S-Nitrosothiols, RSNO

Some acyclic sulfur-nitrogen compounds also exhibit intense colours. For example, S-nitrosothiols RSNO are either green, red or pink (Section 9.7). Their UV-visible spectra show an intense band in the 330-350 nm region (no it ) and a weaker band in the visible region at 550-600 nm... 

S-nitrosothiols (RSNO) have emerged as important species in the storage and transport of nitric oxide. As NO donors these S-N compounds have potential medical applications in the treatment of blood circulation problems. 

Recently, it has been found that NO donors inhibit HIV-1 replication in acutely infected human peripheral blood mononuclear cells (PBMCs), and have an additive inhibitory effect on HIV-1 replication in combination with 3 -azido-3 -deoxythymisylate (AZT) [139, 140]. S-nitrosothiols (RSNOs) inhibit HIV-1 replication at a step in the viral replicative cycle after reverse transcription, but before or during viral protein expression through a cGMP-independent mechanism. In the latently infected U1 cell line, NO donors and intracellular NO production stimulate HIV-1 reactivation. These studies suggest that NO both inhibits HIV-1 replication in acutely infected cells and stimulates HIV-1 reactivation in chronically infected cells. Thus, NO donors may be useful in the treatment of HIV-1 disease by inhibiting acute infection, or reactivating a latent virus. 

Baciu, C., Gauld, J. W., An assessment of theoretical methods for the calculation of accurate stmctures and S-N bond dissociation energies of S-nitrosothiols (RSNOs),/. Phys. 

DNICs are relatively stable and can be stored at —80°C for weeks without much loss of NO [155], however, their stabilities decrease dramatically at room temperature to render unbound NO. NO bound to thiols may account for the low yield of free NO sometimes detected in solutions involving DNICs in the presence of high concentrations of thiols [126]. The decomposition is acid catalyzed to free NO and S-nitrosothiol (RSNO). Of course, protein-bound DNICs are more stable and serve as potential sinks for low molecular weight DNICs. 

S-Nitrosothiols undergo a reversible transnitrosation reaction at zinc tris(pyrazolyl)boratozinc thiolates, " TpZn-SR. These zinc thiolates are rmreactive toward anaerobic NO but rapidly react with NO in the presence of O2 or anaerobically with NO2 to release the S-nitrosothiol RSNO with formation of the corresponding zinc nitrate 125). 

Tsou CC, Liaw WF (2011) Transformation of the Fe (NO)2 9 dinitrosyl iron cranplexes (DNICs) into S-nitrosothiols (RSNOs) triggered by add-base pairs. Chemistry 17 13358-13366... 

Dicks, A., Swift, H., Williams, D., Butler, A., Alsadoni, H., Cox, B., 1996. Identification of Cu as the effective reagent in nitric oxide formation from S-nitrosothiols (RSNO). Journal of the Chemical Society, Perkin Transactions 2, 481-487. 

Thionitrites (or S -nitrosothiols), RSNO, are currently believed to be involved in the storage and transport of nitric oxide in the body. The reactivity of this class of compound is clearly of importance and now the reactions of a number of nitrogen nucleophiles with a model compound, 5-nitrosopenicillamine (168), have been investigated. In addition to primary, secondary, and tertiary aliphatic amines, hydrazine. 

In solution the cis and trans isomers may co-exist, as demonstrated by N NMR and UV-visible spectra. The N NMR chemical shift of the trans isomer is shifted ca. 60 ppm downfield relative to the cis isomer." The visible absorption band of S-nitrosothiols corresponds to a weak n K transition in the 520-590 nm region. The absorption maxima of trans conformers are red-shifted by ca. 30 nm relative to those of the cis isomer. Two absorptions are observed in the 520-590 nm region in the experimental spectra of RSNO derivatives." ... 

S -nitrosothiols, several of which occur naturally, e.g., iS -nitrosocysteine and S-nitrosoglutathione, have an important role in NO transport and regulation in biological systems. Potential applications of RSNO compounds include their use as vasodilators in the treatment of angina and in the search for a cure for male impotence.11 The most convenient route to S-nitrosothiol formation is the nitrosation of thiols. 

The ability of S -nitrosothiols to mimic many of the biological properties of NO itself may emanate from in vivo decomposition to generate NO. This decomposition is catalysed by Cu2+,n and may be important in the development of thrombo-resistant devices used in kidney dialysis or coronary by-pass surgery.196 It is also possible that direct transfer of NO from RSNO occurs in biological systems.197... 

DNICs are spontaneously [128] formed in aqueous media using a simple Fe(II) salt, S-nitrosothiol and thiol, with a ratio of Fe2+/RSH of 1 20. NO is transferred quantitatively from the sulfur atom in the RSNO to the iron. The complete mechanism is yet to be fully determined. A 1 2 ratio results in the formation of an EPR silent yellow dinuclear iron complex ([Fe2(RS)2(NO)4]. At the higherer ratio, the green paramagnetic, mononuclear dinitrosyl predominates. The reaction is very straightforward at pH 7.8, under an inert atmosphere and in water. Under anaerobic conditions the stability of this compound is enhanced, however, in the presence of air and hydrogen peroxide, it readily decomposes to give the dinuclear complex [126] which is similar in structure to the Roussin red salt, as shown in Scheme 5.5. 

Methylanaline could be transnitrosated with nitrite and S-nitrosocysteine and also by a simulated protein bound nitrite. In the latter case, an important factor was the local concentration of nitrosothiol groups on the matrix. The effects of S-nitrosocysteine as an inhibitor of lipid oxidation, as a color developer, and as an anticlostridial, have been reported recently in a turkey product (31). The Molar concentration of RSNO equating to 25 ppm nitrite gave similar results for color and inhibition of lipid oxidation but had less anti-clostridial activity. Transnitrosation between RSNO and heme protein was demonstrated. 

Organic derivatives RSNO (5-nitrosothiols), which have important roles in NO transport and regulation in biological systems, " have been characterized by X-ray crystallography, NMR, and IR spectra. Both syn and anti forms are present in solution. The barriers to rotation about the S-N bond are 11 - 12kcalmoR and the S-N bond dissociation energies are estimated to be 20-30 kcal moR ... 

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