Preparation of 7-(p-Substituted-Benzylamino)-4-Nitrobenzoxadiazole Derivatives and the Study of their Fluorescent Properties in Solution

Abstract

The problem. The objective of this study was to synthesize a series of derivatives of 7-(benzylamino)-4-nitrobenzofurazan and study their fluorescent behavior in aqueous-nonaqueous solvent systems. The parent compound has been used by others as a fluorescent probe to determine the conformation changes of bovine trypsinogen and bacterial libosomes. Fluorescent probes have been used to: (l) establish the degree of polarity of a particular region of a protein; (2) measure distances between groups in a protein; (3) determine the extent of a flexibility of a protein; and (4) measure the rate of very rapid conformational transitions. By selecting those fluorescent probe molecules that have structural features similar to an enzymic substrate molecule, it is expected that the probe molecule will exhibit an affinity for the enzyme. Thus, it may be expected that the probe molecule will be specifically inserted into enzymes to reveal facets of their structure and dynamics. Findings. This study resulted in the characterization of two new compounds, 7-(p-methylbenzylamino)-4-nitrobenzofurazan (BBD-CH3) and 7-(p-chlorobenzylamino)-4- nitrobenzofurazan (BBD-Cl) which may have use as fluorescent probes. The quantum yield studies of this study indicated that the para substituent makes these compounds more sensitive to solvent polarity. No NMR spectra have been reported in the literature. The NMR spectra obtained in this study gave additional identification of these compounds. The changes in quantum yields and wavelengths of maximum emission with solvent polarity changes are reminiscent of other fluorescent probes which are important in protein conformation studies.