Lyotropic Phase Transitions Research Articles

Fourier Transform Near-Infrared Examination of the Coagel-to-Micelle Transition for Sodium Laurate

The solution behavior of surfactants has received considerable attention, because it is known that, for certain equilibrium conditions of concentration, temperature, and pressure, surfactant molecules form stable aggregates in solution. The ability of surfactants to aggregate in aqueous solutions and at solid/liquid interfaces has been shown to be important in many areas of science, including biology, detergency, and mineral flotation. Over the past ten years, infrared radiation has been used to spectroscopically examine thermotropic and lyotropic phase transitions for various surfactant systems such as sodium alkanoates, phospholipids, and sodium alkylsulfates. The results of these studies indicated that many phase changes, especially monomermicelle and coagel-micelle transitions, are accompanied by large (4-8 cm−1) shifts in the fundamental frequencies of the asymmetric and symmetric alkyl stretching bands. These shifts have been attributed to differences in the number of gauche rotational isomers in the alkyl chain of the surfactant studied.

Quantitation of lateral stress in lipid layer containing nonbilayer phase preferring lipids by frequency-domain fluorescence spectroscopy.

Frequency-resolved fluorescence measurements have been performed to quantitate the lateral stress of the lipid layer containing nonbilayer phase preferring dioleoylphosphatidylethanolamine (DOPE). On the basis of a new rotational diffusion model, the wobbling diffusion constant (Dw), the curvature-related hopping diffusion constant (DH), and the two local orientational order parameters ([P2] and [P4]) of 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl] carbonyl]-3-sn-phosphatidylcholine (DPH-PC) in fully hydrated DOPE and DOPE/dioleoylphosphatidylcholine (DOPC) mixtures were calculated from the frequency-domain anisotropy data. The values of [P2], [P4], and DH for DOPE were found to increase significantly at approximately 12 degrees C, the known lamellar liquid crystalline (L alpha) to inverted hexagonal (HII) phase transition temperature of DOPE. Similar features as well as a decline of Dw were detected in the DOPE/DOPC mixtures as the DOPE content was increased from 85% to 90% at 23 degrees C, corresponding to the known lyotropic phase transition of the DOPE/DOPC. In contrast, for DOPC (0-40 degrees C) and DOPE/DOPC (0-100% DOPE at 3 degrees C), which remained in the L alpha phase, these changes were not detected. The most probable local orientation of DPH-PC in the DOPE/DOPC mixtures shifted progressively toward the normal of the lipid/water interface as the content of DOPE increased. We concluded that the curvature-related lateral stress in the lipid layer increases with the content of the nonbilayer phase preferring lipids.

Statistical Theory of Smectic A and Columnar Phases in Hard Rod Fluids

Abstract The free energy of smectic A and columnar phases in parallel hard cylinders with length L and width D are calculated as functions of the order parameters. In the third vial approximation we find the second order nematic to smectic A (N-SA) lyotropic phase transition at a packing fraction η = ηNA = 0.355 where the smectic layer spacing d is dc = 1.35L. These values agree with results by computer simulation: ηNA = 0.35 and dc = 1.27L. Incorporating an attractive potential, we show the system exhibits the second order N-SA phase transition at a temperature TNA, and find for T < TNA the relation (d/dc - 1)/(1 - T/TNA) ∼ 10−1 and the layer compression modulus B - 15(kT/vmol) (1 - T/TNA), where vmol is the molecular volume. The stability of the columnar phase due to the hard core repulsion cannot be proved in the second virial approximation.

Micellar structures in lyotropic liquid crystals and phase transitions

The formation of micellar nematics is discussed with emphasis on the transitions between nematic phases and nematic-smectic transitions. Phase diagrams for MTAB/l-decanol/D,O systems show a direct transition between uniaxial nematics. Electrical conductivity and birefringence measurements on a mixture of sodium decylsulfate. 1-decanol, D,O demonstrate, on the other hand, the existence of a biaxial nemantic range that separates the Uniaxial nematics. On a mixture of cesium perflouroctanoate and H 2O the electrical conductivity and rotational viscosity are used to discuss the relevant features of nematic-lamellar-smectic transitions. The formation of elongated ribbon-like micelles at the nematic-smectic transition is suggested. Transitions between different nematic phases in the MTAB system may be connected with a structural change from long micelles with a fairly circular cross section to similar micelles with a more elliptical cross section.

Freeze/thaw-induced destabilization of the plasma membrane and the effects of cold acclimation.

Disruption of the plasma membrane is a primary cause of freezing injury. In this review, the mechanisms of injury resulting from freeze-induced cell dehydration are presented, including destabilization of the plasma membrane resulting from (a) freeze/thaw-induced osmotic excursions and (b) lyotropic phase transitions in the plasma membrane lipids. Cold acclimation dramatically alters the behavior of the plasma membrane during a freeze/thaw cycle--increasing the tolerance to osmotic excursions and decreasing the propensity for dehydration-induced lamellar to hexagonal-II phase transitions. Evidence for a casual relationship between the increased cryostability of the plasma membrane and alterations in the lipid composition is reviewed.

