1086-80-2Relevant academic research and scientific papers
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.
Aerobic organocatalytic oxidation of aryl aldehydes: Flavin catalyst turnover by Hantzsch's ester
Chen, Shuai,Foss, Frank W.
, p. 5150 - 5153,4 (2012)
The first Dakin oxidation fueled by molecular oxygen as the terminal oxidant is reported. Flavin and NAD(P)H coenzymes, from natural enzymatic redox systems, inspired the use of flavin organocatalysts and a Hantzsch ester to perform transition-metal-free, aerobic oxidations. Catechols and electron-rich phenols are achieved with as low as a 0.1 mol % catalyst loading, 1 equiv of Hantzsch ester, and O2 or air as the stoichiometric oxidant source.
Flavin-iodine coupled organocatalysis for the aerobic oxidative direct sulfenylation of indoles with thiols under mild conditions
Ohkado, Ryoma,Ishikawa, Tatsuro,Iida, Hiroki
, p. 984 - 988 (2018)
A unique coupled redox organocatalysis system using flavin and iodine catalysts efficiently promoted the metal-free aerobic oxidative direct sulfenylation of indoles with thiols at ambient temperature without any sacrificial reagents, except environmentally benign molecular oxygen. Biomimetic flavin catalysis plays multiple roles in aerobic oxidative transformations, not only regenerating I2 from in situ generated I-, but also converting thiols into disulfides.
Electron-deficient alloxazinium salts: Efficient organocatalysts of mild and chemoselective sulfoxidations with hydrogen peroxide
Menova, Petra,Dvorakova, Hana,Eigner, Vaclav,Ludvik, Jiri,Cibulka, Radek
, p. 3451 - 3462 (2013)
A series of substituted alloxazinium perchlorates has been prepared and tested as catalysts for the oxidation of sulfides to sulfoxides with hydrogen peroxide. The logarithms of the observed rate constants of thioanisole oxidation correlate with the Hammett σ constants of the substituents on the alloxazinium catalysts, as well as with their reduction potentials E 0′ and their pKR+ values, representing the alloxazinium salt/pseudobase equilibrium. The stronger the electron-withdrawing substituent, the more efficient is the alloxazinium catalyst. The alloxazinium salts with a cyano or trifluoromethyl group in position 8 proved to be the most efficient, operating at room temperature at small loadings, down to 0.1 mol%, achieving turnover number values of up to 640 and acceleration by a factor of 350 relative to the non-catalyzed oxidation. The 8-cyanoalloxazinium perchlorate was evaluated as the best catalyst; however, due to its relatively good accessibility, the 8-(trifluoromethyl)alloxazinium perchlorate seems to be the catalyst of choice for sulfoxidations with hydrogen peroxide. It was successfully tested for the sulfoxidation of a series of aliphatic and aromatic sulfides on a preparative scale. It produced the corresponding sulfoxides in quantitative conversions and with high isolated yields (87-98%). No over-oxidation to sulfone was ever observed. Copyright
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.
Riboflavin degradation in the presence of quercetin in methanol under continuous UV-B irradiation: The ESI-MS-UHPLC analysis
Stanojevi?, Jelena S.,Zvezdanovi?, Jelena B.,Markovi?, Dejan Z.
, p. 1787 - 1794 (2015)
The presented work deals with continuous UV-B irradiation of riboflavin in MeOH solution, leading to its degradation under anaerobic as well as aerobic conditions (faster in the former case), which is related to riboflavin photosensitizing properties (type I photosensitizer in the first case, and type II in the other one). Addition of quercetin, a well-known antioxidant in the system causes a decrease of the (riboflavin) degradation in both cases. In anaerobic conditions it might be a consequence of quercetin antioxidant scavenging activity, while under aerobic conditions it could be related to singlet oxygen formation. The degradation dynamics - in both systems, in the presence and in the absence of quercetin - is well synchronized with dynamics formation of the two major products, lumiflavin and lumichrome
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.
Effect of caffeine complexation on the photolysis of riboflavin in aqueous solution: A kinetic study
Ahmad, Iqbal,Ahmed, Sofia,Sheraz, Muhammad Ali,Aminuddin, Muhammad,Vaid, Faiyaz Hussain Madni
, p. 1363 - 1370 (2009)
The effect of caffeine complexation with riboflavin on the kinetics of riboflavin photolysis in the pH range 2.0-10.5 has been studied. The photolysis of riboflavin solutions (5×10-5 M) was carried out in the presence of caffeine (0.5-2.5x10su
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.
Engineering of Synechococcus sp. strain PCC 7002 for the photoautotrophic production of light-sensitive riboflavin (vitamin B2)
Kachel, Benjamin,Mack, Matthias
, p. 275 - 286 (2020)
Due to their capability of photosynthesis and autotrophic growth, cyanobacteria are currently investigated with regard to the sustainable production of a wide variety of chemicals. So far, however, no attempt has been undertaken to engineer cyanobacteria for the biotechnological production of vitamins, which is probably due to the light-sensitivity of many of these compounds. We now describe a photoautotrophic bioprocess to synthesize riboflavin, a vitamin used as a supplement in the feed and food industry. By overexpressing the riboflavin biosynthesis genes ribDGEABHT from Bacillus subtilis in the marine cyanobacterium Synechococcus sp. PCC 7002 riboflavin levels in the supernatant of the corresponding recombinant strain increased 56-fold compared to the wild-type. Introduction of a second promoter region upstream of the heterologous ribAB gene – coding for rate-limiting enzymatic functions in the riboflavin biosynthesis pathway – led to a further increase of riboflavin levels (211-fold compared to the wild-type). Degradation of the light-sensitive product riboflavin was prevented by culturing the genetically engineered Synechococcus sp. PCC 7002 strains in the presence of dichromatic light generated by red light-emitting diodes (λ = 630 and 700 nm). Synechococcus sp. PCC 7002 naturally is resistant to the toxic riboflavin analog roseoflavin. Expression of the flavin transporter pnuX from Corynebacterium glutamicum in Synechococcus sp. PCC 7002 resulted in roseoflavin-sensitive recombinant strains which in turn could be employed to select roseoflavin-resistant, riboflavin-overproducing strains as a chassis for further improvement.
