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.

Colorimetric Determination of Stability Constant of Sulfamethoxazole-Cu(II) Complex at Different Temperatures by Continuous Variation Method

“…Similar labile aquo complexes were also proposed by Tirmizi and co-workers in their study of famotidine-Cu complex and cimetidine-Ni complex [11,12]. Labile aquo complex was also reported by Tella and co-workers in their study of acetaminophen-Cu(II) stability constants [9]. This corresponded to metal:ligand ratio of 1:2.…”

“…For several decades, chelating agents have been used as antidote to combat metal poisoning [9]. Biological friendly sequestrating agents have been used effectively to chelate metals in patients with metal overload [9].…”

“…For several decades, chelating agents have been used as antidote to combat metal poisoning [9]. Biological friendly sequestrating agents have been used effectively to chelate metals in patients with metal overload [9]. However, chelating capacity is a function of stability constant indicating that the effectiveness of a drug to chelate with a metal ion depends on the stability constant and other parameters [10] Many authors have reported the study of stability constant of drug-metal complexes [11,12].…”