FLUORESCENCE MONITORING OF THE HYDROPHOBIC SURFACE OF DEXTRIN USING P-TOLUIDINONAPHTHALENESULFONATE

The effect of the linear oligosaccharides dextrin (alpha-1a,4e-D-gluco pyranose) and dextran (alpha-1,6-D-glucopyranose) on the emission prop erties of 2-(p-toluidino)-6-naphthalenesulfonate (TNS) has been studie d in aqueous solution. TNS exhibits a 30-fold fluorescence enhancement on binding to dextrin, while with dextran there is only a marginal in crease in the emission intensity. The polarity values of the binding s ites are estimated by comparing the nonradiative rates of TNS with tho se in aqueous dioxane-water mixtures. The results indicate that the bi nding surface of dextrin is markedly less polar than that of dextran. This difference is attributed to the differing stereochemical constrai nts imposed on the two chains. The binding constants of TNS with the t wo polysaccharides in pure water have been determined in the presence and absence of several salting-in denaturants and salting-out reagents . Salting-in agents cause a decrease in the number of TNS molecules bo und to the dextrin surface and an increase in the local polarity, whil e the salting-out agent LiCl increases the number of TNS molecules bou nd to dextrin. The interaction of TNS with dextran, however, is found to be very weak even in the presence of LiCl. Energy minimization stud ies reveal a hydrophobic surface for dextrin while no such amphiphilic ity is observed in dextran.