Sulfur Cluster Nitrosyls

The interactions of NO with the iron-sulfur cluster moieties of several enzymes generate iron-sulfur-nitrosyl cluster compounds [156]. However, synthetic nitrosyl clusters such as Roussins black salt (RBS), Roussins red salt (RRS), Roussins red ester (RRE) and [FeNOS]4 (Fig. 5.3) are well known [129, 157] and can be synthesized easily [158-164]. For example, the RBS can be prepared by mixing FeS04 with NaN03 and (NH4)2S in aqueous solution [158]. RRE salts are generally insoluble in water, but recently the water soluble sulfonated derivative, Na2[Fe2(SCH2CH2S03)2(N0)4], has been prepared [165]. 

The crystal structures oftetraphenylarsonium [166] and tetraethylammonium [167] salts have been determined and the cluster anion has been found to possess C3V symmetry. Electrochemical studies of stable RBS show the existence of four reduction 

Fe4S3(NO)7 + S Fe4S4(NO)7 nitric oxide from Roussin s red salt. 

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Fig. 5.3 Structures of some well-known iron-sulfur cluster nitrosyls.

The central role of the complexes [Fe(NO)2(SR)2]- in the reaction chemistry of iron-sulfur-nitrosyl complexes and their very ready formation both in in vitro and in vivo (108,123-125,128,129) suggest that the antimicrobial activity of nitrite depends not only upon the disruption of respiration [by destruction of the natural iron-sulfur clusters of redox proteins (70S)] but also specifically upon the formation... 

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