Pulse Radiolysis Studies on Reactions of Hydroxyl Radicals with Selenocystine Derivatives

Abstract

Reactions of hydroxyl radicals (*OH) with selenocystine (SeCys) and two of its analogues, diselenodipropionic acid (SeP) and selenocystamine (SeA), have been studied in aqueous solutions at pHs of 1, 7, and 10 using the pulse radiolysis technique coupled with absorption detection. All of these diselenides react with *OH radicals with rate constants of approximately 10(10) M(-1) s(-1), producing diselenide radical cations ( approximately 1-5 micros after the pulse), with an absorption maximum at 560 nm, by elimination of H(2)O or OH(-) from hydroxyl radical adducts. Assignment of the 560 nm band to the diselenide radical cation was made by comparing the transient spectra with those produced upon reaction of diselenides with specific one-electron oxidants, Cl(2)(*-) (pH 1) and Br(2)(*-) radicals (pHs of 7 and 10). SeP having a carboxylic acid functionality showed quantitative conversion of hydroxyl radical adducts to radical cations. The compounds SeCys and SeA, having an amino functional group, in addition to the radical cations, produced a new transient with lambda(max) at 460 nm, at later time scales ( approximately 20-40 micros after the pulse). The rate and yield of formation of the 460 nm band increased with increasing concentrations of either SeCys or SeA. In analogy with similar studies reported for analogous disulfides, the 460 nm transient absorption band has been assigned to a triselenide radical adduct. The one-electron reduction potentials of the compounds were estimated to be 0.96, 1.3, and 1.6 V versus NHE, respectively, for SeP, SeCys, and SeA at pH 7. From these studies, it has been concluded that the electron-donating carboxylic acid group decreases the reduction potential and facilitates quantitative conversion of hydroxyl radical adducts to radical cations, while the electron-withdrawing NH(3)(+) group not only increases the reduction potential but also leads to fragmentation of the hydroxyl radical adduct to selenyl radicals, which are converted to triselenide radical adducts.

Effect of alkyl chain length on one-electron oxidation of bis(alkyl carboxylic acid) selenides: implication on their antioxidant ability

“…Further, similar experiments with 5 mM SeBA, generated transient absorption spectrum with absorption maxima at 320 nm and 490 nm at 1 ms aer the pulse (Fig. [15][16][17][18][19][20][21] The absorbance at 360 nm can be due to the selenuranyl radical (pSerOH) formed by OH adduct formation at the selenium centre or it may be due to intramolecularly stabilized selenium monomer radical species formed between the selenium centred radical cation and the negatively charged oxygen of the carboxylate functional group. In general, selenium radicals form dimer radical species and the yield of such species increases with increase in the concentration of the selenium compound.…”

“…8 With an aim to develop selenium based antioxidant/radioprotector, [9][10][11][12][13][14] we have earlier reported pulse radiolysis studies on functionalized selenium compounds, wherein the selenium atom was primarily oxidized to form selenium centred radical. 8 With an aim to develop selenium based antioxidant/radioprotector, [9][10][11][12][13][14] we have earlier reported pulse radiolysis studies on functionalized selenium compounds, wherein the selenium atom was primarily oxidized to form selenium centred radical.…”

Selenium‐containing amino acids as direct and indirect antioxidants

“…Mono (RSeR 0 ) and diselenides (RSeSeR 0 ) react with HO with k $10 10 M 21 sec 21 (24,25), consistent with these species acting as radical scavengers and radioprotectors in vivo (26,27). The chemistry of radicals generated from SeMet has been compared with those from Met (28).…”

Fast cleavage of a diselenide induced by a platinum(II)–methionine complex and its biological implications

“…Even diselenide bond in selenoglutathione (GSeSeG) is able to oxidize the common biological cofactor NADPH and the cysteine residue in unfold proteins [15]. For these reasons, studies on diselenide bond have elicited great interests in recent years [16,17]. However, to the best of our knowledge, little attention has been paid to the interactions of platinum drugs with seleno-containing biomolecules besides our own research [18][19][20].…”