Ice Formation in Model Biological Membranes in the Presence of Cryoprotectors

Ice formation in model biological membranes is studied by SAXS and WAXS in the presence of cryoprotectors: dimethyl sulfoxide and glycerol. Three types of phospholipid membranes: DPPC, DMPC, DSPC are chosen for the investigation as well-studied model biological membranes. A special cryostat is used for sample cooling from 14.1C to -55.4C. The ice formation is only detected by WAXS in binary phospholipid/water and ternary phospholipid/cryoprotector/water systems in the condition of excess solvent. Ice formation in a binary phospholipid/water system creates an abrupt decrease of the membrane repeat distance by delta-d, so-called ice-induced dehydration of intermembrane space. The value of delta-d decreases as the cryoprotector concentration increases. The formation of ice does not influence the membrane structure (delta-d = 0) for cryoprotector mole fractions higher than 0.05.Comment: PDF: 9 pages, 3 figures; sourse in MS Wor

A Sucrose Solution Application to the Study of Model Biological Membranes

The small-angle X-ray and neutron scattering, time resolved X-ray small-angle and wide-angle diffraction coupled with differential scanning calorimetry have been applied to the investigation of unilamellar and multilamellar dimyristoylphosphatidylcholine (DMPC) vesicles in sucrose buffers with sucrose concentrations from 0 to 60%. Sucrose buffer decreased vesicle size and polydispersity and increased an X-ray contrast between phospholipid membrane and bulk solvent sufficiently. No influence of sucrose on the membrane thickness or mutual packing of hydrocarbon chains has been detected. The region of sucrose concentrations 30%-40% created the best experimental conditions for X-ray small-angle experiments with phospholipid vesicles.Comment: PDF: 10 pages, 6 figures. MS Word sours

Phase transitions of saturated triglycerides

The α → β phase transition of Tristearin (SSS) has been investigated both by Differential Scanning Calorimetry and Small Angle X-Ray Diffraction as a function of temperature at the same heating rate (2 deg/min) in order to elucidate either this transition occurs in the solid state or is melt mediated

Structural Factors Responsible for the Permeability of Water Vapor through Fat Barrier Films

The influence of structure on the water vapor permeability (WVP) of fat films was determined in this study. Statistically significant (P \u3c 0.1) correlations were found between WVP and chemical composition (% stearic acid), the Avrami index (n), the half-time of crystallization (t1/2), the maximum solid fat content, and crystalline domain size determined by powder X-ray diffraction (XS). Larger domain sizes translate into a smaller grain boundary surface area through which water vapor can migrate, resulting in a lower WVP. High values of XS were associated with fats with high SFC and stearic acid contents. These fats also crystallize rapidly, with low n and t1/2 values

Phase diagram of sodium dodecyl sulfate-water system: 1. A calorimetric study

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Thermal and structural behavior of anhydrous milk fat. 3. Influence of cooling rate

The crystallization behavior of anhydrous milk fat has been examined with a new instrument coupling time-resolved synchrotron x-ray diffraction as a function of temperature (XRDT) at both small and wide angles and high-sensitivity differential scanning calorimetry. Crystallizations were monitored at cooling rates of 3 and 1°C/ min from 60 to –10°C to determine the triacylglycerol organizations formed. Simultaneous thermal analysis permitted the correlation of the formation/melting of the different crystalline species monitored by XRDT to the thermal events recorded by differential scanning calorimetry. At intermediate cooling rates, milk fat triacylglycerols sequentially crystallize in 3 different lamellar structures with double-chain length of 46 and 38.5 Å and a triple-chain length of 72 Å stackings of {alpha} type, which are correlated to 2 exothermic peaks at 17.2 and 13.7°C, respectively. A time-dependent slow sub-{alpha} {leftrightarrow} {alpha} reversible transition is observed at –10°C. Subsequent heating at 2°C/min has shown numerous structural rearrangements of the {alpha} varieties into a single ß' form before final melting. This polymorphic evolution on heating, as well as the final melting point observed (~39°C), confirmed that cooling at 3°C/min leads to the formation of crystalline varieties that are not at equilibrium. An overall comparison of the thermal and structural properties of the crystalline species formed as a function of the cooling rate and stabilization time is presented. The influence on crystal size of the cooling rates applied in situ using temperature-controlled polarized microscopy is also determined for comparison