含咪唑/硫基之雙亞硝基鐵錯合物轉換與亞硝基化[二鐵二硫]鐵硫化合物之倣生物合成探討

Dinitrosyl Iron Complexes (DNICs) with Interconvertible Anionic Imidazole/Thiolate Ligands and Biomimetic Synthesis of DNICs from Nitrosylation of [2Fe-2S] clusters

黃曉雯(Hsiao-Wen Huang)

指導教授 ： 廖文峯

國立清華大學/理學院/化學系/碩士(2007年)

摘要

當以1:2之計量比例亞硝基化生物擬態單芽基之鐵硫錯合物 [(SR)2FeIII(µ-S)2FeIII(SR)2]2- (SR = SPh, SEt, 2-S-C4H3S(1))時，可觀察到dinitrosyl iron complexes (DNICs)的形成，此結果與亞硝基化生物系統二鐵二硫之觀察相符合。 然而， 以一氧化氮修飾二鐵二硫前驅物[(SEt)2FeII(µ-SEt)2FeII(SEt)2]2-時，則會產生mononitrosyl tris(thiolate) iron complexes(MNICs)，此化合物對空氣及光極為敏感。 這些結果似乎暗示著二鐵二硫前驅物[(SR)2Fe(µ-SR)2Fe(SR)2]2-, 二鐵二硫[(RS)2Fe(µ-S)2Fe(SR)2]2-, MNICs [(NO)Fe(SR)3]- and DNICs [(NO)2Fe(SR)2]2-之間存在著相互轉換性質。
[(NO)2Fe(C3H4N2)2]- (2) 的成功合成證實含His之protein-bound Nhis/Nhis-DNIC存在可能性. 將此化合物 2 與硫醇反應後可得到混合配位型式之DNICs [(NO)2Fe(C3H4N2)(SR)]- (R = tBu(3)，Et(4)，Ph(5))。相較於化合物 4 與5 和硫醇的反應結果，化合物[(NO)2Fe(C3H4N2)(StBu)]- (3)即使加入更多的HStBu 仍呈現反應惰性，此結果可以立體障礙來合理解釋之。
化合物 2 及 3 在電子順磁共振光譜中都出現清楚的九線分裂，此特徵與文獻中的amide-containing DNICs。化合物 2 在simulated spectrum中可得其耦和常數為 aN(NO) = 2.2 and aN(Im) = 3.15 G。化合物 3 的耦合常數則為 aN(NO) = 2.35 and aN(Im) = 4.1 G。然而，化合物 4 在電子順磁共振光譜中出現十一線分裂，其耦合常數為 aN(NO) = 2.5, aN(Im) = 4.1 G and aH = 1.55 G。這是第一次在合成型DNICs的電子順磁共振光譜發現有配位基S-CH2-group上的氫耦合現象，此現象和low-molecular weight cysteine-DNIC的EPR觀察結果相符合。

關鍵字

鐵硫化合物 ； 二鐵二硫 ； 雙亞硝基鐵錯合物 ； 咪唑 ； 二鐵二硫前驅物

並列摘要

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.

並列關鍵字

Iron sulfur cluster ； [2Fe-2S] ； DNICs ； Imidazole ； [2Fe-2S]precursor