Solution Equilibrium Study of Divalent Metal Ions with Phenylpropanoid Derivatives and Acetylcysteine Ligands

Solution equilibrium of divalent metal ions (M=Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with caffeic acid (ligand C) or dihydrocaffeic acid (ligand D) in binary system, and with acetylcysteine (ligand N) in ternary system were investigated at condition similar to human physiological temperature of 310.15 K and ionic strength of 0.15 mol·dm^-3 NaCl. Potentiometry technique was used for the determination of formation constant (log β) assisted by spectrophotometry technique. The results indicated the formation of [ML], [MLH], [ML₂], [ML₂H] in binary species and [MLN], [MNLH], [MNLH₂] in ternary species, where L represents ligands C or D. It was found that ligand D formed more stable complexes than that of ligand C, which were affected by the presence of double bond in the carboxylate moiety of ligand C. The speciation diagrams were simulated by HySS and discussed briefly, additionally the tendency of ternary complexes was evaluated from parameters Δ log K_M and log X.