Chiral Selectivity of Porphyrin-ZnO Nanoparticle Conjugates.

The recognition of enantiomers is one of the most arduous challenges in chemical sensor development. Although several chiral systems exist, their effective exploitation as the sensitive layer in chemical sensors is hampered by several practical implications that hinder stereoselective recognition in solid-state. In this paper we report a new methodology to efficiently prepare chiral solid films, by using a hybrid material approach where chiral porphyrin derivatives are grafted onto zinc oxide nanoparticles. Circular Dichroism evidences that the solid-state film of the material retains supramolecular chirality due to porphyrin interactions, besides an additional CD feature in correspondence of the absorbance of ZnO (375 nm), suggesting the induction of chirality in the underlying zinc oxide nanoparticles. The capability of hybrid material to detect and recognize vapours of enantiomer pairs was evaluated fabricating gas sensors based on quartz microbalances. Chiral films of porphyrin on its own were used for comparison. The sensor based on functionalized nanostructures presented a remarkable stereoselectivity in the recognition of limonene enantiomers, whose ability to intercalate in the porphyrin layers make this terpene an optimal chiral probe. Chiroptical and stereoselective properties of hybrid material confirm that porphyrin capped ZnO nanostructures are a viable procedure for the formation of chiral selective surfaces.