59-53-0Relevant academic research and scientific papers
Online Investigation of Aqueous-Phase Electrochemical Reactions by Desorption Electrospray Ionization Mass Spectrometry
Lu, Mei,Liu, Yong,Helmy, Roy,Martin, Gary E.,Dewald, Howard D.,Chen, Hao
, p. 1676 - 1685 (2015/09/22)
Electrochemistry (EC) combined with mass spectrometry (MS) is a powerful tool for elucidation of electrochemical reaction mechanisms. However, direct online analysis of electrochemical reaction in aqueous phase was rarely explored. This paper presents the online investigation of several electrochemical reactions with biological relevance in the aqueous phase, such as nitrosothiol reduction, carbohydrate oxidation, and carbamazepine oxidation using desorption electrospray ionization mass spectrometry (DESI-MS). It was found that electroreduction of nitrosothiols [e.g.; nitrosylated insulin B (13-23)] leads to free thiols by loss of NO, as confirmed by online MS analysis for the first time. The characteristic mass shift of 29 Da and the reduced intensity provide a quick way to identify nitrosylated species. Equally importantly, upon collision-induced dissociation (CID), the reduced peptide ion produces more fragment ions than its nitrosylated precursor ion (presumably the backbone fragmentation cannot compete with the facile NO loss for the precursor ion), thus facilitating peptide sequencing. In the case of saccharide oxidation, it was found that glucose undergoes electro-oxidation to produce gluconic acid at alkaline pH, but not at neutral and acidic pHs. Such a pH-dependent electrochemical behavior was also observed for disaccharides such as maltose and cellobiose. Upon electrochemical oxidation, carbamazepine was found to undergo ring contraction and amide bond cleavage, which parallels the oxidative metabolism observed for this drug in leucocytes. The mechanistic information of these redox reactions revealed by EC/DESI-MS would be of value in nitroso-proteome research and carbohydrate/drug metabolic studies.
Modulation of homocysteine toxicity by S-nitrosothiol formation: A mechanistic approach
Morakinyo, Moshood K.,Strongin, Robert M.,Simoyi, Reuben H.
experimental part, p. 9894 - 9904 (2011/08/08)
The metabolic conversion of homocysteine (HCYSH) to homocysteine thiolactone (HTL) has been reported as the major cause of HCYSH pathogenesis. It was hypothesized that inhibition of the thiol group of HCYSH by S-nitrosation will prevent its metabolic conversion to HTL. The kinetics, reaction dynamics, and mechanism of reaction of HCYSH and nitrous acid to produce S-nitrosohomocysteine (HCYSNO) was studied in mildly to highly acidic pHs. Transnitrosation of this non-protein-forming amino acid by 5-nitrosoglutathione (GSNO) was also studied at physiological pH 7.4 in phosphate buffer. In both cases, HCYSNO formed quantitatively. Copper ions were found to play dual roles, catalyzing the rate of formation of HCYSNO as well as its rate of decomposition. In the presence of a transition-metal ions chelator, HCYSNO was very stable with a halflife of 198 h at pH 7.4. Nitrosation by nitrous acid occurred via the formation of more powerful nitrosating agents, nitrosonium cation (NO +) and dinitrogen trioxide (N2O3). In highly acidic environments, NO+ was found to be the most effective nitrosating agent with a first-order dependence on nitrous acid. N 2O3 was the most relevant nitrosating agent in a mildly acidic environment with a second-order dependence on nitrous acid. The bimolecular rate constants for the direct reactions of HCYSH and nitrous acid, N2O3, and NO+were 9.0 × 10-2, 9.50 × 103, and 6.57 × 1010 M-1 s-1, respectively. These rate constant values agreed with the electrophilic order of these nitrosating agents: HNO2 2O3 +. Transnitrosation of HCYSH by GSNO produced HCYSNO and other products including glutathione (reduced and oxidized) and homocysteineglutathione mixed disulfide. A computer modeling involving eight reactions gave a good fit to the observed formation kinetics of HCYSNO. This study has shown that it is possible to modulate homocysteine toxicity by preventing its conversion to a more toxic HTL by S-nitrosation.
