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The thermal and structural behavior of anhydrous milk fat (AMF) was studied by a technique that allowed simultaneous time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) and high sensitivity differential scanning calorimetry (DSC) to be carried out in the same apparatus from the same sample. In this paper (the first of a series), the less stable crystalline structures made by triacylglycerols (TG) of bulk AMF after its liquid quenching down to -8 degrees C are addressed The coexistence of two lamellar structures characterized by sharp long spacing reflections corresponding to well-defined 3L (70 A) and 2L (47 A) longitudinal stackings but broad short spacing lines related to poorly ordered hexagonal (alpha) lateral packing is shown for the first time, The bilayered structure was very unstable, since it disappeared during a 20-min isothermal recording. Simultaneous DSC and X-ray monitoring of AMF heating in the range -8, +50 degrees C at a rate of 2 degrees C/min allows the same sample to be followed on the evolution of these unstable forms to more stable varieties. The 3L stacking transforms into a new 2L crystalline structure characterized by broad LS reflections corresponding to a ill-defined 2L (37 A) longitudinal stacking but a more compact orthorhombic (beta') lateral packing. A delimitation of the domains of existence of the crystalline structures resulted from the comparison of detailed analysis of the evolutions of positions, intensities, and widths of X-ray peaks as a function of temperature to microcalorimetry recording.

The crystallization behavior of milk fat has been examined on slow cooling at 0.1 degrees C/min from 50 to -15 degrees C, to determine the variations of triacylglycerol organizations as a function of temperature. The experiments have been conducted with an instrument allowing coupled X-ray diffraction (XRD) at both small and wide angles and high-sensitivity differential scanning calorimetry (DSC) recordings from the same sample by taking advantage of the high-energy flux of a synchrotron. On slow cooling, milk fat triacylglycerols sequentially crystallize in four different lamellar structures with double-chain length of 41.5, 48.3, and 39.2 A and a triple-chain length of 62.2 A stackings. Simultaneous wide-angle XRD has shown that initial nucleation occurs in a packing of beta' type at about 24 degrees C. For temperature < 13 degrees C, triacylglycerols crystallize in an hexagonal subcell of alpha type, leading to the coexistence of the beta' + alpha polymorphic forms, which is recorded until -15 degrees C. Thermal analysis allowed to correlate the formation of the different crystalline species monitored by XRDT (XRD as a function of temperature) to the exothermal events recorded simultaneously by differential scanning calorimetry. The evolution of the species formed during crystallization was also monitored on heating at 2 degrees C/min. The absence of polymorphic evolution on heating, as well as the high final melting point observed, about 40 to 41 degrees C, confirmed that cooling at 0.1 degrees C/min leads to quasi equilibrium.

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 degrees C/ min from 60 to -10 degrees 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 A and a triple-chain length of 72 A stackings of alpha type, which are correlated to 2 exothermic peaks at 17.2 and 13.7 degrees C, respectively. A time-dependent slow sub-alpha <--> alpha reversible transition is observed at -10 degrees C. Subsequent heating at 2 degrees C/min has shown numerous structural rearrangements of the alpha varieties into a single beta' form before final melting. This polymorphic evolution on heating, as well as the final melting point observed (approximately 39 degrees C), confirmed that cooling at 3 degrees 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.

In this paper we have investigated via x-ray diffraction the influence of dimethyl sulfoxide (DMSO), known for its biological and therapeutic properties, on the structure of lipid membranes of dipalmitoylphosphatidylcholine (DPPC) in excess of the solvent (DMSO/water) at mole DMSO fractions XDMSO in (0.1) and under equilibrium conditions. At small XDMSO

