Conformational equilibrium study of calix[4]tetrolarenes using Density Functional Theory (DFT) and Molecular Dynamics simulations

The present work deals with the theoretical study of conformational equilibrium of calix4]tetrolarenes (1,2,3 trimethoxy substituted calix4]arene) in gaseous and solvation phases. A total of 64 calculations (four conformations at eight level of theories) were performed using Density Functional Theory (DFT) functionals viz. wB97XD, B97D, B3LYP, CAM-B3LYP with diffused (6–31 + G(d)) and non-diffused basis sets (6-31G(d)). It has been found that the conformational profile of calix4]tetrolarene changes from cone to 1,3-Alternate upon incorporating – OMe group. The B97D and wB97XD functionals gave the most accurate result having rmsd value ~0.73Å followed by B3LYP and CAM-B3LYP > 0.78Å. Furthermore, NBO calculations demonstrated that reduction in charges at lower rim oxygens reduces the chances of hydrogen bonding. Moreover, global reactivity parameters and molecular dynamics also complement the observed trend. Owing to the methoxy substitutions, anion binding study of these new molecules indicates towards the promising capability to bind Cl^? and F^? ions.