Highly Stable C60/Poly(vinylpyrrolidone) Charge-Transfer Complexes Afford New Predictions for Biological Applications of Underivatized Fullerenes

The equilibrium constants for complexation of C(60) with poly(vinylpyrrolidone) (PVP) in water have been determined by UV-visible spectroscopy. The magnitude of the equilibrium constants was found to describe the formation of a charge-transfer (CT) saturated 1:1 complex for [PVP] = 2.62-5.25 x 10(-2) M (K = 1331.3 M(-1)), and a contact-pairs complex for [PVP] = 7.0-12.25 x 10(-2) M (K = 20.64 x 10(-2) M(-1)). These results indicate that the binding affinity of C(60) for drug receptors, base pairs in double-stranded DNA, or AT-rich segments of its minor groove to form CT complexes is limited by the strong coordination in the C(60)/PVP-saturated CT complex or envelopment by the polymer ligand in the contact CT complex.