Photodegradation effect

A significant loss of insulin activity occurred when solutions of amorphous insulin were exposed to ultraviolet radiation (1). The ultraviolet irradiation of phenylephrine HCl results in the formation of a product with demonstrated bronchodilator potency greater than that of the original solution, when tested on perfused guinea pig lungs (2). A solution of epinephrine exposed to radiation from a quartz mercury burner for 35 minutes was reported to produce practically no pressor, but depressor action, when tested on an anesthetized dog. However, the nonirradiated solution produced a marked pressor action with little depressor effect (3). 

The photooxidation of angiotensinamide and its effects on the pressor, oxytocic and gut-stimulating activities of the peptide have been investigated (4). In these studies, control samples showed no loss of oxytocic, pressor and gut-stimulating activities, whereas solutions exposed to VIS radiation for 10 and 30 minutes had losses of 45% and 75%, respectively. 

The antibacterial activity of curcumin is greatly enhanced by UV-VIS radiation (5). Photodegraded solutions of thiomerosal were found to be more active 

The pharmacodynamically active molecular structure of the calcium channel blocker, nifedipine, is photodecomposed by UV-VIS radiation (8). This effect is manifested by a change in color (from yellow to colorless) or the fading of colored preparations, formation of precipitation and alteration of the taste of the product. Such changes during storage may give patients the sense of uneasiness, confusion, and doubt as to the safety and efficacy of the product. 

Solutions of phenylephrine hydrochloride, for example, develop a brown color as a result of photodegradation (2). Many dyes, including FD C dyes, used for coloring liquid pharmaceutical preparations such as syrups and elixirs, fade on exposure to light (9). Curcumin, a natural food colorant, fades on exposure to UV-VIS radiation (10). 

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Generally, the spectrum of sunlight is predominantly visible and infrared. Only about 6% of UV light cases fading and other photodegradation effects in polymers and WPCs, and only wavelengths between 100 and 290 nm are the most destructive. In fact, UV radiation with these wavelengths is filtered out with the earth s ozone layer. 

These additives preferentially absorb the incident UV radiation and so protect the polymer from the radiation. UV absorbers do not themselves degrade rapidly, but they convert UV energy into harmless levels of heat energy, which are dissipated throughout the polymer matrix. UV absorbers are limited in their effectiveness because of the physical limitations of the absorption process, and their ability to absorb is governed by the need for high concentrations of additive and thickness of polymer before sufficient absorption will occur to retard the photodegradation effectively. 

Belbachir, S., Zairi, F., Ayoub, G., Mascbke, U., Nait-Abdelaziz, M., Gloaguen, J.M., et al., 2010. Modelling of photodegradation effect on elastic-viscoplastic behavior of amorphous polylactic acid films. J. Mech. Phys. Solids 58, 241—255. 

Deterioration. The causes of degradation phenomena in textiles (155—158, 164) are many and include pollution, bleaches, acids, alkaUes, and, of course, wear. The single most important effect, however, is that of photodegradation. Both ceUulosic and proteinaceous fibers are highly photosensitive. The natural sensitivity of the fibers are enhanced by impurities, remainders of finishing processes, and mordants for dyes. Depolymerization and oxidation lead to decreased fiber strength and to embrittlement. 

A more effective approach to enhancing the rate of photodegradation of PS is to copolymerize styrene with a small amount of a ketone-containing monomer. Thus the ketone groups are attached to the polymer during its manufacture (Pig. 13) (98,100). 

Hindered Amines. Hiadered amines are extremely effective ia protecting polyolefins and other polymeric materials against photodegradation. They usually are classified as light stabilizers rather than antioxidants. 

PL can be used as a sensitive probe of oxidative photodegradation in polymers. After exposure to UV irradiation, materials such as polystyrene, polyethylene, polypropylene, and PTFE exhibit PL emission characteristic of oxidation products in these hosts. The effectiveness of stabilizer additives can be monitored by their effect on PL efficiency. 

The photodegradation of para-aramid in an 0 atmosphere allows the differentiation between the accelerated experimental photooxidative conditions from its usual daylight exposure effects. This study illustrated an estimation of the rates of photooxidation of a commercial para-aramid product (i.e., DuPont s Kevlar-29 woven fabric) based on the oxygen-18-labelled carbon dioxide ( CC and CC ) decarboxylated from the sample. The oxygen-18-labelled atoms, which are inserted in the macromolecules, were analyzed for the photodegradation processes. This technique also allows the radial l O-distribution measurement from the fiber surface toward the fiber center. 

Arita, S., S. Ando, H. Hosoda et al. 2005. Acceleration effect of sulfides on photodegradation of carotenoids by UVA irradiation. Biosci. Biotechnol. Biochem. 69 1786-1789. 

Perhaps the most interesting feature is exhibited by the copolymers, rather than the homopolymers. We find that the reduction in the quantum yield of photodegradation always exceeds the abundance of o-methylbenzoyl chromophores (5.) Table I illustrates this effect. 

As noted above, there is experimental evidence to indicate that the carbonyl groups of (vinyl chloride)-(carbon monoxide) copolymers are effective sensitizers for the photodegradation of these materials (9,10,11). A reasonable sensitization mechanism can be formulated for this system on the basis of the information now on hand. 

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