Effect of pH, Buffer, and Viscosity on the Photolysis of Formylmethylflavin: A Kinetic Study

Ahmad, Iqbal; Mirza, Tania; Iqbal, Kefi; Ahmed, Sofia; Sheraz, Muhammad Ali; Vaid, Faiyaz H.M.

doi:10.1071/ch12457

Cited by 28 publications

(59 citation statements)

References 28 publications

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“…1) for the reactions carried out in the pH range 3.8-5.6 is somewhat similar to those observed for the photolysis of RF (10,44) and FMF (39) in this range. The rate of photolysis is gradually decreasing and is about 2-3 times lower at pH 5.6 than that of pH 3.8.…”

Section: Acid Range (Ph 38-56)supporting

confidence: 68%

“…It may also be converted directly to LC (k 4 ) by photodealkylation through the [ 1 RF] state (44,57,61). FMF undergoes hydrolysis to LC (k 2 ) and LF (k 3 ) in aqueous media (34,38,39). The equilibria of RF, 1 RF, and 3 RF are not the rate determined steps in the reaction.…”

Section: Mode Of Photodegradationmentioning

confidence: 99%

“…FMF (pKa 3.5) (37) is protonated at pH 2.0, giving a distinct absorption maximum (385 nm) from that of RF (445 nm) and thus making the two-component assay feasible. CMF is a minor photoproduct obtained when FMF is slightly oxidized in the presence of air (38,39). The amount of CMF formed in acidic and alkaline solutions has been estimated to be ∼0.2-0.4% of the degraded RF using TLC.…”

Section: Spectrophotometric Assaymentioning

confidence: 99%

“…This reaction occurs through the formation of FMF as an intermediate to give LC as the final product (10,36,39,44,45). The photolysis of RF in acid solution can be represented by a reaction scheme involving a consecutive first-order reaction as follows:…”

Section: Effect Of Acetate Buffermentioning

confidence: 99%

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Effect of Acetate and Carbonate Buffers on the Photolysis of Riboflavin in Aqueous Solution: A Kinetic Study

et al. 2014

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Abstract. The photolysis of riboflavin (RF) in the presence of acetate buffer (pH 3.8-5.6) and carbonate buffer (pH 9.2-10.8) has been studied using a multicomponent spectrophotometric method for the simultaneous assay of RF and its photoproducts. Acetate and carbonate buffers have been found to catalyze the photolysis reaction of RF. The apparent first-order rate constants for the acetate-catalyzed reaction range from 0.20 to 2.86 ×10 −4 s −1 and for the carbonate-catalyzed reaction from 3.33 to. The second-order rate constants for the interaction of RF with the acetate and the carbonate ions range from 2.04 to 4.33×10 −4 M −1 s −1 and from 3.71 to 11.80×10, respectively. The k-pH profile for the acetate-catalyzed reaction is bell shaped and for the carbonate-catalyzed reaction a steep curve. Both HCO 3 − and CO 3 2− ions are involved in the catalysis of the photolysis reaction in alkaline solution. The rate constants for the HCO 3 − and CO 3 2− ions catalyzed reactions are 0.72 and 1.38×10, respectively, indicating a major role of CO 3 2− ions in the catalysis reaction. The loss of RF fluorescence in acetate buffer suggests an interaction between RF and acetate ions to promote the photolysis reaction. The optimum stability of RF solutions is observed in the pH range 5-6, which is suitable for pharmaceutical preparations.

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Section: Acid Range (Ph 38-56)supporting

confidence: 68%

Section: Mode Of Photodegradationmentioning

confidence: 99%

Section: Spectrophotometric Assaymentioning

confidence: 99%

Section: Effect Of Acetate Buffermentioning

confidence: 99%

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Effect of Acetate and Carbonate Buffers on the Photolysis of Riboflavin in Aqueous Solution: A Kinetic Study

et al. 2014

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“…The absorption maxima of RF and FMF (445 nm, pH 7.0) can be distinguished at pH 2.0 where FMF exists in a protonated form (pK a 3.5) [34] and thus can be assayed by this method. CMF is a minor product of the oxidation of FMF [13,17,35] and has not been considered in the assay scheme.…”

Section: Spectrophotometric Assaymentioning

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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Multicomponent spectrofluorimetric method for the assay of carboxymethylflavin and its hydrolytic products: kinetic applications

et al. 2018

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The simultaneous assay of carboxymethylflavin (CMF), an intermediate in the photolysis of riboflavin, and its hydrolytic side‐chain cleavage products, lumichrome (LC) (acid solution) and LC and lumiflavin (LF) as well as isoalloxazine ring cleavage products, 1,2‐dihydro‐1‐methyl‐2‐keto‐3‐quinoxaline carboxylic acid (KA) and 1,2,3,4‐tetrahydro‐1‐methyl‐2,3‐dioxo‐quinoxaline (DQ) (alkaline solution) has been carried out by a multicomponent spectrofluorimetric method. The method is based on the adjustment of pH of the degraded solutions to 2.0 and extraction of LC and LF with chloroform. The chloroform extract is evaporated to dryness under reduced pressure, the residue dissolved in pH 6.5 citro‐phosphate buffer and LC and LF determined at their fluorescence maxima at 478 and 530 nm, respectively. The pH of the aqueous phase is re‐adjusted to 6.5 and the solution used for the determination of CMF, KA and DQ at the wavelengths of 530, 443 and 420 nm, respectively. The proposed method has been validated according to ICH guidelines. The calibration curves for CMF and its hydrolytic products are linear in the concentration range of 0.5–5.0 × 10−6 M. The mean recovery ranges from 99.0–102.0% with relative standard deviation (RSD) of 0.19–0.99%. The limit of detection (LOD) and the limit of quantification (LOQ) are in the range of 1.17–1.78 × 10−7 M and 3.55–5.40 × 10−7 M, respectively. The uniformity of molar balance of CMF and degradation products during hydrolytic reactions indicates the accuracy of the proposed method for the spectrofluorimetric assay of the compounds. It has been applied to study the kinetics of hydrolytic reactions of CMF.

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Effect of pH, Buffer, and Viscosity on the Photolysis of Formylmethylflavin: A Kinetic Study

Cited by 28 publications

References 28 publications

Effect of Acetate and Carbonate Buffers on the Photolysis of Riboflavin in Aqueous Solution: A Kinetic Study

Effect of Acetate and Carbonate Buffers on the Photolysis of Riboflavin in Aqueous Solution: A Kinetic Study

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

Multicomponent spectrofluorimetric method for the assay of carboxymethylflavin and its hydrolytic products: kinetic applications

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