阳离子[M = H⁺、Li⁺、Na⁺、K⁺、Ca²⁺、Mg²⁺、NH₄⁺和NMe₄⁺]与天然氨基酸芳香基序的相互作用：一项理论研究。

Cation [M = H+, Li+, Na+, K+, Ca2+, Mg2+, NH4+, and NMe4+] interactions with the aromatic motifs of naturally occurring amino acids: a theoretical study.

作者信息

Reddy A Srinivas, Sastry G Narahari

机构信息

Molecular Modeling Group, Organic Chemical Sciences, Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India.

出版信息

J Phys Chem A. 2005 Oct 6;109(39):8893-903. doi: 10.1021/jp0525179.

DOI:10.1021/jp0525179

PMID:16834293

Abstract

Ab initio (HF, MP2, and CCSD(T)) and DFT (B3LYP) calculations were done in modeling the cation (H(+), Li(+), Na(+), K(+), Ca(2+), Mg(2+), NH(4)(+), and NMe(4)(+)) interaction with aromatic side chain motifs of four amino acids (viz., phenylalanine, tyrosine, tryptophan and histidine). As the metal ion approaches the pi-framework of the model systems, they form strongly bound cation-pi complexes, where the metal ion is symmetrically disposed with respect to all ring atoms. In contrast, proton prefers to bind covalently to one of the ring carbons. The NH(4)(+) and NMe(4)(+) ions have shown N-H...pi interaction and C-H...pi interaction with the aromatic motifs. The interaction energies of N-H...pi and C-H...pi complexes are higher than hydrogen bonding interactions; thus, the orientation of aromatic side chains in protein is effected in the presence of ammonium ions. However, the regioselectivity of metal ion complexation is controlled by the affinity of the site of attack. In the imidazole unit of histidine the ring nitrogen has much higher metal ion (as well as proton) affinity as compared to the pi-face, facilitating the in-plane complexation of the metal ions. The interaction energies increase in the order of 1-M < 2-M < 3-M < 4-M < 5-M for all the metal ion considered. Similarly, the complexation energies with the model systems decrease in the following order: Mg(2+) > Ca(2+) > Li(+) > Na(+) > K(+) congruent with NH(4)(+) > NMe(4)(+). The variation of the bond lengths and the extent of charge transfer upon complexation correlate well with the computed interaction energies.

摘要

采用从头算方法（HF、MP2和CCSD(T)）以及密度泛函理论（DFT，B3LYP）对阳离子（H⁺、Li⁺、Na⁺、K⁺、Ca²⁺、Mg²⁺、NH₄⁺和NMe₄⁺）与四种氨基酸（即苯丙氨酸、酪氨酸、色氨酸和组氨酸）的芳香族侧链基序之间的相互作用进行了建模计算。当金属离子接近模型体系的π骨架时，它们会形成强结合的阳离子-π络合物，其中金属离子相对于所有环原子呈对称分布。相比之下，质子更倾向于与环上的一个碳原子共价结合。NH₄⁺和NMe₄⁺离子与芳香族基序表现出N-H…π相互作用和C-H…π相互作用。N-H…π和C-H…π络合物的相互作用能高于氢键相互作用；因此，在铵离子存在的情况下，蛋白质中芳香族侧链的取向会受到影响。然而，金属离子络合的区域选择性由攻击位点的亲和力控制。在组氨酸的咪唑单元中，环氮相对于π面具有更高的金属离子（以及质子）亲和力，有利于金属离子的面内络合。对于所有考虑的金属离子，相互作用能按1-M < 2-M < 3-M < 4-M < 5-M的顺序增加。同样，与模型体系的络合能按以下顺序降低：Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺ 与NH₄⁺ > NMe₄⁺相当。络合时键长的变化和电荷转移程度与计算得到的相互作用能有很好的相关性。