1-[4-(Trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene: Synthesis, Fluorescence Properties, and Use as a Fluorescence Probe of Lipid Bilayers

1-[4-(Trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), a cationic analogue of diphenylhexatriene (DPH), has photophysical properties that are generally similar to those of DPH. In solution the fluorescence lifetime (r) of TMA-DPH is short (<1.5 ns), but r increases to ~7 ns when the probe is embedded in lipid bilayers at temperatures less than the thermal transition temperature (T_c) of the lipid. The cationic charge ensures that the probe is anchored at the lipid-water interface, most likely with the DPH moiety intercalated between the upper portions of the fatty acyl chains. The profiles of changes in steady-state anisotropies (r_ss) and limiting hindered anisotropies (r_∞) are similar for both TMA-DPH and DPH embedded in lipid bilayers, but values for TMA-DPH even at T >> Tc are generally >0.14, e.g., at 35 °C in 1,2-dimyristoylglycero-3- phosphocholine (DMPC) (cf. 0.03 for DPH in DMPC at 35 °C). Electrostatic interactions of the cationic probe with head groups of phospholipids do not appear to significantly influence the apparent dynamics of the probe. TMA-DPH should prove useful in the study of the dynamics of phospholipid monolayers, e.g., in native or reconsituted lipoproteins.