Neutral and cationic sulfonamido derivatives of the fluorescent probe 2-p-toluidinylnaphthalene-6-sulfonate. Properties and mechanistic implications

Abstract

The sensitivity of the fluorescence energy of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) to apparent solvent polarity is considerably greater in methanol-water mixtures and lower primary alcohols than in higher primary alcohols or solvents containing no hydroxyl groups. It is suggested that the behavior of TNS in lower alcohols and their mixtures with water is an anomalous result of the combination of general polarity influences and chanes in the nature of specific interactions of the probe with hydroxyl groups of such solvents. Upon conversion of the sulfonate group of TNS to sulfonamido, the biphasic behavior observed in alcohols is eliminated, and fluorescent probes are obtained which have more nearly equal sensitivites to polarity in the alcohols and nonhydroxyl solvents. The sulfonamido fluorescent probes are more sensitive to general environmental polarity than TNS, and are superior as probes of environmental polarity.