Physicochemical profile of Os (III) complexes with pyrazine derivatives: From solution behavior to DNA binding studies and biological assay

New series of osmium(III) complexes with pyrazinamide (PZA) and its analogues (PTCA, PAOX) were synthesized. The physicochemical features in the solid phase have been identified and confirmed using elemental analysis, mass spectrometry, spectroscopic techniques (FT-IR, 1H NMR) and thermogravimetric analysis. Based on the studies we confirmed bidentate nature of selected pyrazine derivatives and proven involvement azomethine and amine nitrogen atoms in coordination of metal ion. In particular, complex (2) is more stable than (1) and (3), retaining thermal stability up to 120 °C. After one stage dehydration process, the simultaneous destruction of Os(III) complexes architecture was observed with immediate decomposition and elimination of pyrazine derivatives. The acid-base equilibria studies of newly synthesized Os(III) complexes were carried out by combined pH-metric-spectrophotometric and potentiometric titrations in the aqueous solution. Os(III) complexes exhibited rich redox chemistry as demonstrated by cyclic voltammetry. The cyclic voltammograms revealed a well-defined redox couples which correspond to reversible, single-electron OsIII → OsII reduction within ‐1.152 to ‐1.374 V vs Ag/AgCl and OsIII → OsIV oxidation within 0.460–0.831 V vs Ag/AgCl. The binding ability of bioactive ligand and their Os(III) complexes with Calf Thymus DNA (CT-DNA) were investigated by spectrophotometric titration. The observed hypsochromic and bathochromic shifts with simultaneous hyperchromic effect confirmed mixed mode of interaction with biological target. Biological activity of Os(III) complexes, i.e. antimicrobial, cytotoxic, haemolytic and photodynamic potential were studied.