Kai Xian Chen

Noncovalent interaction or chemical bonding between alkaline earth cations and benzene? A quantum chemistry study using MP2 and density-functional theory methods

Abstract Calculations on alkaline earth metal ion–benzene complexes were performed using the density-functional theory (DFT) B3LYP and ab initio MP2 methods. They showed that the interaction is very strong, of the order of magnitude of a normal chemical bond. Electrostatic interaction is not the dominant component, and both charge transfer and induction make a significant contribution. Analysis of molecular orbital interactions indicated that binding of the alkaline earth metal ions to benzene may be attributed to s–π and p–π interactions, which are significantly stronger than those between alkali cations and benzene.

Theoretical studies on opioid receptors and ligands. I. Molecular modeling and QSAR studies on the interaction mechanism of fentanyl analogs binding to ?-opioid receptor

Based on our previous result of the three-dimensional model of the μ-opioid receptor, binding conformations of 13 fentanyl analogs and three-dimensional structures for the complexs of these analogs with μ-opioid receptor were constructed employing the molecular modeling method and our binding conformation search program for ligands (BCSPL). Energetic calculation and quantitative structure–activity relationship (QSAR) analysis indicated a good correlation between the calculated binding energies of fentanyl analogs and their binding affinities, pKis and pKs, and analgesic activities, − log ED50s. Based on the three-dimensional models, the possible interaction mechanism of fentanyl analogs with μ-opioid receptor can be illustrated and the available structure–activity relationship of these analgesic agents can be explained reasonably.

Possible interaction mechanism for quaternary ammonium (QA) ions binding to potassium channels: density functional theory and MP2 studies on the interaction between phenol and ammonium cation†

Tetraethylammonium (TEA) and other quaternary ammonium (QA) ions are potent blockers of potassium channels. In order to shed light on the blockade mechanism of QA ions, we have carried out a series of computations on the phenol–ammonium model with density functional theory (DFT) and Moller–Plesset second order perturbation (MP2) methods at levels of 6-31G* and 6-31G** basis sets. NH–aromatic π interaction and NH–OH hydrogen bond interaction, which are important in biological systems, are responsible for the binding of NH4+ to phenol. From analysis of structures, energies, charge populations and transition state features, both the cation–π interaction and hydrogen bond or electrostatic interaction between QAs and the key amino acid residues at the entryways of K+ channels are seen to be significant in the blockade mechanism of QA ions.