IRON-SULFUR CLUSTERS .2. KINETICS OF LIGAND-EXCHANGE STUDIED ON A WATER-SOLUBLE FE4S4(SR)4N-CLUSTER
IRON-SULFUR CLUSTERS .2. KINETICS OF LIGAND-EXCHANGE STUDIED ON A WATER-SOLUBLE FE4S4(SR)4N-CLUSTER
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DOI：
10.1073/pnas.72.7.2478
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发表时间：
1975-01-01
影响因子：
11.1
通讯作者：
BRUICE, TC
中科院分区：
文献类型：
--
作者：
JOB, RC;BRUICE, TC
制备了水溶性四核铁硫簇离子Fe4S4(SCH2CH2CO2-)46-(II)。II在水中的稳定性足以用光谱法测定其Fe4S4core的pka4为7.4。在我们的研究中，化合物I [Fe4S4(SR)42-, R =烷基或芳基，]的单电子还原是热力学不可逆的，其相关的e1 /2值大于铁氧还蛋白的单电子还原。相比之下，II的单电子还原是热力学可逆的，相关电位（相对于氢电极-0.58 V）接近铁氧化还原素。II的配体交换动力学与pH和硫醇浓度的函数一致，符合四种可逆的硫醇/硫酸盐交换反应，然后通过特定的酸碱催化形成产物。初步实验表明，对II的亲核顺序为Cl-[unk] Br-< HO-< CN-。
The water-soluble tetranuclear iron-sulfur cluster ion Fe4S4(SCH2CH2CO2-)46-(II) has been prepared. The stability of II in water is sufficient to allow the spectrotitrimetric determination of the pKaof its Fe4S4core as 7.4. In our hands the one-electron reductions of compounds I [Fe4S4(SR)42-, R = alkyl or aryl,] are thermodynamically irreversible with associated E1/2values greater than those for one-electron reduction of ferredoxins. In contrast, the one-electron reduction of II is thermodynamically reversible and the associated potential (-0.58 V versus hydrogen electrode) approaches closely that of the ferredoxins. The kinetics for ligand exchange of II as a function of pH and thiol concentration are in accord with four reversible mercaptan/lyate species exchange reactions followed by product formation via specific acid and base catalysis. Preliminary experiments indicate the nucleophilic order towards II to be Cl-[unk] Br-< HO-< CN-.