Les carences nutritionnelles dans les PVD

Un centre de réhydratation et de réhabilitation nutritionnelle a été implanté à Pikine, ville de 650000 habitants, située à 20 km de Dakar, afin de tester des techniques simples, efficaces et peu coûteuses pour traiter la diarrhée et la malnutrition chez les enfants de moins de 5 ans. La réhydratation par voie orale à l'aide d'une solution à base de farine de riz et la renutrition avec des mélanges nutritifs fabriqués localement associées à un traitement médicamenteux standard ont permis d'obtenir des résultats très encourageants. En effet pour les 233 enfants déshydratés et malnutris qui ont bénéficié de ce traitement le gain de poids a été en moyenne de 10 g/kg poids/jour. Ces résultats montrent donc qu'il est possible de traiter efficacement des enfants diarrhéiques et malnutris dans des structures de soint très simples et pour un faible prix de revient. Ces avantages devraient permettre l'installation de tels centres dans les régions les plus reculées et les plus défavorisées là ou ils sont le plus nécessaires. (Résumé d'auteur

Reducing CO2 to methanol using frustrated Lewis pairs : on the mechanism of phosphine-borane mediated hydroboration of CO2

The full mechanism of the hydroboration of CO2 by the highly active ambiphilic organocatalyst 1-Bcat-2-PPh2-C6H4 (Bcat = catecholboryl) was determined using computational and experimental methods. The intramolecular Lewis pair was shown to be involved in every step of the stepwise reduction. In contrast to traditional frustrated Lewis pair systems, the lack of steric hindrance around the Lewis basic fragment allows activation of the reducing agent while moderate Lewis acidity/basicity at the active centers promotes catalysis by releasing the reduction products. Simultaneous activation of both the reducing agent and carbon dioxide is the key to efficient catalysis in every reduction step

Metal-free catalytic C-H bond activation and borylation of heteroarenes

Transition metal complexes are efficient catalysts for the C-H bond functionalization of heteroarenes to generate useful products for the pharmaceutical and agricultural industries. However, the costly need to remove potentially toxic trace metals from the end products has prompted great interest in developing metal-free catalysts that can mimic metallic systems. We demonstrated that the borane (1-TMP-2-BH2-C6H4)2 (TMP, 2,2,6,6-tetramethylpiperidine) can activate the C-H bonds of heteroarenes and catalyze the borylation of furans, pyrroles, and electron-rich thiophenes. The selectivities complement those observed with most transition metal catalysts reported for this transformation

A highly active phosphine-borane organocatalyst for the reduction of CO2 to methanol using hydroboranes

In this work, we report that organocatalyst 1-Bcat-2-PPh2-C6H4 ((1); cat = catechol) acts as an ambiphilic metal-free system for the reduction of carbon dioxide in presence of hydroboranes (HBR2 = HBcat (catecholborane), HBpin (pinacolborane), 9-BBN (9-borabicyclo[3.3.1]nonane), BH3·SMe2 and BH3·THF) to generate CH3OBR2 or (CH3OBO)3, products that can be readily hydrolyzed to methanol. The yields can be as high as 99% with exclusive formation of CH3OBR2 or (CH3OBO)3 with TON (turnover numbers) and TOF (turnover frequencies) reaching >2950 and 853 h(-1), respectively. Furthermore, the catalyst exhibits "living" behavior: once the first loading is consumed, it resumes its activity on adding another loading of reagents

Étude de l’hydrodynamique de fluides rhéologiquement complexes dans un mélangeur Maxblend® par vélocimétrie laser

