Triazinylaniline (TA) derivatives as fluorescence probes. Part 2. Steady-state and time-resolved fluorescence anisotropy studies of TA probes in alkanols and in small unilamellar vesicles of phospholipids

Abstract

The fluorescence behaviour is reported of three functionalized triazinylaniline, TA, dye probes p-Et₂C₆H₄C₃N₃(Cl)N(Me)X, where X = C₄H₇, C₁₈H₃₇ and CH₂[CHOH]₄CH₂OH, solubilized in small unilamellar vesicles of dimyristoyl- and dipalmitoyl-L-α-phosphatidylcholines, DMPC and DPPC respectively, and of DMPC–DPPC binary mixtures.

Steady-state fluorescence yields (ca. 0.15) and anisotropies monitor the phospholipid phase transitions; the glucamine dye probe sensitively reflects the rearrangement of phospholipid head groups in the pre-transition region and probably resides in the vicinity of the glycerol backbone. Fluorescence decays of the probes are complex (mean lifetimes ca. 1.2 ns), but are not influenced strongly by the nature of the lipid phase.

For the vesicle-bound probes the fluorescence anisotropy decays rapidly (lifetime ca. 1 ns) from an initial high value (r= 0.30–0.32) to reach a plateau value (range 0.0–0.24) indicative of a restricted angular rotation of the probes which has been related to the nature of the probe tail; in alkanols the anistropic decay is monoexponential and the pseudo-isotropic rotation rate varies linearly with solvent viscosity.