Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

The dynamic behavior of tetrapropylammonium (TPA) cations in the clear precursor sols for silicalite synthesis has been investigated by 1H diffusion ordered spectroscopy (DOSY), T1, T2, and T1ρ 1H relaxation, as well as 1H→13C cross polarization (CP) nuclear magnetic resonance. The DOSY NMR experiments showed the presence of strong solute–solvent interactions in concentrated sols, which are decreasing upon dilution. Similarities in dependence of diffusion coefficients with fractional power of the viscosity constant observed for nanoparticles, TPA cations and water led to the conclusion that they aggregate as anisotropic silicate-TPA particles. Relaxation studies as well as 1H→13C CP experiments provide information on dynamic properties of ethanol, water and TPA cations, which are function of silicate aggregates. The general tendency showed that the presence of silicate as oligomers and particles decreases the relaxation times, in particular T2 and T1ρH, as a consequence of involvement of these latter in ion-pairing interactions with water-solvated TPA molecules slowing down their mobility. Furthermore, from the 1H→13C CP dynamics curve profiles a change in the CP transfer regime was observed from fast (TCH << T1ρH) for solutions without silicates to moderate (TCH~T1ρH) when silicates are interacting with the TPA cations that may reflect the occlusion of TPA into flexible silicate hydrate aggregates

Unlocking the observation of different proton populations in fluorinated polymers by solid-state 1 H and 19 F double resonance NMR spectroscopy

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Unlocking the observation of different proton populations in fluorinated polymers by solid-state H-1 and F-19 double resonance NMR spectroscopy

Nafion proton exchange membranes (PEMs) for fuel cell applications are extensively studied and commercially applied, but their unique proton conduction capabilities are still somewhat unexplained. For studying proton dynamics in situ, molecular level spectroscopic techniques have been of limited utility so far. By solid-state 1H and 19F double resonance nuclear magnetic resonance (NMR) spectroscopy using the recently revived multiple contact cross-polarization (MC-CP) pulse sequence along with double-quantum 1H-1H filtering, high resolution proton populations distinct from the dominant water resonance were observed in Nafion for the first time. This methodology quenches signal decay due to spin-lattice relaxation in the rotating frame and enables magnetization transfer between the relatively mobile 1H and 19F spin baths in Nafion. Further studies of these previously unrevealed proton populations will lead to a better understanding of the Nafion proton conduction mechanism and proton exchange processes in general.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The PCCP Owner Societies have an exclusive publication licence for this journal history: Received 14 June 2016; Accepted 15 September 2016; Accepted Manuscript published 16 September 2016; Advance Article published 7 October 2016; Version of Record published 19 October 2016status: publishe

Développement d’un procédé industriel de cristallisation d’une molécule d’intérêt pharmaceutique

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EXAFS, Raman and 31P NMR study of amorphous titanium phosphates

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Développement d’un procédé industriel de cristallisation d’une molécule d’intérêt pharmaceutique

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