1,8-Naphthalimide derivatives as probes for protein surface hydrophobicity

Four 4-aryl-N-methoxyethyl-1,8-naphthalimide derivatives were synthesized and evaluated for their fluorescent properties. All four compounds, 4-(p-methoxy)- 3a, 4-(p-amino)- 3b, 4-(p-dimethylamino)- 3c, and 4-(p-acetamido)- 3d are highly fluorescent in chloroform, but their fluorescence intensity is drastically decreased in polar solvents such as DMSO and methanol. Derivative 3c, in particular, showed a 699-fold fluorescence quenching in methanol, as compared in chloroform at 10 mu M dye concentration. Furthermore, dilution of DMSO solutions of probes 3a, 3b and 3d with water led to drastic decrease in fluorescence intensity, and virtually complete fluorescence quenching in the case of 3d. In aqueous solutions containing 3a or 3b, the presence of bovine serum albumin led to 80- and 50-fold increases in fluorescence intensity, respectively.