Photooxidation studies

Ketone photolysis in an inert atmosphere has been widely studied--ft 5-Q. Apart from polymer photooxidation studies, however, little work has been done on their degradative irradiation in an oxidizing medium51 53. 

Photooxidation at 0°C ih a sunshine weatherometer has been found to cause preferential destruction of the methylene groups in PVC (94). On the other hand, preferred removal of the chloro-methylene groups was observed in an earlier photooxidation study carried out at 30°C with 253.7-nm irradiation (96). A possible explanation for this apparent contradiction is that the use of 253.7-nm light enhanced the relative importance of photoinitiation involving C-Cl homolysis. 

Thus, in the course of preparing reactant mixtures for photooxidation studies under typical atmospheric conditions where both N02 and water vapor are present, it is essentially impossible to avoid the production of some HONO, and in the case of studies of amine reactions, some nitrosamines. However, this too is quite relevant, since nitrosamines are carcinogenic in experimental animals. In addition, there are a number of sources that emit nitrosamines directly into the air,... 

Fluorescein and related quinonelike dyes such as eosin have found extensive use as low-energy sensitizers, especially in photooxidation studies. The efficiency of intersystem crossing in fluorescein varies markedly with pH. For the neutral molecule, the quantum yield of fluorescence is only 0.31, while it is 0.91 for the dianion.449 In strong acid solutions, however, protonated fluorescein is strongly phosphorescent. In this state (dissolved in boric acid) fluorescein was the first compound for which T-T absorption in an excited triplet state was observed.7... 

Photooxidation studies have implicated His-188, His-192, His-289 and either His-305 or His-306 as ligands to copper. The structure of the active site is shown in Figure 68. The pair of Cu11 centres may be replaced by two Co11 centres, but an oxy derivative cannot be prepared.1400 It appears probable that the oxytyrosinase is the hydroxylating species. 

At 298K our results demonstrate that reaction 1 in one atmosphere of air proceeds 70% via abstraction and 30% via (irreversible) addition. Photooxidation studies have been reported by Niki, et al. (18) and Hatakeyama and Akimoto (19), where 298K SO2 yields from OH initiated oxidation of CH3SCH3 were reported to be 22% and 21%, respectively. Large yields of methanesulfonic acid were observed in both studies. At present, there is insufficient information to allow SO2 production to be associated with either the abstraction... 

The involvement of methionine sulfonium salts in these chemical cleavage reactions may stimulate experiments to show the significance of special methionine residues in the active centers and the catalytic sites of enzymes. Such an important role for a particular methionine has been postulated for the enzymes phosphoglucomutase and chymotrypsin on the basis of photooxidation studies (Ray et al., 1960). 

M. Mansour, H.Parlar, and F.Korte, Removal of Pollutants from the Aquatic Environment by Photooxidation, Studies in Environmental Science 23 (Chem. Prot. Environment), 1984, 457-461. 

Akimoto et al, Tsukuba 6 m evacuable, thermostated, FEP coated aluminium photooxidant studies... 

Joshi et al. (EPA), Research Triangle Park 440 glass reactor photooxidant studies... 

Pilling, M. J. Aromatic hydrocarbon oxidation the contribution of chamber photooxidation studies. Presented at the NATO EST-ARW Workshop on Environmental Simulation Chambers Apphcation to Atmospheiie Chemical Processes, Zakopane, Poland, October 1-4 (2004). 

The interaction and subsequent oxidative behavior under UV light exposure of nanocomposite using poly(styrene) (PS) as polymer and LDH organomodified by a monomer surfactant as filler were recently investigated [115]. The photooxidation study revealed that the hybrid nanofiller did not modify the photooxidation mechanism of PS. The same products of oxidation were observed with the same proportions. A slightly higher oxidation rate was observed in the case of the sample with 5% of filler. The advantage of this system was its ability to be tailored in order to limit/ control eventual interactions with photostabilizers and antioxidants. 

Photooxidation study of Methylethylketone and Methylvinylketone, in G. Restelli, G. Angeletti (eds). Fifth European Symp. on Physico-Chemical Behaviour of Atmospheric Pollutants, Kluwer Academic Publ., Dordrecht 1990, pp. 364-370. 

Photooxidation study of methylethylketone and methylvinylketone, in P.M. Borrell, P. Borrell, T. CvitaS, W. Seiler (eds), Proc. EUROTRAC Symp. 90, SPB Academic Publ., The Hague 1991, pp. 419-421. 

Photooxidation study of some carbonyl compounds of atmospheric interest,... 

Fourier-transformed infrared spectra of the photodegradated PPV film show a drastic increase in carbonyl groups due to the oxygen in air. Carbonyl moieties act as defects at which nonradiative decay occurs, so that there is a dramatic reduction of PL intensity [209,211]. A photooxidation study of PPV and its derivatives shows that the oxidation results in chain scission by breaking the vinylene group [209,210]. In addition to oxygen, other environmental factors cause degradation of the device, such as moisture and particles in air. In order to avoid them, device fabrication should be carried out under clean-room conditions. 

Anatase and rutile titania nanoparticles and pigmentary titania particles were used for photooxidation studies on a metaUocene PE [4] and proved to be more photochemically active than the pigment particles. On the other hand, titania nanoparticles with enhanced photocatalytic activity (anatase) may be used in nanocomposites coatings having self-cleaning properties. 

Figure 19. Schematic of reaction chamber used for model photooxidation studies of polycarbonate.

Figure 20. Photon flux data for lamp configurations employed in the model photooxidation studies. For comparison purposes, photon fluxes for natural weathering at different sites are also included.

---