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Monoacylglycerol based lipids are highly important modelmembranecomponents and attractive candidates for drug encapsulation and asdelivery agents. However, optimizing the properties of these lipidsfor applications requires a detailed understanding of the thermodynamicfactors governing the self-assembled structures that they form. Here,we report on the effects of hydrostatic pressure, temperature, andwater composition on the structural behavior and stability of inverselyotropic liquid crystalline phases adopted by monolinolein (an unsaturatedmonoacylglycerol having cis-double bonds at carbonpositions 9 and 12) under limited hydration conditions. Six pressure–temperaturephase diagrams have been determined using small-angle X-ray diffractionat water contents between 15 wt % and 27 wt % water, in the range10–40 °C and 1–3000 bar. The gyroid bicontinuouscubic (QIIG) phase is formed at low pressureand high temperatures, transforming to a fluid lamellar (Lα) phase at high pressures and low temperature via a region of QIIG/Lαcoexistence. Pressure stabilizesthe lamellar phase over the QIIGphase; at fixedpressure, increasing the water content causes the coexistence regionto move to lower temperature. These trends are consistent throughoutthe hydration range studied. Moreover, at fixed temperature, increasingthe water composition increases the pressure at which the QIIGto Lαtransition takes place. We discussthe qualitative effect of pressure, temperature, and water contenton the stability of the QIIGphase. [ABSTRACT FROM AUTHOR]

A high pressure cell for small and wide-angle x-ray diffraction measurements of soft condensed matter samples has been developed, incorporating a fully automated pressure generating network. The system allows both static and pressure jump measurements in the range of 0.1–500 MPa. Pressure jumps can be performed as quickly as 5 ms, both with increasing and decreasing pressures. Pressure is generated by a motorized high pressure pump, and the system is controlled remotely via a graphical user interface to allow operation by a broad user base, many of whom may have little previous experience of high pressure technology. Samples are loaded through a dedicated port allowing the x-ray windows to remain in place throughout an experiment; this facilitates accurate subtraction of background scattering. The system has been designed specifically for use at beamline I22 at the Diamond Light Source, United Kingdom, and has been fully integrated with the I22 beamline control systems. [ABSTRACT FROM AUTHOR]

Abstract: Phosphatidylglycerol (PG) is an anionic lipid commonly found in large proportions in the cell membranes of bacteria and plants and, to a lesser extent, in animal cells. PG plays an important role in the regulation and determination of the elastic properties of the membrane. Using small angle X-ray scattering experiments, we obtain that the monolayer spontaneous curvature of dioleoylphosphatidylglycerol (DOPG) is −1/150±0.021nm−1 when measured in 150mM NaCl. When the experiments are carried out in 150mM NaCl and 20mM MgCl2, the value obtained for the monolayer spontaneous curvature is −1/8.7±0.037nm−1. These values are of importance in modelling the effects of curvature elastic stress in membrane lipid homeostasis in the bacterium Acholeplasma laidlawii [Alley, S.H., Barahona, M., Ces, O., Templer, R.H., in press. Biophysical regulation of lipid biosynthesis in the plasma membrane. Biophys. J.] and indicate that divalent cations can play a significant role in altering curvature elastic stress. [Copyright &y& Elsevier]

We have used X-ray diffraction and differential scanning calorimetry (DSC) to study the structure and lyotropic phase behaviour of two synthetic dialkyl glycolipids having β-D-glucose and β-D-galactose headgroups and two saturated tetradecyl (C 14 ) chains. The diastereomeric compounds, 1,2-di-O-tetradecyl-3-O-(β-D-glucopyranosyl)-sn-glycerol (di-14:0-β-D-GlcDAG) and 1,2-di-O-tetradecyl-3-O-(β-D-galactopyranosyl)-sn-glycerol (di-14:0-β-D-GalDAG) show striking differences in their phase behaviour, particularly in the ordered lamellar phase region. Both compounds adopt the fluid lamellar L α phase upon cooling from the H II phase, but below the chain-melting transition,di-14:0-β-D-GlcDAG forms a metastable L β gel phase, whereas di-14:0-β-D-GalDAG forms only crystalline lamellar phases, on the timescale of our measurements. We have determined the limiting hydrations of the various phases, and compare the findings from these glycolipids with those from our previous studies of the phospholipid didodecyl phosphatidylethanolamine (di-12:0-PE). [ABSTRACT FROM AUTHOR]