Blue light, photodegradation

Even with the use of these filters, there is now evidence that blue light in the visible range (400+ nm) will also cause photodegradation (30, 33). The filtration systems presently available do not effectively eliminate this less-active region of the spectrum. 

Photolysis of nicotine (173) in the presence of oxygen and methylene blue with light wavelengths greater than 300 nm gave the pyrrolidone (174, 30%), nicotyrine (175, 23%) and TV-oxide (176, 7%). Under nitrogen, with eosin as photosensitizer, only nicotyrine (14%) was identified in the photodegraded mixture [112]. 

Figure 8 Influence of the blister coloration on the photodegradation of uncoated nifedipine tablets 20 mg (Suntest CPS+, 720 W/m, UV filter), (t) green blister, (v) blue blister, ( ) yellow blister, (o) colorless blister absorbing UV-light, (a) red blister, (a) colorless blister, ( ) orange blister, ( ) without blister. Source. From Ref. 20.

Color additives have been reported to also either enhance drug photodegradation or protect against it. Erythrosin, eosine, role bengal, methylene blue, azure A, and azure B accelerate the photodecomposition of pyridoxine hydrochloride and pyridoxamine HCl (26). Erythrosine was found to enhance the decomposition of phenylbutazone when irradiated with unfiltered light from a 300 W projector bulb, but was stable in the absence of the dye (27). Certain dyes such as methylene blue have been found to enhance the photostability of solutions of daunorubicin (87). 

Photodegradation of methyl blue (MB) in aqueous solution under UV light... 

The photocatalytic activities of TiOa particles with and without Pt nanoparticles were estimated based on the photodegradation reaction of methylene blue. A methylene blue aqueous solution (20 p,M, 20 mL), including TiOa particles with/without Pt nanoparticles (5 mg), was irradiated with UV light (300-350 nm, 10 p,W cm ) for 30 min, and the absorption spectra before and after UV irradiation were measured (Fig. 6.10). The photocatalytic activity of each sample was also estimated using Eq. (6.1). 

Fig. 18.15 Discoloration of Keyacid Blue (0.1 wt%) stain in electrospun nonwoven mats, (a) Exposed to halogen light ( 13 mW/cm ) over a 24 h. (b) Optical absorption spectrum exposed to halogen light ( 27 mW/cm ) as a function of time. The results show that the cellulose core and Ti02 sheath nanofibers mat exhibited the best photodegradation performance (Reprinted with the permission from Ref. [57]. Copyright 2010 American Chemical Society)...

Zhou W, Cao M, Su S, Li N, Zhao X, Wang J, Li X, Hu C (2013) A newly-designed polyoxometalate-based plasmonic visible-light catalyst for the photodegradation of methyl blue. J Mol Catal A 371 70-76... 

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