HYDRATION OF PHOSPHATES IN RELATION TO THE TOPOLOGICAL ARRANGEMENTS OF PHOSPHOLIPIDS IN AQUEOUS SOLUTIONS.

BOUCHET, ANA; FRIAS, M DE LOS ANGELES; DIAZ, S.B.; LAIRION, F.; DISALVO, E.A.

Montevideo

Congreso; 34 Annual Meeting Argentine Biophysical Soc; 2007

Sociedad Argentina de BIofisica

It is well known that molecules with different molecular shapes stabilize in water forming different supramolecular structures. Cylindrically-shaped molecules, such as phosphatidylcholines, stabilize forming lamellar structures. Conical shaped molecules such as lysoPCs forms spherical micelles with the polar groups facing the aqueous phase and segregating the acyl chains. Finally, some inverted-cone molecules such as phosphatidylethanolamines in which the area of the polar groups is lower than that corresponding to the acyl chain stabilized in the hexagonal HII form, which consist of cylinder in which the head groups is oriented to the center of the cylinder. These different arrangements may give place to different exposures of the hydration centers i.e. the phosphate groups. In this work we have determined by FTIR spectrometry the antisymmetric stretching bands of phosphate groups in DMPC, DMPE, DOPE and LysoPC at different temperatures and correlated the position of the band center with the topological phase stable at each condition. When lysoPC micelles are formed, the phosphate groups have a hydration state comparable to DMPC in the gel state. In DOPE and EggPE, in which it is likely the presence of hexagonal HII phases the phosphate groups’ band is displaced to much lower frequencies, suggesting a higher hydration than in the gel state of DMPC. A preliminary sequence of the position of the phosphate from the highest to the lowest frequencies is as follows:   DMPC (gel) > lysoPC (micelles) > DMPE (gel) > DOPE (HII) > eggPC (fluid) > DMPC (fluid)     The influence of the lateral interaction and the hydration on the position of the bands s discussed taking into account the area per groups measured in monolayers.