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Photochemical bleaching of fluorescent glycosylation products.

We have examined the effect of visible light and ultraviolet on the non-enzymatic glycosylation of lysine in vitro. Glucose and L-lysine were mixed and incubated under white light, UV-A, UV-B, or in the dark. During 15 days of incubation in the dark, a heterogeneous mixture of intensely brown chromophores developed, with a dominant fluorescence excitation maximum at 350 nm and emission maxima near 425 nm. The process was delayed or inhibited to a moderate extent by white light, whereas under UV-A and UV-B this effect was more pronounced. We conclude that non-enzymatic glycosylation can be photochemically modulated by both visible light and ultraviolet.

Fluorometry↗
PubMed1999

Changes in ultraviolet absorption of sunscreens after ultraviolet irradiation.

The incidence of skin cancer is increasing rapidly and sunscreens have been recommended in order to reduce damage from sunlight. In this investigation we have studied the change in the absorption spectrum of some photoactive organic species in sunscreens after ultraviolet A and ultraviolet B irradiation in a dose normally encountered during a full day in the sun. Samples of a number of photoactive compounds commonly used in sunscreens were irradiated with ultraviolet A and ultraviolet B light. A UVASUN 2000 MUTZHAS sunlamp was used for ultraviolet A irradiation and an Esshå Corona mini, equipped with two Philips TL12 20 W lamps, was used as the ultraviolet B source. The ultraviolet A dose was 100 J per cm2. The ultraviolet B dose corresponded to 20 minimal erythema doses. The absorption spectra of the compounds were recorded before and after irradiation. The absorbance of 2-ethylhexyl 4-methoxycinnamate was reduced significantly, whereas 3-(4-methylbenzyliden)camphor seemed to be rather stable. The benzophenones studied seemed to be relatively stable. In the case of 4-tert. butyl-4'-methoxy-dibenzoylmethane there was a rapid decrease in the ultraviolet A absorption leading to unsatisfactory protection in the ultraviolet A region. 4-Isopropyl-dibenzoylmethane also lost most of its ultraviolet protective capacity after irradiation with ultraviolet A. Ultraviolet B seemed to have a minor effect on all the samples. It is important for the clinician not only to know the initial absorption spectrum in the ultraviolet region for a specific sunscreen substance, but also whether it is altered during irradiation and in what way. This study including gas chromatography and mass spectrometry analysis indicates that some of the photoactive organic species commonly used today in sunscreens are unstable following ultraviolet irradiation.

Drug Stability↗
PubMed1986

The presence of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in smoked dry bonito (katsuobushi).

Smoked dry bonito (katsuobushi), an everyday food item for most Japanese people, was found to contain 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), the content of which was estimated at about 2 ng/g. This content is similar to the known MeIQx content of cooked beef. The katsuobushi also contained another mutagenic component, the total activity of which was 1/6-1/3 that of the MeIQx. This component was similar to 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx) with respect to its behavior in high-pressure liquid chromatography and its ultraviolet absorption spectrum.

Chromatography, High Pressure Liquid↗