A comparative monomolecular film study of 1,2-di-O-palmitoyl-3-O-(alpha- and beta-D-glucopyranosyl)-sn-glycerols.
The polar headgroup contribution to monolayer behavior of dipalmitoylglucosylglycerol has been examined through studies of 1,2-di-O-palmitoyl-3-O-(alpha-D-glucopyranosyl)-sn-glycerol (di-16:0-alpha GlcDG) and 1,2-di-O-palmitoyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol (di-16:0-beta GlcDG) in which the sugar headgroup is linked via an alpha or beta linkage to the diacylglycerol moiety. The results indicate that the limiting areas per molecule of the resultant condensed states are smaller than those of the corresponding phosphatidylcholine (DPPC) but larger than those of dipalmitoylphosphatidylethanolmine (DPPE). In the expanded state, while the areas per molecule are similar to those of DPPC at low pressures, both glycolipids occupy smaller areas at higher pressures. The expanded-state areas of the glucolipids are also slightly greater than those of DPPE. The initial compressional phase transition pressure of the glucolipid liquid-expanded/liquid-condensed transition (pi t) is, however, less sensitive to temperature than are the pi t values of phospholipids. Both of these effects must relate to strong headgroup/water interactions, which, in turn, result in a stabilization of the liquid-expanded states. In the expanded states the alpha anomers are slightly less tightly packed than the beta anomers, as is indicated by the somewhat higher areas per molecule of the expanded states and the lower transition temperatures. These differences in chain-melting temperatures are slightly smaller than those observed in bilayers. While the areas per molecule of the dipalmitoyl glucolipids are greater than those of dipalmitoylphosphatidylethanolamine, they nevertheless exhibit a greater tendency to form nonbilayer structures. Such observations indicate that other factors besides geometric shape play a role in bilayer/nonbilayer transitions.
Asgharian
B
B
Department of Chemistry, State University of New York, Buffalo 14214.
Cadenhead
D A
DA
Mannock
D A
DA
Lewis
R N
RN
McElhaney
R N
RN
D006017:Glycolipids; D007536:Isomerism; D008051:Lipid Bilayers; D008962:Models, Theoretical; D010743:Phospholipids; D011312:Pressure; D013329:Structure-Activity Relationship; D013499:Surface Properties; D013816:Thermodynamics
D006017:Glycolipids; D008051:Lipid Bilayers; D010743:Phospholipids; C061753:1,2-di-O-palmitoyl-3-O-(glucopyranosyl)glycerol