Curvature-induced conformational changes of carbonyl groups in lipid membranes

FRIAS, M. DE LOS ANGELES; DIAZ, SONIA; DISALVO, E ANIBAL

Buenos Aires

Workshop; International worshop on INfrared Spectroscopy Applied to Biological and Biomimetic Systems; 2007

Grupo Fisicoquimica de Membranas lipidicas

Carbonyl groups in the ester PC is a hydration center of the lipid membranes. It has been shown that the CO stretching band can be deconvoluted in two narrower bands. This has been ascribed to two populations of carbonyls: one hydrated and another poorly hydrated. These results suggest that the carbonyls are directed to media of different polarities such as some of them are pointing to the aqueous phase the other towards the hydrocarbon core. The populations are the dynamical results of the oscillations of the sn1 and sn2 carbonyls across the hydrocarbon- water interface. As the modulation of the hydration properties of the lipid interphase appears essential for biological functions, it was of interest to study this distribution in conditions in which the bilayer was modified by temperature and by water content. For this reason we determined the separation of the deconvoluted bands in planar gel phase and ripple gel phase. It was shown that when ripples were formed the separation was the maximum achieved. In contrast, when the bilayer was in the planar gel the deconvolution was misleading since the separation of the two bands was less than 10 cm-1. The separation of the carbonyl population in the ripple phase is congruent with the appearance of defects in the bilayer onto which harpoons molecules can be inserted. In addition, when the planar gel phase was subject to an osmotic hypertonic shock the separation of the carbonyls was higher and defects were formed. It is concluded that both spontaneous and induced curvature affect the orientation of the carbonyls change the exposure to water and hence the hydration degree of the interface, at least in locally in restricted domains. 61