SYNTHESIS AND ELECTRON DELOCALIZATION OF [FE4S4]-S-FE(III) BRIDGED ASSEMBLIES RELATED TO THE EXCHANGE-COUPLED CATALYTIC SITE OF SULFITE REDUCTASES
SYNTHESIS AND ELECTRON DELOCALIZATION OF [FE4S4]-S-FE(III) BRIDGED ASSEMBLIES RELATED TO THE EXCHANGE-COUPLED CATALYTIC SITE OF SULFITE REDUCTASES
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DOI：
10.1021/ja00095a021
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发表时间：
1994-08-10
影响因子：
15
通讯作者：
HOLM, RH
中科院分区：
文献类型：
--
作者：
CAI, LS;HOLM, RH
由于普遍存在的磁耦合siroheme和Fe 4S 4单位在同化和异化亚硫酸盐和亚硝酸盐还原酶，我们已经进行了合成的硫桥组装Fe 4S 4-S-血红素作为一个可能的类似物的某些同化酶的活性位点。该方法利用了[Fe_4S_4（LS（3））L ′]（2-）型铁亚基分化簇，其在独特的亚基上进行区域特异性取代。[Fe 4S 4（LS（3））（SEt）]（2-）与有限的H2S在乙腈中反应得到官能化簇[Fe 4S 4（LS（3））（SH）]（2-）（4），其与μ-S双立方烷{[Fe 4S 4（LS（3）]S-2}（4-）（6）和H2S平衡存在。化合物4与[Fe（salen）]O-2反应生成桥联结构[Fe_4S_4（LS（3））-S-Fe-III（salen）]（2-）（8）。设计了6条路线来实现相关的血红素组装：4与[Fe（OEP）]O-2、[Fe（OEP）（OMe）]、[Fe（OEP）（OC（Me）= CH_2）]和[Fe（OEP）（OClO_3）]/Et（3）N的定向酸碱偶联;[Fe_4S_4（LS（3））（SSiEt（3））]（2-）与[Fe（OEP）F]反应中的Si-S键断裂;[Fe-II（OEP）]与μ-S-2双立方烷{[Fe 4S 4（LS（3））]S-2（2）}（4-）（7）的二硫键氧化加成。在每种情况下，产物为[Fe 4S 4（LS（3））-S-Fe-III（OEP）]（2-）（9），可通过UV-可见吸收和H-1 NMR光谱识别。8和9都含有[Fe 4S 4]（2+）和高自旋Fe（III）碎片。各向同性的位移主要是接触的起源，增强了7-12的因素相比，前体集群4，居里型温度依赖性的位移9，起源于广泛的自旋本地化从Fe（III）片段的集群。这种效应需要在片段之间存在共价桥，并且与合成方法和其他光谱观察一起，提供了桥接组件的结构证明。这些物种维持两个单电子还原反应，其他反应9，改变或切割的桥梁，进行了总结。桥接组件，如8和9的电子功能接近内在的磁性和光谱性质的结构相似的单位在氧化酶和潜在的提供了一种手段，这种单位的识别。（LS（3）= 1，3，5-三[（4，6-二甲基-3-巯基苯基）硫基]-2，4，6-三（对甲苯硫基）苯（3-）; OEP八乙基卟啉（2-）; salen = 1，2-双（水杨醛基）乙烷（2-）。）
Because of the pervasive occurrence of magnetically coupled siroheme and Fe4S4 units in assimilatory and dissimilatory sulfite and nitrite reductases, we have undertaken the synthesis of the sulfide-bridged assembly Fe4S4-S-heme as a possible analogue to the active sites of certain assimilatory enzymes. The approach has utilized iron subsite-differentiated clusters of the type [Fe4S4(LS(3))L'](2-), which undergo regiospecific substitution at the unique subsite. Reaction of [Fe4S4(LS(3))(SEt)](2-) with limited H2S in acetonitrile affords the functionalized cluster [Fe4S4(LS(3))(SH)](2-) (4), which exists in equilibrium with the mu-S double cubane {[Fe4S4(LS(3))]S-2}(4-) (6) and H2S. Reaction of 4 and [Fe(salen)]O-2 gave the bridged assembly [Fe4S4(LS(3))-S-Fe-III(salen)](2-) (8), detectable by its characteristic isotropically shifted H-1 NMR spectrum. Six routes were devised to a related heme-based assembly: directed acid-base coupling of 4 with [Fe(OEP)]O-2, [Fe(OEP)(OMe)], [Fe(OEP)(OC(Me)=CH2)], and [Fe(OEP)(OClO3)]/Et(3)N; Si-S bond cleavage in the reaction of [Fe4S4(LS(3))(SSiEt(3))](2-) with [Fe(OEP)F]; oxidative addition of [Fe-II(OEP)] to the disulfide bond of the mu-S-2 double cubane {[Fe4S4(LS(3))]S-2(2)}(4-) (7). In each case, the product was [Fe4S4(LS(3))-S-Fe-III(OEP)](2-) (9), recognizable by UV-visible absorption and H-1 NMR spectra. Both 8 and 9 contain [Fe4S4](2+) and high-spin Fe(III) fragments. Isotropic shifts mainly contact in origin that are enhanced by factors of 7-12 compared to those of precursor cluster 4, and the Curie-type temperature dependence of the shifts of 9, originate from extensive spin localization from the Fe(III) fragment to the cluster. This effect requires the existence of a covalent bridge between the fragments and, together with the methods of synthesis and other spectroscopic observations, provides structure proof of the bridged assemblies. These species sustain two one-electron reduction reactions; other reactions of 9, which alter or cleave the bridge, are summarized. The electronic features of bridged assemblies such as 8 and 9 approach the intrinsic magnetic and spectroscopic properties of a structurally similar unit in the oxidized enzymes and potentially provide a means of identification of such units. (LS(3) = 1,3,5-tris[(4,6-dimethyl-3-mercaptophenyl)-thio]-2,4,6-tris(p-tolylthio)benzene(3-); OEP octaethylporphyrinate(2-); salen = 1,2-bis(salicylidenearnino)ethane-(2-).)