ENERGY-TRANSFER AND FORMATION OF EXCIPLEX BETWEEN THIACYANINE AND ACRIDINE-ORANGE FACILITATED BY ANIONIC BIOPOLYMERS AND SYNTHETIC-POLYMERS

The fluorescence of thiacyanine (THIA) dye is greatly enhanced on bind ing to polyanions due to the reduction in internal conversion of the e xcitation energy of the dye. Glycosaminoglycans (chondroitin sulphates (CS) A, B and C; heparin) and the synthetic polyanion poly(vinylsulph ate) (PVS), in addition to enhancing the fluorescence of THIA, facilit ate the formation of an exciplex between excited THIA and cool acridin e orange (AO), both bound to the polymers. Of the three chondroitin su lphates, chondroitin sulphate C (CSC) is the most efficient in enhanci ng the fluorescence of THIA and facilitating the formation of an excip lex. The efficiency of heparin in this respect is comparable with that of CSC, and poly(vinyl sulphate) is even more efficient. In 20% (v/v) ethanol the association constant of THIA-CSC is reduced to one-tenth of its value in water. Aqueous ethanol also partially inhibits exciple x formation between the two dyes bound to chondroitin sulphates, altho ugh the effect is less prominent in the case of CSC.