Theoretical Investigation of the Complexation Reaction of Procaine-hydrochloride by β-cyclodextrin

 Quantum-chemical calculations were performed to study the complexation of drug molecule procaine hydrochloride with beta cyclodextrin (β-CD) in the gas phase and in water. The inclusion process was optimized by the semi empirical method PM3 and the obtained complex structure was further refined by ONIOM method (DFT: PM3). It is found that (B3LYP/6-31G(d,p) : PM3) provides the best energy minimum for the complex, compared to M06-2X and WB97XD functional. Given the energy profile, the configuration of the complex formed indicates that the benzene ring is completely included in the hydrophobic cavity of the β-CD. The thermodynamic parameters analysis has shown that the procaine/β-CD complexation is enthalpically favorable, and the complex is well structured. Natural bond orbital (NBO) analysis indicates that no hydrogen bond interaction exists, and the procaine/β-CD complex is mainly stabilized by Van der Waals forces. 1D 1H NMR spectra analysis shows that the procaine molecule penetrates into the cavity of this CD with the aromatic ring.