¹Department of Analytical Chemistry, Faculty of Pharmacy, Marmara University, Basıbuyuk 34854 Istanbul, Turkey DOI : 10.29228/jrp.2024.00 Metal complex structures are important in many biological processes where coordination can occur between various metal ions and a wide variety of ligands. Here we compared bivalent transition metal(II) ions- ternary complexes with penicillin class amoxicillin and cephalosporin class cefaclor actives in the presence of aliphatic amino acids. The complex formation conditions and compositions of the complexes formed by the classical, economical and reproducible Irving-Rossotti method were investigated. Therefore, the formation conditions and compositions of binary and ternary complexes were investigated by the Irving Rossotti procedure. Ternary complexes are prepared by mixing metal(II) with active ingredients and the appropriate amount of primary ligand or L-asparagine (ASP) or L-glutamic acid (Glut). In the ternary systems, ASP and Glut are primary ligands (L) whereas amoxicillin (Amox) and cefaclor (Cefa) behave as a secondary ligand (Y). From the calculated formation constants of the complexes formed by the selected blactam antibiotics and amino acids with Cu(II) and Zn(II) metals, it was determined that the metal-ligand mole ratios were 1:1:1 (M:L:Y). At room temperature, the formation constants of the complexes were found by adjusting the ionic strength to 0.11 mol dm-3 with NaCIO₄: logb(_{Cu(II)-ASP-Amox})=15.83±0.01; logb (_{Cu(II)-Glut-Amox})=20.76±0.01; logb(Cu(II)-ASPCefa)= 16.59±0.01; logb(_{Cu(II)-Glut-Cefa})=5.72±0.01; logb(_{Zn(II)-ASP-Amox})=5.32±0.01; logb(_{Zn(II)-Glut-Amox})=4.62±0.01; logb(Zn(II)-ASPCefa)= 5.46±0.01; logb(_{Zn(II)-Glut-Cefa})=4.52±0.01 respectively. The relative stabilities of the ternary complexes (ΔlogK) were interpreted by comparison with the stabilities of the corresponding binary complexes, with negative ΔlogK values observed for all complexes. Keywords : Amoxicillin; Cefaclor; L-asparagine; L-glutamic acid; Ternary complex