Water Behavior at the Phase Transition of Phospholipid Matrixes Assessed by FTIR Spectroscopy

Lipid membranes are one of the most important biological matrixes in which biochemical processes take place. This particular lipid arrangement is driven by different water disposition interacting with it, which is related to different water states with different energy levels at the interphase. In our work, we report changes in water content and distinctive water states by Fourier transform infrared (FTIR) spectroscopy of this self-assembled matrix at different water contents and temperatures. To determine whether water properties at lipid interphases depend on the group of the lipid molecule at which it is bound the phase-transition temperature of 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (14:0 diether PC) was followed by the changes in frequency of the different groups of the lipids by attenuated total reflection (ATR)-FTIR spectroscopy at different humidities. A comparison of these two lipids enables us to put into relevance the contribution of the CO groups as a hydration site. These changes were compared with those occurring at the water band, and a value of the enthalpic change was evaluated from them. The -OH stretching in the liquid water IR spectrum is the principal region used to understand its molecular organization (4000-3000 cm^-1). The strength of hydrogen bonding depends on the cooperative/anticooperative nature of the surrounding hydrogen bonds, with the strongest hydrogen bonds giving the lowest vibrational frequencies. Thus, we can use water as a mirror of the membrane state in this kind of biological systems. Different phospholipids associate water at particular modes according to their structures. This may produce modulation of packing and hydration suitable for the incorporation of amino acids, peptides, and enzymes.