Dynamics of small molecules complexed with calixarenes: Toward an understanding of organic solid state porosity

CHED 976

Jack R. Cox, Andrew J. Christiano, ajcdk3@mizzou.edu, Carol A. Deakyne, deakynec@missouri.edu, and John E. Adams, AdamsJE@missouri.edu. Department of Chemistry, University of Missouri, Columbia, MO 65211-7600
Although the ability of certain calixarene polymorphs to sorb small gas molecules has been demonstrated experimentally, why some species are retained within the organic solid more readily than others remains uncertain. Here we examine the dynamics of host-guest complexes of t-butylcalix[4]arene and its analogs with small molecules such as CO2, CH3OH, CH4, CHCl3, and C2H2 in the gas phase and in solution. By means of molecular dynamics simulations carried out using the AMBER gaff force field parameterization and RESP partial charges, we are able to evaluate how the shape and electrostatic environment of the host cavity affects the binding of the guest molecule and to suggest how the host dynamics may lead to "gating" of the entry of a gas molecule into the cavity in the solid state. We also are able to explain the reported difficulty in determining the binding site of some sorbed species in terms of the dynamic disordering of the guest molecules.