Postmarketing Surveillance for the Photosensitised Oxidation of Vegetable Oils in the Marketplace.

This study conducts postmarketing surveillance for the photosensitised oxidation of vegetable oils (VOs) stored in different conditions in the marketplace during commercialisation. Coconut oil, palm kernel oil, soybean oil and sunflower oil were exposed to direct sunlight and kept in the dark for six weeks. The results showed a significant (p < 0.05) increase in PV and a severe decrease in the iodine value, chlorophyll, ß-carotene, colour content, and the fatty acid compositions (oleic and linoleic acids mainly) in the light-exposed VOs. The FTIR analysis also identified the formation of the hydroperoxides (3444 cm-1), secondary oxidation products (1743 - 1723 cm-1) and the loss of the cis-disubstituted olefins (723 cm-1) bands in the light-exposed VOs. This indicated that oils exposed to light for an extended period of time could undergo photosensitised oxidation due to photosensitisers like chlorophyll. In contrast, the unexposed VOs showed no significant change (p > 0.05) in their chemical compositions. The photosensitised oxidation increased in the order: coconut oil < palm kernel oil < soybean oil < sunflower oil.

Spectroscopic and Dynamic Properties of Electronically Excited Pendant Porphyrin Polymers with Backbones of Differing Flexibility.

A zinc porphyrin-pendant norbornene polymer with a rigid backbone characterized by a 2:1 E/Z isomeric structure ratio has been synthesized, and its spectroscopic and photophysical properties are examined. Zinc tetraphenylporphyrin, the porphyrin-substituted norbornene monomer, and a previously reported zinc porphyrin-pendant polymer with a flexible polymethylene backbone have been used as comparators. Unlike its flexible counterpart, the rigid norbornene polymer exhibits clear exciton splitting of its Soret band, much more rapid relaxation rates of its excited singlet states, and a very small yield of an unusually short-lived triplet state. Unlike the flexible pendant polymer, which exhibits excimeric S2 fluorescence as a result of chromophore rotation, anti-Kasha emission from the norbornene polymer originates primarily from the unperturbed porphyrin E region. The low triplet yield in the polymer is attributed to greatly increased rates of competing internal conversion within the singlet manifold. Nevertheless, upconverted delayed fluorescence that is quenched by oxygen is observed upon intense steady-state Q-band excitation of degassed polymer solutions, signaling direct triplet involvement. Consistent with the polymer's rigid structure, this biexcitonic process is assigned to ultrafast singlet exciton migration and triplet-triplet annihilation following absorption of a second photon by the small steady-state concentration of polymer triplets.