Iron porphyrins with different imidazole ligands. A theoretical comparative study.
Iron porphyrins with different imidazole ligands. A theoretical comparative study.
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DOI：
10.1021/jp1052216
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发表时间：
2010-09-09
影响因子：
2.9
通讯作者：
Watts, John D.
中科院分区：
文献类型：
--
作者：
Liao, Meng-Sheng;Huang, Ming-Ju;Watts, John D.
采用DFT方法对一系列五配位和六配位铁卟啉FeP(L)和FeP(L)(O2)进行了理论比较研究，其中P=卟啉，L=咪唑(Im)、1-甲基咪唑(1-MeIm)、2-甲基咪唑(2-MeIm)、1,2-二甲基咪唑 (1,2-Me2Im)、4-乙基咪唑 (4-EtIm) 或组氨酸 (His)。研究中还纳入了两种连接的“栅栏”铁卟啉 FeTpivPP(2-MeIm) 和 FeTpivPP(2-MeIm)(O2) 进行比较。为了获得可靠的结果，在计算中使用了许多密度泛函。我们详细研究了 FeP、FeP(Im) 和 FeP(Im)(O2) 的泛函性能和基组效应，对此有一定的实验信息，并且文献中有一些先前的计算可供比较。揭示了不同咪唑配体对脱氧铁卟啉和氧铁卟啉的结构和能量的影响的许多细微差别。虽然 FeP(2-MeIm) 被认为是高自旋 (S = 2)，但 FeP(1-MeIm) 的基态可能是高自旋 (S = 2) 和中自旋 (S = 1) 态的混合。 FeP(L)(O2) 的基态可能因 L 的不同而不同。较弱的 Fe-L 键更有可能导致氧配合物的开壳层单线态基态。 2-MeIm 中的 2-甲基可增加配体与卟啉骨架之间的空间接触，削弱 Fe-O2 键，因此铁卟啉与 2-MeIm 模拟 T 态（低亲和力）血红蛋白。计算出的 FeP(2-MeIm)–O2 键能与 FeTpivPP(2-MeIm)–O2 键能相当，这与“栅栏”铁卟啉与 O2 的结合亲和力与肌红蛋白相似的事实一致，但与 CPMD 方案获得的结果不同。 Im 和 4-EtIm 与生物学轴基 His 非常相似，因此可以使用 Im 安全地简化未来血红素蛋白模型的计算。
A theoretical comparative study of a series of five- and six-coordinate iron porphyrins, FeP(L) and FeP(L)(O2), has been carried out using DFT methods, where P = porphine and L = imidazole (Im), 1-methylimidazole (1-MeIm), 2-methylimidazole (2-MeIm), 1,2-dimethylimidazole (1,2-Me2Im), 4-ethylimidazole (4-EtIm), or histidine (His). Two ligated “picket fence” iron porphyrins, FeTpivPP(2-MeIm) and FeTpivPP(2-MeIm)(O2), were also included in the study for comparison. A number of density functionals were employed in the computations in order to obtain reliable results. The performance of functionals and basis set effects were investigated in detail on FeP, FeP(Im), and FeP(Im)(O2), for which certain experimental information is available and there are some previous calculations in the literature for comparison. Many subtle distinctions in the effects of the different imidazole ligands on the structures and energetics of the deoxy- and oxy iron porphyrins are revealed. While FeP(2-MeIm) is identified to be high spin (S = 2), the ground state of FeP(1-MeIm) may be an admixture of a high-spin (S = 2) and an intermediate-spin (S = 1) state. The ground state of FeP(L)(O2) may be different with different L. A weaker Fe-L bond more likely leads to an open-shell singlet ground state for the oxy complex. The 2-methyl group in 2-MeIm, which increases steric contact between the ligand and the porphyrinato skeleton, weakens the Fe-O2 bond, and thus iron porphyrins with 2-MeIm mimic T-state (low affinity) hemoglobin. The calculated FeP(2-MeIm)–O2 bonding energy is comparable to the FeTpivPP(2-MeIm)–O2 one, in agreement with the fact that the “picket-fence” iron porphyrin binds O2 with affinity similar to that of myoglobin, but different from the result obtained by the CPMD scheme. Im and 4-EtIm closely resemble His, the biologically axial base, and so future computations on hemoprotein models can be simplified safely by using Im.
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