1. Chemical and physical properties of riboflavin
Domina Petric, MD

2. Essential features of the chemical structure:
Substituted isoalloxazine nucleus
D-ribityl side chain
Reducible nitrogen atoms in nucleus
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

3. Chemical structures of riboflavin and its nucleotide forms:
Flavin mononucleotide (FMN)
Flavin adenine dinucleotide (FAD)
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

4. ChemSpider.com
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

5. Riboflavin nomenclature
Riboflavin is the trivial designation of the compound 7,8-dimethyl-10-(1′-d-ribityl) isoalloxazine, formerly known as vitamin B2, vitamin G, lactoflavine or riboflavine.
The metabolically active forms are commonly called flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

6. 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.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

7. 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.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

8. 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.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

9. 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.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

10. 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.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

11. 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.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

12. Chemical and physical properties
Flavins can also serve as cofactors in the two-electron reduction of O2 to H2O, and in the reductive four-electron activation and cleavage of O2 in the monooxygenase reactions.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

13. 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.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

14. Chemical and physical properties
Differences in the affinities of the associated apoprotein for each shape affect the redox potential of the bound flavin.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

15. Riboflavin antagonists
Analogs of the isoalloxazine ring: diethylriboflavin, dichlororiboflavin.
Analogs of the ribityl side chain: D-araboflavin, D-galactoflavin, ethylriboflavin.
November 21, 2018
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc

16. Literature
Combs GF. The Vitamins. Fundamental Aspects in Nutrition and Health. Elsevier Inc
November 21, 2018