title: Aqueous-phase behavior and vesicle formation of natural glycolipid biosurfactant, mannosylerythritol lipid-B.
abstract: Mannosylerythritol lipids (MELs) are one of the most promising glycolipid biosurfactants produced by yeast strains of the genus Pseudozyma. In this study, the aqueous-phase behavior of a new monoacetyl MEL derivative, 1-O-beta-(2',3'-di-O-alka(e)noyl-6'-O-acetyl-d-mannopyranosyl)-d-erythritol (MEL-B), was investigated using polarized optical microscopy, small-angle X-ray scattering (SAXS), confocal laser scanning microscopy (CLSM), and differential scanning calorimetry (DSC). The present MEL-B was found to self-assemble into a lamellar (L(alpha)) phase over remarkably wide concentration and temperature ranges. According to SAXS measurement, the interlayer spacing (d) was estimated to be almost constant (about 4.7 nm) at the low MEL-B concentration (<or=60 wt.%) region where the L(alpha) phase is in equilibrium with the excess water phase (L(alpha)+W). On the other hand, at high MEL-B concentration (>60 wt.%) region, the d-spacing gradually decreased to 3.1 nm with an increase in the MEL-B concentration. The thermal stability of the liquid crystalline phase was investigated by DSC measurement. The obtained L(alpha) phase was found to be stable up to 95 degrees C below a MEL-B concentration of 85 wt.%; then, the melting temperature of the liquid crystalline phase dramatically decreased with an increase in MEL-B concentration (above 85 wt.%). Furthermore, we found relatively large vesicles (1-5 microm) at the low MEL-B concentration using CLSM observation. The trapped volume of the obtained MEL-B vesicle was estimated to be about 0.42 microL/mumol by glucose dialysis method. These results suggest that the natural glycolipid biosurfactant, the newly found MEL-B, would be useful in various fields of applications as an L(alpha) phase- and/or vesicle-forming lipid.
authors.affiliation: Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
authors.forename: Wannasiri
authors.initials: W
authors.lastname: Worakitkanchanakul
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Imura
authors.forename: Tokuma
authors.initials: T
authors.lastname: Fukuoka
authors.forename: Tomotake
authors.initials: T
authors.lastname: Morita
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
authors.forename: Ratana
authors.initials: R
authors.lastname: Rujiravanit
authors.forename: Sumaeth
authors.initials: S
authors.lastname: Chavadej
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Minamikawa
authors.forename: Dai
authors.initials: D
authors.lastname: Kitamoto
mesh_terms: D002152:Calorimetry, Differential Scanning; D006017:Glycolipids / Q000737:chemistry*; D053838:Scattering, Small Angle; D013237:Stereoisomerism; D013501:Surface-Active Agents / Q000737:chemistry*; D053835:Unilamellar Liposomes / Q000138:chemical synthesis*; D014587:Ustilaginales / Q000737:chemistry / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D006017:Glycolipids; D013501:Surface-Active Agents; D053835:Unilamellar Liposomes