Phase behavior of synthetic phytanyl-chained glycolipid/water systems

We have synthesized 1,3-di-O-phytanyl 2-O-(glycosyl)glycerols possessing maltooligosaccharide head-groups, Mal(N)(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 Mal(N)(Phyt)(2) are well below 0 degrees C, so that Mal(N)(Phyt)(2) are in a liquid crystalline state above 0 degrees C. The structures of the aqueous Mal(N)(Phyt)(2) are largely determined by N; a weakly birefringent mesophase for a glucolipid, Glc(Phyt)(2), an H-II phase for Mal(2)(Phyt)(2), and an L-alpha phase for Mal(3)(Phyt)(2) and Mal(5)(Phyt)(2). This indicates an increasing tendency for the Mal(N)(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., similar to 1.0 nm(2)/lipid for an L-alpha phase) compared with those of the straight-chained counterparts (0.65-0.75 nm(2)/lipid). A state of alkyl chain disorder appears similar in both phytanyl- and straight-chained lipids. The phase behavior of Mal(N)(Phyt)(2) is compared with that of straight-chained glycolipids.