FLUORESCENCE SPECTROSCOPY OF 9-ANTHROYLOXY FATTY-ACIDS IN SOLVENTS

A series of anthroyloxy fatty acid (AF) fluorescent probes, with the a nthroyloxy group covalently linked at various positions along the alky l chain, were studied in solvents exhibiting a wide range of polarity and hydrogen-bond donor (H-d) and acceptor (H-a) ability. These probes were sensitive to the solvent polarity as reflected by the Stokes' sh ift observed in steady state fluorescence. As determined by multi-line ar regression analysis of the observed Stokes' shift and solvent param eters, such as orientation polarizability (Delta f), H-d and H-a of th e solvents, all the probes were sensitive to the H-d of solvents but w ere not affected by the H-a of solvents except the 2-AF. Due to the pr oximity of the polar headgroup to the fluorophore, it appears that som e intramolecular hydrogen-bonding is present in 2-AF, an interaction t hat is sensitive to the pH of the solvent, but is less sensitive to th e H-d and H-a of the solvents. Fluorescence lifetimes measured by the multi-frequency phase-modulation technique in mixtures of hexane and e thanol reflect a modified Stern-Volmer behavior suggesting the second solvent, ethanol, specifically interacts with the probe, in part throu gh collisional quenching. Also, the lifetime data were sensitive to ve ry low concentrations of the second solvent (0-0.1%, by vol.). The res ults from this study provide insight into the intrinsic differences be tween the different AF positions that must be taken into consideration while investigating the dynamics of lipid bilayer systems. Moreover, this study illustrates the utility and resolving power of lifetime bas ed measurements needed for the interpretation of heterogeneous biophys ical environments.