Les fluides d’usage industriel présentent très souvent une rhéologie complexe qui a un impact significatif sur la performance des opérations unitaires en génie chimique. Dans le cas du mélange, l’hydrodynamique et la consommation de puissance dépendent fortement de la viscosité et du régime d’écoulement. L’élasticité et la rhéofluidifiance peuvent influer dramatiquement sur l’hydrodynamique. Afin de mieux connaître l’impact d’une rhéologie complexe sur le Maxblend®, qui est reconnu comme un système d’agitation industriel performant, l’écoulement de fluides rhéologiquement complexes a été étudié dans celui-ci. Le Maxblend est utilisé dans des procédés comportant des fluides rhéofluidifiants et viscoélastiques et, comme pour la majorité des systèmes d’agitation, peu d’information existe sur le comportement de ceux-ci en cuve agitée. Une étude expérimentale a été menée avec des fluides newtoniens et non-newtoniens en régime laminaire et de transition. Le fluide newtonien était des solutions diluées de glucose et le Stéol a servis de modèle de fluide très rhéofluidifiant. Un fluide non-newtonien élastique était composé de CMC et de glucose. Les expériences ont été réalisées dans une cuve contenant 35.4L muni d’un Maxblend de 255mm de diamètre et de deux chicanes. Les champs de vitesse ont été mesurés dans le but d’établir des liens entre l’hydrodynamique et la rhéologie. Une forte rhéofluidifiance (n 0.3) ont été étudiés. Le temps de relaxation du fluide viscoélastique était de dix fois supérieure au temps de relaxation du Stéol. Ceci a démontré une élasticité largement supérieure du fluide viscoélastique, ainsi le Stéol a été considéré inélastique dans cette étude. Les champs de vitesse ont été mesurés par vélocimétrie laser (Particle Image Velocimetry ou PIV) bidimensionnelle. Cent mesures se sont révélées suffisantes pour l’atteinte de la convergence des composantes de la vitesse pour chaque régime étudié. Le caractère laiteux de la solution de CMC a été contourné en ajoutant une forte concentration de glucose au solvant. L’observation des champs de vitesses très rhéofluidifiants a révélé la présence de zones ségrégées qui ont été confirmées par la méthode de décoloration. En régime laminaire, l’élasticité a provoqué le renversement du patron d’écoulement et une rotation plutôt solide dans le bas de la cuve. Il a été observé que l’amplitude et la largeur de la distribution des vitesses étaient réduites par la présence de forces élastiques. L’augmentation de la consommation de puissance avec un fluide viscoélastique a été imputée à son caractère élastique. L’analyse de pompage bidimensionnelle obtenue à partir des résultats de la PIV pour un fluide newtonien a démontré l’existence de deux valeurs constantes du nombre de pompage, soit une en régime laminaire (Re < 10) et une en début de transition (Re ≈ 100).------------ Industrial fluids often exhibit complex rheology, which has a significant impact on the performance of unit operations in chemical engineering. In mixing, hydrodynamics and power draw are highly dependent on both viscosity and flow regime. Added effects of shear-thinning and elasticity can dramatically affect fluid dynamics. To better understand the impact of rheologically complex fluids on the Maxblend®, an effective industrial mixer, the dynamics of rheologically complex fluids were studied. The Maxblend mixer is used in processes involving shear-thinning viscoelastic fluids and, as for many impellers, little has been published regarding this rheological behaviour. An experimental study was carried out using Newtonian and non-Newtonian fluids in laminar and early transitional regimes. Diluted glucose fluids where used for the Newtonian model and Steol was used for the highly shear-thinning model. A non-Newtonian elastic fluid was composed of CMC and glucose. The experimental setup consisted of a 35.4-litre tank equipped with two baffles and a 255-mm Maxblend impeller. Flow fields were measured in order to evaluate the effects of high shear-thinning (n 0.3) and relate hydrodynamics and rheology. The measured relaxation times revealed different amounts of elasticity between the highly shear-thinning and the viscoelastic fluids, to a point that the highly shear-thinning was considered inelastic for the purpose of this study. Flow fields were measured by two-dimensional particle image velocimetry (PIV). A total of 100 measurements proved to be sufficient in order to reach convergence of the velocity components for all studied regimes. The turbidity of the aqueous CMC solution was eliminated by adding glucose to the solvent. Isolated zones in the highly shear-thinning case were confirmed by the discoloration technique. Elasticity in the laminar regime produced a reversal of the flow field and a solid body rotation in the bottom region of the tank. Fluid velocity magnitude and spread were observed to be reduced by elastic forces. Elasticity was shown to raise the power draw for the viscoelastic fluid. Two-dimensional pumping number analysis calculated from PIV results showed a constant value in laminar regime (Re < 10) and another constant value in the transitional regime (Re ≈ 100)

