Computer-simulation studies of β-quinol clathrate with various gases. Molecular interactions and crystal structure.

The crystal structure of β-quinol clathrate was investigated by empirical force-field calculations using two sets of potential functions—AMBER and CVFF. The crystal was approximated by the fragments containing 3402 and 15 750 quinol atoms. It was shown that the AMBER potentials are more precise when describing the experimental data on structure of β-quinol clathrate. The bond stretching, valence angle and out-of-plane bendings, dihedral torsion, van der Waals and electrostatic interactions, and hydrogen bonding were taken into account in the potential energy U. The contribution of each of these energies to the formation of structure was estimated. The energy U was minimized with respect to the independent coordinates of the lattice, unit-cell parameters, and both translation and orientation parameters of included molecules. The equilibrium states of encaged guest molecules, β-quinol lattice structure, and energy of clathrate formation were determined for 27 encaged guest molecules. It was shown that the β-quinol lattice can contract as well as expand depending on the type of an encaged molecule. The distribution of charges around the cage favors the positively charged atoms of the molecule to be located in the center of a cage, in contrast with those negatively charged which occupy the sites in the vicinity of peripheral hydroxyl hexagons. The electrostatic component of guest–guest interaction strongly affects the equilibrium position of guest molecules with large dipole moment. Quantitative estimates of various structural and energetic characteristics for β-quinol clathrate prove to be in good agreement with experimental data. [ABSTRACT FROM AUTHOR]