Iron complexes thiols

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. 

Because a-alkoxyalkyl iron complexes are thermally unstable [467] they cannot be stored for long periods of time. More suitable carbene precursors are the corresponding a-(dimethylsulfonium)alkyl complexes, which can be stored indefinitely under ambient conditions [468-473], These complexes are prepared by S-alkylation of a-(methylthio)alkyl complexes, which can be prepared by alkylation of metallates with a-halothioethers, by addition of C-nucleophiles to (alkylthio)carbene complexes, or by addition of thiols to carbene complexes. 

In order to produce a high initial rate we suggest that the iron complex must produce radicals by attacking a reactant, and the thiol is the most likely one. This proposal is supported by the recent demonstration by Wallace (25) that ferric octanoate readily reacts with thiols at ambient temperature to give RS radicals which are effectively captured by an olefin, provided the ratio of thiol to iron concentrations is not greater than 10. 

At the present time we have no certain knowledge of the state of the heme in these 450 nm species. We do not know if there are heme aggregates although they are unlikely. It is therefore reasonable to look at systems where the haem is aggregated as well as those where it is not in order to see how the absorption spectra can be mimic-ed. It seems reasonable to assume that the iron is low-spin in the carbon monoxide, isocyanide, and nitric oxide complexes as no high-spin iron complexes of this type are known. In the high-spin or low-spin state it may be that the thiol is weakly bound, if at all, for Fe(II) heme in models or in hemoglobin does not bind to thiols. In an attempt to understand these spectra we shall use a semi-empirical approach based on the theoretical discussion in the previous article (52) and elaborated in what follows immediately. Only Fe(II) complexes will be analysed as the Fe(III) proteins have been previously examined (52). 

Reaction of Resin-Bound Iron Complex (54) with Alkyl Mercaptans, Thiophenols, and Phenols (Fig. 9)31. Sodium thiolates are prepared analogously to the alkoxides from thiol and sodium hydride, except that dry DMF is used as a solvent. The substitution on the polymer-bound arene (54) is performed at 70° in DMF within 16 h. The resin is filtered and washed with DMF (2 x 50 ml), MeOH (2 x 50 ml), H20 (2 x 50 ml), MeOH (2 x 50 ml), and CH2CI2 (3 x 50 ml) and then dried in vacuo at 40° to yield a red resin. 

The process implies a first electrochemical step with a very fast conversion of the ferroceno/ferrocinium couple, due to the short length of the alkyl chain, and a second chemical step with a simple electron transfer between the iron complex in solution and that of the monolayer. Moreover, the thiols block the gold surface in such a way that the Fe(CN)g- oxidation will take place due solely to the ferrocene mediation at the monolayer, and with a very high efficiency (i.e., the catalytic way is observed at potentials 500 mV lower than those corresponding to a gold electrode with a C6SH monolayer). 

These Fp-alkene complexes react with a variety of other nucleophiles,3 5 including water, alcohols, amines,3 6 phosphines, and thiols as well as carbon nucleophiles (enamines, organocuprates, enolates),3 2,3l8 and dialkyl cadmium reagents.3 9 Diene complexes such as 487 were converted to the corresponding cationic complexes (488), for example, and reaction with malonate gave 489. The iron complex was removed with trimethylamine N-oxide (Me N-O) to give 490.320... 

Wiegant FA, Malyshev lY et al (1999) Dinitrosyl iron complexes with thiol-containing ligands and S-nitroso-D, L-penicillamine as inductors of heat shock protein synthesis in H35 hepatoma cells. FEBS Lett 455 179-182... 

Vanin AF, Sanina NA et al (2007) Dinitrosyl-iron complexes with thiol-containing ligands spatial and electronic structures. Nitric Oxide 16 82-93... 

Vanin AF, Stukan RA, Manukhina EB (1996) Physical properties of dinitrosyl iron complexes with thiol-containing ligands in relation with their vasodilator activity. Biochim Biophys Acta 1295 5-12... 

Vanin AF (1991) Endothelium-derived relaxing factor is a nitrosyl iron complex with thiol ligands. FEBS Lett 289 1-3... 

Vanin AF, Serezhenkov VA et al (1998) The 2.03 signal as an indicator of dinitrosyl-iron complexes with thiol-containing ligands. Nitric Oxide 2 224-234... 

Alencar JL, Chalnpsky K et al (2003) Inhibition of arterial contraction by dinitrosyl-iron complexes critical role of the thiol ligand in determining rate of nitric oxide (NO) release and formation of releasable NO stores by S-nitrosation. Biochem Pharmacol 66 2365-2374... 

It is of interest to note that the activating effect of ascorbic acid on papain occurs only if ferrous ions are present otherwise the effect of the vitamin is depressant (Maschmann and Helmert, 1934). There is evidence suggesting that the ascorbic acid-iron complex activates by first reducing dithiol compounds associated with the enzyme, and that these thiol compounds in turn activate the enzyme (Purr, 1935). Similar reactions may be involved in the activation of arginase by the ascorbic acid-iron complex (Purr, 1933). 

Dinitrosyl Iron Complexes with Natural Thiol-Containing Ligands Physicochemistry, Biology, and Medicine... 

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