and kinetic absorption spectro-photometry. Dithiodiacetic acid, dithiodipropionic acid, cystine, cystamine, cystine dimethyl ester, penicillamine disulfide, glutathione disulfide, and lipoic acid were investigated. The reaction rate constants of eaq-with these disulfide compounds (RSSR) were determined and were found to be markedly dependent upon the state of protonation of the amino groups (for the amino acid disulfides), with the rate decreasing on deprotonation of the NH3+ groups. The absorption maxima, extinction coefficients, and decay kinetics of the disulfide radical anions, RSSR-, produced on reaction with eaq-were determined. For most compounds, the maxima were in therange 400-420 nm, with extinction coefficients—'7—15 X 10s M-1 cm-1, andthe decays followed a first-order process, except for lipoate which decayed by second-order kinetics. At pH> 7, the decay rate of the RSSR-radicals of dithiodiacetic, dithiodipropionic, and lipoic acids and of glutathione were independent of pH, whereas all the other disulfides showed an increase in the rate with increase in pH. This increase was shown to follow the p of the amino groups. At pH< 7, the decay rate was found toincrease again. This increase in rate was found to be dependent upon [H+], and the kinetics of protonation of the disulfide radical anions were measured. Values ranged from 6.0= 1.5 X 10s to 7.0±1.5 X 10 M-1 sec-1 for cystine dimethyl ester and glutathione disulfide, respectively. The protonation of RSSR-probably produces the short-lived sulfenium radical which decomposes to form thiyl RS· radicals (Xmax—'330 nm) and RSH. Thiyl radicals were produced by an independent reaction and the transient spectra observed with Xmax~ 330 nm were shown to be identical with the corresponding radicals formed on protonation of RSSR-radicals. The reaction of H atoms with these disulfides in acidic solutions was found to produce the same intermediates as those observed from the protonation of RSSR-radicals, with absorp-tion maxima at—^ 330 nm and low extinction coefficients indicating a similar rupture of SS linkages. Decay rates of thiyl radicals ranging from~ 3.4 X 109 to 1.4 X 1010 M-1 sec-1 were determined. These results are discussed on the basis of the physicochemical properties of the disulfide linkage. The reaction of the radicals produced from lipoic acid differ from those of the other disulfides studied and are discussed separately.
