Cleavage of [4Fe-4S]-type clusters: breaking the symmetry.
Cleavage of [4Fe-4S]-type clusters: breaking the symmetry.
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[4Fe-4S]型团簇的裂解：打破对称性。
DOI：
10.1021/jp900402y
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Ichiye,Toshiko
中科院分区：
文献类型：
--
作者：
Niu,Shuqiang;Ichiye,Toshiko
[4Fe <$4S]型簇的裂解被认为在蛋白质如Fe <$4S支架蛋白和固氮酶中是重要的。然而，蛋白质中的大多数[4Fe <$4S]2+簇具有两个反铁磁耦合的高自旋层，其中少数自旋在每一层中离域，从而形成对称的Fe 2.5 +<$Fe 2.5+对，并且由于共享电子，铁之间如何发生裂解是令人困惑的。我们提出了一种新的机制，将[4Fe <$4S]核裂变为两个[2Fe <$2S]核，其中少数自旋局限于一个铁上，从而打破对称性并产生两个Fe 3 +<$Fe 2+对的过渡态。首先通过弱Fe ~（2+）→ S键断裂降低了活化能。在这里，我们提出了一个测试这种机制：打破对称性的集群通过改变配体，以促进自旋本地化，这应该提高反应性。采用对称性破缺密度泛函理论研究了[Fe 4S 4L 4]2-（L = SCH 3，Cl，H）和[Fe 4S 4（SCH 3）2L 2]2-（L = Cl，H）簇合物在气相中的裂解反应.在异质配体团簇中，弱电子给体配位使铁原子上的少数自旋局域化，降低了反应能和断裂活化能，这与我们提出的机理雅阁，也与光电子能谱和碰撞诱导解离实验一致.这些研究表明，在其生物功能中需要其[4Fe <$4S]簇容易分裂的蛋白质可能具有自旋局域的[4Fe <$4S]簇。
The cleavage of [4Fe4S]-type clusters is thought to be important in proteins such as FeS scaffold proteins and nitrogenase. However, most [4Fe4S]2+clusters in proteins have two antiferromagnetically coupled high-spin layers in which a minority spin is delocalized in each layer, thus forming a symmetric Fe2.5+Fe2.5+pair, and how cleavage occurs between the irons is puzzling because of the shared electron. Previously, we proposed a novel mechanism for the fission of a [4Fe4S] core into two [2Fe2S] cores in which the minority spin localizes on one iron, thus breaking the symmetry and creating a transition state with two Fe3+Fe2+pairs. Cleavage first through the weak Fe2+S bonds lowers the activation energy. Here, we propose a test of this mechanism: break the symmetry of the cluster by changing the ligands to promote spin localization, which should enhance reactivity. The cleavage reactions for the homoligand [Fe4S4L4]2−(L = SCH3, Cl, H) and heteroligand [Fe4S4(SCH3)2L2]2−(L = Cl, H) clusters in the gas phase were examined via broken-symmetry density functional theory calculations. In the heteroligand clusters, the minority spin localized on the iron coordinated by the weaker electron-donor ligand, and the reaction energy and activation barrier of the cleavage were lowered, which is in accord with our proposed mechanism and consistent with photoelectron spectroscopy and collision-induced dissociation experiments. These studies suggest that proteins requiring facile fission of their [4Fe4S] cluster in their biological function might have spin-localized [4Fe4S] clusters.