Carbonyl Configuration And Hydration Of Curved And Ripples States Of Lipid Interphases

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

Long Beach CA EEUU

Congreso; Biophysical Soc Meeting, IUPAB Congress; 2008

Biophysical Society, IUPAB

The Lâ and the Lá phases of phosphatidylcholine are characterized by the levels of hydration. The Pâ phase is assumed to have an intermediate hydration state between the Lâ (5-7 water molecules per lipid) and the Lá phase (20 water molecules) and has been related with the appearance of ripples.In this regard, defective packing has been detected as a consequence of the coexistence of gel and fluid domains.Carbonyls in the ester union of the phospholipids are distributed in two populations: one of them normal to the bilayer plane and the other parallel to it. The first one is in contact with water and hence, the frequency corresponding to its stretching mode is shifted to lower values with respect to the low hydrated population, which in turn, falls very near to that corresponding to dried phospholipids.In this paper, we show by FTIR analysis that the extents of hydration of the ripples correspond with a clear separation of the center bands corresponding to the two populations. When temperature is decreased and the gel planar phase is attained the difference falls to values that makes impossible to distinguish between the two populations by deconvolution analysis.Compounds that avoid the pretransition produces a shift in the carbonyl population congruent with the disappearance of the ripples phase. In this condition, when an osmotic shock is applied, the separation of the bands returns to those observed in ripples. It is concluded that both spontaneous and induced curvature induces defects at the interphase as consequence of the fluctuations in the orientation and hydration of the carbonyl groups at the water -hydrocarbon interface. This interpretation is compatible with reported values of water penetration beyond that plane.: