Rodriguez José A, Abreu Isabel A
Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
J Phys Chem B. 2005 Feb 24;109(7):2754-62. doi: 10.1021/jp0405355.
Iron atoms bonded to sulfur play an important role in proteins, heterogeneous catalysts, and gas sensors. First-principles density functional calculations were used to investigate the structure and chemical activity of a unique [2Fe-2S] center in the split-Soret cytochrome c (Ssc) from Desulfovibrio desulfuricans. In agreement with a previously proposed structural model [Abreu et al., J. Biol. Inorg. Chem. 2003, 8, 360], it is found that the [2Fe-2S] cluster is located in a surface pocket of the Ssc and bonded to only three cysteines. The [2Fe-2S] center in the Ssc is nonplanar and somewhat distorted with respect to canonical [2Fe-2S] centers seen in proteins where the iron-sulfur unit is bonded to four cysteines. In the Ssc, the lack of one Fe-cysteine bond is partially compensated by the separation between the cysteines that minimizes electrostatic repulsion among these ligands. The unique structure of the [2Fe-2S] center in the Ssc makes the center more chemically active than canonical [2Fe-2S] centers in proteins, (RS)(4)[2Fe-2S] inorganic complexes, and an FeS2(100) surface. A [2Fe-2S] center in the Ssc interacts efficiently with electron acceptors (O2, NO, CO) and poorly with a Lewis base such as H2O. The interaction with molecular oxygen is so strong that eventually oxidatively destroys the [2Fe-2S] unit. The bonding energy of the ligands to the [2Fe-2S] centers and FeS2(100) surface increases following the sequence: H2O << CO < NO < O2. The higher the electron affinity of the ligand, the larger its bonding energy. A relatively large positive charge on the Fe cations in FeS2(100) makes this sulfide surface less reactive toward O2, CO, and NO than the [2Fe-2S] centers in proteins and inorganic complexes.
与硫结合的铁原子在蛋白质、多相催化剂和气体传感器中起着重要作用。采用第一性原理密度泛函计算方法，研究了脱硫脱硫弧菌（Desulfovibrio desulfuricans）的分裂索雷特细胞色素c（Ssc）中独特的[2Fe-2S]中心的结构和化学活性。与先前提出的结构模型一致[阿布雷乌等人，《生物无机化学杂志》2003年，第8卷，第360页]，发现[2Fe-2S]簇位于Ssc的表面口袋中，且仅与三个半胱氨酸结合。Ssc中的[2Fe-2S]中心是非平面的，相对于蛋白质中典型的[2Fe-2S]中心有些扭曲，在这些蛋白质中，铁硫单元与四个半胱氨酸结合。在Ssc中，一个铁-半胱氨酸键的缺失部分地由半胱氨酸之间的间隔所补偿，该间隔使这些配体之间的静电排斥最小化。Ssc中[2Fe-2S]中心的独特结构使其比蛋白质、（RS）(4)[2Fe-2S]无机配合物和FeS2(100)表面中的典型[2Fe-2S]中心具有更高的化学活性。Ssc中的[2Fe-2S]中心与电子受体（O2、NO、CO）有效相互作用，而与诸如H2O的路易斯碱相互作用较弱。与分子氧的相互作用非常强烈，最终会氧化破坏[2Fe-2S]单元。配体与[2Fe-2S]中心和FeS2(100)表面的结合能按以下顺序增加：H2O << CO < NO < O2。配体的电子亲和力越高，其结合能越大。FeS2(100)中铁阳离子上相对较大的正电荷使得该硫化物表面对O2、CO和NO的反应性低于蛋白质和无机配合物中的[2Fe-2S]中心。
