Combination of 13 C/ 113 Cd NMR, potentiometry, and voltammetry in characterizing the interactions between Cd and two models of the main components of soil organic matter

International audienceThis work allowed the characterization of the Cd-binding sites of two compounds taken as models for exudates, the main components of soil organic matter (SOM). The studied compounds were exopolysaccharides (EPS), specifically exudates of roots (polygalacturonic acid) and of soil bacteria (Phytagel). Potentiometric acid– base titrations were performed and fitting of the obtained results indicated the presence of two main classes of acidic sites, defined by their pK a values, for both EPS but of a different nature when comparing the two compounds. The two studied exopolysaccharides presented different acidic/ basic site ratios: 0.15 for Phytagel and 0.76 for polyga-lacturonic acid. Spectroscopic techniques (13 C/ 113 Cd NMR, FTIR) distinguished different Cd surroundings for each of the studied EPS, which is in agreement with the titration results. Furthermore, these analyses indicated the presence of –COOH and –OH groups in various proportions for each exopolysaccharide, which should be linked to their reactiv-ity towards cadmium. Cadmium titrations (voltammetric measurements) also differentiated different binding sites for each compound and allowed the determination of the strength of the Cd-binding site of the EPS. Fitting of the results of such voltammetric measurements was performed using PROSECE (Programme d'Optimisation et de Speci-ation Chimique dans l'Environnement), a software coupling chemical speciation calculation and binding parameter optimization. The fitting, taking into account the Cd 2+ /H

Quantitative In Vivo Magnetic Resonance Spectroscopy Using Synthetic Signal Injection

Accurate conversion of magnetic resonance spectra to quantitative units of concentration generally requires compensation for differences in coil loading conditions, the gains of the various receiver amplifiers, and rescaling that occurs during post-processing manipulations. This can be efficiently achieved by injecting a precalibrated, artificial reference signal, or pseudo-signal into the data. We have previously demonstrated, using in vitro measurements, that robust pseudo-signal injection can be accomplished using a second coil, called the injector coil, properly designed and oriented so that it couples inductively with the receive coil used to acquire the data. In this work, we acquired nonlocalized phosphorous magnetic resonance spectroscopy measurements from resting human tibialis anterior muscles and used pseudo-signal injection to calculate the Pi, PCr, and ATP concentrations. We compared these results to parallel estimates of concentrations obtained using the more established phantom replacement method. Our results demonstrate that pseudo-signal injection using inductive coupling provides a robust calibration factor that is immune to coil loading conditions and suitable for use in human measurements. Having benefits in terms of ease of use and quantitative accuracy, this method is feasible for clinical use. The protocol we describe could be readily translated for use in patients with mitochondrial disease, where sensitive assessment of metabolite content could improve diagnosis and treatment

Relation between the corrosion resistance and the chemical structure of hybrid sol-gel coatings with interlinked inorganic-organic network

International audienceOrganic-inorganic hybrid coatings have been prepared by a sol-gel route from 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) with triethylenetetramine (TETA) added in the sol formulation. The main goal of this research was to evaluate how the chemical structure of the GPTMS/TEOS/TETA hybrid coatings influences the corrosion of mild steel. The presence of TETA as an epoxy opening agent offers the possibility to form interconnected epoxy-amine and silica networks. It was found by means of 29Si HRMAS NMR spectroscopy that TETA acted as an efficient basic catalyst for the condensation of GPTMS and TEOS. This accelerates the gelation and gives limited shelf life to GPTMS/TEOS/TETA sols. Structural characterization of the cured hybrid coatings was performed using 13C and 29Si Solid State NMR spectroscopies. The results show that the epoxy amine reaction is the principal epoxide ring opening reaction. The slow formation of diol units with sols prepared with an excess of epoxy groups has also been observed. It was found that the polymerization of the organic network hindered the polymerization of the siloxane network. As a result, the film based on an epoxy rich off-stoichiometric formulation had a higher Persoz hardness value compared to the stoichiometric film.The corrosion behavior of the coatings in neutral chloride solution was studied through electrochemical impedance spectroscopy (EIS). The results revealed that barrier properties have been improved by the addition of TETA to sol-gel films. The films based on epoxy rich off-stoichiometric formulation and those base on stoichiometric formulation resulted in similar barrier properties but a higher resistance to interfacial delamination was observed for the epoxy rich off-stoichiometric films. The relationship between the film structure and its corrosion behavior was discussed

