A Kinetic Investigation of the Supramolecular Chiral Self-Assembling Process of Cationic Organometallic (2,2′:6′,2″-terpyridine)methylplatinum(II) Complexes with Poly(L-glutamic Acid)

The cationic platinum(II) organometallic complex [Pt(terpy)Me]+ (terpy = 2,2 ':6 ',2 ''-terpyridine) at mild acidic pH interacts with poly(L-glutamic acid) (L-PGA) in its alpha-helix conformation, affording chiral supramolecular adducts. Their kinetics of formation have been investigated in detail as a function of the concentrations of both reagents and changing pH, ionic strength, the length of the polymeric scaffold and temperature. After a very fast early stage, the kinetic traces have been analyzed as three consecutive steps, suggesting a mechanism based on the electrostatic fast formation of a not-organized aggregate that subsequently evolves through different rearrangements to form the eventual supramolecular adduct. A model for this species has been proposed based on (i) the attractive electrostatic interaction of the cationic platinum(II) complexes and the polyelectrolyte and (ii) the pi-stacking interactions acting among the [Pt(terpy)Me]+ units.