Abstract
Formation equilibria of Zn(II) with tryptophan (L1) as a representative example of amino acids in presence of some carboxylic acid nonsteroidal anti-inflammatory drugs (NSAIDS) such as aspirin, ibuprofen and naproxen (L2) studied using the pH-metric titrations. The protonation constants of the ligands (pKa) and their stability constants (log β) were determined in 50% (v/v) EtOH-H2O solutions at 25±0.1°C and I = 0.1 mol dm-3 NaClO4. The stepwise formation of the complexes has been established in the pH region studied. The species distribution in solutions as a function of pH was determined using the HYSS program. The relative stabilities of the ternary complexes are compared with those of the corresponding binary complexes in terms of Δlog K and percentage of relative stabilization (% R. S.) values.