Studies on Colors and Chemical Structures in the Solid States of Riboflavin Tetracarboxylates

Abstract

Riboflavin tetraesters such as riboflavin tetraacetate, tetrapropionate, tetrabutyrate and tetrabenzoate were prepared. These powdered esters showed three different colors, i. e., orange (A-type), dark yellow (B-type) and yellow (C-type), according to the kinds of solvents used for the crystallization (A-and C-type) or heating procedure (B-type). The chemical structures of these esters were discussed by comparing visual absorption, ¹H nuclear magnetic resonance, X-ray diffraction, electron spin resonance, excitation, emission and infrared spectra.
The color of riboflavin tetraesters in the solid state did not rely upon the kinds of ester groups but upon the interactions between their isoalloxazine groups.