title: Temperature- and pressure-dependent phase behavior of monoacylglycerides monoolein and monoelaidin.
abstract: We used x-ray and neutron diffraction to study the temperature- and pressure-dependent structure and phase behavior of the monoacylglycerides 1-monoelaidin (ME) and 1-monoolein (MO) in excess water. The monoacylglycerides were chosen for investigation of their phase behavior because they exhibit mesomorphic phases with one-, two-, and three-dimensional periodicity, such as lamellar, an inverted hexagonal and bicontinuous cubic phases, in a rather easily accessible temperature and pressure range. We studied the structure, stability, and transformations of the different phases over a wide temperature and pressure range, explored the epitaxial relations that exist between different phases, and established a relationship between the chemical structure of the lipid molecules and their phase behavior. For both systems, a temperature-pressure phase diagram has been determined in the temperature range from 0 to 100 degrees C at pressures from ambient up to 1400 bar, and drastic differences in phase behavior are found for the two systems. In MO-water dispersions, the cubic phase Pn3m extends over a large phase field in the T,p-plane. At temperatures above 95 degrees C, the inverted hexagonal phase is found. In the lower temperature region, a crystalline lamellar phase is induced at higher pressures. The phases found in ME-water include the lamellar crystalline Lc phase, the L beta gel phase, the L alpha liquid-crystalline phase, and two cubic phases belonging to the crystallographic space groups Im3m and Pn3m. In addition, the existence of metastable phases has been exploited. Between coexisting metastable cubic structures, a metric relationship has been found that is predicted theoretically on the basis of the curvature elastic energy approximation only.
authors.affiliation: University of Dortmund, Institute of Physical Chemistry I, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Czeslik
authors.forename: R
authors.initials: R
authors.lastname: Winter
authors.forename: G
authors.initials: G
authors.lastname: Rapp
authors.forename: K
authors.initials: K
authors.lastname: Bartels
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D005989:Glycerides / Q000737:chemistry*; D066298:In Vitro Techniques; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D009502:Neutrons; D011312:Pressure; D012542:Scattering, Radiation; D013696:Temperature; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D005989:Glycerides; D014867:Water; C005953:monoolein