Effect on photodegradation

Habib MJ, Hasker AF. Complex formation between metronidazole and sodium urate effect on photodegradation of metronidazole. Pharm Res 1989 6 58-61. 

Having observed that C6 substitution had a major effect on photodegradation, Gautron prepared a series of C6-substituted derivatives and studied their behavior with respect to photoexcitation. The results presented in Table 3 show that indeed electron-donor groups at C6 efficiently stabilize the photochrome against photodegradation (cf. 33, 36, and 3 3 and 33 vs. 34 and 6). 

Two distinct mechanistic pathways have been proposed on the basis of the results obtained and they are shown in Schemes 13 and 14 for short and long wavelength irradiation conditions. All the products shown were identifiable. At high humidity the kinetics of the photooxidation of polycarbonate is influenced to some extent in that on short-wavelength irradiation only products which are soluble in water appear to be produced. Furthermore, the presence of the moisture has an accelerating effect on photodegradation of the polymer. The life expectancy of stabilised polycarbonate is expected to be at least... 

Photodegradation may be contributed by some free radicals attack like hydroxyl hydroperoxyl radicals. Therefore, free-radical scavenger - carbonate was added to determine it s effect on photodegradation. 

The early studies of stress effects on photodegradation rates were often contradictory in the sense that tensile stress sometimes seemed to cause a rate acceleration and other times a rate decrease. It was speculated that this inconsistency might be attributable to changes in reaction parameters other than stress that were not recognized... 

For PVC siding products, temperature and moisture have a significant synergistic effect on photodegradation. For colored specimens, inclusion of moisture in the accelerated test was necessary to match the outdoor test results from Ohio. For white specimens, replicating the Arizona environment was critical. 

The following tin stabilizers of the type RjSnYj have been investigated for their effect on photodegradation of poly(vinyl chloride) ... 

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