Diffraction techniques for nonlamellar phases of phospholipids

A neutron diffraction method applicable to nonlamellar phases of substrate-supported lipid membranes is described and validated. When prepared on a flat substrate, the resulting nonlamellar phases have layered symmetry which provides some advantages over powder diffraction for detailed structure determination. This approach recently led to the detection of a rhombohedral phase and a distorted hexagonal phase of lipids. Here the determination of intensity and phase information for such phases is demonstrated by application to the hexagonal phase of diphytanoyl phosphatidylcholine (DPhPC). The hexagonal symmetry is used to verify the data reduction procedure for the intensities of the diffraction peaks. Diffraction intensities measured while varying the D2O/H2O ratio in the relative humidity was used to solve the phase problem. The neutron scattering length density distribution of the hexagonal phase was constructed and analyzed to elucidate the packing of the lipid molecules. The structure of DPhPC in the hexagonal phase is of interest in connection with its stalk structure in the rhombohedral phase. We also found that the incorporation of tetradecane into the DPhPC hexagonal phase is limited, similar to the case for dioleoyl phosphatidylethanolamine.     

Intergranular giant magnetoresistance in a spontaneously phase separated perovskite oxide

We present small-angle neutron scattering data proving that, on the insulating side of the metal-insulator transition, the doped perovskite cobaltite La(1-x)Sr(x)CoO(3) phase separates into ferromagnetic metallic clusters embedded in a nonferromagnetic matrix. This induces a hysteretic magnetoresistance, with temperature and field dependence characteristic of intergranular giant magnetoresistance (GMR). We argue that this system is a natural analog to the artificial structures fabricated by depositing nanoscale ferromagnetic particles in a metallic or insulating matrix; i.e., this material displays a GMR effect without the deliberate introduction of chemical interfaces.     

Concentration-independent spontaneously forming biomimetric vesicles

In this Letter we present small-angle neutron scattering data from a biomimetic system composed of the phospholipids dimyristoyl and dihexanoyl phosphorylcholine (DMPC and DHPC, respectively). Doping DMPC-DHPC multilamellar vesicles with either the negatively charged lipid dimyristoyl phosphorylglycerol (DMPG, net charge -1) or the divalent cation, calcium (Ca2+), leads to the spontaneous formation of energetically stabilized monodisperse unilamellar vesicles whose radii are concentration independent and in contrast with previous experimental observations.     

Thermal decomposition of basic aluminium potassium sulfate. Part II. Kinetics of the reaction

The kinetics of individual stages of thermal dissociation of basic aluminium potassium sulfate (BAPS) were studied thermogravimetrically under isobaric and isothermal conditions at a reduced pressure of the order of 10^?3 hPa and in the atmosphere of gaseous products of the reaction (H₂O, SO₂).The kinetic parameters of all the reaction stages have been identified and the nature of the stages and the effect of changes of the reaction of conditions on the course of the processes have been determined.     

Spontaneously Forming Unilamellar Phospholipid Vesicles

Unilamellar vesicles (ULV) consisting of a single lipid bilayer are of special interest as drug delivery vehicles. Here, we report on a spontaneously forming ULV system composed of the short- and long-chain phospholipids, dihexanoyl (DHPC) and dimyristoyl (DMPC) phosphorylcholine, respectively, doped with the negatively charged lipid, dimyristoyl phosphorylglycerol (DMPG). Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) were employed to systematically investigate the effects of lipid concentration, salinity, and time on vesicle stability. It is found that ULV size is practically constant over a range of lipid concentration and temperature. The spontaneously formed ULV are stable for periods of four months, or greater, without the use of stabilizers.