Suresh Cherumuttathu H, Mohan Neetha, Vijayalakshmi K Periya, George Renjumon, Mathew Janice M
Computational Modeling and Simulation Section, National Institute for Interdisciplinary Science and Technology, Trivandrum.
J Comput Chem. 2009 Jul 15;30(9):1392-404. doi: 10.1002/jcc.21162.
A systematic study of CH...pi, OH...pi, NH...pi, and cation...pi interactions has been done using complexes of phenylalanine in its cationic, anionic, neutral, and zwitterionic forms with CH(4), H(2)O, NH(3), and NH(4) (+) at B3LYP, MP2, MPWB1K, and M06-2X levels of theory. All noncovalent interactions are identified by the presence of bond critical points (bcps) of electron density (rho(r)) and the values of rho(r) showed linear relationship to the binding energies (E(total)). The estimated E(total) from supermolecule, fragmentation, and rho(r) approaches suggest that cation...pi interactions are in the range of 36 to 46 kcal/mol, whereas OH...pi, and NH...pi interactions have comparable strengths of 6 to 27 kcal/mol and CH...pi interactions are the weakest (0.62-2.55 kcal/mol). Among different forms of phenylalanine, cationic form generally showed the highest noncovalent interactions at all levels of theory. Cooperativity of multiple interactions is analyzed on the basis of rho(r) at bcps which suggests that OH...pi and NH...pi interactions show positive, whereas CH...pi and cation...pi interactions exhibit negative cooperativity with respect to the side chain hydrogen bond interactions. In general, side chain interactions are strengthened as a result of aromatic interaction. Solvation has no significant effect on the overall geometry of the complex though slight weakening of noncovalent interactions by 1-2 kcal/mol is observed. An assessment of the four levels of theory studied herein suggests that both MPWB1K and M06-2X give better performance for noncovalent interactions. The results also support the fact that B3LYP is inadequate for the study of weak interactions.
利用苯丙氨酸的阳离子、阴离子、中性和两性离子形式与CH(4)、H(2)O、NH(3)和NH(4)+形成的配合物，在B3LYP、MP2、MPWB1K和M06-2X理论水平上对CH...π、OH...π、NH...π和阳离子...π相互作用进行了系统研究。所有非共价相互作用都通过电子密度（ρ(r)）的键临界点（bcps）的存在来识别，并且ρ(r)的值与结合能（E(total)）呈线性关系。从超分子、碎片和ρ(r)方法估计的E(total)表明，阳离子...π相互作用在36至46千卡/摩尔范围内，而OH...π和NH...π相互作用具有相当的强度，为6至27千卡/摩尔，CH...π相互作用最弱（0.62 - 2.55千卡/摩尔）。在苯丙氨酸的不同形式中，阳离子形式在所有理论水平上通常表现出最高的非共价相互作用。基于bcps处的ρ(r)分析了多重相互作用的协同性，这表明OH...π和NH...π相互作用表现出正协同性，而CH...π和阳离子...π相互作用相对于侧链氢键相互作用表现出负协同性。一般来说，由于芳香相互作用，侧链相互作用会增强。溶剂化对配合物的整体几何结构没有显著影响，尽管观察到非共价相互作用略有减弱，减弱幅度为1 - 2千卡/摩尔。对本文研究的四个理论水平的评估表明，MPWB1K和M06-2X在非共价相互作用方面表现更好。结果还支持了B3LYP不足以用于弱相互作用研究这一事实。
