Monolayer characteristics of some glycolipids at the air-water interface.

Surface pressure and surface potential versus molecular area data have been obtained for some galactosyldiglycerides and some galactosphingolipids at the air-water interface. The physical states of galactolipid monolayers (and bilayers) parallel those of the phospholipids. The molecular packing of the monolayers is determined primarily by the interactions between the hydrocarbon chains and chain melting causes the transition from condensed to expanded monolayer. Thus the long saturated chain cerebrosides from myelin have high chain-melting temperatures and form condensed monolayers with the chains in a quasi-crystalline array. The galactosyldiglycerides from chloroplast membranes contain polyunsaturate chains and form liquid-expanded monolayers. The surface potentials of monolayers of neutral galactosyldiglycerides are similar to those of equivalent lecithins; the contributions of the hydrated galactose and phosphorylcholine moieties to the surface potential are approximately equal. The various galactosphingolipid monolayers studied have quite different surface potentials; this indicates that relatively small variations in molecular structure which do not lead to appreciable changes in the average packing density can cause large changes in surface potential.