Structural and topological studies of methionine radical cations in dipeptides: electron sharing in two-center three-electron bonds.
Structural and topological studies of methionine radical cations in dipeptides: electron sharing in two-center three-electron bonds.
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二肽中蛋氨酸自由基阳离子的结构和拓扑研究：二中心三电子键中的电子共享。
DOI：
10.1021/jp911983a
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
C. Houée
中科院分区：
文献类型：
--
作者：
I. Fourré;J. Bergès;C. Houée
肽中甲硫氨酸的单电子氧化高度依赖于局部结构。以硫为中心的自由基阳离子可以与来自相邻残基或来自肽键的氧、氮或其他硫原子络合，形成分子内S因此X双中心三电子键（X = S、N、O）。这种稳定性进行了研究计算在自由基阳离子的三种肽，蛋氨酸甘氨酸（Met Gly）和它的反向序列Gly Met，和Met Met。在BH&HLYP/6- 31 G（d）理论水平上进行了几何优化，并使用连续模型（CPCM）考虑了溶剂化的影响。对于每种肽，考虑多达7种稳定构象，其中5-10元环的形成涉及来自肽键或胺的氮、来自肽键或羧酸酯基团的氧或来自Met Met的其他残基的硫。在TD-BH&HLYP/6-311+G（d，p）//BH&HLYP/6- 31 G（d）理论水平下计算的每个复合物的sigma-> sigma* 跃迁对应的吸收波长从S因此O键的近紫外到S因此S键的绿色可见光不等。对于X = N，它们随着SN距离的增加而增加，正如2c-3e键所预期的那样，而对于X = O，它们略有减少。利用ELF和AIM拓扑分析，这些2c-3e键作为序列的函数的表征显示了S因此X键的不同性质，对于X = S，其为纯2c-3e，对于X = N，主要为2c-3e，具有部分静电相互作用，对于X = O，主要为静电相互作用。
One electron oxidation of methionine in peptides is highly dependent on the local structure. The sulfur-centered radical cation can complex with oxygen, nitrogen, or other sulfur atoms from a neighboring residue or from the peptidic bond, forming an intramolecular S therefore X two-center three-electron bond (X = S, N, O). This stabilization was investigated computationally in the radical cations of three peptides, methionine glycine (Met Gly) and its reverse sequence Gly Met, and Met Met. Geometry optimizations were done at the BH&HLYP/6-31G(d) level of theory and the effect of solvation was taken into account using a continuum model (CPCM). Up to seven stable conformations were considered for each peptide, with formation of 5-10 member cycles involving nitrogen from the peptidic bond or from the amine, oxygen from the peptidic bond or from the carboxylate group, or sulfur from the other residue for Met Met. The absorption wavelengths corresponding to the sigma --> sigma* transition calculated for each complex at the TD-BH&HLYP/6-311+G(d,p)//BH&HLYP/6-31G(d) level of theory vary from the near-UV for the S therefore O bonds to the green visible for the S therefore S bonds. For X = N, they increase with the SN distance as expected for a 2c-3e bond, whereas for X = O they slightly decrease. Characterization of these 2c-3e bonds as a function of the sequence, using the ELF and the AIM topological analyses, shows the different natures of the S therefore X bonds, which is purely 2c-3e for X = S, mainly 2c-3e with a part of electrostatic interaction for X = N and mainly electrostatic for X = O.