Influence of surface conductivity on the apparent zeta potential of amorphous silica nanoparticles

Zeta potential is a physico-chemical parameter of particular importance in describing ion adsorption and double layer interactions between charged particles [1]. However, for metal oxide nanoparticles, the conversion of electrophoretic mobility measurements into zeta potentials is a complex problem. This complexity arises because of their high surface electrical conductivity, which is inversely proportional to the size of the particle [2]. To describe the electrochemical properties of amorphous silica nanoparticles, we use a basic Stern model whose parameters are independently adjusted by potentiometric titration and electrophoretic mobility measurements at high salinity (10-1 M NaCl) [3]. At low ionic strengths, because of the strong retardation and relaxation effect due to charged counter-ions at the silica/water interface, amplitude of the predicted zeta potential is significantly higher than that of the apparent zeta potential estimated with electrophoretic mobility measurements and Smoluchowski equation. Electrophoretic mobilities are calculated using Henry's electrokinetic model [4] with the predicted specific surface conductivities and zeta potentials. The very good agreement between calculated and measured electrophoretic mobilities confirms that the magnitude of the true zeta potential corresponds to the magnitude of the electrical potential located at the outer Helmholtz plane. Therefore, the assumption of the presence of a stagnant diffuse layer at the amorphous silica/water interface is not required. This study was done within the framework of the NANOMORPH Project (ANR-2011-NANO-008) coordinated by BRG

Combining Gene Transfer and Nonhuman Primates to Better Understand and Treat Parkinson’s Disease

Parkinson's disease (PD) is a progressive CNS disorder that is primarily associated with impaired movement. PD develops over decades and is linked to the gradual loss of dopamine delivery to the striatum, via the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). While the administration of L-dopa and deep brain stimulation are potent therapies, their costs, side effects and gradual loss of efficacy underlines the need to develop other approaches. Unfortunately, the lack of pertinent animal models that reproduce DA neuron loss and behavior deficits-in a timeline that mimics PD progression-has hindered the identification of alternative therapies. A complementary approach to transgenic animals is the use of nonhuman primates (NHPs) combined with the overexpression of disease-related genes using viral vectors. This approach may induce phenotypes that are not influenced by developmental compensation mechanisms, and that take into account the personality of animals. In this review article, we discuss the combination of gene transfer and NHPs to develop "genetic" models of PD that are suitable for testing therapeutic approaches

Distinct Transcriptome Expression of the Temporal Cortex of the Primate Microcebus murinus during Brain Aging versus Alzheimer's Disease-Like Pathology

Aging is the primary risk factor of neurodegenerative disorders such as Alzheimer's disease (AD). However, the molecular events occurring during brain aging are extremely complex and still largely unknown. For a better understanding of these age-associated modifications, animal models as close as possible to humans are needed. We thus analyzed the transcriptome of the temporal cortex of the primate Microcebus murinus using human oligonucleotide microarrays (Affymetrix). Gene expression profiles were assessed in the temporal cortex of 6 young adults, 10 healthy old animals and 2 old, “AD-like” animals that presented ß-amyloid plaques and cortical atrophy, which are pathognomonic signs of AD in humans. Gene expression data of the 14,911 genes that were detected in at least 3 samples were analyzed. By SAM (significance analysis of microarrays), we identified 47 genes that discriminated young from healthy old and “AD-like” animals. These findings were confirmed by principal component analysis (PCA). ANOVA of the expression data from the three groups identified 695 genes (including the 47 genes previously identified by SAM and PCA) with significant changes of expression in old and “AD-like” in comparison to young animals. About one third of these genes showed similar changes of expression in healthy aging and in “AD-like” animals, whereas more than two thirds showed opposite changes in these two groups in comparison to young animals. Hierarchical clustering analysis of the 695 markers indicated that each group had distinct expression profiles which characterized each group, especially the “AD-like” group. Functional categorization showed that most of the genes that were up-regulated in healthy old animals and down-regulated in “AD-like” animals belonged to metabolic pathways, particularly protein synthesis. These data suggest the existence of compensatory mechanisms during physiological brain aging that disappear in “AD-like” animals. These results open the way to new exploration of physiological and “AD-like” aging in primates

Effect of citrate on phosphorus availability in soils with constrasted mineralogy : a modelling approach

