Chemical and physical properties of riboflavin Domina Petric

Chemical and physical properties of riboflavin Domina Petric, MD

Essential features of the chemical structure: Substituted isoalloxazine nucleus D-ribityl side chain Reducible nitrogen atoms in nucleus January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 2

Chemical structures of riboflavin and its nucleotide forms: Riboflavin Flavin mononucleotide (FMN) Flavin adenine dinucleotide (FAD) January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 3

Chem. Spider. com January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 4

Riboflavin nomenclature • Riboflavin is the trivial designation of the compound 7, 8 -dimethyl-10 -(1′-d-ribityl) isoalloxazine, formerly known as vitamin B 2, vitamin G, lactoflavine or riboflavine. • The metabolically active forms are commonly called flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 5

Chemical and physical properties • Riboflavin is a yellow tricyclic molecule that is usually phosphorylated (to FMN and FAD) in biological systems. • In FAD, the isoalloxazine and adenine nuclear systems are arranged one above the other and are nearly coplanar. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 6

Chemical and physical properties • The flavins are light sensitive, undergoing photochemical degradation of the ribityl side chain, which results in the formation of such breakdown products as lumiflavin and lumichrome. • The handling of riboflavin must be done in the dark or under subdued red light. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 7

Chemical and physical properties • Riboflavin is moderately soluble in water (10 -13 mg/dl) and ethanol, but insoluble in ether, chloroform and acetone. • It is soluble but unstable under alkaline conditions. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 8

Chemical and physical properties • Because riboflavin can not be extracted with the usual organic solvents, it is extracted with chloroform as lumiflavin after photochemical cleavage of the ribityl side chain. • Flavins show two absorption bands at ∼ 370 nm and ∼ 450 nm with fluorescence emitting at 520 nm. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 9

Chemical and physical properties The catalytic functions of riboflavin are carried out primarily at positions N-1, N-5 and C-4 of the isoalloxazine nucleus. The methyl group at C-8 participates in covalent bonding with enzyme proteins. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 10

Chemical and physical properties • The flavin coenzymes are highly versatile redox cofactors because they can participate in either one- or two-electron redox reactions, thus serving as switching sites between obligate two-electron donors and obligate one-electron acceptors. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 11

Chemical and physical properties Flavins can also serve as cofactors in the twoelectron reduction of O 2 to H 2 O, and in the reductive four-electron activation and cleavage of O 2 in the monooxygenase reactions. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 12

Chemical and physical properties In the redox reactions, riboflavin undergoes changes in its molecular shape: from a planar oxidized form to a folded reduced form. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 13

Chemical and physical properties Differences in the affinities of the associated apoprotein for each shape affect the redox potential of the bound flavin. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 14

Riboflavin antagonists Analogs of the isoalloxazine ring: diethylriboflavin, dichlororiboflavin. Analogs of the ribityl side chain: D-araboflavin, D-galactoflavin, 7 -ethylriboflavin. January 17, 2022 Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. 15

Literature • Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc. 2008. January 17, 2022 16