A diaminostilbene dye as a hydrophobic probe for proteins

Abstract

A monobenzoylated derivative of 4,4′-diaminostilbene 2,2′-disulfonate was found to be one of the compounds that showed very low fluorescence in water but fluoresced considerably in solvents of low polarity and when bound to certain proteins. The dye (p K a approx. 3.4) was found to form a 1:1 complex with human serum albumin at pH 8.1 with about 100-fold intensification of fluorescence and with the red shift of the absorption maximum and the blue shift of the emission maximum. The fluorescence quantum yield, emission maximum and band width of this dye as a whole varied as a function of solvent polarity, though the quantum yield was considerably influenced by viscosity and the type of chemical grouping of solvents. Several lines of evidence have shown that the interactions between the dye and certain proteins are hydrophobic in nature. Therefore, this dye is considered to be useful for the survey of apolar binding sites of protein molecules.