Ahmad Iqbal, Fasihullah Q, Vaid Faiyaz H M
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Karachi, Karachi 75270, Pakistan.
J Photochem Photobiol B. 2006 Jan 2;82(1):21-7. doi: 10.1016/j.jphotobiol.2005.08.004. Epub 2005 Oct 11.
A study of the effect of light intensity and wavelengths on photodegradation reactions of riboflavin (RF) solutions in the presence of phosphate buffer using three UV and visible radiation sources has been made. The rates and magnitude of the two major photodegradation reactions of riboflavin in phosphate buffer (i.e., photoaddition and photoreduction) depend on light intensity as well as the wavelengths of irradiation. Photoaddition is facilitated by UV radiation and yields cyclodehydroriboflavin (CDRF) whereas photoreduction results from normal photolysis yielding lumichrome (LC) and lumiflavin (LF). The ratios of the photoproducts of the two reactions at 2.0 M phosphate concentration, CDRF/RF (0.09-0.22) and CDRF/LC (0.54-1.75), vary with the radiation source and are higher with UV radiation than those of the visible radiation. On the contrary, the ratios of LF/LC (0.15-0.25) increase on changing the radiation source from UV to visible. The rate is much faster with UV radiation causing 25% degradation of a 10(-5) M riboflavin solution in 7.5 min compared to that of visible radiations in 150-330 min.
利用三个紫外和可见辐射源，研究了光强度和波长对核黄素（RF）溶液在磷酸盐缓冲液存在下光降解反应的影响。磷酸盐缓冲液中核黄素的两个主要光降解反应（即光加成和光还原）的速率和程度取决于光强度以及照射波长。紫外辐射促进光加成反应，生成环脱氢核黄素（CDRF），而光还原是由正常光解产生发光色素（LC）和发光黄素（LF）。在2.0 M磷酸盐浓度下，两个反应的光产物比例，即CDRF/RF（0.09 - 0.22）和CDRF/LC（0.54 - 1.75），随辐射源而变化，且紫外辐射下的比例高于可见辐射。相反，将辐射源从紫外变为可见时，LF/LC（0.15 - 0.25）的比例增加。紫外辐射的速率要快得多，10(-5) M核黄素溶液在7.5分钟内有25%降解，而可见辐射则需要150 - 330分钟。
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