Molecular modeling investigation of para-nitrobenzoic acid interaction in β-cyclodextrin

Geometry optimizations of para-nitrobenzoic acid (PNBA)beta-cyclodextrin complex were carried out using MM+, PM3 and density function theory B3LYP/6-31G*. Calculations were performed upon the inclusion complexation of beta-cyclodextrin (CD) with neutral (PNBA1) and anionic (PNBA2) species of para-nitrobenzoic acid. The results obtained from both methods consistently indicate that the complex of PNBA2/beta-CD (B) is significantly more favorable than the others energetically. The negative enthalpy changes calculated from the statistical thermodynamic calculation suggest that both the inclusion complexation is favored enthalpy-driven process. The geometry of the most stable complex shows that the aromatic ring is deeply self-included inside the hydrophobic cavity of beta-CD and also intermolecular hydrogen bonds were established between host and guest molecules. This suggests that hydrophobic effect and hydrogen bond play an important role in the complexation process. (C) 2011 Elsevier B.V. All rights reserved.