Biomolecular Affinities and Cytotoxicity of Copper(I) and Silver(I) Phosphine–Pyridinyl Complexes Against CACO-2 and CASKI Cell Lines

A series of three copper (I) and three silver (I) complexes with the general formula [M L(PPh₃)₂]NO₃, (M = Cu for complexes 1–3 and Ag for complexes 4–6) are synthesized by reacting copper(I) or silver(I)-nitrate and triphenylphosphine with the bidentate ligands, (E)-1-(pyridin-2-yl)-N-(o-tolyl)methanimine L1, (E)-N-isopropyl-1-(pyridine-2-yl)methanimine L2, or (E)-N-(2,6-dimethylphenyl)-1-(pyridine-2-yl)methanimine L3. The structures of these complexes are elucidated using a combination of NMR spectroscopy, FTIR, UV–visible, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction. Structural analysis revealed that the Schiff bases coordinate to the metal centers in a bidentate fashion, with triphenylphosphine occupying the remaining coordination sites in complexes 1, 2, and 5. In contrast, in complexes 3, 4, and 6, one coordination site is occupied by a nitrate anion instead of triphenylphosphine. All six complexes exhibit a distorted tetrahedral geometry around the metal center, as confirmed by τ₄ values ranging from 0.54 to 0.87. Binding studies with calf-thymus DNA demonstrated that complexes 1–6 interact via intercalation, with complex 5 exhibiting the highest binding constant. Furthermore, all complexes showed strong binding affinity toward bovine serum albumin. Cytotoxicity studies revealed significant cytotoxicity of complexes 1–6 against human colon adenocarcinoma (Caco-2) and human cervical epidermoid carcinoma (Caski) cell lines.