Evaluation of Stoichiometry, Stability Constants and Gibbs Free Energies of Acetaminophen-Zn (II) complex at Different Temperatures

Abstract

Acetaminophen also known as paracetamol, is a drug used in the treatment of pain and fever. It is essentially used for the relief of mild to moderate pain. The presence of phenol and carbonyl oxygen atom enables acetaminophen to behave as a bidentate ligand. The stoichiometry, stability constants and Gibbs free energies of acetaminophen-Zn (II) were determined colorimetrically at 25 and 40 ^oC using continuous variation and mole  ratio methods. The formation of Zn (II) complex with acetaminophen was studied colorimetrically at an absorption maximum of 630 nm at different temperatures. The data showed that Zn (II) and acetaminophen combine in the molar ratio of 1:1 at pH 7.4 with ionic strength maintained using 0.1M KNO₃. Calculated stability constants values were 2.70 x 10³ and 2.20 x 10³ using continuous variation method and 7.21 x 10³ and 7.21 x 10³ using mole ratio methods at 25 and 40 ^oC respectively. Calculated ΔGƟ for the complex were - 1.96 x 10⁴ and -1.98 x 10⁴ J using continuous variation method and -2.2 x 10⁴ J and - 2.31 x 10⁴ J using mole ratio method at 25 and 40 ^oC respectively. The stability constant and Gibbs free energy results suggested that acetaminophen used in the study is a good chelating agent and can be an efficient antidote in the therapy of Zn (II) overload or poisoning.

Keywords: Acetaminophen, Zinc, complex, stability constant, Gibbs free energy.