Use of soil properties and major element composition to predict background levels of trace elements in soils

The usefulness of various soil parameters to predict naturally occurring levels of some metallic trace elements (MTE) in soils has been studied for some agricultural and forest soils of Southern Belgium. The driving factors of the content in Cu, Ni, Pb, and Zn were investigated through multi-scale comparisons. This paper deals with multivariate and regression analysis of the results

Poly( -caprolactone)-g-alginate: synthèse, caractérisation physico-chimique en solution aqueuse et application à la séquestration et à la libération contrôlée

L objectif de cette étude est de synthétiser un nouveau polysaccharide hydrosoluble amphiphile, par greffage d un polyester hydrophobe, biocompatible et biodégradable, la poly(e-caprolactone) (PCL), sur un polysaccharide anionique, l alginate, via des fonctions ester. La synthèse est réalisée en phase hétérogène (émulsion eau/huile) en présence de tensioactif. Les copolymères amphiphiles (PCL-g-alginate) ont été synthétisés avec des chaînes de PCL de masse molaire variable (530 et 1250 g/mol) et des taux de greffage compris entre 3,5%mol et 15%mol. En solution aqueuse, les PCL-g-alginates ont un comportement classique de polyélectrolyte associatif hydrosoluble. Aux faibles concentrations, les interactions hydrophobes intramoléculaires sont prédominantes (conformations compactes), et au-dessus d une concentration critique, des interactions intermoléculaires hydrophobes s établissent (fort accroissement de viscosité). En milieu salin, le comportement est atypique pour les copolymères obtenus avec la PCL à 530 g/mol avec une forte prédominance d interactions intramoléculaires sur une large gamme de concentrations, tandis qu avec les copolymères à base de PCL 1250 g/mol, nous retrouvons un comportement de pseudo-gel. Ces propriétés originales en milieu salin ont été exploitées par l élaboration d un système à libération contrôlée de principes actifs hydrophobes ou amphiphiles, obtenu par réticulation ionotropique des PCL-g-alginates avec des ions calcium. Les hydrogels obtenus peuvent protéger un principe actif amphiphile (la théophylline) dans un simulacre de fluide gastrique (pH 1,2), et permettent de ralentir sa cinétique de libération dans un simulacre de fluide intestinal (pH 6,8) grâce, notamment, à des interactions hydrophobes entre le principe actif et les microdomaines hydrophobes formés par les PCL-g-alginates. En relation avec l étude physico-chimique en solution saline, la série 530-x présente les meilleures conditions de rétention du principe actif. Les cinétiques de libération peuvent également être fortement ralenties et contrôlées en recouvrant les matrices de PCL-g-alginate/Ca2+ par une membrane de polyélectrolyte à base d un polysaccharide cationique, le chitosane.The aim of this study is to synthesize a new hydrophobically associating water-soluble polysaccharide, prepared by covalent fixation of an hydrophobic, biodegradable and biocompatible polyester, poly(e-caprolactone) (PCL), side chains onto alginate (an anionic polysaccharide) via ester function. Synthesis takes place in heterogeneous media (o/w emulsion) stabilized by a tensioactive. Amphiphilic copolymers (PCL-g-alginate) with two different molar masses of PCL (530 and 1250 g/mol) were synthesized with molar hydrophobe contents ranged from 3.5% to 15%. These new amphiphilic compounds exhibit, in aqueous solution, the typical properties of hydrophobically associating water-soluble polyelectrolytes. At high dilution, data suggest the formation of compact conformations, resulting from intramolecular hydrophobic associations. Above a critical polymer concentration, intermolecular hydrophobic interactions take place and enhance dramatically the viscosity of copolymer solutions. In salt media, nature of hydrophobic interactions depends on the length of PCL chains. For MPCL=530 g/mol, intramolecular hydrophobic interactions are predominant for a wide range of concentration and for longest PCL chains (MPCL=1250 g/mol) strong intermolecular hydrophobic interactions form and can lead to the formation of a pseudo-gel. Finally, a new amphiphilic drug delivery system was obtained by ionotropic gelation of PCL-g-alginate with calcium ions. It was demonstrated PCL-g-alginate hydrogels can protect an amphiphilic drug (theophylline) in simulated gastric fluid (pH 1.2), and slow down its kinetic release in simulated intestinal fluid (pH 6.8) due to hydrophobic interactions between amphiphilic drug and hydrophobic clusters formed by PCL-g-alginate. Results can be correlated with the physico-chemical properties in salt media and 530-x copolymers present a better drug retention. Kinetics release can also be controlled and strongly slow downed by covering the matrices with a polyelectrolyte membrane based on a cationic polysaccharide, chitosan.ROUEN-BU Sciences (764512102) / SudocROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Age-related decline of abiotic stress tolerance in young Drosophila melanogaster adults

International audienceStress tolerance generally declines with age as a result of functional senescence. Age-dependent alteration of stress tolerance can also occur in early adult life. In Drosophila melanogaster, evidence of such a decline in young adults has only been reported for thermotolerance. It is not known whether early adult life entails a general stress tolerance reduction and whether the response is peculiar to thermal traits. The present work was designed to investigate whether newly eclosed D melanogaster adults present a high tolerance to a range of biotic and abiotic insults. We found that tolerance to most of the abiotic stressors tested (desiccation, paraquat, hydrogen peroxide, deltamethrin, and malathion) was high in newly eclosed adults before dramatically declining over the next days of adult life. No clear age-related pattern was found for resistance to biotic stress (septic or fungal infection) and starvation. These results suggest that newly eclosed adults present a culminating level of tolerance to extrinsic stress which is likely unrelated to immune process. We argue that stress tolerance variation at very young age is likely a residual attribute from the previous life stage (ontogenetic carryover) or a feature related to the posteclosion development

pH-dependent stability of scleroglucan borate gels

International audienceScleroglucan, a neutral exopolysaccharide, forms strong physical gels by crosslinking with borate anions, and undergoes a conformational transition at pH > 13 (triple-helix to coil). A study of stability of scleroglucan/borate gels has been carried out over a wide range of pH and we have clearly observed a pH-dependence on the structure of these systems. The gel is dissolved in very alkaline media due to the conformational transition of scleroglucan and in acidic media, in agreement with thermodynamical competition between dissociation constant of boric acid and complexation constant of scleroglucan/borate system. Influence of polymer and borax concentrations have been also studied and it appeared that erosion of these matrices could be easily controlled as a function of the density of the network and pH. The pH-dependence of scleroglucan/borate gels could be used for controlling the release of macromolecular active substances

Rationalization of the entrapping of bioactive molecules into a series of functionalized porous zirconium terephthalate MOFs

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