Density, DSC, X-ray and NMR measurements through the gel and lamellar phase transitions of 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC): observation of slow relaxation processes and mechanisms of phase transitions.

Dialkyl lecithin dispersions in water exhibit two phase transitions upon cooling from the lamellar phase (L(α)). At the main transition (T(M)) the L(α) phase changes to a ripple (gel) phase (P(ß')) which then transforms to a second gel phase (L(ß')) at the "pretransition" (T(P)). We have made accurate density measurements through the various phases for two lecithins having unequal chains: 1-myristoyl-2-stearoyl-sn-glycero-3-phosphatidylcholine (MSPC) and 1-stearoyl-2-myristoyl-sn-glycero-3-phosphatidylcholine (SMPC). The measurements were carried out over five heat/cool cycles from 5 to 55 °C, followed by cooling back to 5 °C. The samples were then held at 50 °C for 24 hours, followed by a further three cool/heat cycles. For SMPC we observe an increase in density of the gel phases over the first 5 cycles, followed by much smaller changes after incubation at 50 °C. The lamellar phase also shows an increase in density, albeit much smaller. This parallels the behaviour of 1,2-di-palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-di-myristoyl-sn-glycero-3-phosphatidylcholine (DMPC) reported earlier (Jones et al., Liquid Crystals 32, 1465 (2005)). For MSPC we observe a decrease in density within the gel phases while T(P) almost disappears after the first cycle. The lamellar phase shows little evidence of any change with each cycle. Within the lamellar phases there is a marked reduction in density on approaching T(M), which is attributed to the formation of transitory gel phase domains. Additional measurements by DSC and X-ray diffraction show that the changes in densities are not accompanied by large changes in transition enthalpies or phase structures. NMR data indicate that the pretransitional event within the L(α) phase is accompanied by ordering of the alkyl chains. The results indicate that the exact nature of the lipid alkyl chains could play a key role in the formation of gel phase patches within membrane bilayers. Their detailed chemical structures merit more attention than by simply assuming a uniform "bending energy" to describe the behaviour.

Chromonic liquid crystal formation by Edicol Sunset Yellow.

The solution and liquid crystalline phases formed by dissolution of the dye Edicol Sunset Yellow (ESY) in water have been examined using optical microscopy, multinuclear NMR (1H, 2H, 13C, 23Na), and X-ray diffraction. From the solution 1H and 13C spectra (particularly 13C), it is clear that the tautomeric form present in all these phases is the hydrazone, NH, structure, not the usually given azo, OH, form. Two chromonic mesophases occur: a nematic (N) phase at approximately 30-40 wt % and a hexagonal (M) phase at approximately 40-45 wt %. X-ray diffraction data show that the aggregates in the mesophases are single molecule stacks, with a typical spacing of approximately 3.5 angstroms, as expected for these systems. The NMR quadrupole splittings (2H2O, 23Na) are similar to those observed for surfactant lyotropic mesophases, suggesting that there are no water molecules or counter ions that are tightly bound to the ESY aggregates. An unusual feature of the X-ray diffraction pattern of the mesophases is the occurrence of diffuse off-axis reflections at approximately 6.8 angstroms. It is proposed that these arise from a head-to-tail packing of the molecules within the stacks.

In situ NMR and XRD studies of the growth mechanism of SBA-1.

In situ 17O, 14N and 29Si nuclear magnetic resonance (NMR) coupled with in situ energy dispersive X-ray diffraction (EDXRD) have been used to investigate the growth of the siliceous mesoporous material, SBA-1, synthesised under acidic conditions from a micellar solution of the surfactant hexadecyltriethylammonium bromide (HTEAB) and tetraethylorthosilicate (TEOS). For the last decade, the mechanism of growth of such materials has been thought to be driven by electrostatic interactions described as a co-assembly process between the silica species (I+) and the micelles (S(+)X(-)). However, this postulated model referred to as the "charge density matching model" has never been fully supported by experimental data for the acidic syntheses. We have carried out a detailed in situ study which challenges the so-called S(+)X(-)I(+) pathway and instead suggests that a salting-out effect coupled with a drastic change in the water activity are responsible for the composite I(1)3 (SBA-1 space group Pm3n) mesophase precipitation. Substantial reorganisation of the precipitated phase then results in the final structure.

