Chain order/disorder phospholipid monolayers

A FIGURE 5-7 Gel and fluid forms of the phospholipid bilayer. (Top) Depiction of gel-to-fluid transition. Phospholipids with long saturated fatty acyl chains tend to assemble into a highly ordered, gel-like bilayer in which there is little overlap of the nonpolar tails in the two leaflets. Heat disorders the nonpolar tails and induces a transition from a gel to a fluid within a temperature range of only a few degrees. As the chains become disordered, the bilayer also decreases in thickness. Bottom) Molecular models of phospholipid monolayers in gel and fluid states, as determined by molecular dynamics calculations. 

From studies of the interactions between lipopolysaccharide and phosphatidyl ethanolamine in molecular monolayers at air-water interfaces, it was concluded that each lipopolysaccharide molecule is surrounded by approximately sixteen phosphatidyl ethanolamine molecules. The hydrocarbon chains of lipopolysaccharides can undergo a reversible thermal order-disorder transition, as shown by thermal phase-transition studies.The ordered conformation of lipopolysaccharides interpreted from wide angle JT-ray studies is considered less developed than that in normal phospholipid bilayers. 

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