Reaction of nitric oxide with the iron(III) complex of N-(dithiocarboxy)sarcosine: a new type of reductive nitrosylation involving iron(IV) as an intermediate

Abstract

Reaction of NO with the iron complex of N-(dithiocarboxy)sarcosine (H₂DTCS) was investigated by UV/VIS absorption spectroscopy, HPLC, LC-ESI MS and pulse radiolysis. The results of HPLC and LC-ESI MS clearly showed that the reaction products of NO with [Fe^III(DTCS)₃]³⁻ are [NO–Fe^II(DTCS)₂]²⁻ and a dimer of DTCS in which two DTCS bind through a disulfide bond. On pulse radiolysis of a deaerated aqueous solution of [Fe^III(DTCS)₃]³⁻ in the presence of sodium nitrite the absorption changes consisted of three phases, as judged from kinetic difference spectra. In the faster phase, radiolytically generated NO reacted with [Fe^III(DTCS)₃]³⁻ to form a transient intermediate I with a second-order rate constant of (4.8 ± 0.9) × 10⁸ dm³ mol⁻¹ s⁻¹. Subsequently, I reacted with unchanged [Fe^III(DTCS)₃]³⁻ to give an intermediate II with an absorption maximum at 460 nm. In the third step II was found to decay on a timescale of seconds. The final product in the sequence of the reactions was [NO–Fe^II(DTCS)₂]²⁻. From the spectra obtained, the intermediate II is discussed in relation to the iron(IV) complex of N,N-diethyldithiocarbamate. These results suggest that the proposed reaction mechanism is a new type of reductive nitrosylation involving iron(IV) as an intermediate.