Paper Title
Complex Stability in Aqueous Solution of Metal Ions (Cu2+, Zn2+, and Mn2+) with Pyrocatechuic Acid Ligand

Abstract
A natural phenolic compound namely pyrocatechuic acid or 2,3-dihydroxybenzoic acid has been known for its biological activity as antioxidant and antimicrobial agent. This compound shows a potential chelating ability to bind metal ions through its three oxygen donor atoms. This ability seems to be promising for metal intoxication by chelation. In this study, the chelating ability of PA towards metal ion was expressed as �equilibrium constant� which shown the stability of the chelate complex formed. The investigated metal ions are Cu2+, Zn2+, and Mn2+. Potentiometric method was used for the determination of the equilibrium constant. The potentiometric method was carried out in aqueous solution which mimic human body fluid, with ionic strength of 0.15 mol�dm-3 NaCl at temperature 37�C. The formation of chelate complex was confirmed by spectrophotometric measurements. The result showed that the two oxygen donor atoms from hydroxyl group of PA were found to bind the metal ion. The stability of the metal complexes were increased as the ionic radius of the metal ion is decreased, where the complex that has highest stability is Cu2+ > Zn2+ > Mn2+. Additionally, the species distribution of the metal complexes in function of pH was presented graphically by using HySS2009. Keywords- Chelate Complex, Potentiometric, Stability Constant, Pyrocatechuic Acid, 2,3-Dihydroxybenzoic Acid.