On the interaction of C₆₀ fullerene with poly(L-lactic acid) or poly(lactide)

Abstract

C₆₀ fullerene forms an association complex with poly(l-lactic acid) (PLLA) in dichloromethane solution. The equilibrium constant of the complex was determined spectrophotometrically and found K’ = 956 M⁻¹. A new band in the ultraviolet, i.e., at 230 nm was assigned to the charge-transfer interaction between PLLA and C₆₀, whereas the former acts as electron donor through the ketone of the ester group and the latter as electron acceptor being and electron-deficient olefin. The PLLA-C₆₀ complex in CH₂Cl₂ solution was also studied by optical rotatory dispersion (ORD) spectroscopy. The complex showed a complicate induced Cotton effect in correspondence of the C₆₀ electronic transitions at 404 and 326 nm confirming that PLLA and C₆₀ are in close contact each other and suggesting a kind of host-guest interaction where the helical conformation of PLLA is able to induce the optical activity to the achiral C₆₀ electronic transitions. The PLLA-C₆₀ complex is thermoreversible and more stable at lower temperatures.

Keywords:

• C₆₀
• PLLA
• poly(l-lactic acid)
• poly(lactide)
• association complex
• charge-transfer complex
• host-guest interaction
• induced cotton effect
• UV-VIS
• ORD

Acknowledgements

I take the occasion to express my thanks to Dr. Ottorino Ori who has introduced myself into certain intriguing topics involving the structure and properties of the intrinsically chiral isotactic PLLA.