Studies on the binary and ternary complexes of mercury [II] with gallic acid and adrenaline

ABSTRACT

The interaction of mercury[II] ions with gallic acid [3,4,5-trihydroxybenzoic acid] [GAL] and adrenaline [epinephrine] [1-[3,4-dihydroxyphenyl]-2-methylaminoethanol] [ADR] were investigated by potentiometric and optical means. The stoichiometries and stability constants of the binary and ternary complexes have been determined pH-metrically in aqueous solution at 25°C and in ionic strength 0.1 M [NaNO3]. The complex formation equilibria involving adrenaline were characterized. The equilibrium Hg[GAL]2+Hg[ADR]2 2Hg[GAL][ADR], the corresponding constant is logX=4.22. The constant due to delta log k[Hg]= log k[Hg] [GAL] [Hg] [GAL] [ADR] - log k [Hg] [HG] [ADR] is 0.75. The results indicate that the overall ratio of the ternary complex Hg[GAL][ADR] is 111 and the mixed-ligand complex is more stable than one expected from purely statistical reasons. UV-Vis spectroscopy gave additional support to the results. There is a strong evidance from FT-IR spectrum that adrenaline chelates by the phenolic groups