LIGHT DEGRADATION

Since they are capable of intervening at various steps in the light-degradation process, TMP derivatives must be regarded as multifunctional UV stabilizers. 

The 1,4-dUiydropyridines, for example, nifedipine, nicardipine and amlodip-ine, are a well-established class of anti-hypertensive drugs. They are photolabile, some markedly so, for example, nifedipine. In all cases, the major light degradation product is the resonance-stabilised, fuUy aromatic, pyridine analogue [38]. 

Specifically the situation may involve a patent covering a method of reducing ultraviolet light degradation of plastic materials by... 

Because of its high crystallinity, the hnmopolymer (PVDV) is insoluble in most solvents at room temperature. However, since the regularity of repeating units in the chain is decreased by copolymerization, Saran is soluble in cyclic ethers and aromatic ketones. This copolymer (100 g) is plaslicized by die addition of a-melhyl-benzyl ether (5 g), stabilized against ultraviolet light degradation by 5-chloro-2-hydroxybenzophenone (2.0 g) and heat stabilized by phenoxypropylene oxide (2.0 g). 

Reaction (6.110) to Reaction (6.114) show that only H202 is consumed during the light degradation process, as seen below ... 

Simazine is virtually nonvolatile and resists ultraviolet light degradation. These characteristics result in long residual activity. Simazine is relatively insoluble, remaining within the top few inches of most soils. The amount of simazine moving downward in the soil usually increased as the rate per acre was increased. 

Nylon 6, or nylon caprolactam, is a polymeric fiber derived from only one constituent, caprolactam, giving the polymer [-(CH2)5CONH-] . It has a lower melting point than nylon 6,6, but it is superior to it in resistance to light degradation, elastic recovery, fatigue resistance, and thermal stability. 

Fig. 6. Long term visible light degradation of 4-CP at 4.0% H2[PtCl6]/TH in the presence of 0.01 M NaHCOa X > 400 nm (10) for details see text.

Fibers of Polymer IV show a comparatively strong resistance to light degradation (Table V). These values compare favorably with the... 

Table V. Resistance of Fibers of Polymer IV to Light Degradation...

Reports on long-term performance of man-made fibers are few. However, an analysis has been made of 20 nylon climbing ropes that had been used for up to 18 years, and it was found that significant deterioration had occurred. Note, however, that the deterioration was related to the amount and type of use and not to age. Loss in strength was a result primarily of fiber abrasion of the rope surface, and there was no evidence of significant light degradation (92). 

The E-P copolymer (2.98 moI% C2H4) was stabilized [134] against heat find light degradation by incorporation in the copolymer matrix dialkyl thiodipro-pionate or 2-(2 -hydroxyphenyl)-2,4,4-trimethyldialkyl-5,6-dinonyl or alkylidene-... 

Gu L, Chiang H-S, Johnson D. Light degradation of ketrolac tromethamine. Int J Pharm 1988 41 105-113. 

Persistence in the soil is generally low (half-life under aerobic and anaerobic conditions is 21 and 68 days, respectively). In sterile soil, the half-life is almost 1 year. Azinphos-methyl adsorbs strongly to soil particles and has low solubility in water. Biodegradation and evaporation are the primary routes of elimination from soil but azinphos-methyl is also degraded by ultraviolet light. Degradation is more rapid at higher temperatures. Azinphos-methyl has a short half-life in surface waters (2 days). Hydrolysis is more prominent under alkaline conditions but the compound is relatively stable in water below pH 10. The half-life on crops is 3-5 days under normal conditions. 

Case Study A.9 Scaled-Up Light Degradation and LC/MS and NMR Characterization... 

In terms of the kinetics, light degradation in dilute solution is first order however, in more concentrated solutions, decomposition approaches pseudo-zero order. The reason for this is that as the solution becomes more concentrated, degradation becomes limited due to the limited number of incident quanta and quenching reactions between the molecules. It should be noted that ionizable compounds, for example, ciprofloxacin, can show large differences in photostability between the ionized and unionized forms. 

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