Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
J Phys Chem B. 2009 Oct 1;113(39):13096-106. doi: 10.1021/jp9059328.
We explored the reactivity of the active center of the [FeFe]-hydrogenases detached from the enzyme and immersed in acidified water by first-principles Car-Parrinello molecular-dynamics simulations. We focused on the identification of the structures that are stable and metastable in acidified water and on their activity for hydrogen production. Our calculations revealed that the naked active center could be an efficient catalyst provided that electrons are transferred to the cluster. We found that both bridging and terminal isomers are present at equilibrium and that the bridging configuration is essential for efficient hydrogen production. The formation of the hydrogen molecule occurs via sequential protonations of the distal iron and of the N-atom of the S-CH(2)-NH-CH(2)-S chelating group. H(2) desorption does not involve a significant energy barrier, making the process very efficient at room temperature. We established that the bottleneck in the reaction is the direct proton transfer from water to the vacant site of the distal iron. Moreover, we found that even if the terminal isomer is present at the equilibrium, its strong local hydrophobicity prevents poisoning of the cluster.
我们通过第一性原理 Car-Parrinello 分子动力学模拟研究了从酶中分离出来并沉浸在酸化水中的 [FeFe]-氢化酶活性中心的反应性。我们专注于确定在酸化水中稳定和亚稳定的结构及其对氢气生成的活性。我们的计算表明，裸露的活性中心可以是一种有效的催化剂，只要电子被转移到簇上。我们发现桥连和末端异构体都处于平衡状态，并且桥连构型对于高效产氢至关重要。氢分子的形成通过远端铁和 S-CH(2)-NH-CH(2)-S 螯合基团的 N-原子的连续质子化来发生。H(2)解吸不涉及显著的能量障碍，使得该过程在室温下非常高效。我们确定反应的瓶颈是从水中直接向远端铁的空位转移质子。此外，我们发现即使末端异构体处于平衡状态，其强烈的局部疏水性也能防止簇中毒。