Equilibrium and kinetics studies of transnitrosation between S-nitrosothiols and thiols
Wang, Kun,Wen, Zhong,Zhang, Wei,Xian, Ming,Cheng, Jin-Pei,Wang, Peng George
, p. 433 - 436 (2007/10/03)
Using UV-vis spectrometrical measurements, equilibrium constants for NO transfer between S-nitroso-N-acetyl-penicillamine (SNAP) and different thiols as well as kinetic data for NO transfer from S-nitroso bovine serum albumin (BSANO) to thiols have been obtained. NO transfer from SNAP to other primary/secondary thiols are thermodynamically favorable, whereas other S-nitrosothiols exhibit similar NO transfer potential. The obtained Gibbs free energy, enthalpy and entropy data indicated that NO transfer reactions from SNAP to four thiols are exothermic with entropy loss. The kinetic behavior of BSANO/RSH transfer can be related to both the acidity of sulfhydryl group and the electronic structure in thiol.
Reactivity of sulfur nucleophiles towards S-nitrosothiols
Munro, Andrew P.,Williams, D. Lyn H.
, p. 1794 - 1797 (2007/10/03)
Rate constants have been measured for the reactions of a range of S-nitrosothiols with the following sulfur-centred nucleophiles: sulfite ion, thiourea, thiocyanate ion, thiosulfate ion, thiomethoxide ion and sulfide ion. Many of the reactions were very fast and were followed in a stopped-flow spectrophotometer. For the sulfite reaction the reactive species over the pH range 4-8 was shown to be exclusively SO32-. For two RSNO species the reactivity sequence was established as: SO32- > MeS- > S2O32- ? SC(NH2)2 SCN-. The reaction with sulfide ion was also rapid and generated a fairly stable yellow species (λmax 410 nm), which was probably the nitrosodisulfide ion ONSS-, but the absorbance-time data were too complex for a simple kinetic analysis. This reaction could have some potential as an analytical procedure for the determination of RSNO species. The kinetic results are discussed in terms of the factors affecting nucleophilicity and are compared with the corresponding reactions of other nitrosating species.
Reaction of ascorbic acid with S-nitrosothiols: Clear evidence for two distinct reaction pathways
Holmes, Anthony J.,Williams, D. Lyn H.
, p. 1639 - 1644 (2007/10/03)
Ascorbate reacts with S-nitrosothiols generally, in the pH range 3-13 by way of two distinct pathways, (a) at low [ascorbate], typically below ～1 × 10-4 mol dm-3 which leads to the formation of NO and the disulfide, and (b) at higher [ascorbate] when the products are the thiol and NO. Reaction (a) is Cu2+-dependent, and is completely cut out in the presence of EDTA, whereas reaction (b) is totally independent of [Cu2+] and takes place readily whether EDTA is present or not. For S-nitrosoglutathione (GSNO) the two reactions can be made quite separate, although for some reactants the two reactions overlap. In reaction (a), ascorbate acts as a reducing agent, generating Cu+ from Cu2+, which in turn reacts with RSNO forming initially NO, Cu2+ and RS-. The latter can then play the role of reducing agent for Cu2+, leading to disulfide formation. Ascorbate will initiate reaction when the free thiolate has initially been reduced to a very low level by the synthesis of RSNO from a large excess of nitrous acid over the thiol. Reaction (b) is interpreted in terms of nucleophilic attack by ascorbate at the nitroso-nitrogen atom, leading to thiol and O-nitrosoascorbate which breaks up, by a free-radical pathway, to give dehydroascorbic acid and NO. A similar pathway is the accepted mechanism in the literature for the nitrosation of ascorbate by nitrous acid and alkyl nitrites. The rate constant for the Cu2+-independent pathway increases sharply with pH and analysis of the variation of the rate constant with pH identifies a reaction pathway via both the mono- and di-anion forms of ascorbate, with the latter being the more reactive. As expected the entropy of activation is large and negative. Some aspects of structure-reactivity trends are discussed.
