Pulsradiolyse des Schwefelwasserstoffs in wäßriger Lösung

Abstract

The reactions of the OH radical with H2S and SH⊖ are very fast (k = 1.1·1010 and 5.4·109 mole-1 liter sec-1, respectively). The hydrated electron reacts with H2S (1.1·1010) but does not react with SH⊖. The rate constant of the reaction CNS+SH⊖ CNS⊖ +SH was found to be equal to 9.8·108. Species absorbing at 3800 Å (e ∼ 104 mole-1 liter cm-1) are formed in these reactions of H2S and SH⊖ The intensity of this absorption is very low in strongly acid solutions, increases with pH, goes through a broad maximum at about pH=7, reaches a lower plateau between pH = 8.5 -10.5 and decreases in strongly alkaline solutions. At pH values below 7, the intensity is dependent on the concentrations of both SH⊖ and free H2S, i. e. at constant SH⊖ concentration a stronger absorption occurs if more free H2S is present. In the plateau below pH = 8.5 -10.5, the intensity is practically independent of the SH⊖ concentration above 4·10-5 mole/l. The decay of the 3800 A absorption after the pulse is first order with τ1/2 = 5 μsec independent of the OH⊖ and SH⊖ concentrations in alkaline solutions.Below pH = 7, the absorption disappears by second order, the rate constant being larger at lower pH values. SH or S⊖ absorb weakly in the near UV and do not contribute to the 3800 Å absorption. This absorption is attributed to the ions H2S2⊖ or H2S2⊖ in alkali and to H2S2⊖or higher complexes such as H3S4⊖ in acid. The first order decay of 5 μsec is attributed to the spontaneous decomposition of S2H2⊖ into S⊖ +SH⊖. Two S⊖ ions form S22⊖ (2 k=2·109 mole-1 liter sec-1). The complex H2S2⊖ is formed in the fast reaction SH + SH⊖ ↔ S2H2⊖ (dissociation constant about 4·10-5 mole/l). The formation of an intermediate complex SHOH⊖ in the reaction of OH with SH⊖ is discussed. This intermediate reacts with either SH⊖ to form S2H2⊖ or with OH⊖ (or other proton acceptors such as ΗΡΟ42Θ) to form SΘ+ H2O+OHΘ.

Chemical Characterization of the Smallest S-Nitrosothiol, HSNO; Cellular Cross-talk of H2S and S-Nitrosothiols

“…Initially, HO • add to HS – , reaction 7, 15 with a rate constant k 1 = 5.4 × 10 9 M –1  s –1 and, given the concentrations used, with a half-life of 110 ns. This oxidation step is followed by addition of hydrogen sulfide anion to yield disulfanuidyl, or dihydrogen disulfide radical anion (HSSH •– ).…”

Remarkable photocytotoxicity in hypoxic HeLa cells by a dipyridophenazine copper(II) Schiff base thiolate

“…Interestingly, the complexes show significant DNA cleavage activity under argon in UV-A light. Since the phenanthroline bases are known to be photoactive under aerobic medium, the observed DNA cleavage under argon could be due to photoactivation of the thiolate ligand (satp) [18,[58][59][60][61]. The observed variation in the anaerobic DNA cleavage activity of the complexes could be related to their DNA binding strengths.…”

Electron Photodetachment from Aqueous Anions. 3. Dynamics of Geminate Pairs Derived from Photoexcitation of Mono- vs Polyatomic Anions

“…Since hydrosulfide is a strong base, hydroxide is always present in its aqueous 29 The only exception to this rule is hydroxyl radical (derived from OH -)…”