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.