Reduction Potential of the Sulfhydryl Radical. Pulse Radiolysis and Laser Flash Photolysis Studies of the Formation and Reactions of SH and HSSH in Aqueous Solutions
T N. Das, Robert E. Huie, Pedatsur Neta, S Padmaja
Formation and reactions of the SH/ S and HSSH /HSS 2- radicals in aqueous solutions have been studied by excimer laser flash photolysis and by pulse radiolysis. Acidic H2S solutions with 193-nm laser pulses produce a transient species with λ max at 240 nm, ascribed to the SH/ S radical. Solutions of SH can be photolyzed also with 248 nm laser pulses to produce the SH/ S / S radical. The same radical is formed by oxidation of SH ions with SO4 . and CO3 radicals. At pH > 5 SH/ S reacts with SH (kf = 4 x 109 L mol s , k r = 5 x 105 s ) to form HSSH.-/HSS2.-, with λmax at 380 nm. Both SH/ S and HSSH /HSS react rapidly with O2; the former produces SO2 (k = 5 x 109 L mol s ) and the latter produces O2 (k = 4 x 108 L mol s ). Both radicals react with olefinic compounds. The monomeric radical oxidizes Fe(CN)64-, SO3 , ClO2 , and chlorpromazine. The dimeric radical is a weaker oxidant toward ferrocyanide but reduces N-methylpyridinium compounds. The reduction potential for the dimeric radical at pH 7 was determined from one-electron transfer equilibria with Mo(CN)8 and with the 4-methoxyaniline radical cation and found to be (0.69 0.03) V vs NHE. From the equilibrium constant K = [HSS ]/[SH ][ S ] = 8 x 10 L mol , the reduction potential for ( S ,H /SH ) is calculated to be 0.92 V.
, Huie, R.
, Neta, P.
and Padmaja, S.
Reduction Potential of the Sulfhydryl Radical. Pulse Radiolysis and Laser Flash Photolysis Studies of the Formation and Reactions of SH and HSSH in Aqueous Solutions, Journal of Physical Chemistry A
(Accessed June 4, 2023)