生物擬態四鐵四硫蛋白質之亞硝基化及雙鐵核四亞硝基錯合物與雙亞硝基鐵錯合物之相互轉換研究

Nitrosylation of Biomimetic [4Fe4S] Clusters and Interconversion among Neutral/Anionic Roussin’s Red Ester and Dinitrosyl Iron Complexes

鄒智欽(Chih-Chin Tsou)

指導教授 ： 廖文峰

國立清華大學/理學院/化學系/碩士(2007年)

摘要

本研究探討了有關生化擬態模型化合物[Fe4S4(SR)4]2–與前驅物[Fe4(SR)10]2– (R = Ph, Et)亞硝基化產生DNIC的反應機制，其中[Fe4S4(SR)4]2–必定要先經由NO(g)亞硝基化得到[Fe4S3(NO)7]– (2)後，接著complex 2中的雙亞硝基鐵核才可被[SR]– (R = Ph, Et)攻擊才可產生[(RS)2Fe(NO)2]– (5)，若是complex 2中的單亞硝基鐵核被[SR]– (R = Ph, Et)攻擊則會產生[Fe4S3(NO)7]2–。並提供生物體中[4Fe-4S] clusters與NO反應降解成DNICs之EPR光譜的可能變化情形，包含中間物[Fe4S4(NO)4]– (3) (g = 1.624 at 4 K)以及[Fe4S3(NO)7]2– (g = 2.020 at 250 K)。前驅物[Fe4(SR)10]2–與NO(g)反應可以得到[(RS)3Fe(NO)]– (7)，再進一步地與NO(g)反應則可得到[(RS)2Fe(NO)2]– (5)與[Fe(μ-SR)(NO)2]2 (8)；有趣的是，當[Fe4(SPh)10]2–與[NO2]–反應則只能得到[(PhS)3Fe(NO)]– (7-Ph)。
研究中也合成出syn-與anti-[Fe(μ-SEt)(NO)2]2– (9)，並且由X-ray Fe K-edge與L-edge吸收光譜得知complex 9之鐵核的氧化態約為+0.87，也首次直接證實[Fe(μ-SEt)(NO)2]2 (8-Et)的鐵核氧化態為+1。對[Fe(μ-SR)(NO)2]2 (8)而言，不同的親核基([SEt]– vs [(EtS)2Fe(NO)2]– vs [(PhS)2Fe(NO)2]–)可控制反應走向不同的途徑(橋接含硫取代基斷裂反應 vs 還原反應 vs 不反應)。實驗也證實[(EtS)2Fe(NO)2]– (5-Et)與[Fe(μ-SEt)(NO)2]2– (9)皆可被NO(g)氧化而得到complex 8，進而提供在FNR亞硝基化的實驗中[Fe(μ-SR)(NO)2]2是主要產物的可能原因。很重要的是，[Fe(μ-SEt)(NO)2]2– (9)也與先前研究所認為的d9-DNIC ([(RS)2Fe(NO)2]–的還原態)具有非常類似的EPR光譜以及合成步驟。

關鍵字

四鐵四硫 ； 雙亞硝基鐵錯合物

並列摘要

The formation mechanisms of DNIC produced by nitosylation of the biomimetic ferredoxin [Fe4S4(SR)4]2- and [4Fe-4S] cluster precursor[Fe4(SR)10]2– (R = Et, Ph) was exhibited. After isolating [Fe4S3(NO)7]– (2) from nitosylation of [Fe4S4(SR)4]2-, the dinitrosyl or mononitrosyl iron cores of complex 2 degraded to DNICs [(RS)2Fe(NO)2]– (5) or reduced to [Fe4S3(NO)7]2– via nucleophilic attack of [SR]– (R = Ph, Et), respectively. Complexes [Fe4S4(NO)4]– (3) (g = 1.624 at 4 K) and [Fe4S3(NO)7]2– (g = 2.020 at 250 K), intermediate and byproduct of [Fe4S4(SR)4]2- degradation, suggested the variety of EPR spectra for modification of [4Fe-4S] clusters with NO in biological system. Nitrosylation of the [4Fe-4S] cluster precursors [Fe4(SR)10]2- (R = SPh, SEt) led to the formation of the MNICs [(RS)3Fe(NO)]– (7), then DNICs [(RS)2Fe(NO)2]– (5) and RRE [Fe(μ-SR)(NO)2]2 (8) were also demonstrated in further nitrosylation. Interestingly, reaction of [Fe4(SPh)10]2– and [NO2]– only resulted in the formation of [(PhS)3Fe(NO)]– (7-Ph).
In this work, anionic RRE syn/anti-[Fe(μ-SEt)(NO)2]2– (9) and [Fe(μ-SEt)(NO)2]2 (8-Et) was synthesized, and the oxidation state of iron cores were about +0.87 and +1.0, respectively, characterized by X-ray Fe K-edge and L-edge absorption spectra. The different nucleophile ([SEt]– vs [(EtS)2Fe(NO)2]– vs [(PhS)2Fe(NO)2]–) functions to control the reaction pathways (bridged-thiolate cleavage vs reduction vs no reaction) upon reaction of [Fe(μ-SR)(NO)2]2 (8) and nucleophiles. It was confirmed [(EtS)2Fe(NO)2]– (5-Et) and [Fe(μ-SEt)(NO)2]2– (9) can be oxidized to form complex 8 by NO, and supported the probable factor that [Fe(μ-SR)(NO)2]2 was major product in the nitrosylation of FNR. Importantely, [Fe(μ-SEt)(NO)2]2– (9) and d9-DNIC (proposed reduced form of [(RS)2Fe(NO)2]–) have very similar synthetic method and EPR spectra.

並列關鍵字

4Fe4S ； Dinitrosyl Iron Complex ； Roussin’s Red Ester

參考文獻

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