Energetics of small molecule and water complexation in hydrophobic molecular containers immobilized on surfaces

I&EC 118

Justin M. Notestein, notesten@uclink.berkeley.edu1, Enrique Iglesia, iglesia@cchem.berkeley.edu2, and Alexander Katz, katz@cchem.berkeley.edu1. (1) Department of Chemical Engineering, University of California, Berkeley, 201 Gilman Hall, MC-1462, Berkeley, CA 94720-1462, (2) Department of Chemical Engineering, University of California, 201 Gilman Hall, Berkeley, CA 94720
Calixarenes rigidly grafted on silica are uniform molecular containers that host aromatic guests with 1:1 stoichiometry independent of calixarene surface density. The silica surface is accessible to water and the hydrophobic sites are accessible to guests. Adsorption thermodynamics of substituted aromatics in aqueous solution and vapor are compared by (i) describing guest chemical potentials vs. pure guest, which removes aqueous solvation and condensation effects, and (ii) using water or salts to passivate residual guest adsorption sites on silica. Heats of adsorption increase with bulkier calixarene cavities, but otherwise depend only upon saturation vapor pressures, indicating these calixarenes are condensation nuclei, without apparent contributions from directional interactions. We also show that calixarene-water interfaces are stabilized by ~20 kJ/mol relative to water-vapor interfaces, indicating significant competition by water at these ostensibly hydrophobic cavities. This result is useful for understanding models of water interactions with other concave hydrophobic molecular containers.
 

Computational Material Design in Chemical Industries, Sponsored by Novel Chemistry with Industrial Applications Sub-Division
1:30 PM-5:00 PM, Monday, 11 September 2006 Moscone Center -- Room 252/254, Oral

Division of Industrial & Engineering Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006