Mobility of organic pollutants in soil components. What role can magic angle spinning NMR play ?

International audienceThe adsorption-desorption mechanisms at the interface between organic and inorganic soil colloids influence the movement of pesticides and hence their bioavailability and biotransformation processes. Direct analyses of soils have been reported in the literature with the use of solid-state nuclear magnetic resonance (NMR) spectroscopy on dry samples. We recently demonstrated the potential of the 1H high resolution magic angle spinning (MAS) NMR technique to study such mechanisms in situ on highly hydrated samples. By using a well-characterized soil model, it was possible to distinguish the mobile and immobile pesticide unambiguously. In the present communication, a short review of MAS NMR techniques that allow covalent and non-covalent bond analysis is provided. The results obtained in our group on the adsorption of some pollutants such as phosphonomethylglycine (glyphosate), MCPA and 2-benzothiazole sulphonate are also presented. Specifically, we focus on the potential of MAS NMR spectroscopy for probing the behaviour (mobility) of these organic pollutants loaded onto the surface of different clays. The influence of clay hydration on NMR spectra has also been evaluate

Instantaneous stereocomplex driven self-assembly of enantiomeric poly(vinyl alcohol)-graft-oligo(lactide) copolymers in DMSO and thin film formation thereof

International audienceThe ability of enantiomeric graft copolymers composed of partially acetylated poly(vinyl alcohol) (PVA) as backbone and oligo(L-lactide) (OLLA) or oligo(D-lactide) (DP in lactate units = 20) as grafts to form stereocomplex in bulk and in solution is described. First, the copolymers are obtained by grafting onto the backbone through esterification, the oligomers that are priorly synthesized by ring-opening polymerization of the corresponding monomer and subsequently derived. By controlling the reaction time or the molar ratio between the reactants, this synthetic strategy makes it possible to tune the extent of modification of PVA for a given molecular weight of grafts. Then, racemic mixture of PVA-g-OLLA and PVA-g-ODLA is prepared in solution using DMSO as solvent: an Inter Polymer Complex is spontaneously and instantaneously formed, due to quantitative stereocomplexation-driven self assembly between the OLLA and ODLA grafts. This fastest ever reported stereocomplexation opens new perspectives in the design of PVA-based materials with biodegradable crosslinks, as demonstrated with the successive spin-coating of the racemic mixture on a flat substrate to readily form thin films that are not obtained when a homochiral graft copolymer-containing solution is used

Formation of new alkyl functionalized poly(ethylene terephthalate) oligomers through exchange reactions with titanium alkoxides in melt conditions

International audienceA new and original method to recycle the PET into low molar masses di-alkyl functionalized oligomers is proposed. Ti(OnBu)4 and Ti(OnPr)4 used through alkoxide ligand exchange reactions, with a vertical twin-screw micro-extruder laboratory process, allow in a very short range of time around 10 min at high temperature to shorten the PET chains length. In homogeneous-like considered conditions fast decreases of molecular chains length and melting temperatures were observed. The structures of these oligomers were identified by 1H NMR, MALDI-ToF and SEC methods, and then correlated with physical properties determined by DSC and TGA analyses. Very useful tools are proposed to control the chemical reaction in order to scale up this process to reactive extrusion at relatively low temperatures

1 H and 29Si NMR Spectroscopy as a Powerful Analytical Tool to Evaluate the Activity of Various Platinum-Based Catalysts in Model Olefin Hydrosilylation

International audienc

Mobility of absorbed organic pollutants on clays monitored by various mass NMR approaches

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Mobility of organic pollutants adsorbed on clays monitored by various MAS NMR approaches.

Poste

Analysis of hydroxycinnamic acids degradation in Agrobacterium fabrum reveals a CoA-dependent, beta-oxidative deacetylation pathway

International audienceThe soil and rhizosphere inhabiting bacterium Agrobacterium fabrum (genomospecies G8 of the A. tumefaciens species complex) is known to have species-specific genes involved in ferulic acid degradation. Here, we characterized by genetic and analytical means intermediates of degradation as feruloyl-CoA, 4-hydroxy-3-methoxyphenyl-β-hydroxypropionyl-CoA, 4-hydroxy-3-methoxyphenyl-β-ketopropionyl-CoA, vanillic acid and protocatechuic acid. Genes atu1416, atu1417 and atu1420 have been experimentally shown necessary for the degradation of ferulic acid. Moreover, genes atu1415 and atu1421 have been experimentally demonstrated to be essential for this degradation and are proposed to encode a phenylhydroxypropionyl-CoA dehydrogenase and a HMPKP-CoA β-keto-thiolase, respectively. We thus demonstrated that the A. fabrum-hydroxycinnamic degradation pathway is an original coenzyme-A-dependent β-oxidative deacetylation that could also transform p-coumaric and caffeic acids. Finally, we showed that this pathway enables metabolism of toxic compounds from plants and their use for growth, likely providing this species an ecological advantage in hydroxycinnamic-rich environments such as plant roots or decaying plant materials

Fluorescent gold nanoparticles with chain-end grafted RAFT copolymers: influence of the polymer molecular weight and type of chromophore

International audienceFluorescent gold nanoparticles (GNPs) were prepared by chain-end grafting of RAFT copolymers bearing multiple fluorophores distributed along the chain. Two different synthetic approaches in water were first studied with well-defined and biocompatible homopolymers. Both led to very stable samples and the corona thickness at the gold surface increased with the polymer molecular weight. The two-step ligand exchange approach was then selected to synthesize GNPs grafted with polymer–chromophore conjugates exhibiting different molecular weights, backbone architectures and chromophores. Again, the thickness of the organic corona increased with the polymer molecular weight but was also dependent on the conformation of the conjugate chains which depends on the nature of the chromophores. By adjusting these parameters, it was possible to control the average chromophore–gold distance which is of paramount importance for the fluorescence properties of the nanoparticles. We indeed showed that the fluorescence of the hybrid nano-objects increased with the corona thickness

Chiral Truxene‐Based Self‐Assembled Cages: Triple Interlocking and Supramolecular Chirogenesis

Incorporating chiral elements in host‐guest systems currently focuses much attention, which results from the major impact such structures may have onto a wide range of applications, from pharmaceuticals to materials science and beyond. Moreover, the development of multi‐responsive and ‐functional systems is highly desirable since they offer numerous benefits. In this context, we describe herein the construction of a metal‐driven self‐assembled cage that associates a chiral truxene‐based ligand and a bis‐ruthenium complex. The maximum separation between both facing chiral units in the assembly is fixed by the intermetallic distance within the lateral bis‐ruthenium complex (8.4 Å). The resulting chiral cavity was shown to encapsulate polyaromatic guest molecules, but also to afford a chiral triply interlocked [2]catenane structure. The formation of the latter occurs at high concentration, while its disassembly could be achieved by addition of a planar achiral molecule. Interestingly the latter exhibits induced circular dichroism signature when trapped within the chiral cavity, demonstrating the cage ability for inducing supramolecular chirogenesis.</p