The influence of dimethyl sulfoxide (DMSO) on membrane thickness, multilamellar repeat distance, and phase transitions of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) was investigated by X-ray diffraction and small-angle neutron scattering (SANS). The differential scanning calorimetry (DSC) study of water freezing and ice melting was performed in the ternary DPPC /DMSO /water and binary DMSO /water systems. The methods applied demonstrated the differences in membrane structure in three sub-regions of the DMSO mole fraction (X DMSO ): from 0.0 to 0.3 for the first, from 0.3 to 0.8 for the second, and from 0.9 to 1.0 for the third sub-region. The thickness of the intermembrane solvent at T =20 o C decreases from 14.4 ± 1.8 Å at X DMSO =0.0 to 7.8 ± 1.8 Å at X DMSO =0.1. The data were used to determine the number of free water molecules in the intermembrane space in the presence of DMSO. The results for 0.0 ≤ X DMSO ≤ 0.3 were explained in the framework of DMSO-induced dehydration of the intermembrane space.Keywords: dimethyl sulfoxide, cryoprotection, phospholipid, dehydration, scattering. Journal of Alloys and Compounds 286 (1999) 195-202 INTRODUCTIONDimethyl sulfoxide has two very important biological properties: a) ability to protect a variety of cells from the damaging effects of freezing and storage at a very low temperature, b) the modification of X-ray induced damage in cells and whole animals when DMSO is present before and during exposure to radiation [1].The main purpose of cryobiology is to find an "optimal" way of cooling biological systems to low temperatures (about the temperature of liquid nitrogen) and, at the same time, prevent the formation of ice inside the biological tissue. The mechanism of DMSO cryoprotection is still debated and, on the molecular level, it is not clear [2].DMSO makes hydrogen bonds with water molecules. The structure of the binary DMSO /water system has been studied by means of the spin-lattice relaxation and the chemical shift behavior of water and DMSO protons [3]. It was found that DMSO and water molecules tend to form hydrogen bonds in the relation 1/2 (mole DMSO fraction X DMSO = 0.33) or 1/3 (X DMSO = 0.25). The DMSO /water phase diagram is well known [4] and the phase behavior of the binary DPPC /water system has been investigated by calorimetry [5]. The influence of DMSO fraction on the pre-transition existence and on the repeat distance of the DPPC multilamellar structure has been studied for the region of a small DMSO mole fraction, X DMSO ≤ 0.13. From the calculation of the electron density profile, it was established that the intermembrane solvent space decreases with the increasing DMSO concentration [6].In the present paper, the influence of DMSO on 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) membranes was studied by X-ray diffraction, small-angle neutron scattering (SANS), and differential scanning calorimetry (DSC). Our purpose was to obtain information on changes in the structure of DPPC in the presence of DMSO at T=20 o C ...

The behavior of fluorinated surfactant F(CF2)8C2H4(OC2H4)9OH in water solution was investigated, and the preparation ofmesoporous molecular sieves was achieved. A direct micellar phase (L1) and a hexagonal (H1) liquid crystal were found. Small-angle X-ray scattering measurements proved that the hydrophobic chains are completely extended and that the cross sectional area remains constant in H1. At 80 degrees C, materials with a hexagonal array of their channel are prepared via a cooperative templating type mechanism in a wide range of surfactant concentrations (5-20 wt %). Decreasing the hydrothermal temperature leads to the formation ofwormhole-like structure. In this case the channel arrangement is no longer governed by the surfactant behavior but by the silica condensation and polymerization. An increase of the mean pore diameter with heating temperature is noted. This result is associated with changes of aggregation number with temperature. A comparison of the characteristics of the materials obtained with both hydrogenated and fluorinated surfactants is also made.

-Crystallization and polymorphic evolutions of triacylglycerols (TG), at 4 o C, in cream and anhydrous milk fat (AMF) samples were studied using high-sensitivity differential scanning calorimetry (DSC), time-resolved synchrotron X-ray diffraction (XRD) and density measurement, and compared as a function of time after quenching from 60 to 4 o C. The evolution of the two crystalline structures initially formed in both samples, corresponding to a metastable 2L (47 Å) and a 3L (70.5 Å) lamellar organization with hexagonal chain packings (α form), were monitored in isothermal conditions at 4 o C as a function of time t. For t > 15 min, short spacings showed the formation of a β' packing of the chains in coexistence with the α form. In AMF, the occurrence of some β form was also recorded. For long spacings, a 2L (39 Å) structure was formed in cream with the 3L (70.5 Å) structure still being preponderant after conditioning for 30 min at 4 o C. In AMF samples, a TG polymorphic transition 3L (70.5 Å) → 2L (39 Å) + 3L (66 Å), correlated with an exothermic peak recorded simultaneously by DSC, was clearly visible. At t > 100 h conditioning at 4 o C, the same crystalline structures were found in cream and AMF with the coexistence of at least a 2L (40.5 Å) and a 3L (54.2 Å) longitudinal organization, associated with α, β' 2 , β' 1 and β packings of the chains. The melting behaviors of cream and AMF were monitored on heating at 2 o C . min -1 by coupled XRD as a function of temperature and DSC experiments. The absence of further structural evolution and polymorphic transition until final melting demonstrates the relative stability of the structure formed. The evolution of cream density after quenching to 4 o C revealed two transitions, the amplitudes, rates and duration of which coincided with DSC and XRD experiments. All data are in agreement in demonstrating that two transitions, a fast and a slow one, occur in dairy products after fast cooling to 4 o C. Cristallisation / polymorphisme / triacylglycérol / diffraction des rayons X / calorimétrie