H-1-NMR STUDIES ON THE SELF-ASSOCIATION OF CHLOROQUINE IN AQUEOUS-SOLUTION

The concentration dependences of 1H-NMR chemical shifts and spin-lattice relaxation rates were measured for chloroquine in aqueous solution. The weak self-association constant was evaluated according to a dimerization equilibrium with the formation of self-stacked adducts (K̄d = 4.52 ± 0.68 1 mol-1). The motional correlation times were evaluated for the monomer and the dimer by measuring intramolecular dipolar cross-relaxation rates of aromatic vicinal protons (τcm = 0.06 ns and τcd = 0.26 ns). The geometry of the stacked dimer was elucidated by measuring intermolecular dipolar cross-relaxation rates and interpreted in terms of partial superposition of quinoline moieties. © 1990.