| Summary: | 碩士 === 國立清華大學 === 化學系 === 95 === Nitrosylation of the biomimetic monodentate ferredoxin [(SR)2FeIII(µ-S)2FeIII(SR)2]2- (SR = SPh, SEt, 2-S-C4H3S(1)) in 1:2 stoichiometry led to the formation of DNICs, consistent with the observation in biochemistry. However, modification of [(SEt)2FeII(µ-SEt)2FeII(SEt)2]2- with nitric oxide led to the formation of the extremely air- and light-sensitive mononitrosyl tris(thiolate) iron complexes(MNICs) [(NO)Fe(SEt)3]-. These results support the assumption of the interconversion among precursor [(SR)2Fe(µ-SR)2Fe(SR)2]2-, iron-sulfur cluster [(RS)2Fe(µ-S)2Fe(SR)2]2-, MNICs [(NO)Fe(SR)3]- and DNICs [(NO)2Fe(SR)2]2-.
Synthesis of the anionic {Fe(NO)2}9[(NO)2Fe(C3H4N2)2]- (2) supports the existence of protein-bound Nhis/Nhis-DNIC. Reaction of the imidazole-containing DNIC [(NO)2Fe(C3H4N2)2]- (2) and alkyl/aryl thiol led to the formation of [(NO)2Fe(C3H4N2)(SR)]- (R = tBu (3), Et (4), Ph (5)) with mixed imidazole/thiolate coordinated ligands. Steric effect was adopted to rationalize that [(NO)2Fe(C3H4N2)(StBu)]- (3) is inert to the further addition of HStBu, compared to the formation of [(NO)2Fe(SR)2]- upon reaction of [(NO)2Fe(C3H4N2)(SR)]- and HSR (R = Ph, Et).
The EPR spectrum of complexes 2 and 3 exhibit the well-resolved nine-line EPR signal at g = 2.027, consistent with the reported amide-containing DNICs in biology. The simulated spectrum of complex 2 reveals the following values of the coupling constants: aN(NO) = 2.2 and aN(Im) = 3.15 G. The simulative values of complex 3 are aN(NO) = 2.35 and aN(Im) = 4.1 G. However, the EPR signals of anionic complex (4) exhibits the well-resolved eleven-line hyperfine structure with simulated values aN(NO) = 2.5, aN(Im) = 4.1 G and aH = 1.55 G. It is the first detection, in the synthesized DNICs, of EPR spectrum with the obvious coupling with H of the coordinated S-CH2-group, consistent with the observation of the low-molecular weight cysteine-DNIC.
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