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We have synthesized 1,3-di-O-phytanyl-2-O-(glycosyl) glycerols possessing maltooligosaccharide headgroups, MalN(Phyt)2, as model archaebacterial glycolipids (the number of glucose units N = 1, 2, 3, and 5) and investigated the phase behavior of the lipid/water systems using small-angle X-ray scattering and differential scanning calorimetry. The hydrated-solid to liquid-crystalline phase transition temperatures of MalN(Phyt)2 are well below 0, so that MalN(Phyt)2 are in a liquid crystalline state above 0. The structures of the aqueous MalN(Phyt)2 are largely determined by N; a weakly birefringent mesophase for a glucolipid, Glc(Phyt)2, an HII phase for Mal2(Phyt)2, and an La phase for Mal3(Phyt)2 and Mal5(Phyt)2. This indicates an increasing tendency for the MalN(Phyt)2 monolayers to curve toward apolar regions with increasing N. The salient feature of the phytanyl chain lies in significantly larger cross section areas of the lipids at the hydrophobic part-headgroup interface (e.g.,`1.0 nm2/lipid for an La phase) compared with those of the straight-chained counterparts (0.65-0.75 nm2/lipid). A state of alkyl chain disorder appears similar in both phytanyl- and straight-chained lipids. The phase behavior of MalN(Phyt)2 is compared with that of straight-chained glycolipids.
