Phase Characteristics of 1-Monopalmitoyl-rac-glycerol Monolayers at the Air/Water Interface

Abstract

1-Monopalmitoyl-rac-glycerol is omnipresent in numerous biological and applied systems. Systematic GIXD measurements of 1-monopalmitoyl-rac-glycerol monolayers are carried out over a large pressure interval at 5, 10, and 15 °C to construct the phase diagram on the basis of reliable 2D lattice structures. These studies are complemented by other monolayer characteristics, such as π-A isotherms and mesoscopic domain topographies. A phase transition is found between the two orthorhombic structures with NN and NNN tilted alkyl chains at low temperatures (5 and 10 °C). It increases linearly with increasing temperature. With a further increase in temperature to 15 °C, only NN-tilted orthorhombic lattices are observed in the whole pressure region. The cross-sectional area, A0, is less affected by surface pressure and temperature and amounts to values of between 19.7 and 19.8 Å(2), as expected for a rotator phase at the lower limit. The tilt angle t with respect to the surface normal decreases with increasing pressure and is only slightly influenced by the temperature. The transition pressure to untilted alkyl chains, as determined by the extrapolation of 1/cos(t) to zero tilt angle, is >50 mN/m for all temperatures. The results of lattice distortion d versus sin 2(t) suggest for 10 and 15 °C the tilt of the aliphatic chains as the reason for the monolayer lattice distortion whereas at 5 °C the nonzero-tilt-angle intercept d0 could be an indication of the prevention of hexagonal packing. The generic π-T phase diagram of racemic monoacylglycerol monolayers is constructed on the basis of the phase diagrams of 1-monopalmitoyl-rac-glycerol and 1-monostearoyl-rac-glycerol, which shows that for 1-monopalmitoyl-rac-glycerol monolayers the oblique phase can occur only close to and below 0 °C. The possible phase behavior of other racemic monoacylglycerol monolayers with alkyl chain lengths of C14 and C20 is discussed on the basis of the generic phase diagram.

Influence of linkage type (ether or ester) on the monolayer characteristics of single-chain glycerols at the air–water interface

“…Generic phase diagrams can be obtained by systematically shifting the temperature axis by a certain value per additional methylene group. 31 In the present case, we can compare the first-order phase transition between the liquid and the condensed phases. Doing so, one has to shift the temperature axis of the C16-compound by 19 degrees.…”

Assembly of the Cutin Polyester: From Cells to Extracellular Cell Walls

“…A non-assisted diffusion could occur based on the peculiar self-assembly properties of cutin precursors. In this aqueous and polysaccharide-rich environment, it is important to take into account the self-assembly properties of MAG and their adsorption at air-water and oil-water interfaces as other surfactants [ 48 ]. In aqueous media MAG can form lyotropic liquid-crystalline mesophases such as cubic, reverse hexagonal, or lamellar mesophases according to the structure of the fatty acyl chain, temperature and water content [ 49 ].…”

Thermodynamics of interaction of ionic liquids with lipid monolayer

“…Another thermodynamic parameter, the excess Gibbs free energy involved in the mixing of two chemical components, could provide us with information about the type of interactions between the components. In a recent paper, Vollhardt and Brezesinski (2016) characterized the phases of 1-monopalmitoyl-rac-glycerol monolayer at the airwater interface by studying the enthalpy and entropy changes associated with the in-plane organization of these molecules. In this work, they have used the two-dimensional Clausius-Clapeyron equation to obtain the change in enthalpy due to the liquid extended to liquid condensed phase transition.…”