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Dinitrosyl Iron Complexes (DNICs) [L2Fe(NO)2]- (L = Thiolate):  Interconversion among {Fe(NO)2}9 DNICs, {Fe(NO)2}10 DNICs, and [2Fe-2S] Clusters, and the Critical Role of the Thiolate Ligands in Regulating NO Release of DNICs

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posted on 08.08.2005, 00:00 by Fu-Te Tsai, Show-Jen Chiou, Ming-Che Tsai, Ming-Li Tsai, Hsiao-Wen Huang, Ming-Hsi Chiang, Wen-Feng Liaw
Dinitrosyl iron complex [(−SC7H4SN)2Fe(NO)2]- (1) was prepared by reaction of [S5Fe(NO)2]- and bis(2-benzothiozolyl) disulfide. In synthesis of the analogous dinitrosyl iron compounds (DNICs), the stronger electron-donating thiolates [RS]- (R = C6H4-o-NHCOCH3, C4H3S, C6H4NH2, Ph), compared to [−SC7H4SN]- of complex 1, trigger thiolate-ligand substitution to yield [(−SC6H4-o-NHCOCH3)2Fe(NO)2]- (2), [(−SC4H3S)2Fe(NO)2]- (3), and [(SPh)2Fe(NO)2]- (4), respectively. At 298 K, complexes 2 and 3 exhibit a well-resolved five-line EPR signal at g = 2.038 and 2.027, respectively, the characteristic g value of DNICs. The magnetic susceptibility fit indicates that the resonance hybrid of {Fe+(NO)2}9 and {Fe-(+NO)2}9 in 2 is dynamic by temperature. The IR νNO stretching frequencies (ranging from (1766, 1716) to (1737, 1693) cm-1 (THF)) of complexes 14 signal the entire window of possible electronic configurations for such stable and isolable {Fe(NO)2}9 [(RS)2Fe(NO)2]-. The NO-releasing ability of {Fe(NO)2}9 [(RS)2Fe(NO)2]- is finely tuned by the coordinated thiolate ligands. The less electron-donating thiolate ligands coordinated to {Fe(NO)2}9 motif act as better NO-donor DNICs in the presence of NO-trapping agent [Fe(S,S-C6H4)2]22-. Interconversion between {Fe(NO)2}9 [(RS)2Fe(NO)2]- and {Fe(NO)2}10 [(Ph3P)2Fe(NO)2] was verified in the reaction of (a) [(RS)2Fe(NO)2]-, 10 equiv of PPh3 and sodium-biphenyl, and (b) 2 equiv of thiol, [RS]-, and [(Ph3P)2Fe(NO)2], respectively. The biomimetic reaction cycle, transformation between {Fe(NO)2}9 [(RS)2Fe(NO)2]- and {Fe(NO)2}9 [(R‘S)2Fe(NO)2]-, reversible interconversion of {Fe(NO)2}9 and {Fe(NO)2}10 DNICs, and degradation/reassembly of [2Fe−2S] clusters may decipher and predict the biological cycle of interconversion of {Fe(NO)2}9 DNICs, {Fe(NO)2}10 DNICs, and the [Fe−S] clusters in proteins.