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

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. [ABSTRACT FROM AUTHOR]