Effect of a tridentate ligand on the structure, electronic structure, and reactivity of the copper(I) nitrite complex: Role of the conserved three-histidine ligand environment of the type-2 copper site in copper-containing nitrite reductases
Effect of a tridentate ligand on the structure, electronic structure, and reactivity of the copper(I) nitrite complex: Role of the conserved three-histidine ligand environment of the type-2 copper site in copper-containing nitrite reductases
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DOI：
10.1021/ja075575b
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发表时间：
2008-05-14
影响因子：
15
通讯作者：
Fujii, Hiroshi
中科院分区：
文献类型：
--
作者：
Kujime, Masato;Izumi, Chiemi;Fujii, Hiroshi
亚硝酸铜（I）络合物是含铜亚硝酸还原酶（Cu-NiRs）催化亚硝酸盐还原为一氧化氮（NO）气体的关键反应中间体。为了研究Cu-NiR的结构与功能的关系，我们合成了五种新的亚硝酸铜配合物，（4-咪唑基）甲醇[Et-TIC = tris（1-甲基-2-乙基-4-咪唑基）甲醇和iPr-TIC =三（1-甲基-2-异丙基-4-咪唑基）甲醇]或三[Me-TPM =三（3，5-二甲基-1-吡唑基）甲烷; Et-TPM =三（3，5-二乙基-1-吡唑基）甲烷;和iPr-TPM =三（3，5-二异丙基-1-吡唑基）甲烷]。所有这些亚硝酸铜（II）配合物的X-射线晶体结构是单核的η（1）-N-结合的亚硝酸根配合物与扭曲的四面体几何形状。配合物的电子结构进行了研究，通过吸收，磁性圆二色性（MCD），NMR和振动光谱。所有这些配合物是良好的功能模型的Cu-NiR，形成NO和铜（II）乙酸配合物以及从反应与乙酸在厌氧条件下。这些配合物，包括以前报道的（iPr-TACN）Cu（NO2）[iPr-TACN = 1，4，7-三异丙基-1，4，7-三氮杂环壬烷]的反应性的比较，清楚地表明了三齿配体对Cu-NiR活性的剧烈影响。与Cu-NiR催化位点中高度保守的三组氨酸（（HiS）（3））配体环境相似的Et-TIC配体的亚硝酸铜（I）配合物具有最高的Cu-NiR活性。这一结果表明，（HiS）（3）配体环境是必不可少的加速Cu-NiR反应。Et-TIC配合物的最高Cu-NiR活性可以通过本文提出的结构和光谱表征以及分子轨道计算来解释。在此基础上，讨论了（HiS）（3）配体环境在Cu-NiR中的作用。
It is postulated that the copper(I) nitrite complex is a key reaction intermediate of copper containing nitrite reductases (Cu-NiRs), which catalyze the reduction of nitrite to nitric oxide (NO) gas in bacterial clenitrification. To investigate the structure-function relationship of Cu-NiR, we prepared five new copper(I) nitrite complexes with sterically hindered tris(4-imidazolyl)carbinois [Et-TIC = tris(1-methyl-2-ethyl-4-imidazolyl)carbinol and iPr-TIC = tris(1-methyl-2-isopropyl-4-imidazolyl)carbinol] or tris(1-pyrazolyl)methanes [Me-TPM = tris(3,5-dimethyl-1-pyrazolyl) methane; Et-TPM = tris(3,5-diethyl-1-pyrazolyl) methane; and iPr-TPM = tris(3,5-diisopropyl-1-pyrazolyl) methane]. The X-ray crystal structures of all of these copper(II) nitrite complexes were mononuclear eta(1)-N-bound nitrite complexes with a distorted tetrahedral geometry. The electronic structures of the complexes were investigated by absorption, magnetic circular dichroism (MCD), NMR, and vibrational spectroscopy. All of these complexes are good functional models of Cu-NiR that form NO and copper(II) acetate complexes well from reactions with acetic acid under anaerobic conditions. A comparison of the reactivity of these complexes, including previously reported (iPr-TACN)Cu(NO2) [iPr-TACN = 1,4,7-triisopropyl-1,4,7-triazacyclononane], clearly shows the drastic effects of the tridentate ligand on Cu-NiR activity. The copper(I) nitrite complex with the Et-TIC ligand, which is similar to the highly conserved three-histidine ((HiS)(3)) ligand environment in the catalytic site of Cu-NiR, had the highest Cu-NiR activity. This result suggests that the (HiS)(3) ligand environment is essential for acceleration of the Cu-NiR reaction. The highest Cu-NiR activity for the Et-TIC complex can be explained by the structural and spectroscopic characterizations and the molecular orbital calculations presented in this paper. Based on these results, the functional role of the (HiS)(3) ligand environment in Cu-NiR is discussed.