Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 9. Novel Heterobimetallic Macrocycles and Related Hydrosoluble Hexacations as Potentially Active Photo/Chemotherapeutic Anticancer Agents

New homo- and heterobimetallic porphyrazine complexes of general formula [(M'Cl-2)LM] (L = tetrakis-2,3-[5,6-di-(2-pyridyl)pyrazino]porphyrazinato dianion), with M = Zn-II, Mg-II(H2O), or Pd-II in the central cavity and one M'Cl-2 unit (M' = Pd-II, Pt-II) peripherally coordinated at the pyridine N atoms of one of the dipyridinopyrazine fragments, were prepared and characterized by elemental analyses and IR/UV-visible spectroscopy. Related water-soluble salt-like species, carrying the hexacations [(PtCl2)(CH3)(6)LM](6+) (neutralized by I- ions), were also prepared and similarly characterized. Retention of clathrated water molecules is a common feature of all the compounds. A detailed H-1 and C-13 NMR investigation in dimethylformamide (DMF-d(7)) and dimethyl sulfoxide (DMSO-d(6)) provided useful information on the type of arrangement in the neutral and hexacationic species of the metalated dipyridinopyrazine fragments, in which the metal centers (Pd-II/Pt-II) are bound to the pyridine N atoms ("Py-Py" coordination) with formation of N2(pyr)PdCl2 or N2(pyr)PtCl2 coordination sites, the latter one featuring a cis-platin-like functionality. Data obtained in DMF solution of the quantum yield (Phi(Delta)) for the generation of singlet oxygen, O-1(2), the cytotoxic agent in photodynamic therapy (PDT), indicate that all the neutral and charged complexes, among them particularly those carrying centrally Zn-II or Pd-II, exhibit excellent photosensitizing properties, this qualifying the externally platinated complexes as potential bimodal PDT/chemotherapeutic anticancer agents. Fluorescence data ((Phi(F)) provided additional information on the photoactivity of all the species studied. The following companion paper describes the observed interaction of the Zn-II hexacation [(PtCl2)(CH3)(6)LZn](6+) with a G-quadruplex (G4) structure of the telomeric DNA sequence 5'-d[AGGG(TTAGGG)(3)]-3' in water