Effect of temperature on the induced cotton effects of acid polysaccharide-basic dye complexes.

Abstract

AbstractThe induced Cotton effect of some acid polysaccharide–thiazine dye complexes were studied at various temperatures. When the equivalent ratio of the anionic site of the polymer to the cationic dye was near unity, all the complexes examined showed remarkable Cotton effects corresponding to their absorption bands in the visible and ultraviolet regions, at neutral pH and room temperature. Although the structure of the hyaluronate complex resembles the carbohydrate backbone, the sign of the Cotton effects was opposite that of chondroitin sulfate complexes.When the temperature was raised, the hyaluronate–toluidine blue complex decreased the metachromatic shift in the absorption spectrum gradually; the amplitude of the Cotton effects of this complex decreased also. With a polysaccharide which has a carboxylate group as its only anionic site (such as carboxymethylcellulose or pectic acid), a similar effect of temperature was observed on its induced Cotton effects.With the chondroitin 4‐sulfate–toluidine blue complex, some reverse of the metachromatic shift was observed at higher temperature. However, the amplitude of its Cotton effects decreased up to 70 °C, then the sign of the effects reversed and the amplitude subsequently increased. A similar inversion of the sign of the Cotton effects was found with the chondroitin 6‐sulfate–toluidine blue complex, but at a lower temperature (about 40 °C).Charonin sulfate, a highly sulfated cellulose‐like glucan from a marine mollusca, showed a marked metachromatic effect on methylene blue even at the elevated temperature. The induced Cotton effects of this complex were also affected by temperature and the inversion of the sign was observed.When the pH was lowered, the amplitude of the Cotton effects of the hyaluronate‐toluidine blue complex decreased and diminished at pH 3, at room temperature. With chondroitin 4‐sulfate, the induced Cotton effects were remarkable at such a low pH; however, the amplitude of the effects decreased with elevated temperature and no inversion was observed. The optical rotatory dispersion of the chondroitin 6‐sulfate–toluidine blue complex was reversed by acidifying to pH 3, and the amplitude of the Cotton effects decreased by elevating the temperature.