Hemoglobin-stabilized tetranitrosyl binuclear iron complex with pyridine-2-yl in aqueous solutions

The tetranitrosyl iron complex with pyridine-2-yl [Fe2(SC5H4N)2(NO)4] (1) has higher NO-donating activity in 3% aqueous solutions of DMSO (pH 7.0, 25 °C) than the organic NO donor, viz., adduct of NO with diethylenetriamine (NO-adduct). The NO concentration was determined by the spectrophotometric method based on the formation of an NO complex with hemoglobin (Hb). The apparent first-order rate constants of the studied reactions are (6.15±0.6)·10−1 s−1 and (0.8±0.08)·10−1 s−1 for complex 1 and the NO-adduct, respectively, at an Hb concentration of 2·10−1 mol L−1 and the ratio [NO donor]/[Hb] = 10. The effect of Hb and [NO donor]/[Hb] ratio on the rate of NO generation from a solution of complex 1 was studied. For a fourfold decrease in the concentration of complex 1 the reaction rate constant decreases to 0.5·10−4 s−1, whereas the fourfold increase in the Hb concentration results in the stabilization of complex 1.