Transformation of {Fe(NO)(2)}(10) dinitrosyliron complex (DNIC) Fe(CO)(2)(NO)(2) into [{Fe(NO)(2)}(9)](2) Roussin's red ester (RRE) [(mu-S(CH2)(2)NH2)Fe(NO)(2)](2) (3) triggered by cysteamine via the reaction pathway (intermediates) [{Fe-(NO)(2)}(10)]2[(NO)(2)Fe(mu-CO)(mu-S(CH2)(2)NH3)Fe(NO)(2)] (1) -> {Fe(NO)(2)}(9){Fe(NO)(2)}(10)[(NO)(2)Fe(mu-S(CH2)(2)NH2)(mu-S(CH2)(2)-NH3)Fe(NO)(2)] (2) -> RRE 3 is demonstrated. The 1-to-2-to-3 conversion is promoted by proton transfer followed by O-2 oxidation and deprotonation. Additionally, a study on facile conversion of complex 3 to complexes [(SR)(S(CH2)(2)NH3)Fe-(NO)(2)] [SR = 2-aminoethanethiolate (4), benzenethiolate (5)] and [(CysS))(S(CH2)(2)NH3)Fe(NO)(2)] (6) via reaction with thiols and the further utility of complex 5 as a template for synthesizing mixed-thiolate-containing reduced RRE (rRRE)[(mu-SC6H5)(mu-S(CH2)(2)NH3)Fe-2(NO)(4)] (7) provide the methodology for the synthesis and isolation of neutral, pure cysteine-/ mixed-thiolate-containing DNIC/RRE. Compared to the conversion of complex 2 to complex 3 via reaction with O-2, diphenyl disulfide triggers oxidation of complex 2 to lead to formation of the neutral {Fe(NO)(2)}(9) DNIC 5 and RRE 3. S-S bond activation of diphenyl disulfide by rRRE 2 may support the decay (oxidation) of rRRE species in ToMOC via the reduction of adjacent protein residues such as cystins, proposed by Lippard.