19F NMR: a valuable tool for studying biological events

With the spectacular advancement of NMR techniques and the flourishing of fluorine chemistry allowing the synthesis of various fluorinated molecules, (19)F NMR represents a compelling option for studying myriad biological events ranging from the structure and function of biomolecules, enzymatic mechanisms, and metabolic pathways, through to drug screening and discovery as well as medical imaging. In this tutorial review, we aim to provide readers with a brief overview of the recent applications of (19)F NMR in various areas relating to biological and biomedical research, together with a brief introduction of specific hardware improvements permitting the practical implementation of (19)F NMR

Profiling of metabolite content of Moringa oleifera leaf samples using solid-state 13C NMR

International audienceMoringa oleifera (MO) is a multipurpose tree widespread in tropical countries. Many studies have shown that MO leaves have a high nutritional value and a wide range of biological activities [1,2]. Numerous products derived from MO leaf powders (MOLP) are easily available and without quality control. The aim of this study was to find a rapid method to control the quality of MOLP. Solid-state 13C NMR associated to multivariate analysis applied on MOLP samples from various geographic origins have shown that it is possible to discriminate samples on the basis of relative areas calculated from specific spectral NMR regions [3]. Principal Component (PC) Analysis on NMR data allowed to differentiate samples according to PC1 and PC2 (with 65% and 25% of explained variance respectively). The signal of alkyl carbons was assigned to lipids; O-alkyl and di-O-alkyl carbons signals were mainly attributed to carbohydrates and polysaccharides while methoxyl carbons came from polysaccharides and lignin. Aromatic and phenolic carbons signals were attributed to lignin and amino acids while carboxyl carbon signals were assigned to esters or acids along with carbon atoms from the peptide bond. Samples from Egypt, Cameroon and Burkina Faso appeared to be richer in carbohydrates and polysaccharides according to PC1, whereas samples from Chad, Indonesia and Dominican Republic were characterized by a highest lipid and lignin content. According to PC2, both sample sets from Burkina Faso and Cameroon presented one sample with relatively high phenolic and aromatic contents. While this approach could not give absolute metabolite content, it appeared to be efficient to classify different MOLP and select their provenance in order to choose a particular sample considering phytochemical and/or pharmacological interests and furthermore to ensure a consistent quality of the material

Profiling of metabolite content of Moringa oleifera leaf samples using solid-state 13C NMR

International audienceMoringa oleifera (MO) is a multipurpose tree widespread in tropical countries. Many studies have shown that MO leaves have a high nutritional value and a wide range of biological activities [1,2]. Numerous products derived from MO leaf powders (MOLP) are easily available and without quality control. The aim of this study was to find a rapid method to control the quality of MOLP. Solid-state 13C NMR associated to multivariate analysis applied on MOLP samples from various geographic origins have shown that it is possible to discriminate samples on the basis of relative areas calculated from specific spectral NMR regions [3]. Principal Component (PC) Analysis on NMR data allowed to differentiate samples according to PC1 and PC2 (with 65% and 25% of explained variance respectively). The signal of alkyl carbons was assigned to lipids; O-alkyl and di-O-alkyl carbons signals were mainly attributed to carbohydrates and polysaccharides while methoxyl carbons came from polysaccharides and lignin. Aromatic and phenolic carbons signals were attributed to lignin and amino acids while carboxyl carbon signals were assigned to esters or acids along with carbon atoms from the peptide bond. Samples from Egypt, Cameroon and Burkina Faso appeared to be richer in carbohydrates and polysaccharides according to PC1, whereas samples from Chad, Indonesia and Dominican Republic were characterized by a highest lipid and lignin content. According to PC2, both sample sets from Burkina Faso and Cameroon presented one sample with relatively high phenolic and aromatic contents. While this approach could not give absolute metabolite content, it appeared to be efficient to classify different MOLP and select their provenance in order to choose a particular sample considering phytochemical and/or pharmacological interests and furthermore to ensure a consistent quality of the material

