Basic Principles of Deuterium and Phosphorus-31-Magnetic Resonance
Membranes are ordered fluids and because of this have a number of properties in common with liquid crystals. Most important, the normal to the surface of the lipid bilayer constitutes an axis of motional averaging. From an optical point of view the membrane therefore behaves like an uniaxial crystal with the bilayer normal as the optical axis. This unique axis of the fluid bilayer is also called the director \(\vec n\). For the sake of the argument let us represent the phospholipids constituting the bilayer by rigid rods. If we follow the movements of an individual rod over a long enough period of time the most probable orientation of the molecule will be parallel to the director axis. However, due to thermal energy the molecules will continuously execute angular excursions around this preferred orientation and an instantaneous picture may look as is illustrated in figure 1. As a quantitative measure for the angular excursions and fluctuations around the director \(\vec n\) the concept of order parameters has been introduced .
KeywordsLipid Bilayer Quadrupole Splitting Fluid Bilayer Angular Excursion Selective Deuteration
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