Theoretical study of hydrogen bonded picolinic acid-water complexes

Quantum chemical calculations have been performed on the hydrogen bonded picolinic acid-water complexes by Hartree-Fock, second-order Moller-Plesset perturbation theory, density functional theory, and density functional theory with dispersion correction using 6-311++G(d,p) basis set. For the isolated picolinic acid moiety, four stable stationary points, corresponding to four different conformers are found at all levels of calculation. The structure with intramolecular COO-H center dot center dot center dot N hydrogen bond is found to be the most stable conformer at all levels of theory. Taking the lowest energy conformer as the starting geometry, three different conformers are predicted for the binary complexes of picolinic acid with water. Geometrical parameters, interaction energy, vibrational analysis in detail have been investigated. The intramolecular hydrogen bond is retained in two complexes while structural deformation occurs in one complex due to cleavage of the intramolecular hydrogen bond. The natural bond orbital analysis and atoms in molecules theory have been applied to understand the nature of interaction present in picolinic acid-water complexes.