The binding of calcium ion with different groups of superplasticizers studied by three DFT methods, B3LYP, M06-2X and M06

Abstract

Three different DFT methods, B3LYP, M06-2X and M06, with PCM (polarized continuum model) solvent environment were performed to study the binding of Ca2+ with different groups of superplasticizers. Small monomers contained one or two groups, respectively, called as phosphonate, phosphate, carboxylate, sulfonate, sulfate and alkoxide were selected as theoretical models. The stable binding conformations of Ca2+ with monomers containing a single group optimized by the three DFT methods are similar and the binding strength follows the order, phosphonate ≈ phosphate > carboxylate > sulfonate ≈ sulfate > alkoxide ≈ water. The chemical reactivity and the electrophilic attack, not the natural atomic charges, of those monomers contribute significantly to the binding strength with Ca2+. The stable conformations of monomers containing two groups binding with Ca2+ are complex and the structures of the complexes by the three DFT methods are different for the phosphonate and phosphate. However, the order of the binding energies of those monomers with calcium ions calculated by the three DFT method are consistent and also agree with that of the monomers containing a single group. The values of the binding energies are two times more than the binding energies of the monomers containing single group.