A Molecular Modeling Study of Zinc(II) Extraction by Substituted 8-Hydroxyquinolines in the Presence of Various Pyridinic Adducts

Abstract

Molecular modeling is used to account for the extraction of zinc(II) by 8-hy-droxyquinoline and 2-methyl and 4-methyl analogues in chloroform in the presence of pyridine and its 2-methyl, 4-methyl, and 2,4,6-trimethyl derivatives. The species of formula ZnQ₂B and ZnQ₂B(H₂O) are modeled, where Q⁻ is an 8-hydroxyquino-linate anion and B is the 8-hydroxyquinoline itself or a pyridinic adduct. Each complex has an energy value which characterizes its steric and electrostatic parts and which allows comparison among complexes. This study accounts for the steric hindrances produced by methyl groups in the 2-and 6-positions of the pyridine ring and those produced by the methyl group in the 2-position of the 8-hydroxy-quinolinate anion. It also accounts for the improvement of the stability of complexes when the 8-hydroxyquinolinate anion has a methyl group in the 4-position. The energy of the modeled pyridinic adduct complexes decreases when the extraction constant is increased, as has been observed for other species in previous work.