Cation sitting in aromatic cages: ab initio computational studies on tetramethylammonium–(benzene)_n (n=3–4) complexes

Abstract

Quantum chemistry study was performed on interaction between tetramethylammonium (TMA) and aromatic cages by means of the MP2 method to show how TMA sits in an aromatic cage that is composed of benzenes. The MP2 calculations on TMA-(benzene) n complexes demonstrate that the more the benzene molecules in the aromatic cage, the stronger the binding strength between the cage and TMA. In details, the structure of TMA-(benzene) n (n ¼ 1-4) complexes can be easily constructed by superimposing n TMA-benzene complexes via TMA, and the binding energies of the TMA-(benzene) n complexes are the sum of the n corresponding TMA-benzene systems. For instance, the distances between the N of TMA and the plane of the benzene ring are 4. 238, 4.252, 4.264 ,and 4.276 Å , respectively, for TMA-(benzene) n (n ¼ 1-4) complexes, and the BSSE corrected binding energies at MP2/6-311þþG ÃÃ level are À8.8, À17.3, À25.8 and À34.3 kcal/mol, respectively, for TMA-(benzene) n (n ¼ 1-4) complexes. Thus, this study provides us useful information on how a cation interacts with an aromatic cage in terms of complex geometry and binding strength.

Research progress in cation-π interactions

“…The binding energies of the π-TMA-π sandwiches are the sums of the two corresponding TMA-π systems. Cheng et al [43] performed quantum chemistry study on TMA-(benzene) n (n = 1-4) complexes, and also revealed additivity of both the geometries and the binding energies in TMA-(benzene) n (n = 1-4) systems. The structure of TMA-(benzene) n (n = 2-4) complexes can be derived by adding benzene in a tetrahedral fashion taking advantage of the C-H interaction.…”

“…Different cation-π systems possess different proportions of binding components. Since 1997, Zhu and Jiang et al [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] have performed systematic investigations on cation-π interactions by quantum chemical methods. The investigated cations included alkali metal, alkaline-earth metal, NH 4 + , CH 3 NH 3 + , and tetramethylammonium (TMA); the aromatic systems included benzene, substituted benzene, 5-membered and 6-membered aromatic heterocyclic rings, 8-membered aromatic rings, all kinds of aromatic residues and nucleobases.…”

The open-close mechanism of M2 channel protein in influenza A virus: A computational study on the hydrogen bonds and cation-π interactions among His37 and Trp41

“…The most potent cation-π interaction was found in system D2 with a binding energy of −18.84 kcal·mol −1 , while the weakest one was found in system F1 with a binding energy of −17.81 kcal·mol −1 . According to the additivity properties of cation-π interactions [16,17] , the total binding energy of the 4 T-shaped cation-π interactions could be −72 kcal·mol −1 , and might play an essential role in maintaining the open structure and function of the M2 ion channel.…”

“…The binding strengths of the parallel stacking cation-π interactions are relatively weaker as compared with that of the T-shaped ones. Considering the additivity properties of cation-π interactions [16,17] , the total binding energy values of the 4 parallel stacking cation-π interactions could be 40-50 kcal·mol −1 , and might exert possible influence on the structure and function of the M2 ion channel.…”

“…In the present study, a model system of 4-methyl-imidazoles was used for mimicking the hydrogen bonds between His37 residues, and another model system composed of 4-methyl-imidazolium and indole was chosen to represent the cation-π interactions between His37 and Trp41. Combining our previous research experience with noncovalent interactions [15][16][17] , ab initio quantum chemistry calculations were performed to investigate the structural and energetic properties of the hydrogen bond and cation-π interactions, and to explore their possible roles in the open and close processes of the M2 ion channel. This study might be helpful not only to better understanding the roles of M2 protein in the viral life cycle, but also to designing more effective inhibitors of M2 channel as antiflu drugs.…”