Combined Crystallographic and Solution Molecular Dynamics Study of Allosteric Effects in Ester and Ketone p-tert-Butylcalix[4]arene Derivatives and Their Complexes with Acetonitrile, Cd(II), and Pb(II)

Author(s)

de Araujo, Alexandre S. ^[1] ; Piro, Oscar E. ^{[2, 3]} ; Castellano, Eduardo E. ^[1] ; de Namor, Angela F. Danil ^[4]

Affiliation

^[1] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13566590 Sao Carlos, SP - Brazil

^[2] CCT La Plata, CONICET, IFLP, RA-1900 La Plata - Argentina

^[3] Natl Univ La Plata, Fac Ciencias Exactas, Dept Fis, RA-1900 La Plata - Argentina

^[4] Univ Surrey, Dept Chem, Lab Thermochem, Guildford GU2 5XH, Surrey - England

• Document type: Journal article
• Source: Journal of Physical Chemistry A; v. 112, n. 46, p. 11885-11894, NOV 20 2008.
• Web of Science Citations: 12

Abstract

We describe here a procedure to bridge the gap in the field of calixarene physicochemistry between solid-state atomic-resolution structural information and the liquid-state low-resolution thermodynamics and spectroscopic data. We use MD simulations to study the kinetics and energetics involved in the complexation of lower rim calix{[}4]arene derivatives (L), containing bidentate ester (1) and ketone (2) pendant groups, with acetonitrile molecule (MeCN) and Cd2+ and Pb2+ ions (M2+) in acetonitrile solution. On one hand, we found that the prior inclusion of MeCN into the calix to form a L(MeCN) adduct has only a weak effect in preorganizing the hydrophilic cavity toward metal ion binding. On the other hand, the strong ion-hydrophilic cavity interaction produces a wide open calix which enhances the binding of one MeCN molecule (allosteric effect) to stabilize the whole (M2+)1(MeCN) bifunctional complex. We reach two major conclusions: (i) the MD results for the (M2+)1(MeCN) binding are in close agreement with the ``endo{''}, fully encapsulated, metal complex found by X-ray diffraction and in vacuo MD calculations, and (ii) the MD structure for the more flexible 2 ligand, however, differs from the also endo solid-state molecule. In fact, it shows strong solvation effects at the calixarene lower bore by competing MeCN molecules that share the metal coordination sphere with the four C=O oxygens of an ``exo{''} (M2+)2(MeCN) complex. (AU)