International audienceAims and Background Plants can exude large amount of carboxylates which ultimately increase phosphate ( P) availability. Both anions compete for adsorption onto soil minerals. Mechanistic modelling approach can be profitably used to understand these competitive interactions in soils. The aim of this study was to use such an approach to investigate citrate effect on P desorption in soils of contrasted mineralogy. Methods As Devau et al., 2011a, three adsorption models w ere used to simulate citrate and P competition onto the major sorbents of the studied soils; 1- pK Tr iple Plane, simple ion exchange and Nica- Donnan. Tested c itrate concentrations w ere representative of those found in the rhizosphere. We considered a large range of pH values. Results At high citrate concentration (100ìM), the larger increase of P availability was found at high pH in Luvisol and Chromic Cambisol and at low pH in Ferralsols. At low er citrate concentration (10ìM), the maximum increase w as predicted at acidic pH in Ferralsols. Surprisingly, a decrease of P availability was calculated in Luvisol and Chromic Cambisol. Conclusion The extent of P desorption is a function of citrate release, soil pH and mineralogy. Predicting the effect of citrate on P availability requires to account for the interactions with clay minerals, not only Fe oxides

Reply to the Comment by JP Gustafsson and D. G. Lumsdon on "Citrate adsorption can decrease soluble phosphate concentration in soils : results of theoretical modeling' by M. Duputel, N. Devau, M. Brossard, B. Jaillard, DL Jones, P. Hinsinger, and F. Gerard

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Citrate adsorption can decrease soluble phosphate concentration in soils : results of theoretical modeling

A major problem for 21st century agriculture is the prospect of P scarcity. Adsorption of PO4 on the soil's solid phase is the primary mechanism regulating P availability. Release of citrate by roots is generally thought to increase the availability of P, which in turn improves P acquisition by plants. However, the interaction between citrate and PO4 remains poorly understood in soils and conflicting results are found in the literature. Here modeling is used to investigate the effects of citrate adsorption on P availability in a chromic cambisol, a luvisol and two ferralsols over a range of soil pH values. The effect of different levels of exchangeable Ca, soil organic C (SOC), dissolved organic C (DOC) and PO4 fertilization were also tested in order to cover a wider range of environmental conditions. Results showed that the competition of citrate for PO4 binding sites was not the only mechanism regulating P availability. Citrate adsorption can also increase PO4 adsorption through electrostatic interactions with adsorbed Ca2+ ions and actively reduce P availability. More precisely, it was found that the addition of 10 lmol citrate kg (1) soil decreased P availability in both chromic cambisol and luvisol. The same trend was predicted by the model with 100 mu mol of citrate kg (1) soil in the chromic cambisol, whereas available P was found to increase in the luvisol. In contrast, the addition of citrate at these two concentrations always increased P availability in the two ferralsols. Increasing exchangeable Ca further decreased P availability in the chromic cambisol and luvisol, while it further increased available P in ferralsols. Additional sensitivity tests showed that DOC concentration had little influence on these results. In contrast, increasing SOC concentration massively counteracted the deleterious influence of citrate in chromic cambisol, while the effect was amplified in luvisol. In ferralsols, it was mainly observed that the increase of SOC further promoted P availability. To conclude, it was found that citrate can either increase or decrease P availability in soil, depending mainly on the occurrence of 2:1 clay minerals and on the concentrations of citrate, adsorbed Ca, and soil organic C. Special attention should, therefore, be given to possible adverse effects of rhizosphere management for improved P nutrition

Acquisition of phosphorus and other poorly mobile nutrients by roots. Where do plant nutrition models fail ?

In the context of increasing global food demand, ecological intensification of agroecosystems is required to increase nutrient use efficiency in plants while decreasing fertilizer inputs. Better exploration and exploitation of soil resources is a major issue for phosphorus, given that rock phosphate ores are finite resources, which are going to be exhausted in decades from now on. We review the processes governing the acquisition by plants of poorly mobile nutrients in soils, with a particular focus on processes at the root-soil interface. Rhizosphere processes are poorly accounted for in most plant nutrition models. This lack largely explains why present-day models fail at predicting the actual uptake of poorly mobile nutrients such as phosphorus under low input conditions. A first section is dedicated to biophysical processes and the spatial/temporal development of the rhizosphere. A second section concentrates on biochemical/biogeochemical processes, while a third section addresses biological/ecological processes operating in the rhizosphere. New routes for improving soil nutrient efficiency are addressed, with a particular focus on breeding and ecological engineering options. Better mimicking natural ecosystems and exploiting plant diversity appears as an appealing way forward, on this long and winding road towards ecological intensification of agroecosystems