Redox cycling of iron complexes of N-(dithiocarboxy)sarcosine and N-methyl- d-glucamine dithiocarbamate

Abstract

Iron(II)–dithiocarbamate complexes are used to trap nitrogen monoxide in biological samples, and the resulting nitrosyliron(II)–dithiocarbamate is detected and quantified by ESR. As the chemical properties of these compounds have been little studied, we investigated whether iron dithiocarbamate complexes can redox cycle. The electrode potentials of iron complexes of N -(dithiocarboxy)sarcosine (dtcs) and N -methyl - d -glucamine dithiocarbamate (mgd) are 56 and −25 mV at pH 7.4, respectively, as measured by cyclic voltammetry. The autoxidation and Fenton reaction of iron(II)–dtcs and iron(II)–mgd were studied by stopped-flow spectrophotometry with both iron(II) complexes and dioxygen or hydrogen peroxide in excess. In the case of excess iron(II)–dtcs and –mgd complexes, the rate constants of the autoxidation and the Fenton reaction are (1.6–3.2) × 10 4 and (0.7–1.1) × 10 5 M −1 s −1, respectively. In the presence of nitrogen monoxide, the oxidation of iron(II)–dtcs and iron(II)–mgd by hydrogen peroxide is significantly slower (ca. 10–15 M −1 s −1). The physiological reductants ascorbate, cysteine, and glutathione efficiently reduce iron(III)–dtcs and iron(III)–mgd. Therefore, iron bound to dtcs and mgd can redox cycle between iron(II) and iron(III). The ligands dtcs and mgd are slowly oxidized by hydrogen peroxide with rate constants of 5.0 and 3.8 M −1 s −1, respectively.