TABLE 1.

Summary of experimental methods used to characterize domain formation and some physicochemical properties in bilayers

Experimental method and measured characteristic	References
Deuterium quadrupole splittings: order parameters	29,31,36,38,39,49
Vesicle deformation and orientation in a magnetic field: bending energy	29
Micropipet aspiration: area expansion modulus	29,31,50
Fluorescence microscopy: lateral organization	44,45
Fluorescence correlation spectroscopy: lateral diffusion	45
Permeability of water, small molecules, and ions	33,34,36,51,52
Fluorescence quenching: domain stability	25,40,43,53
Triton X100 solubility: domain packing	25,35,40,43
Fluorescence anisotropy: domain packing	28,40,52,53
Dynamic light scattering: lateral tension, surface viscosity	32
Differential scanning calorimetry: transition temperatures and enthalpies	26,35,38,49
Resonance energy transfer: domain formation	35
Pulsed field gradient NMR: lateral diffusion	11–15,18,37
Electron paramagnetic resonance: order parameters	39

The l_o phase is characterized by a high degree of ordering of the lipids, which results in large order parameters, stiffer and less compressible membranes, low lateral diffusion, low permeability, resistance to Triton X100 solubilization, and high fluorescence anisotropy. The effectiveness of different sterols in changing these characteristics is utilized to rank their domain-forming ability.