Preparation of Some Novel S-Nitroso Compounds as Potential Slow-release Agents of Nitric Oxide in vivo
Moynihan, Humphrey A.,Roberts, Stanley M.
, p. 797 - 806 (2007/10/02)
The optimum conditions for the preparation of N-acetyl-S-nitrosopenicillamine (SNAP) 3 were determined and applied to the synthesis of the corresponding N-formyl compound 7.The nitrosation of penicillamine dipeptides was investigated and bis-thionitroso compounds 13, 18, 26 and 27 were isolated.S,S'-Dinitroso dithiol 13 showed biological activity akin to that of glyceryl trinitrate in decreasing systemic arterial blood pressure in anaesthetized rats and rabbits.Concomitant inhibition of collagen- or ADP-induced platelet aggregation was observed.
Studies Related to Thietan-2-ones. Part 1. Conversion of D-Penicillamine into DL-2-Methylpenicillamine using Thietan-2-one-based Chemistry
Al-Zaidi, Shakir M.R.,Crilley, Martine M. L.,Stoodley, Richard J.
, p. 2259 - 2266 (2007/10/02)
A series of N-substituted derivatives of (3R)-3-amino-4,4-dimethylthietan-2-one has been prepared from D-penicillamine (3).Attempts to effect the methylathion at position 3 of the N-acetyl (7a), N,N-diacetyl (12), N-benzyloxycarbonyl (7b), or N-(p-nitrobenzylidene) derivative (15a) were unrewarding.Although the N-benzylidene and N-furfurylidene derivatives (15b) and (15c) were successfully methylated at position 3 by using iodomethane and potassium t-butoxide in tetrahydrofuran (THF), best results were achieved by treating the N-(2-hydroxy-1-naphthylmethylene) derivative (15d) with iodomethane and sodium hydride in N,N-dimethylformamide.Cleavage of the imine linkage of the methylated derivatives of the thietanones (15c) and (15d), i.e. compounds (19b) and (19c), was effected by using, respectively, toluene-p-sulphonic acid in THF and dilute hydrochloric acid in acetone.The derived salts of (3RS)-3-amino-3,4,4-trimethylthietan-2-one, i.e. (21a) and (21b), underwent hydrolysis in boiling water to give the corresponding salts of DL-2-methylpenicillamine, i.e. (22a) and (22b).
A Kinetic Investigation of the Thionitrite from (+/-)-2-Acetylamino-2-carboxy-1,1-dimethylethanethiol as a Possible Nitrosating Agent
Al-Kaabi, Sharifa S.,Williams, D. Lyn H.,Bonnett, Raymond,Ooi, Suan L.
, p. 227 - 230 (2007/10/02)
In strongly aqueous acid solution (+/-)-2-acetylamino-2-carboxy-1,1-dimethylethyl thionitrite (RSNO) undergoes denitrosation to give the corresponding thiol.The reaction is reversible and normally lies well over on the side of the thionitrite, but can proceed in the denitrosation direction in the presence of traps for free nitrous acid such as added sodium azide or sulphamic acid.At sufficiently high trap concentration to ensure complete irreversibility, the reaction was found to be first-order in RSNO and acid-catalysed; the observed reaction rate constant is approximately proportional to h0.Catalysis was observed by Cl(1-), Br(1-), SCN(1-), and SC(NH2)2 and the second-order rate constants were 4.6*10-3, 13.0*10-3, 34*10-3, and 27*10-3 l mol-1s-1, respectively.The order of reactivity is as expected with the exception of that of thiourea.N-Methyl-4-nitroaniline was converted quantitatively to the corresponding nitrosamine by RSNO, but in the presence of added sodium azide, no nitrosamine was detected; this shows that RSNO like nitrosamines generally and alkyl nitrites, acts as a nitrosating agent towards amines etc., under these experimental conditions, by prior hydrolysis or via nitrosyl halide etc. formation.A kinetic analysis has enabled the reactivity of the nitrous acid traps hydrazoic acid and sulphamic acid to be established quantitatively.