Para-Sulfonated Calixarenes Used as Synthetic Receptors for Complexing Photolabile Cholinergic Ligand

International audienceThe water‐soluble tetra‐, hexa‐ and octasulfonated calix[4]arenes, calix[6]arenes, and calix[8]arenes 1–3, respectively, were investigated as potential synthetic receptors for photolabile cholinergic ligand A, a photolytic precursor of choline. Ligand A is a bifunctional molecule carrying a photolabile 2‐nitrobenzyl group at one end and a choline moiety at the other end. Results from NMR studies have shown that calixarenes 1–3 form stable 1 : 1 complexes with A, having similar binding potential to that observed with the cholinergic enzymes acetylcholinesterase and butyrylcholinesterase. Further studies have suggested that calix[8]arene forms a ditopic complex by binding concomitantly to both the cationic choline moiety and the aromatic photolabile group of A, whereas calix[4]arene and calix[6]arene form monotopic complexes with A. The ditopic complex between calix[8]arene and A results from mutually induced fitting process, while the monotopic complexes between calix[4]arene and A can be regulated by pH: at neutral pH, calix[4]arene specifically binds the cationic choline moiety, while, at acidic pH, it complexes unselectively both the cationic choline moiety and the aromatic group of A. Our results show that para‐sulfonated calixarenes are versatile artificial receptors which bind in various ways to the bifunctional photolabile cholinergic ligand A, depending on their size, geometry, and state of protonation

Tracking the fate of γ-aminopropyltriethoxysilane from the sol state to the dried film state

International audienceIn this work, 29Si nuclear magnetic resonance and Fourier-transformed infrared spectroscopy were combined to study the hydrolysis and polycondensation of γ-aminopropyltriethoxysilane (γ-APS), both in the liquid sol state and in the film state. γ-APS sols were prepared in methanol or ethanol solvent in the pH range from 5.7 to 11 and deposited. The aim of the present study was to get the most complete picture in regard to the chemical events and time scale of these events. Transesterification reactions between γ-APS and methanol result in faster kinetics in methanol compared to ethanol. γ-APS films were deposited on aluminium and dried at ambient conditions (23 °C, 55% relative humidity). The silane films reached a chemical equilibrium in a couple of minutes (natural pH of 11) to 1 h (pH 7) depending on the pH of the silane solution. From a practical perspective, the results obtained here might give some clues to define an optimized schedule for the application of γ-APS coupling agent to metals

Does anthracene affect microbial activities and organic matter decomposition ? A comparative study in Pinus halepensis litters from Mediterranean coastal and inland areas

The widespread concern about pollution caused by Polycyclic Aromatic Hydrocarbons (PAHs) raises the question of how they affect soil microbial communities which are potentially involved in the transformation of these pollutants. Using microcosms, we describe the effect of anthracene, a model PAH, on microbial communities inhabiting a Pinus halepensis litter from both coastal (COS) and inland (INL) Mediterranean sites. The microcosms were incubated over 3 months (25 degrees C, 60% WHC) and the effects of anthracene on microbial activities of both litters were monitored. Different enzyme activities (laccase, cellulase, beta-glucosidase and acid phosphatase) and microbial respiration were measured and variations in litter chemical composition over incubation were determined using C-13 Nuclear Magnetic Resonance (NMR) from both sites. Our results show that lignocellulolytic enzymes increased markedly after a 3-month incubation in COS microcosms, especially in the presence of anthracene, whereas INL microcosms were not similarly affected. These results show that anthracene not only has no toxic effect on the microbial activities tested but actually enhances the lignocellulolytic activities of the fungal communities from coastal litters, demonstrating the detoxification potential and resistance of stressed Mediterranean coastal ecosystems