Synthesis and Structural Studies of Metal Complexes of the Biological Ligand 2-Quinaldic Acid: Utilization of the Polymer Pendant Analog PS-2-QA for Selective Aluminum Ion Removal from Aqueous Solution.

Abstract

The synthetic reactions of quinaldic acid (2-QA, 1), a ligand with potential implications in Al(3+) ion biological transport and in pharmaceutical applications and of use for the removal and recovery of Al(3+) ions from environmental waste sites, were studied with tri- and divalent metal ions that encompass Al(3+), Fe(3+), Ga(3+), Zn(2+), Ni(2+), Mn(2+), and Co(2+). The Al(3+), Fe(3+), and Ga(3+) metal ion complexes, 2-4, of 1 were characterized by FT-IR, FAB/MS, NMR, and elemental analysis and provided the following structural formula with 1 of 2-QA(4)M(2)(&mgr;-OH)(2).S, where S = H(2)O or pyridine. In the case of the Ga(3+ )analog, 4.Py, the unequivocal &mgr;-OH dimer structure was determined by single-crystal X-ray analysis [space group, P1; a = 13.387(3) Å; b = 14.016(2) Å; c = 14.549(2) Å; alpha = 87.74(2) degrees; beta = 73.44(2) degrees; gamma = 82.61(2) degrees; Z = 2; volume = 2592.6 Å(3)]. A description of the X-ray crystal structure of 2-QA(4)Ga(2)(&mgr;-OH)(2).4 pyridine, 4.Py, will also be presented. The corresponding bis(2-QA) metal complexes of Zn(2+), Ni(2+), Mn(2+), and Co(2+), 5-8, were also studied and all provided a formula of 2-QA(2)M.1.5 H(2)O, which were also characterized by many of the above-mentioned spectroscopic techniques. The polymer-supported (PS) version of 1, PS-2-QA, bonded to modified, macroporous 6% cross-linked polystyrene-divinylbenzene beads, was synthesized by an electrophilic substitution reaction on the aromatic ring of a 2-QA derivative, ethyl 2-quinaldate, with the chloromethylated precursor, PS-CH(2)Cl, followed by subsequent ester hydroysis to the free PS-2-QA ligand. The PS-2-QA ligand was found to selectively remove Al(3+) ions from aqueous acidic solution (pH = 3-5) in the presence of other divalent metal ions, namely, Cu(2+), Zn(2+), Ni(2+), Mn(2+), and Co(2+) as well as a trivalent metal ion, Cr(3+).