PH RESPONSE OF COLORED COPOLYPEPTIDE HYDROGEL CONTAINING TRYPTOPHAN TREATED WITH TRIFLUOROACETIC-ACID

The coloration phenomenon of L-tryptophan (Trp) treated with trifluoro acetic acid (TFA) was observed under varying pH, i.e., from yellow (ab ove pH 5.5) to red (below pH 4.0). In order to elucidate the coloratio n mechanism, the coloured compounds were fractionated and investigated spectroscopically. It was found that Trp forms a yellow compound cons isting of a tricyclic structure, and that the change in colour with th e variation of pH is due to the dissociation of the nitrogen atom in a n indole ring. Coloured copolypeptide hydrogel containing Trp residues was also prepared by a method similar to that for Trp. The colour cha nge was also observed for the hydrogel. The FH dependence of such memb rane properties as degree of swelling, solute permeability, and the me chanical property was investigated. These properties changed drastical ly in the pH region of the colour change. This can be explained by the dissociation of Trp residues. (C) 1998 Elsevier Science Ltd. All righ ts reserved.