金属离子（Li⁺、Na⁺、K⁺、Mg²⁺、Ca²⁺、Ni²⁺、Cu²⁺和Zn²⁺）及水配位对甘氨酸和两性离子甘氨酸结构的影响
Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure of glycine and zwitterionic glycine.
作者信息
Remko Milan, Rode Bernd Michael
机构信息
Department of Pharmaceutical Chemistry, Comenius University, Odbojarov 10, SK-832 32 Bratislava, Slovakia.
出版信息
J Phys Chem A. 2006 Feb 9;110(5):1960-7. doi: 10.1021/jp054119b.
Interactions between metal ions and amino acids are common both in solution and in the gas phase. Here, the effect of metal ions and water on the structure of glycine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water on structures of Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (m = 0, 2, 5) complexes have been determined theoretically by employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. Selected calculations were carried out also by means of CBS-QB3 model chemistry. The interaction enthalpies, entropies, and Gibbs energies of eight complexes Gly.Mn+ (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) were determined at the B3LYP density functional level of theory. The computed Gibbs energies DeltaG degrees are negative and span a rather broad energy interval (from -90 to -1100 kJ mol(-1)), meaning that the ions studied form strong complexes. The largest interaction Gibbs energy (-1076 kJ mol(-1)) was computed for the NiGly2+ complex. Calculations of the molecular structure and relative stability of the Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+; m = 0, 2, and 5) systems indicate that in the complexes with monovalent metal cations the most stable species are the NO coordinated metal cations in non-zwitterionic glycine. Divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ prefer coordination via the OO bifurcated bonds of the zwitterionic glycine. Stepwise addition of two and five water molecules leads to considerable changes in the relative stability of the hydrated species. Addition of two water molecules at the metal ion in both Gly.Mn+ and GlyZwitt.Mn+ complexes reduces the relative stability of metallic complexes of glycine. For Mn+ = Li+ or Na+, the addition of five water molecules does not change the relative order of stability. In the Gly.K+ complex, the solvation shell of water molecules around K+ ion has, because of the larger size of the potassium cation, a different structure with a reduced number of hydrogen-bonded contacts. This results in a net preference (by 10.3 kJ mol(-1)) of the GlyZwitt.K+H2O5 system. Addition of five water molecules to the glycine complexes containing divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ results in a net preference for non-zwitterionic glycine species. The computed relative Gibbs energies are quite high (-10 to -38 kJ mol(-1)), and the NO coordination is preferred in the Gly.Mn+(H2O)5 (Mn+ = Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) complexes over the OO coordination.
金属离子与氨基酸之间的相互作用在溶液和气相中都很常见。在此，研究了金属离子和水对甘氨酸结构的影响。通过采用混合B3LYP交换相关泛函并使用扩展基组，从理论上确定了金属离子（Li⁺、Na⁺、K⁺、Mg²⁺、Ca²⁺、Ni²⁺、Cu²⁺和Zn²⁺）和水对Gly·Mⁿ⁺(H₂O)ₘ和GlyZwitt·Mⁿ⁺(H₂O)ₘ（m = 0、2、5）配合物结构的影响。还通过CBS - QB3模型化学方法进行了选定的计算。在B3LYP密度泛函理论水平下确定了八个配合物Gly·Mⁿ⁺（Mⁿ⁺ = Li⁺、Na⁺、K⁺、Mg²⁺、Ca²⁺、Ni²⁺、Cu²⁺和Zn²⁺）的相互作用焓、熵和吉布斯自由能。计算得到的吉布斯自由能ΔG°为负值，且跨越相当宽的能量区间（从 - 90到 - 1100 kJ·mol⁻¹），这意味着所研究的离子形成了强配合物。对于NiGly²⁺配合物，计算得到的最大相互作用吉布斯自由能为 - 1076 kJ·mol⁻¹。对Gly·Mⁿ⁺(H₂O)ₘ和GlyZwitt·Mⁿ⁺(H₂O)ₘ（Mⁿ⁺ = Li⁺、Na⁺、K⁺、Mg²⁺、Ca²⁺、Ni²⁺、Cu²⁺和Zn²⁺；m = 0、2和5）体系的分子结构和相对稳定性的计算表明，在与单价金属阳离子形成的配合物中，最稳定的物种是在非两性离子甘氨酸中通过N、O配位的金属阳离子。二价阳离子Mg²⁺、Ca²⁺、Ni²⁺、Cu²⁺和Zn²⁺更倾向于通过两性离子甘氨酸的O、O分叉键进行配位。逐步添加两个和五个水分子会导致水合物种的相对稳定性发生显著变化。在Gly·Mⁿ⁺和GlyZwitt·Mⁿ⁺配合物中，在金属离子处添加两个水分子会降低甘氨酸金属配合物的相对稳定性。对于Mⁿ⁺ = Li⁺或Na⁺，添加五个水分子不会改变稳定性的相对顺序。在Gly·K⁺配合物中，由于钾阳离子尺寸较大，K⁺离子周围水分子的溶剂化壳具有不同的结构，氢键接触数量减少。这导致GlyZwitt·K⁺H₂O₅体系有净偏好（相差10.3 kJ·mol⁻¹）。向含有二价阳离子Mg²⁺、Ca²⁺、Ni²⁺、Cu²⁺和Zn²⁺的甘氨酸配合物中添加五个水分子会导致对非两性离子甘氨酸物种有净偏好。计算得到的相对吉布斯自由能相当高（ - 10到 - 38 kJ·mol⁻¹），并且在Gly·Mⁿ⁺(H₂O)₅（Mⁿ⁺ = Mg²⁺、Ca²⁺、Ni²⁺、Cu²⁺和Zn²⁺）配合物中，N、O配位比O、O配位更受青睐。
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