Phosphazenes : efficient organocatalysts for the catalytic hydrosilylation of carbon dioxide

Phosphazene superbases are efficient organocatalysts for the metal-free catalytic hydrosilylation of carbon dioxide. They react with CO2 to form the respective phosphine oxides, but in the presence of hydrosilanes, CO2 can be selectively reduced to silyl formates, which can in turn be reduced to methoxysilanes by addition of an extra loading of silanes. Activities reach a TOF of 32 h−1 with a TON of 759. It is also shown that unexpectedly, N,N-dimethylformamide can reduce CO2 to a mixture of silyl formates, acetals and methoxides in the absence of any catalyst

Acting as a molecular tailor : dye structural modifications for improved sensitivity towards lysophosphatidic acids sensing

Lysophosphatidic acids (LPA) are key biomarkers for several physiological processes, the monitoring of which can provide insights into the host’s health. Common lab-based techniques for their detection are cumbersome, expensive and necessitate specialized personnel to operate. LPA-sensitive fluorescent probes have been described, albeit for non-aqueous conditions, which impedes their use in biological matrices. In this paper, we explore in detail the influence of structure on the extent of aggregation-induced fluorescence quenching using specially synthesized styrylpyridinium dyes bearing structural adaptations to bestow them enhanced affinity towards LPA in aqueous media. Spectroscopic investigations supported by time-resolved fluorimetry revealed the contribution of excimer formation to the fluorescence quenching mechanism displayed by the fluorescent probes. Experimental observations of the influence of structure on detection sensitivity were supported by DFT calculations

Adequacy of child anthropometric indicators for measuring nutritional stress at population level: a study from Niakhar, Senegal

Abstract Objective To compare the responsiveness of different anthropometric indicators for measuring nutritional stress among children in developing countries. Design Growth was studied within 6-month intervals in a rural Senegalese community during one dry and two rainy (hungry) seasons. Responsiveness was defined as the change divided by the standard deviation of each anthropometric indicator. Contrast was defined as the difference in responsiveness between dry and rainy seasons. Setting The study was conducted in Niakhar, a rural area of Senegal under demographic surveillance, with contrasted food and morbidity situations between rainy and dry seasons. Subjects Some 5000 children under 5 years of age were monitored at 6-month intervals in 1983-1984. The present analysis was carried out on a sub-sample of children aged 6-23 months with complete measures, totalling 2803 children-intervals. Results In both univariate and multivariate analysis, mid-upper arm circumference was found to be more responsive to nutritional stress than the commonly used weight-for-height Z-score (contrast = −0·64 for mid-upper arm circumference v. −0·53 for weight-for-height Z-score). Other discriminant indicators were: muscle circumference, weight-for-height, BMI and triceps skinfold. Height, head circumference and subscapular skinfold had no discriminating power for measuring the net effect of nutritional stress during the rainy season. Conclusions The use of mid-upper arm circumference for assessing nutritional stress in community surveys should be considered and preferred to other nutritional indicators. Strict standardization procedures for measuring mid-upper arm circumference are required for optimal us

Computing expectation values for RNA motifs using discrete convolutions

BACKGROUND: Computational biologists use Expectation values (E-values) to estimate the number of solutions that can be expected by chance during a database scan. Here we focus on computing Expectation values for RNA motifs defined by single-strand and helix lod-score profiles with variable helix spans. Such E-values cannot be computed assuming a normal score distribution and their estimation previously required lengthy simulations. RESULTS: We introduce discrete convolutions as an accurate and fast mean to estimate score distributions of lod-score profiles. This method provides excellent score estimations for all single-strand or helical elements tested and also applies to the combination of elements into larger, complex, motifs. Further, the estimated distributions remain accurate even when pseudocounts are introduced into the lod-score profiles. Estimated score distributions are then easily converted into E-values. CONCLUSION: A good agreement was observed between computed E-values and simulations for a number of complete RNA motifs. This method is now implemented into the ERPIN software, but it can be applied as well to any search procedure based on ungapped profiles with statistically independent columns