Polymethacrylic zinc porphyrin: a new approach to chiral recognition

Novel optically active methacrylic homopolymers bearing in the side-chain both one or more chiral groups of one single configuration (L-lactic acid residue) and tetraphenylporphyrin moieties have been successfully synthesized and fully characterized. These intrinsically chiral polymers exhibit remarkable thermal stability, with glass transition temperature in the range 250-315°C and decomposition temperatures in the range 360–390°C. Spectroscopic, thermal and chiroptical characterizations indicate the occurrence of dipolar interactions among the side chain moieties and the presence of chiral helix conformation at least for chain segments of the macromolecules. The macromolecular chromophoric materials resulted able to bind chiral guests through nitrogen/zinc coordination to form complexes which exhibit exciton-coupled bisignate Circular Dichroism (CD) spectra with the signs reflecting the absolute configurations of the optically active compound (to determine the absolute configuration of ,-diamines). This behavior is due to the formation of diastereomeric complexes which lead to a preferred porphyrin helicity, at least for chain segments. The method turns out very sensitive, requiring only few microgram quantities of guest compound.