Liquid crystals and microemulsions formed by mixtures of a non-ionic surfactant with palm oil and its derivatives.

The phase behaviour of palm olein (PO) and its derivative oils (palm oil methyl esters and medium chain triglycerides) with Imbentin coco 6.9EO, an ethoxylated C12-14 alcohol, in water has been investigated to identify compositions where microemulsions occur. The techniques used were the optical microscope phase penetration scan and small angle X-ray diffraction (SAXS). Mixed surfactant/oil samples were prepared at wt. ratios of 0.1:1, 0.25:1, 0.5:1 and 1:1 for the phase penetration scan. For SAXS analysis, the initial concentration of surfactant in water (W) was fixed at 38% (w/w), which forms a hexagonal mesophase (H1). Palm oil methyl esters (POME) and medium chain triglycerides (MCT) were added to this at 0.04:1 (or 0.05:1 for MCT), 0.1:1, 0.2:1 (or 0.25:1 for MCT), 0.5:1 and 1:1 ratios of oil to surfactant. Schematic phase diagrams were constructed to document the changes of phase structures using both bulk samples and phase penetration scans techniques. The extent of microemulsion formation (or solubilisation) decreases in the sequence POME > MCT > PO, and increases substantially with temperature, particularly for POME and MCT. All of the oils destabilize the hexagonal phase; for POME and MCT there is an increase in the surfactant cloud point temperature by ca. 10 degrees C or more, but the temperature for the onset of the lamellar (Lalpha) phase dispersion region (W + Lalpha) is hardly affected. There was a pronounced tendency for the lamellar phase formed in the presence of high oil concentrations and low water levels to have a reduced melting point. With the highest MCT levels a bicontinuous cubic phase (probably V2) is present at 25 degrees C, although this phase is not present in the binary surfactant/water system. The X-ray diffraction results show that the average area per head group (ao) at the micelle surface is decreased by the addition of the oils, consistent with the observation of a V2 phase. Possible molecular mechanisms for this observation are discussed.

Macro-cellular silica foams: synthesis during the natural creaming process of an oil-in-water emulsion.

The room-temperature synthesis of a macro-mesoporous silica material during the natural creaming process of an oil-in-water emulsion is reported. The material has 3-dimensional interconnected macropores with a strut-like structure similar to meso-cellular silica foams with mesoporous walls of worm-hole structure. The material has very high surface area (approximately 800 m2 g(-1)) with narrow mesopore size distribution.

A novel approach for the crystallization of soluble proteins using non-ionic surfactants.

Crystallization trials using three polyoxyethylene surfactants as precipitating agents are described. Of the eight soluble proteins screened, five were successfully crystallized at the first attempt. These included lysozyme, catalase, ferritin, ribonuclease A and ubiquitin. Further work suggested that these surfactants could also be suitable for cryo-crystallographic analysis of crystals. At the concentrations used in the crystallization trials [10-40%(v/v)], they are capable of promoting the formation of non-crystalline glasses at cryogenic temperatures (77K). This would facilitate crystal mounting and allow the minimization of crystal irradiation damage. Results from this study also suggest that proteins remain stable at high concentrations of these surfactants [40%(w/v)] and over long time periods (>1 month). A number of membrane proteins were also screened for crystallization. These included photosystems I and II and light harvesting complexes I and II from spinach and bacteriorhodopsin from Halobacterium halobium++. The trial s were unsuccessful both in the absence and presence of heptane-1,2,3-triol and over a wide range of surfactant concentrations.