Highly phosphorescent N∧C∧N platinum(II)peptide nucleic acid conjugates: synthesis, photophysical studies and hybridization behaviour†

The synthesis of novel highly phosphorescent N<^>C<^>N tridentate platinum(ii)-complex-peptide nucleic acid (PNA) bioconjugates was accomplished through the solid-phase approach. Melting temperature measurements and circular dichroism spectroscopy studies demonstrated that these conjugates maintain the PNA ability to recognize complementary ssDNA and ssRNA, though the length of the spacer between the metal center and the PNA sequence affects their hybridization properties. Noteworthy, the conjugation of PNA to this family of Pt(ii) complexes significantly enhanced the luminescent features of the organometallic moiety, leading to increased quantum yields (82.8%, 10-5 M), even in the presence of oxygen (48.6%, 10-5 M). An in vitro cytotoxicity study of Pt(ii)-PNA conjugates on HeLa cells showed no significative effect on cell growth in the dark (1 mu M for 72 h).