|
The interaction of reduced riboflavin-2",3", 4", 5"-tetrabutyrate with salicylic acid, aspirin, and salicylamide has been spectroscopically investigated to determine the binding mechanism. Hydrogen-1 and carbon-13 nuclear magnetic resonance, infrared, and absorption spectra were measured in chloroform-d and chloroform. The association of the reduced riboflavin with salicylic acid derivatives is different from that oxidized one. Salicylic acid and the reduced riboflavin form a cyclic hydrogen bonded complex through the imino (3-N, 5-N) protons and the carbonyl (2-C, 4-C) oxygens of the isoalloxazine ring of the latter, and the carboxylic hydroxyl proton and cirbonyl oxygen of the former. Aspirin and the reduced riboflavin form a complex by the same mode as salicylic acid. Salicylamide forms a cyclic hydrogen bonded complex with the reduced riboflavin through the imino (3-N, 5-N) protons and the carbonyl (2-C, 4-C) oxygens of the isoalloxizine ring, and the amino proton and the carbonyl oxygen of salicylmidc. It appears that both the oxidized and reduced form of riboflavin are associated with salicylic acid derivatives.
|