Kinetics of Lyotropic Liquid Crystal Phase Transitions: A Time Resolved X-Ray Diffraction Study

Abstract Phase transitions in the fully saturated monogalactosyldiacylglycerol in water system have been studied using time resolved x-ray diffraction. Three mechanisms for phase transitions are identified in these studies and can be correlated with the transit times involved in the transformations. The relationship between these observations and previous reports on phospholipid and surfactant phase transitions is discussed.

New Nematic Phase in Lyotropic Binary Liquid Crystals Detected by Positron Annihilation Techniquest

Abstract A new nematic phase in lyotropic binary liquid crystalline systems consisting of sodium dodecyl sulfate-water was detected, for the first time, in the absence of additives by utilizing positron annihilation techniques. Lyotropic and thermotropic phase transitions were also investigated by the same methods. The positron annihilation parameters have also indicated a better definition of the concentration ranges at which each phase exists in the system studied. Crossed polarized light microscopy was applied to substantiate these results.

Light transmission at the uniaxial-biaxial lyotropic nematics phase transitions

Results are reported on light transmission versus the temperature near the phase transitions between lyotropic nematics. Strong pretransitional effects are observed when the phase transitions occur between biaxial nematic and uniaxial phases. The light is strongly depolarized both at the calamitic-biaxial and at biaxial-discotic phase transitions. The results are qualitatively explained.

Lyotropic phase transitions in single crystals of l- and dl-dipalmitoylglycerophosphocholines

Lyotropic phase transition behaviour of solution-grown mono-domain thin layered crystals of L- and DL-dipalmitoylglycerophosphocholines (dipalmitoyl-GPC) was investigated in a low hydration region at room temperature. X-Ray diffraction measurements and observations by a polarising microscope were performed on the same crystal. In the layer plane of the as-grown thin layered crystal of l- or dl-dipalmitoyl-GPC, which was considered to be dihydrated (phase II), an optical anisotropy was observed. Through a slight absorption of water, the dihydrated crystal showed a monotropic phase transition to a lyotropic mesophase (phase III), in which the optical axis was rotated by about 90° in the plane of the layer. Associated with this phase transition, anisotropic changes both in the unit cell and the crystal dimension occurred. Further absorption of water induced a second lyotropic phase transition for each of the two substances, where the optical anisotropy in the layer plane vanished (phase IV). Combined X-ray measurements suggested that the optical anisotropies observed in phase II and III were caused not only by the inclination of the long aliphatic chains but also by the arrangement of the polar groups of the molecules, and that the binding of water to dipalmitoyl-GPC slightly differed in the l- and dl-molecules in the thin layered crystals and also in as-received powder (phase 1) from as-grown crystals.

Lipid participation in intracellular freezing avoidance mechanisms of lettuce seed

Freeze-fracture electron microscopy was used to study water content related freezing resistance in Grand Rapids lettuce seeds. Consistent and recognizable conformational changes occurred in lipid-water phases of lettuce seeds at different moisture contents. In air-dry lettuce seed cotyledons, the lipids lying in spherical lipid bodies near the cell wall appeared amorphous, while the structure was crystalline above 20% water content. The lipid bodies interassociated into membrane bilayers in seeds containing 20 to 25% water. Such lyotropic phase transitions in membrane lipids during lettuce seed hydration are believed to contribute to the biphasic freezing behavior observed in lettuce seeds at different moisture contents and to provide a natural freezing tolerance mechanism for highly desiccated plant tissues such as seeds.

Combined lyotropic and thermotropic phase transitions of deoxycholic acid

Phase transitions of deoxycholic acid have been examined by studying systems which form a clathrate during crystallization. It has been shown that, depending upon the type of solvent molecule present, the deoxycholic acid clathrate may or may not form a thermotropic liquid crystal. In this manner, the simultaneous occurrence of both lyotropic and thermotropic effects was observed.

Membrane properties of saturated fatty acid mutants of yeast revealed by spin labels

(I) Several yeast mutants deficient in the synthesis of saturated fatty acids were isolated. (II) These mutants cannot grow when supplemented with a highly purified unsaturated fatty acid. They demonstrate a rigid requirement for a dietary saturated fatty acid. (III) They can be enriched with different fatty acids including odd chain length fatty acids. (IV) The enriched mutants demonstrate a characteristic lyotropic mesomorphic phase transition dependent on fatty acid composition but independent of pre-enzyme or physical treatment. (V) It is inferred that the ionic interaction between membrane lipids and membrane proteins is detectable by spin labels. (VI) The apparent “fluidity” of membranes detectable by spin labels requires re-evaluation.