Binding Ni(II) ions to chitosan and its N-heterocyclic derivatives: Density functional theory investigation

Abstract Here we report the results of density functional theory (DFT) investigations of Ni 2+ complexes with chitosan and its N-heterocyclic derivatives – N-(2-pyridylethyl) chitosan (2-PEC), N-(4-pyridylethyl)chitosan (4-PEC), and N-(5-methyl-4-imidazolyl)methyl chitosan (IMC). 11 model structures corresponding to ‘bridge’ and ‘pendant’ types of complexes have been calculated. We have shown that in most cases formation of ‘pendant’ complexes is more favorable. It was found that nitrogen atoms of chitosan and its N-heterocyclic derivatives played a governing role in Ni 2+ binding and that the degree of charge transfer from the ligand to the central ion in the complexes correlated with the complex stability. A row of complexes stability depending on the type of functional substitute in chitosan macromolecules (IMC ≈ 2-PEC > chitosan > 4-PEC) was in a good agreement with experimental data obtained from the nickel ion sorption isotherms on chitosan, 2-PEC, 4-PEC and IMC.