Spectroscopic characterization of 2-amino-N-hexadecyl-benzamide (AHBA), a new fluorescence probe for membranes

We report the results of investigation on the spectroscopic properties of a new fluorescent lipophylic probe. The fluorophore o-aminobenzoic acid was covalently bound to the acyl chain hexadecylamine, producing the compound 2-amino-N-hexadecyl-benzamide. The behavior of the probe was dependent on the polarity of the medium: absorption and emission spectral position, quantum yield and lifetime decay indicate distinct behavior in water compared to ethanol and cyclohexane. The probe dissolves in the organic solvents, as indicated by the very low value of steady state fluorescence anisotropy and the short rotational correlation times obtained from fluorescence anisotropy decay measurements. On the other hand, the probe has low solubility in water, leading to the formation of aggregates in aqueous medium. The complex absorption spectrum in water was interpreted as originating from different forms of aggregation, as deduced from the wavelength dependence of anisotropy parameters. The probe interacts with surfactants in pre-micellar and micellar forms, as observed in experiments in the presence of sodium n-dodecylsulphate (SDS), n-cetyltrimethylammonium bromide (CTAB); 3-(dodecyl-dimethylammonium) propane-1-sulphonate (DPS) and 3-(hexadecyl-dimethylammonium) propane-1-sulphonate (HPS), and with vesicles of the phospholipid dimiristoyl-phosphatidylcholine (DMPC). The results demonstrate that AHBA is able to monitor properties like surface electric potential and phase transition of micelles and vesicles.