title: Aqueous-phase behavior of natural glycolipid biosurfactant mannosylerythritol lipid A: sponge, cubic, and lamellar phases.
abstract: The aqueous-phase behavior of mannosylerythritol lipid A (MEL-A), which is a glycolipid biosurfactant produced from vegetable oils by yeast strains of the genus Pseudozyma, was investigated using polarized optical microscopy, small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC). MEL-A was found to self-assemble into a variety of distinctive lyotropic liquid crystals including sponge (L3), bicontinuous cubic (V2), and lamella (Lalpha) phases. On the basis of SAXS measurements, we determined the structure of the liquid crystals. The estimated lattice constant for Lalpha was 3.58 nm. DSC measurement revealed that the phase transition enthalpies from the liquid crystal to the fluid isotropic phase were in the range of 0.22-0.44 kJ/mol. Although the present MEL-A phase diagram closely resembled that obtained from relatively hydrophobic poly(oxyethylene) or fluorinated surfactants, the MEL-A L3 region was spread considerably over a wide temperature range (20-65 degrees C) compared to L3 of those surfactants: this is probably due to the unique structure which is molecularly engineered by microorganisms. In this paper, we clarify the aqueous phase diagram of the natural glycolipid biosurfactant MEL-A, and we suggest that the obtained lyotropic crystals are potentially useful as novel nanostructured biomaterials.
authors.affiliation: Research Institute for Innovation in Sustainable Chemistry and Nanoarchitectonics Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5-2, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Imura
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Hikosaka
authors.forename: Wannasiri
authors.initials: W
authors.lastname: Worakitkanchanakul
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
authors.forename: Masaaki
authors.initials: M
authors.lastname: Konishi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Minamikawa
authors.forename: Dai
authors.initials: D
authors.lastname: Kitamoto
mesh_terms: D001688:Biological Products / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D006017:Glycolipids / Q000737:chemistry*; D015394:Molecular Structure; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D001688:Biological Products; D006017:Glycolipids; D013501:Surface-Active Agents; C439671:mannosylerythritol lipid; D014867:Water