Interphase Properties of Lipid Membranes II: Does FTIR allow to differentiate hydration sites in phospholipids?

ANTONIO S. ROSAS; JIMENA P. CEJAS; HUGO A. PÉREZ; DISALVO, ANIBAL

San Luis

Congreso; VIII Encuentro de Física y Química de Superficies; 2018

The physical state of water in lipid membranes has a determinant role in the physiological reactions. Water  sorption  characteristics  are  reflective  of  the  chemical  and  structural  composition  of  lipid membranes and the temperature at which hydration takes place. Changes in the sorption characteristics with  temperature  and  hydration  level  suggest  that  water  induces  structural  changes  that  can  be confirmed  and  correlated  with  molecular  vibration  frequencies  by  FTIR-ATR  techniques.  The  main purpose of this work is to demonstrate that FTIR is a suitable technique to study and differentiate the structural changes that take place during water sorption in a lipid membrane. Water sorption in lipids can take place at different sites characterized by different affinities: strong binding related to Phosphate and Carbonyl groups, weak ones related to confined water between acyl chains, and water binding to already  adsorbed  water  molecules.  D´Arcy/Watt  mathematical  model was  developed  to  describe sorption on a wide range of systems considering different energies of sorption sites and it?s a convenient model  to  describe  water  sorption  in  membranes.  Dipalmitoyl  phosphatidylcholine  liposomes  (DPPC) were  selected  to  apply  D´Arcy/Watt  model.  DPPC  membranes  present  saturated  bonds  and  the  two main strong hydration sites: phosphate and carbonyl groups. It is also important to consider acyl chains as a new center of hydration. The relevance of this data in relation to the dynamic properties of lipid bilayers are discussed in correlation to fluorescence and monolayers results (See poster I and III).