The Photochemistry of Riboflavin and Related Compounds

Halwer, Murray

doi:10.1021/ja01154a118

Cited by 56 publications

(31 citation statements)

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“…An increase in the rate of photodegradation of RF has been found with increasing ionic strength [23,25–26 30,35,38,81,86,91]. Moreover, an increase in divalent ions also leads to an increase in the formation of CDRF and decrease in LC concentration indicating a variable distribution of these photoproducts through intramolecular photoaddition and photoreduction, respectively [23,25–26 30,35].…”

Section: Reviewmentioning

confidence: 99%

Photo, thermal and chemical degradation of riboflavin

Sheraz¹,

Kazi²,

Ahmed³

et al. 2014

Beilstein J. Org. Chem.

208

156

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SummaryRiboflavin (RF), also known as vitamin B2, belongs to the class of water-soluble vitamins and is widely present in a variety of food products. It is sensitive to light and high temperature, and therefore, needs a consideration of these factors for its stability in food products and pharmaceutical preparations. A number of other factors have also been identified that affect the stability of RF. These factors include radiation source, its intensity and wavelength, pH, presence of oxygen, buffer concentration and ionic strength, solvent polarity and viscosity, and use of stabilizers and complexing agents. A detailed review of the literature in this field has been made and all those factors that affect the photo, thermal and chemical degradation of RF have been discussed. RF undergoes degradation through several mechanisms and an understanding of the mode of photo- and thermal degradation of RF may help in the stabilization of the vitamin. A general scheme for the photodegradation of RF is presented.

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Section: Reviewmentioning

confidence: 99%

Photo, thermal and chemical degradation of riboflavin

Sheraz¹,

Kazi²,

Ahmed³

et al. 2014

Beilstein J. Org. Chem.

208

156

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“…The rate of 2,4-D loss was greatest during the initial 1-2 h of exposure, and 2,4-D photolysis proceeded at a slower rate thereafter, ostensibly due to the loss of riboflavin and possibly the concurrent formation of less efficient photosensitizers of 2,4-D. It is well-established that riboflavin is quite photolabile, yielding lumichrome as a principal photoproduct (Halwer, 1951) as confirmed later in the pH experiment. In addition, some photoproduct(s) of riboflavin and/or 2,4-D may have had an inhibitory effect on sensitization of 2,4-D photolysis after prolonged exposure (Larson et al, 1992).…”

Section: Resultsmentioning

confidence: 59%

“…This rapid initial loss was generally followed by a much slower degradation rate in both light regimes, except at pH 7.5 under +UV, where riboflavin was completely photolyzed within 1 h. Halwer (1951) reported that the nitrogen atom in position 10 of the isoalloxazine ring of riboflavin becomes protonated at low pH, preventing the protonation of the position 9 nitrogen and thereby preventing riboflavin photolysis.…”

mentioning

confidence: 99%

Light regime, riboflavin, and pH effects on 2,4-D photodegradation in water

Harrison¹,

Venkatesh²

1999

J. of Env. Sc. & Hlth., Part B

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A laboratory study was conducted to determine the effects of light regime, riboflavin, and pH on photodegradation of 2,4-D in aqueous solution. In controlled-environment chamber experiments, riboflavin sensitized 2,4-D photolysis in a concentration-dependent manner under both attenuated UV (-UV) and enhanced UV (+UV) light regimes. The photolysis half-life of 2,4-D in solutions containing 10 mg L-1 riboflavin was 9.7 and 12.5 h when exposed to +UV and -UV, respectively, compared to no photolysis in the absence of riboflavin. In contrast, the extrapolated half-life of 2,4-D in solutions containing 2.5 mg L-1 riboflavin was 46 h under +UV and 72 h under -UV. The rate of 2,4-D photolysis in the presence of riboflavin increased under both light regimes as initial pH of the solution was decreased from 7.5 to 4.5. The half-life of 2,4-D in the presence of 10 mg L-1 riboflavin at pH 4.5 and exposed to +UV was 1.6 h. Lumichrome, a principal photoproduct of riboflavin, did not photosensitize 2,4-D. Concentrations of 2,4-dichlorophenol formed as a result of riboflavin-sensitized 2,4-D photolysis were higher under the -UV than the +UV regime. These results indicate that riboflavin concentration, solution pH, and light regime are interacting factors that may be manipulated to enhance rates of aqueous 2,4-D photolysis.

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“…Several studies have been carried out to evaluate the effect of buffer species on the photolysis of riboflavin (RF). These studies include the catalytic effect of acetate [7] and phosphate buffers [8][9][10][11][12][13][14] and the inhibitory effect of borate [15] and citrate buffers [16]. It has been shown that the monovalent phosphate ions (H 2 PO 4 -) exert a catalytic effect on the normal photolysis or photoreduction (side-chain cleavage) of RF [11,17] and the divalent phosphate ions (HPO 4 2-) on the photoaddition (side chain cyclization) reactions of RF [9][10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Effect of phosphate buffer on the complexation and photochemical interaction of riboflavin and caffeine in aqueous solution: A kinetic study

Sheraz

Kazi

Ahmed

et al. 2014

Journal of Photochemistry and Photobiology A: Chemistry

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a b s t r a c tA study of the photodegradation of 5 × 10 −5 M riboflavin (RF) in 0.2-1.0 M phosphate buffer in the presence and absence of 2.50 × 10 −4 M caffeine at pH 6.0-8.0 has been carried out. RF in phosphate buffer is photodegraded simultaneously by normal photolysis (photoreduction) and photoaddition reactions giving rise to lumichrome (LC) and cyclodehydroriboflavin (CDRF) as the main final products, respectively. RF and its photoproducts, formylmethylflavin (FMF), lumiflavin (LF), LC and CDRF in degraded solution have been determined by a specific multicomponent spectrophotometric method with an accuracy of ±5%. The apparent first-order rate constants for the photodegradation of RF and for the formation of LC and CDRF are 5.47-15.05 × 10 −3 min −1 , 1.06-8.30 × 10 −3 min −1 and 4.31-8.05 × 10 −3 min −1 , respectively. An increase in phosphate concentration leads to an increase in the rate of formation of CDRF and alters the photodegradation of RF in favor of the photoaddition reaction. This photoaddition reaction is further enhanced in the presence of caffeine which results in a further decrease of the fluorescence of RF in phosphate buffer. Caffeine may facilitate the photoaddition reaction by suppression of the photoreduction pathway of RF.

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The Photochemistry of Riboflavin and Related Compounds

Cited by 56 publications

References 0 publications

Photo, thermal and chemical degradation of riboflavin

Photo, thermal and chemical degradation of riboflavin

Light regime, riboflavin, and pH effects on 2,4-D photodegradation in water

Effect of phosphate buffer on the complexation and photochemical interaction of riboflavin and caffeine in aqueous solution: A kinetic study

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