A Multiparametric Fluorescence Probe to Understand
the Physicochemical Properties of Small Unilamellar Lipid Vesicles
in Poly(ethylene glycol)-Water Medium
FDAPT
(2-formyl-5-(4′-N,N-dimethylaminophenyl)thiophene)
efficiently senses the minimum alteration
of lipid bilayer microenvironment with all six different fluorescence
parameters namely emission wavelength, fluorescence intensity, steady-state
anisotropy, and their corresponding time-dependent parameters (Sahu
et al., J. Phys. Chem. B2018, 122,
7308–7318). In the present work, the effect of poly(ethylene
glycol) on the small unilamellar vesicle is demonstrated with the
emission behavior of the FDAPT probe. A medium and a high molecular
weight PEG were chosen to perturb the lipid vesicles. The alteration
of the bilayer polarity, water content inside bilayer, lipid packing
density in the perturbed vesicles reflect significant changes in different
fluorescence parameters of FDAPT probe. The effect of PEG on the unilamellar
vesicle was rationalized with the alteration of the emission behavior,
fluorescence lifetime, steady-state anisotropy and anisotropy decay
of the probe. The simple and convenient fluorescence measurements
provide new insights into the effect of PEG on the packing density,
water volume, micro polarity, and microviscosity of the small unilamellar
vesicle. The physiological understanding was extended to rationalize
the cryoprotecting behavior of PEG.