Studies on photocatalytically active materials containing structure elements of a pyridinium alkaloid from Punica granatum

Abstract

The alkaloid punicin from Punica granatum, N-(2′,5′-dihydroxyphenyl)pyridinium chloride, forms heterocyclic mesomeric betaines and radicals, which were examined by ESR measurements and DFT calculations, in aqueous solution. By reaction of poly(4-vinylpyridine) with p-benzoquinone under two different reaction conditions, polymeric structures with punicin constituents were prepared and characterized. The ESR signals of these polymers were calculated and discussed. The 4,4′-bipyridine derivative of these polymers was prepared starting from Merrifield resin which was subsequently reacted with 4,4′-bipyridine and p-benzoquinone, or, alternatively, with N-(2″-5″-dihydroxyphenyl)-4-(4′-pyridine)pyridinium chloride. The properties of these new materials in reversible photocatalytic processes via radical species were examined. Therefore, solutions or suspensions were irradiated in water in the presence of proflavinium as a sensitizer, and EDTA as a sacrificial donor under an inert atomsphere. Oxygen (air) recovers the starting materials by formation of hydroxide ions which were determined by pH measurements.