Solution electronic spectra of brassinosteroid and a synthesized conjugate of a steroid and a fluorescent label

Abstract

Electronic absorption spectra of 24-epicastasterone and 24-epibrassinolide solutions have been recorded and analyzed. The long-wavelength band in solution spectra of the former steroid with maxima in the region 292–286 nm is assigned to the electronic nπ*-transition of a carbonyl chromophore. The latter steroid contains an O-C=O group, for which the extinction coefficient in this spectral region is approximately one order of magnitude less. These differences can be used to identify the studied steroids. A method to synthesize the conjugate of 24-epicastasterone with a fluorescent label, dansylhydrazine, which shows intense fluorescence and absorption, is described. Absorption spectra of the label and conjugate in diethylether, tetrahydrofuran, ethanol, and acetonitrile solutions are practically independent of the solvent properties. The exceptions are solutions of the conjugate in hexane and water. All investigated solutions of label and conjugate show intense fluorescence. As the dielectric constant of the solvent increases, the fluorescence spectra shift to long-wavelength. The fluorescence energetic and time characteristics of both the label and conjugate are similar, which enables the conjugate to be used in developing a method for immunofluorescent analysis of the brassinosteroid 24-epicastasterone.