DEFINITION OF REACTION SEQUENCES RESULTING IN SELF-ASSEMBLY OF [FE4S4(SR)4]2- CLUSTERS FROM SIMPLE REACTANTS
DEFINITION OF REACTION SEQUENCES RESULTING IN SELF-ASSEMBLY OF [FE4S4(SR)4]2- CLUSTERS FROM SIMPLE REACTANTS
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DOI：
10.1021/ja00404a013
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发表时间：
1981-01-01
影响因子：
15
通讯作者：
HOLM, RH
中科院分区：
文献类型：
--
作者：
HAGEN, KS;REYNOLDS, JG;HOLM, RH
已通过分光光度法和* H NMR 光谱检查了由简单反应物组装出生物学相关的 [Fe4S4 (SPh) 4] 2~ 簇 (1) 的几种反应系统，以确定反应顺序并鉴定中间体。系统 I 和 II 分别基于反应物摩尔比 PhS"/FeCl3/S=3.5/1/1 和 > 5/1/1，并在乙腈和甲醇溶液中进行。在系统 I 中，第一个可识别的中间体是金刚烷类物质 [Fe4 (SPh) i0] 2~(4)，它在两种溶剂中以全有或全无的过程与硫反应，得到 1。没有其他在系统 II 中，第一个可识别的中间体是四面体 [Fe (SPh) 4] 2"(2)。 2 与硫在乙腈中反应生成双核[Fe2S2 (SPh) 4] 2~(3)，但在同样由2 和硫生成的甲醇3 中，在缓慢反应中自发形成1。因此，系统 II 提供了第一个通过单核和双核中间体精心制作四核簇的实例。在甲醇中，当用分光光度法测定时，由初始反应物提供 1 的总反应是定量的。中间体2、3和4的盐已独立合成，并且反应4+ S-* 1和2+ S-*· 3已在制备规模上以良好的收率进行。反应物摩尔比PhS”/FeCl 3 /S 2 ”＝1.5/1/1的反应系统III以82％的分光光度产率提供1，但对于通过所采用的方法检测中间体而言进行得太快。结果用于解释先前报道的 [Fe4S4 (SR) 4] 2" 簇制备方法中的反应序列。注意到研究的某些局限性。第一个铁硫蛋白活性位点的合成类似物 [Fe4S4-(SCH2Ph) 4] 2~ 的制备于 1972 年完成。2 此后不久，合成过程被证明适用于各种 R= 烷基和芳基取代基，3提供了现在广泛的立方烷型 [Fe4S4 (SR) 4] 2" 簇 4、5 家族的一部分（1，图 1）。这些物质很容易在环境温度下用简单、廉价的试剂在厌氧条件下制备，其限制化学计量是反应1（表I）的化学计量。簇很容易从甲醇反应溶液中分离出来，并以季铵盐的形式纯化； 50-80% 的纯化产物产率在该实验室中很常见。通过直接合成形成的簇通常可用作不同取代物质的前体，通过硫醇盐配体取代反应 (2) 4" 7 或通过用一般亲电子试剂 YX 处理（反应 3）。 8, 9 反应 2 已证明在掺入半胱氨酰基方面特别有用
Several reaction systems which result in the assembly of the biologically relevant [Fe4S4 (SPh) 4] 2~ cluster (1) from simple reactants have been examined by spectrophotometry and* H NMR spectroscopy in order to define reaction sequences and identify intermediates. Systems I and II were based on the reactant mole ratios PhS"/FeCl3/S=3.5/1/1 and> 5/1/1, respectively, and were conducted in acetonitrile and methanol solutions. In system I the first identifiableintermediate is the adamantane-Iike species [Fe4 (SPh) i0] 2~(4), which reacts with sulfur in an all-or-nothing process in both solvents to afford 1. No other intermediates were identified in thissystem. In system II the first recognizable species formed is tetrahedral [Fe (SPh) 4] 2"(2). Reaction of 2 with sulfur in acetonitrile yields binuclear [Fe2S2 (SPh) 4] 2~(3), but in methanol 3, which also results from 2 andsulfur, spontaneously forms 1 in a slow reaction. Thus system II provides the first demonstrated instance of elaboration of a tetranuclear cluster through mononuclear and binuclear intermediates. In methanol the overall reactions affording 1 from initial reactants are quantitative when assayed spectrophotometrically. Salts of intermediates 2, 3, and 4 have been independently synthesized, and the reactions 4+ S-* 1 and 2+ S-*· 3 have been executed in good yield on a preparative scale. Reaction system III, having the reactant mole ratio PhS"/FeCl3/S2"= 1.5/1/1, affords 1 in 82% spec-trophotometric yield but proceeds too rapidly for detection of intermediates by themethods employed. The results are used to interpret reaction sequences in previously reported preparative methods for [Fe4S4 (SR) 4] 2" clusters. Certain limitations of the investigation are noted.The preparation of the first synthetic analogue [Fe4S4-(SCH2Ph) 4] 2~ of an iron-sulfur protein active site was accom-plished in 1972.2 Shortly thereafter the synthetic procedure was shown to be general for a variety of R= alkyl and aryl substituent groups, 3 affording a portion of the now extensive family of cu-bane-type [Fe4S4 (SR) 4] 2" clusters4, 5 (1, Figure 1). These species are readily prepared anaerobically from simple, cheap reagents at ambient temperature in a process whose limiting stoichiometry is that of reaction 1(Table I). Clusters are readily isolated from the methanol reaction solution and purified as quaternary am-monium salts; 50-80% yields of purified products are common in this laboratory. Clusters formed by direct synthesis are frequently useful as precursors to differently substituted species by means of the thiolate ligand substitution reaction (2) 4" 7 or by treatment with the general electrophile YX (reaction 3). 8, 9 Reaction 2 has proven of particular use in incorporating cysteinyl