1086-80-2Relevant articles and documents
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Strauss,Nickerson
, p. 3187 (1961)
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Effect of phosphate buffer on the complexation and photochemical interaction of riboflavin and caffeine in aqueous solution: A kinetic study
Sheraz, Muhammad Ali,Kazi, Sadia Hafeez,Ahmed, Sofia,Mirza, Tania,Ahmad, Iqbal,Evstigneev, Maxim P.
, p. 17 - 22 (2014)
A 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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Koziol et al.
, p. 1812,1813 (1981)
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Karrer et al.
, (1935)
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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.
, p. 579 - 585 (2013)
The kinetics of the photolysis of formylmethylflavin, a major intermediate product in the aerobic and anaerobic photolysis of riboflavin, was studied in the pH range 2.0-11.0. Formylmethylflavin and its photoproducts, lumichrome and lumiflavin, were determined in degraded solutions using a specific multicomponent spectrophotometric method. The photolysis of formylmethylflavin in alkaline medium takes place by first-order kinetics and the rate constants (kobs) at pH 7.5-11.0 range from 0.27×10-4 to 3.88×10-4 and 0.36×10-4 to 5.63×10-4s-1 under aerobic and anaerobic conditions respectively. In acid medium, the photolysis involves a second-order mechanism and the rate constants at pH 2.0-7.0 range from 1.37 to 2.11 and 2.03 to 2.94M-1s-1 under aerobic and anaerobic conditions respectively. The rate-pH profiles for the photolysis reactions indicate the highest rate of formylmethylflavin degradation is at ~pH 4 and above pH 10. In the alkaline region, the increase in rate with pH is due to higher reactivity of the flavin triplet state. The photolysis of formylmethylflavin is catalyzed by phosphate ions and is affected by the solvent viscosity.
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Bardos et al.
, p. 4704,4706,4708 (1957)
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Tul'cinskaja et al.
, (1968)
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Synthesis of quinoxalines under focussed microwave irradiation
Villemin,Martin
, p. 2319 - 2326 (1995)
Quinoxalines were obtained by the condensation of α-diones with o-diaminobenzenes without solvent under focussed microwave irradiation.
A study of photochemistry of flavins in pyridine and with a donor.
Kurtin,Latino,Song
, p. 247 - 259 (1967)
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Organocatalytic Dakin oxidation by nucleophilic flavin catalysts
Chen, Shuai,Hossain, Mohammad S.,Foss, Frank W.
, p. 2806 - 2809 (2012)
Flavin catalysts perform the first organocatalytic Dakin oxidation of electron-rich arylaldehydes to phenols under mild, basic conditions. Catechols are readily prepared, and the oxidation of 2-hydroxyacetophenone was achieved. Aerobic oxidation is displayed in the presence of Zn(0) as a reducing agent. This reactivity broadens the scope of biomimetic flavin catalysis in the realm of nucleophilic oxidations, providing a framework for mechanistic investigations for related oxidations, such as the Baeyer-Villiger oxidation and Weitz-Scheffer epoxidation.
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Cresswell,Wood
, p. 4768,4772 (1960)
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Photoirradiation products of flavin derivatives, and the effects of photooxidation on guanine
Kino, Katsuhito,Kobayashi, Teruhiko,Arima, Eiji,Komori, Rie,Kobayashi, Takanobu,Miyazawa, Hiroshi
, p. 2070 - 2074 (2009)
Photoirradiation in the presence of riboflavin led to guanine oxidation and the formation of imidazolone. Meanwhile, riboflavin itself was degraded by ultraviolet light A (UV-A) and visible light (VIS) radiation, and the end product was lumichrome. VIS radiation in the presence of riboflavin oxidized guanine similarly to UV-A radiation. Although UV-A radiation with lumichrome oxidized guanine, VIS radiation with lumichrome did not. Thus, UV-A radiation with riboflavin can oxidize guanine even if riboflavin is degraded to lumichrome. In contrast, following VIS radiation degradation of riboflavin to lumichrome, VIS radiation with riboflavin is hardly capable of oxidizing guanine. The consequences of riboflavin degradation and guanine photooxidation can be extended to flavin mononucleotide and flavin adenine dinucleotide. In addition, we report advanced synthesis; carboxymethylflavin was obtained by oxidation of formylmethylflavin with chlorite and hydrogen peroxide; lumichrome was obtained by heating of formylmethylflavin in 50% AcOH; lumiflavin was obtained by incubation of formylmethylflavin in 2 M NaOH, followed by isolation by step-by-step concentration.
Photolysis of carboxymethylflavin in aqueous and organic solvent: A kinetic study
Ahmad, Iqbal,Mirza, Tania,Musharraf, Syed Ghulam,Anwar, Zubair,Sheraz, Muhammad Ali,Ahmed, Sofia,Ejaz, Muhammad Ahsan,Khurshid, Adeela
, p. 26559 - 26571 (2019/09/06)
This is the first study on the photolysis of carboxymethylflavin (CMF), an intermediate in the photolysis of riboflavin (RF). CMF is photodegraded by removal of side-chain to lumichrome (LC) in acid solution and to LC and lumiflavin (LF) in alkaline solution. It also undergoes alkaline hydrolysis to 1,2-dihydro-1-methyl-2-keto-3-quinoxaline carboxylic acid (KA) and 1,2,3,4-tetrahydro-1-methyl-2,3-dioxoquinoxaline (DQ) by cleavage of isoalloxazine ring. CMF degrades to LC in organic solvents. The formation of LC in acid solution and organic solvents takes place by second-order reaction and those of LC, LF, KA and DQ in alkaline solution by first-order reactions. The values of second-order rate constants for the photolysis of CMF at pH 2.0 to 7.0 are in the range of 1.13 to 2.45 M-1 s-1 and those of first-order rate constants (kobs) at pH 8.0-12.0 from 1.53 to 4.18 × 10-4 s-1 and for the formation of photoproducts from 0.37 to 16.6 × 10-5 s-1. The photolysis of CMF is enhanced, with pH, in the alkaline region since the excited state is sensitive to alkaline hydrolysis. The photolysis and fluorescence quantum yields of CMF in aqueous and organic solvents have been reported. CMF and photoproducts have been assayed spectrofluorimetrically. The mode of CMF photolysis is discussed.