Density functional studies of endosulphan and its interaction with glycine and GABA#

Abstract

Density functional theoretic (DFT) methods are employed to study the interactions between endosulphan and two amino acids, namely glycine and γ-aminobutyric acid (GABA). Two conformers of each isomer α- and β-endosulphan are considered in the study. The DFT methods B3LYP, M05, M05–2X, M06 and M06–2X in conjunction with the basis set 6–31+ +G** are used. The complexes of α- and β-endosulphan with amino acids are stabilized by a strong hydrogen bond. In addition, there are several weak C–H⋯O interactions present between the two moieties. Among the DFT methods used, M06–2X method shows the highest stabilization energy for all the complexes. The M06–2X/6–31+ +G** method predicts that among the four conformers of endosulphan, the α conformer in which the S=O points up, forms the most stable complex with both glycine and GABA, with stabilization energies −15.24 kcal/mol and −14.39 kcal/mol, respectively. The β conformer in which the S=O points down, forms the least stable complex with both amino acids with stabilization energies −7.14 and −7.85 kcal/mol, respectively. Interactions between various conformers of the organo-chloro pesticide endosulphan and the amino acids (glycine and GABA) have been studied using the MP2 and density functional methods. The results indicated that endosulphan binds strongly with both glycine and GABA. In addition to the one strong hydrogen bond, several weak interactions (C–H…O and C–H...N) participate in stabilizing the complex.