Potentiometric Determination of Stability Constants of Binary and Ternary Complexes of L-Tryptophan and Anti-Inflammatory Drugs with Zn(II)

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 13) were determined in 50% (v/v) EtOH-H2O solutions at 25+/-0.1 degrees 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 Delta log K and percentage of relative stabilization (% R. S.) values.

Automated summary

Formation equilibria of Zn(II) with tryptophan as a representative example of amino acids in presence of certain NSAIDS such as aspirin, ibuprofen and naproxen were studied using pH-metric titrations. The study determined the protonation constants and stability constants of the ligands in EtOH-H2O solutions. The formation of complexes in different pH regions was established, and the relative stabilities of the ternary complexes were compared with those of the corresponding binary complexes.