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Transformation of the {Fe(NO)2}9 Dinitrosyl Iron Complexes (DNICs) into S-Nitrosothiols (RSNOs) Triggered by Acid–Base Pairs

Authors

  • Chih-Chin Tsou,

    1. Department of Chemistry, National Tsing Hua University, Hsinchu 30013 (Taiwan), Fax: (+886) 3-5711082
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  • Prof. Dr. Wen-Feng Liaw

    Corresponding author
    1. Department of Chemistry, National Tsing Hua University, Hsinchu 30013 (Taiwan), Fax: (+886) 3-5711082
    • Department of Chemistry, National Tsing Hua University, Hsinchu 30013 (Taiwan), Fax: (+886) 3-5711082
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Abstract

S-Nitrosation of the coordinated thiolate of dinitrosyl iron complexes (DNICs) to generate S-nitrosothiols (RSNOs) was demonstrated. Transformation of [{(NO)2Fe(μ-StBu)}2] (1-tBuS) into the {Fe(NO)2}9 DNIC [(NO)2Fe(StBu)(MeIm)] (2-MeIm) occurs under addition of 20 equiv of 1-methylimidazole (MeIm) into a solution of 1-tBuS in THF. The dynamic interconversion between {Fe(NO)2}9 [(NO)2Fe(S-NAP)(dmso)] (2-dmso) (NAP=N-acetyl-D-penicillamine) and [{(NO)2Fe(μ-S-NAP)}2] (1-NAP) was also observed in a solution of complex 1-NAP in DMSO. In contrast to the reaction of complex 2-MeIm and bis(dimethylthiocarbamoyl) disulfide ((DTC)2) to yield {Fe(NO)}7 [(NO)Fe(DTC)2] (3) (DTC=S2CNMe2) accompanied by (tBuS)2 and NO(g), transformation of {Fe(NO)2}92-MeIm (2-dmso) into RSNOs (RS=tBuS, NAP-S) along with complex 3 induced by the Brønsted acid solution of (DTC)2 demonstrated that Brønsted acid may play a critical role in triggering S-nitrosation of the coordinated thiolate of DNICs 2-MeIm (or 2-dmso) to produce RSNOs. That is, DNIC-mediated S-nitrosation requires a Brønsted acid–Lewis base pair to produce RSNO. Transformation of DNICs into RSNOs may only occur on the one-thiolate-containing {Fe(NO)2}9 DNICs, in contrast to protonation of the two-thiolate-containing DNICs [(NO)2Fe(SR)2] by Brønsted acid to yield [{(NO)2Fe(μ-SR)}2]. These results might rationalize that the known protein-Cys-SNO sites derived from DNICs were located adjacent to acid and base motifs, and no protein-bound SNO characterized to date has been directly derived from [protein–(cysteine)2Fe(NO)2] in biology.

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