583-89-1Relevant articles and documents
Kinetics and thermodynamics of oxidation mediated reaction in L-cysteine and its methyl and ethyl esters in dimethyl sulfoxide-d6 by NMR spectroscopy
Dougherty, Ryan J.,Singh, Jaideep,Krishnan
, p. 196 - 200 (2016/11/29)
L-Cysteine (L-Cys), L-Cysteine methyl ester (L-CysME) or L-Cysteine ethyl ester (L-CysEE), when dissolved in dimethyl sulfoxide, undergoes an oxidation process. This process is slow enough and leads to nuclear magnetic resonance (NMR) spectral changes that could be monitored in real time. The oxidation mediated transition is modeled as a pseudo-first order kinetics and the thermodynamic parameters are estimated using the Eyring's formulation. L-Cysteine and their esters are often used as biological models due to the remarkable thiol group that can be found in different oxidation states. This oxidation mediated transition is due to the combination of thiol oxidation to a disulfide followed by solvent-induced effects may be relevant in designing cysteine-based molecular models.
The reaction of S-nitrosothiols with thiols at high thiol concentration
Dicks, Andrew P.,Li,Munro, Andrew P.,Swift, Helen R.,Williams, D. Lyn H.
, p. 789 - 794 (2007/10/03)
Reactions of S-nitrosothiols (RSNO) with their corresponding thiols (RSH) present in a large excess (>20-fold) proceed readily to give the disulfide. Ammonia is formed together with some nitrite anion, and these constitute >90% of the 'nitrogen' products. This is in marked contrast with the reaction at low thiol concentration, where nitric oxide is the major initial 'nitrogen' product, which is rapidly converted in the presence of oxygen in water to nitrite anion. Also in marked contrast to the 'low thiol concentration' reaction, the reaction at high thiol concentration is not affected by added Cu2+, nor by the metal-ion scavenger EDTA. Kinetically all reactions were excellent first-order processes, and the reactions were also strictly first order in thiol concentration. A large range of nitrosothiols were studied and the generality of the reaction established. Some reactions of RSNO with other thiols (R'SH) were examined and the results readily interpreted in terms of a prior rapid equilibrium transnitrosation. The pH dependence for the reaction of S-nitrosocysteine with cysteine clearly showed that the reactive species is the cysteine thiolate anion. The results are discussed along with those of two other recent reports of these reactions, in terms of thiolate attack initially at the nitroso nitrogen atom, and subsequently at sulfur atoms, eliminating RSSR and yielding hydroxylamine, which is rapidly reduced by thiolate ion to ammonia. The results are also discussed in connection with the release of NO from nitrosothiols and with the important biological consequences, both for the in vivo reactions of NO and for the potential of nitrosothiols as NO-releasing drags for medical use.
Catalysis by Cu2+ of nitric oxide release from S-nitrosothiols (RSNO)
Askew, Stuart C.,Barnett, D. Jonathan,McAninly, John,Williams, D. Lyn H.
, p. 741 - 746 (2007/10/02)
The decomposition of a range of S-nitrosothiols (thionitrites) RSNO, based on cysteine derivatives, yields in water at pH 7.4 nitrite ion quantitatively.If oxygen is rigorously excluded then no nitrite ion is formed and nitric oxide can be detected using an NO-probe.The reaction is catalysed by trace quantities of Cu2+ (there is often enough present in distilled water samples) and also to a lesser extent by Fe2+, but not by Zn2+, Cu2+, Mg2+, Ni2+, Co2+, Mn2+, Cr3+ or Fe3+.The rate equation (measuring the disappearance of the absorption at ca. 350 nm due to RSNO) was established as v = k*2+> + k' over a range of 2+> typically 5-50 μmol dm-3.The constant term k' represents the component of the rate due to residual Cu2+ in the solvent and buffer components, together with the spontaneous thermal reaction.Decomposition can be virtually halted by the addition of EDTA.Reactions carried out in the presence of N-methylaniline gave a quantitative yield of N-methyl-N-nitrosoaniline, but a negligible yield when oxygen was rigorously excluded.Values of the second-order rate constant k were obtained for a range of S-nitrosothiols.Reactivity is highest for the S-nitrosothiols derived from cysteamine and penicillamine, when Cu2+ can be complexed both with the nitrogen atom of the nitroso group and the nitrogen atom of the amino group, via a six-membered ring intermediate.If there is no amino (or other electron donating group) present, reaction is very slow (as for RSNO derived from a tert-butyl sulfide).N-Acetylation of the amino group reduces the reactivity drastically as does the introduction of another CH2 group in the chain.There is evidence of a significant gem-dimethyl effect.Kinetic results using the S-nitrosothiols derived from mercaptoacetic, thiolactic and thiomalic acids suggests that coordination can also occur via one of the oxygen atoms of the carboxylate group.EPR experiments which examined the Cu2+ signal showed no spectral change during the reaction suggesting that the mechanism does not involve oxidation and reduction with Cu2+ Cu+ interconversion.
