Intercalation of Alkynylplatinum(II) Terpyridine Complexes into a Helical Poly(phenylene ethynylene) Sulfonate:...

The interactions of two anionic poly(phenylene ethynylene) sulfonate-conjugated polyelectrolytes (mPPESO₃^- and pPPESO₃^-) with two alkynylplatinum(II) terpyridine complexes (Pt²⁺ and Pt³⁺) were studied. The Pt(II) complexes interact with helical mPPESO₃^- by intercalation within the polymer helix to form a "guest-host" ensemble. Titration of Pt(II) complexes into an aqueous solution of mPPESO₃^- gives rise to efficient quenching of the polymer's fluorescence; meanwhile, triplet metal-metal-to-ligand charge transfer (³MMLCT) state emission from the intercalated Pt(II) complexes appears when the ensembles are excited into the polymer's absorption band. The ³MMLCT state emission implies that the Pt(II) complexes aggregate or dimerize on the mPPESO₃^- scaffold. The responses of the mPPESO₃^- and Pt(II) complex ensembles to various proteins were examined by monitoring the mPPESO₃^- fluorescence change. Negatively charged proteins recover the mPPESO₃^- fluorescence more than the positively charged proteins under physiological pH, indicating that electrostatics play an important role in the protein-ensemble interaction.