Formation of the Distinct Redox‐Interrelated Forms of Nitric Oxide from Reaction of Dinitrosyl Iron Complexes (DNICs) and Substitution Ligands

Release of the distinct NO redox-interrelated forms (NO(+), *NO, and HNO/NO(-)), derived from reaction of the dinitrosyl iron complex (DNIC) [(NO)(2)Fe(C(12)H(8)N)(2)](-) (1) (C(12)H(8)N=carbazolate) and the substitution ligands (S(2)CNMe(2))(2), [SC(6)H(4)-o-NHC(O)(C(5)H(4)N)](2) ((PyPepS)(2)), and P(C(6)H(3)-3-SiMe(3)-2-SH)(3) ([P(SH)(3)]), respectively, was demonstrated. In contrast to the reaction of (PyPepS)(2) and DNIC 1 in a 1:1 stoichiometry that induces the release of an NO radical and the formation of complex [PPN][Fe(PyPepS)(2)] (4), the incoming substitution ligand (S(2)CNMe(2))(2) triggered the transformation of DNIC 1 into complex [(NO)Fe(S(2)CNMe(2))(2)] (2) along with N-nitrosocarbazole (3). The subsequent nitrosation of N-acetylpenicillamine (NAP) by N-nitrosocarbazole (3) to produce S-nitroso-N-acetylpenicillamine (SNAP) may signify the possible formation pathway of S-nitrosothiols from DNICs by means of transnitrosation of N-nitrosamines. Protonation of DNIC 1 by [P(SH)(3)] triggers the release of HNO and the generation of complex [PPN][Fe(NO)P(C(6)H(3)-3-SiMe(3)-2-S)(3)] (5). In a similar fashion, the nucleophilic attack of the chelating ligand P(C(6)H(3)-3-SiMe(3)-2-SNa)(3) ([P(SNa)(3)]) on DNIC 1 resulted in the direct release of [NO](-) captured by [((15)NO)Fe(SPh)(3)](-), thus leading to [((15)NO)((14)NO)Fe(SPh)(2)](-). These results illustrate one aspect of how the incoming substitution ligands ((S(2)CNMe(2))(2) vs. (PyPepS)(2) vs. [P(SH)(3)]/[P(SNa)(3)]) in cooperation with the carbazolate-coordinated ligands of DNIC 1 function to control the release of NO(+), *NO, or [NO](-) from DNIC 1 upon reaction of complex 1 and the substitution ligands. Also, these results signify that DNICs may act as an intermediary of NO in the redox signaling processes by providing the distinct redox-interrelated forms of NO to interact with different NO-responsive targets in biological systems.