Analysis of Laurdan fluorescence spectra in vesicles formed by esters and ethers lipid

AGUSTIN GONZALES PAZ; GIMÉNEZ, RODRIGO E; FRÍAS, M. DE LOS ÁNGELES; DISALVO, EDGARDO ANIBAL; HUGO A. PÉREZ

San Luis

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Biofísica.; 2019

Sociedad Argentina de Biofísica

Many works study the behaviourof model membranes of varied characteristics using fluorescent probes sensitiveto their environment. Among them Laurdan isspecifically sensitive to the hydration of the membrane interphase. Themembrane interphase has dynamic and dielectric properties different from thoseof the bulk aqueous phase and the hydrophobic region. With this purpose, theGeneralized Polarization (GP) is calculated from the intensity of the emissionand excitation wavelengths.In this work, we report that using differentemission maxima in gel phase and liquid crystalline phase different curves forGP of Laurdan vs temperature can be built. The results show that, for the samelipid vesicles, the curves of GP vs.Temperature differ when thewavelength chosen to perform the calculation is modified. This dependence of GPcurves with wavelength makes it difficult to extract conclusions regarding thepolarity of the membrane. Furthermore, since different lipids present differentmaxima, the choice of wavelengths becomes rather arbitrary and therefore theconclusions misleading. However, using Log-Normal deconvolution a parameteranalogous to GP, independent of the wavelength, can be obtained. This parameter(DS) is obtained by calculating the differencebetween the relative area of the non-relaxable and the relaxable populations ofsolvent molecules (water in the interphase). The log-normal deconvolution of the emission spectra gives thecontributions of relaxable and non-relaxable populations of Laurdan in largeunilamellar vesicles (LUV) of ester and ether lipids, lipids that differ onlyon the kind of bond between the glicerol and the hydrophobic chain that givesdifferent hydration states.Using the DS parameters, we obtain more reliable dataindicating that LUVs of ether lipids present a higher dipolar relaxation(relaxable population) than LUVs of ester lipids.