The material development containing trytophan residues for the visual recognition of the interaction with drugs by its coloration

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We have reported that the coloration phenomenon of L-tryptophan(Trp) treated with trifluoroacetic acid (TFA) was observed with varying pH, i. e., from yellow to red. In order to elucidate the coloration mechanism, the colored compounds were fractionated and investigated. It was found that Trp forms the yellow compound consisting of a tricyclic structure, and that the change in color with the variation of pH is due to the dissociation of the nitrogen atom in the indole ring. The Trp residues within copoly (L-glutamic acid-co-Trp) (GAT) was also found to form the same tricyclic structure by the treatment with TFA and to show the reversible color change from yellow (above pH 8.0) to red (below pH 7.0) through the positive-dissociation at the neutral pH region. The interaction between TFA-treatment GAT (GAT-T) and anionic molecules was investigated by VIS and fluorescence spectrophotometry. The Trp residues within GAT-T were found to electrostatically interact with bulky anionic drugs such as watrfarin (Wf), clofibric acid (Cf) and phenylbutazone (Pb) besides the hydrophobic interaction, resulting in the color change from red to yellow. Release behavior of the anionic drugs from GAT-T microspheres (Ms) was also investigated. The amount and the retention time of the bound anionic drugs in the GAT-T Ms were found to be superior to those for untreatment GAT Ms. Moreover, GAT-T interacts strongly with the anionic drugs in the order of Cf > Pb > Wf. This originates in the acidity of the anionic drugs used.