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

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

Atmospheric deposition of PAHs to an urban site, Paris, France

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Atmospheric bulk deposition of trace metals to the Seine river basin : concentrations, sources and evolution during 1988-2001.

Concentrations of Cd, Cu, Ni, Pb and Zn were determined in bulk atmospheric deposition collected at five stations in the Seine River basin (France), to evaluate sources and fluxes of atmospheric trace metals. Bulk deposition (wet + dry) was sampled weekly from March 2001 to February 2002 for 4 sites and from March to December 2001 for the last one. The concentrations of the elements in bulk deposition (dissolved + particulate form) followed the order: Zn > Pb > Cu > Ni > Cd. Concentrations of Zn, Pb and Ni were highly correlated with one another, suggesting a common source, related to the combustion of coal and heavy fuel. Metal concentrations in bulk deposition did not exhibit a high degree of temporal variability over the annual cycle and were not obviously related to meteorological parameters (rainfall, wind). Estimates of the total annual direct atmospheric deposition of metals to the Seine Estuary ranged from 16 kg yr− 1 for Cd to 5600 kg yr− 1 for Zn. Loadings of Cd, Cu and Ni from direct atmospheric inputs were less than 1% of those contributed by the Seine River and loadings of Pb and Zn represented 1.27% and 1.56% of the Seine contribution. Direct atmospheric inputs are negligible compared to fluvial inputs, but the indirect atmospheric deposition to the estuary was not estimated. Based on these results, trace metal concentrations in Paris have decreased by a factor of 4.6 for Zn and by a factor of 50 for Ni from 1988 to 2001. Of particular interest is the continued decrease in bulk deposition of Pb during this period, underlining the impact of policy initiatives concerning the reduction of lead on emissions in France

A Single Law to Describe Atmospheric Nitrogen Bulk Deposition versus Rainfall Amount: Inputs at the Seine River Watershed Scale

International audienceAtmospheric nitrogen species (NH 4-N and (NO 3 +NO 2)-N) were determined in weekly samples of atmospheric bulk deposition (dry plus wet), collected in France at seven sites over the course of a year. Rural, semi-rural and industrialised-urban sites were chosen in the Seine river watershed from the Seine estuary to upstream from Paris. Mean NH 4-N concentrations varied from 0.7 to 1.7 mg L −1. Mean (NO 3 +NO 2)-N concentrations were approximately 0.5 mg L −1 for all sites except Paris (0.7 mg L −1), which has a local impact on the fallout contamination from urban emissions. The relation between concentration and rainfall amount obeys a power law, in the form of y = ax b. When the nitrogen sources are very local, this relationship turns into a dilution law. Annual atmospheric nitrogen deposition (NH 4-N+(NO 3 +NO 2)-N) was calculated and varied from 7.8 kg ha −1 yr −1 in the neighbourhood of a rural town to 17.3 kg ha −1 yr −1 in a very industrialised harbour. 58% of the atmospheric nitrogen deposition occurred during 'spring + summer' period. The total nitrogen atmospheric input to the Seine estuary, via direct deposition + indirect input via the watershed, was estimated to about 5% of the total nitrogen load within the Seine river basin

The Water Vapor Permeability of Polycrystalline Fat Barrier Films

The water vapor permeability of fat barrier films has been associated with structural characteristics such as polymorphism, crystal size, and chemical composition, among others. However, no mechanistic models have been proposed to describe this relationship. In this study, we have determined the effects of processing conditions on the structure and physicochemical characteristics of four fats and their relationship to water vapor permeability. Results suggest that the solids\u27 volume fraction and the domain size of the fat crystals seem to be the most important factors controlling water vapor migration. Moreover, materials with relatively large crystalline domains will yield malleable films with relatively low storage and loss moduli and strain/stress at the limit of linearity high tan δ values. The structural effects on the permeability of fat films are related to the nanoscale of the material

Cristallisation de la matière grasse dans une émulsion de MGLA dans l'eau : apport de différentes techniques physiques combinées

[Departement_IRSTEA]EA [TR1_IRSTEA]TEPSA / IRMFOODNational audienceStructural characteristics of a same oil-in-milk fat emulsion was determined using different physical techniques. Emulsion stability was monitored through determination of fat droplet size distribution and proportion of adsorbed proteins at the fat droplet surface. Thermogrammes observed by differential scanning calorimetry (DSC), showed that ∆T (difference between temperature of initial crystallization and melting completion) was higher in emulsified milk fat than in bulk fat sample (∆T~10°C). In addition, isothermal treatment at 4°C leads to a peak time value tmax (4°C), which was ~12 min lower than in bulk fat. Evolution of viscoelastic properties under cooling and re-heating reflected not only contribution of crystalline fat in the emulsion during the the ageing step at 4°C, but also a contribution of gelatine which was added for structuration of the aqueous continuous phase. The coupling with DSC of time-resolved synchrotron X-ray diffraction at both small and wide angles, showed that fat crystallization behave differently under cooling and re-heating: under cooling we observed (subα) -> α polymorphic transition, and α -> β' during the re-heating scan. Finally, separation of proton relaxation between aqueous and fat phases observed by low field nuclear magnetic resonance revealed that crystalline fat formed at 4°C is much more affected by the presence of emulsifiers than by emulsification. Results obtained using different approches were presented and explained in regards with their potentiality to give complementary information on emulsion structural properties.Nous avons utilisé différentes techniques physiques pour la caractérisation structurale d'une émulsion de matière grasse laitière (MGL), dont nous avons évalué les paramètres de stabilité physique (distribution de taille des globules gras, fraction de protéines adsorbées à la phase grasse). Les signaux obtenus en microcalorimétrie différentielle (MCD) ont montré que ∆T, différence entre la température de début de cristallisation et celle de fin de fusion de la MGL, ainsi que tmax (4°C), temps nécessaire à l'observation du pic de cristallisation à 4°C, sont supérieurs de près de 10°C et 12min, respectivement, pour la MGL émulsionnée que pour la MGL non émulsionnée. L'analyse des structures cristallines par application simultanée de la MCD et de la diffraction de rayons X a montré que la MGL émulsionnée cristallise sous forme α (après un très bref début de cristallisation sous forme subα) puis se maintient sous cette variété instable jusqu'à ce que celle-ci se transforme en variété β' lors du chauffage. Des essais rhéologiques en mode dynamique ont mis en évidence la contribution de la cristallisation des globules gras à la consistance de l'émulsion pendant la mataturation à 4°C, qui s'ajoute à celle de la gélatine contenue dans la phase continue, en cours de chauffage ou refroidissement. Enfin, la séparation des signaux de relaxation du proton de l'eau et de la matière grasse observés par résonance magnétique, a indiqué que la fraction de la matière grasse cristallisée à 4°C semble être modifiée par la présence de tensio-actifs, en milieu émulsionné ou non. Ces résutats sont présentés et discustés en fonction de la potentialité des différentes techniques utilisées pour la catactérisation structurale des émulsions