Thermotropic and Lysotropic Mesomorphism of Phospholipids

Phase transition can be followed by various physical techniques, such as differential scanning calorimetry (DSC), 2H-NMR, and electronic spin resonance (ESR), Fourier transform infrared (FTIR), and fluorescence spectroscopy. The various methods have been reviewed and their characteristics compared [97] (see also Chapter 3). 

In addition to this thermotropic mesomorphism, a lysotropic mesomorphism is observed [98]. The phase transition temperature, Tt, for the transition from the crystalline to the liquid crystalline state decreases as a function of water content. The decrease in Ttis due to destabilization of the crystal lattice in the head group region by water molecules. This, in turn, decreases the interaction between the fatty acid chains. When the water content reaches a certain level, the phospholipids assume a thermodynamically optimal arrangements whereby the fatty acids are directed to the 

2-distearoyl-sn-3-glycero-3-phosphatidylcholine numbers preceding PC indicate wether both or only the second chain is substituted 

Upon heating, very pure uniform phospholipids show an additional small transition below the crystalline to liquid crystalline phase transition. According to Janiak et al. [104], this is due to a structural change in the head groups. The occurrence of pretransition is mainly determined by the structure of the head groups and their environment. 

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