Abstract
Transformation of {Fe(NO)2}10 dinitrosyl iron complex (DNIC) Fe(CO)2(NO)2 into [{Fe(NO)2}9]2 Roussin’s red ester (RRE) [(μ-S(CH2)2NH2)Fe(NO)2]2 (3) triggered by cysteamine via the reaction pathway (intermediates) [{Fe(NO)2}10]2 [(NO)2Fe(μ-CO)(μ-S(CH2)2NH3)Fe(NO)2] (1-NH3) → {Fe(NO)2}9-{Fe(NO)2}10 [(NO)2Fe(μ-S(CH2)2NH2)(μ-S(CH2)2NH3)Fe(NO)2] (2) → RRE 3 was demonstrated. The 1-NH3-to-¬2-to-3 conversion is promoted by proton transfer followed by O2 oxidation and deprotonation. Additionally, study on facile conversion of complex 3 to complexes [(SR)(S(CH2)2NH3)Fe(NO)2] (SR = 2-aminoethanethiolate (4), benzenethiolate (6)) and [(CysS))(S(CH2)2NH3)Fe(NO)2] (7) via reacting with thiols and the further utility of complex 6 as a template for synthesizing mixed-thiolate-containing rRRE [(μ-SC6H5)(μ-S(CH2)2NH3)Fe2(NO)4] (9) provide the methodology for syntheses and isolation of neutral, pure cysteine-/mixed-thiolate- containing DNIC/RRE. Compared to the conversion of complex 2 to complex 3 via reacting with O2, diphenyl disulfide triggered the oxidation of complex 2 to lead to the formation of the neutral {Fe(NO)2}9 DNIC 6 and RRE 3. S–S bond activation of diphenyl disulfide by reduced RRE 2 (rRRE) may support the decay (oxidation) of rRRE species in ToMOC via the reduction of adjacent protein residues such as cystins, proposed by Lippard.