Stability Constant and Thermodynamic Parameters Determination of A Semi-synthetic Penicillin Derivative with Various Bivalent Metal Ions (Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Sn2+, Hg2+ and Pb2+): A Potentiometric Study

Abstract

This present work is a report on the stability constant values of a worthy antibiotic, Ampicillin Trihydrate; D[-]-α-aminobenzyl penicillin; ABP; a semi-synthetic derivative of penicillin with various biologically vital bivalent metal ions (Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Sn 2+ , Hg 2+ and Pb 2+ ) recorded in water-ethanol medium 50% V/V at three different temperatures (298K, 308K, 318K)maintaining ionic strength at 0.1M KNO 3 . The effect of temperature was also studied and the corresponding thermodynamic functions ∆Gº, ∆Hº and ∆Sº were calculated and discussed. It is significant to study the stability constants of drugs with these metal ions as they may already be present in human body. The proton-ligand and metal-ligand stability constants were determined by Calvin-Bjerrum pH titration techniques as modified by Irving and Rossitti. This analysis was carried out in order to determine the pk 1 H and log k 1 , values at 298 K, 308 K and 318 K. The metal to ligand mole ratio was maintained at 1:5 in order to fulfil the maximum coordination number of metal ion. The titrations were done in a titration cell with three openings, kept immersed in a thermostated bath.

Revisiting the hydrolysis of ampicillin catalyzed by Temoneira‐1 β‐lactamase, and the effect of Ni(II), Cd(II) and Hg(II)

“…Complex formation between metal ions and the antibiotics yielding adducts with a lower toxicity than that of the metal ions themselves could be an explanation of this observation. Although, there is an ambiguity in the literature about the stabilities of the complexes of these metal ions with ampicillin, generally a weak binding is suggested (log K 1 ~ 2) (Fazakerley et al, 1976; Orabi, 2005; Zaworotko et al, 2006; Gupta, 2013). Nevertheless, metal complex formation may occur under the applied conditions, since ampicillin was applied at a high (27‐fold) excess referred to metal ions in our systems.…”