Dynamic nuclear polarisation NMR of nanosized zirconium phosphate polymer fillers

International audience; Surface functionalisation with organic modifiers of multi-layered zirconium phosphate (ZrP) nanoparticles used as polymer fillers can be directly probed by dynamic nuclear polarisation NMR, which provides unambiguous evidence of the presence of P-O-C chemical bonds at the surface of the ZrP layers, thereby confirming successful functionalisation

Evaluation of the Effect of Chemical or Enzymatic Synthesis Methods on Biodegradability of Polyesters

International audienceThis work compares the biodegradability of polyesters produced by an esterification reaction between glycerol and oleic di-acid (D 18:1) issued from green chemical pathways, via either classical thermo-chemical methods, or an enzymatic method using the immobilized lipase of Candida antartica B (Novozym 435). An elastomeric polymer synthesized by enzymatic catalysis is more biodegradable than an elastomeric thermo-chemical polyester synthesized by a standard chemical procedure. This difference lies in percentage of the dendritic motifs, in values of the degree of substitution, and certainly in cross-links inducing an hyper-branched structure less accessible to the lipolytic enzymes in a waste treatment plant. However, when the elastomeric polymer synthesized by enzymatic catalysis is processed at high temperature as required for certain industrial applications, it presents an identical rate of biodegradation than the chemical polyester. The advantages of the thermo-chemical methods are greater speed and lower cost. Enzymatic synthesis appears be suited to producing polyesters, devoid of metallic catalysts, which must be used without processing at high temperature to keep a high biodegradability

A strategy for probing the evolution of crystallization processes by low-temperature solid-state NMR and dynamic nuclear polarization

Crystallization plays an important role in many areas, and to derive a fundamental understanding of crystallization processes, it is essential to understand the sequence of solid phases produced as a function of time. Here, we introduce a new NMR strategy for studying the time evolution of crystallization processes, in which the crystallizing system is quenched rapidly to low temperature at specific time points during crystallization. The crystallized phase present within the resultant “frozen solution” may be investigated in detail using a range of sophisticated NMR techniques. The low temperatures involved allow dynamic nuclear polarization (DNP) to be exploited to enhance the signal intensity in the solid-state NMR measurements, which is advantageous for detection and structural characterization of transient forms that are present only in small quantities. This work opens up the prospect of studying the very early stages of crystallization, at which the amount of solid phase present is intrinsically low

Characterization of hydroxytyrosol-β-cyclodextrin complexes in solution and in the solid state, a potential bioactive ingredient

This study focused for the first time on characterizing the inclusion complexes between β-cyclodextrin (β-CD) and hydroxytyrosol (HT) in the solid state. In solution, HT and β-CD are able to form a 1:1 inclusion complex with an association constant of 33.2 ± 3.7 M-1. In the solid state, the inclusion complexes prepared by freeze-drying and spray-drying of an equimolar mixture of both partners were characterized and compared by 13C NMR and SEM. After dissolution, their free radical-scavenging ability was also determined by UV–visible spectroscopy. The results show that β-CD and drying processes have no effect on the efficiency of HT to reduce the DPPH radical. The solid state 13C NMR data provided information on the spatial proximity between β-CD and HT and suggest the formation of inclusion complexes for both drying processes compared to the physical mix. However, the morphology of the solids obtained was significantly different, as spherical particles were formed by spray-drying while freeze-drying only provided irregular shapes

Exploiting solid-state dynamic nuclear polarization NMR spectroscopy to establish the spatial distribution of polymorphic phases in a solid material

Solid-state DNP NMR can enhance the ability to detect minor amounts of solid phases within heterogenous materials. Here we demonstrate that NMR contrast based on transport of DNP-enhanced polarization can be exploited in the challenging case of early detection of a small amount of a minor polymorphic phase within a major polymorph, and we show that this approach can yield quantitative information on the spatial distribution of the two polymorphs. We focus on the detection of a minor amount (<4%) of polymorph III of m-aminobenzoic acid within a powder sample of polymorph I at natural isotopic abundance. Based on proposed models of the spatial distribution of the two polymorphs, simulations of 1H spin diffusion allow NMR data to be calculated for each model as a function of particle size and the relative amounts of the polymorphs. Comparison between simulated and experimental NMR data allows the model(s) best representing the spatial distribution of the polymorphs in the system to be established

Monitoring crystallization processes in confined porous materials by dynamic nuclear polarization solid-state nuclear magnetic resonance

Establishing mechanistic understanding of crystallization processes at the molecular level is challenging, as it requires both the detection of transient solid phases and monitoring the evolution of both liquid and solid phases as a function of time. Here, we demonstrate the application of dynamic nuclear polarization (DNP) enhanced NMR spectroscopy to study crystallization under nanoscopic confinement, revealing a viable approach to interrogate different stages of crystallization processes. We focus on crystallization of glycine within the nanometric pores (7–8 nm) of a tailored mesoporous SBA-15 silica material with wall-embedded TEMPO radicals. The results show that the early stages of crystallization, characterized by the transition from the solution phase to the first crystalline phase, are straightforwardly observed using this experimental strategy. Importantly, the NMR sensitivity enhancement provided by DNP allows the detection of intermediate phases that would not be observable using standard solid-state NMR experiments. Our results also show that the metastable β polymorph of glycine, which has only transient existence under bulk crystallization conditions, remains trapped within the pores of the mesoporous SBA-15 silica material for more than 200 days

Insights into the crystallization and structural evolution of glycine dihydrate by in situ solid-state NMR spectroscopy

In situ solid‐state NMR spectroscopy is exploited to monitor the structural evolution of a glycine/water glass phase formed on flash cooling an aqueous solution of glycine, with a range of modern solid‐state NMR methods applied to elucidate structural properties of the solid phases present. The glycine/water glass is shown to crystallize into an intermediate phase, which then transforms to the β polymorph of glycine. Our in situ NMR results fully corroborate the identity of the intermediate crystalline phase as glycine dihydrate, which was first proposed only very recently

Applications et développements des méthodes de résonance magnetique nucléaire haute résolution à l'état solide pour les matériaux organiques et inorganiques

On présente des applications de la résonance magnétique nucléaire (RMN) du solide sur des matériaux organiques et inorganiques. Après une brève introduction aux concepts de la RMN du solide, on introduit les principales techniques RMN pour l'analyse des matériaux organiques (MAS, CPMAS) appliquées ensuite à l'étude du papier "LINTERS". Les résultats des expériences de relaxation (T1r,), de filtre dipolaire et 2D WISE sont traités pour estimer les dimensions des pores contenant l'eau. On présente les techniques RMN adaptées à l'étude des matériaux inorganiques et on applique la technique MQMAS à l'étude de la turquoise. Une nouvelle technique d'édition spectrale, ORIACT, spécifique aux noyaux quadripolaires est décrite. On rappelle les concepts des impulsions SPIN-LOCK pour les transferts adiabatiques des cohérences et on démontre expérimentalement l'augmentation de résolution obtenue avec la méthode 23NA ORIACT, par rapport au RIACT, sur l'étude des zéolithes.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF