Reactivity of Polysulfides

CARLLINNI COLOMBO, MELISA; PALERMO, JUAN CRUZ; BOUBETA, FERNANDO MARTÍN; ESTRIN, DARÍO ARIEL; BARI, SARA ELIZABETH

Buenos Aires

Simposio; Exploring the Frontiers of Chemistry: Challenges for the 21st Century; 2019

Facultad de Ciencias Exactas y Naturales - UBA

Hydrogen polysulfides, H2Sn (n>1), are gaining growing interest because some of the physiological roles formerly attributed to endogenous hydrogen sulfide, H2S, are better described as a consequence of their action.1,2 Particularly, H2Sn with n=2,3 have been demonstrated to be products of the 3-mercaptopyruvate sulfurtransferase,1,3 an enzyme of the H2S biosynthesis. Recent studies on polysulfides speciation in aqueous solution reveal that interconversion occurs, resulting on equilibria that depend on the experimental conditions.4 Also, the currently used chemicals for derivatization may cleave polysulfide chains, and hence the reliable analysis of polysulfide mixtures still represents an analytical challenge in the field. As a consequence of our studies on the reactivity of Na2S and metmyoglobin (FeIIIMb),5 we present herein a study of the kinetics of the interaction of synthetic disodium disulfane, Na2S2, with FeIIIMb at neutral pH, and the strategy to analyze the polysulfide contents of the dissolved Na2S2 preparation.We prepared Na2S2 by the comproportionation of an equimolar mixture of disodium sulfide, Na2S, and sulfur, S8, according to described procedure.6 Although the product matches the UV-vis aqueous spectrum of a commercial vendor, the dissolution in organic solvents aided by cryptands revealed the formation of the blue trisulfide radical anion, S3.-. Derivatization of polysulfide chains of different lengths with benzyl chloride may provide the product composition in solution. Upon reaction with FeIIIMb 8 x 10-6 M, in the presence of aqueous Na2S2 (R disulfane/ Mb = 10, 20, 30; pH 6.8, anaerobic, 25ºC) the reduced hemeprotein, FeIIMb, was formed, following an exponential growth.The reaction is relevant to the understanding of the sulfide-mediated detoxification by hemeproteins,7 and to the metal centered reduction of ferric hemeproteins.