120 research outputs found

    In situ study of reaction kinetics using compressed sensing NMR.

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    We demonstrate the application of Compressed Sensing-NMR to decrease the data acquisition time of 2D COSY NMR from >5 h to ∼1.5 h such that the kinetics of a reaction are followed, along with identification of intermediate and product species.The authors would like to acknowledge the financial support of the EPSRC (Grants No. EP/G011397/1, EP/F047991/1 and EP/ K039318/1) and Microsoft Research.This is the final published version. It first appeared at http://pubs.rsc.org/en/Content/ArticleLanding/2014/CC/c4cc06051b#!divAbstract

    Surface diffusion in catalysts probed by APGSTE NMR

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    In this work we report the application of a recently developed experimental protocol using Pulsed Field Gradient (PFG) Nuclear Magnetic Resonance (NMR) techniques to simultaneously assess bulk pore and surface diffusion coefficients in liquid saturated porous catalysts. This method has been developed to study solvent effects on the diffusion of methyl ethyl ketone (MEK) in mesoporous 1 wt% Pd/Al2O3 catalyst trilobes. The selection of solvents used in this work is known to have a complex effect on reaction rates and hence catalyst performance in heterogeneous liquid phase catalysis. Here, we report the bulk pore and surface diffusion characteristics of MEK, water and isopropyl alcohol (IPA) in 1 wt% Pd/Al2O3 catalyst trilobes. The results show that the physicochemical interactions of molecules in the porous catalyst matrix are very different for the different molecules. We also find that the mobility of water appears to be affected strongest by the catalyst surface

    Diffusion and swelling measurements in pharmaceutical powder compacts using terahertz pulsed imaging.

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    Tablet dissolution is strongly affected by swelling and solvent penetration into its matrix. A terahertz-pulsed imaging (TPI) technique, in reflection mode, is introduced as a new tool to measure one-dimensional swelling and solvent ingress in flat-faced pharmaceutical compacts exposed to dissolution medium from one face of the tablet. The technique was demonstrated on three tableting excipients: hydroxypropylmethyl cellulose (HPMC), Eudragit RSPO, and lactose. Upon contact with water, HPMC initially shrinks to up to 13% of its original thickness before undergoing expansion. HPMC and lactose were shown to expand to up to 20% and 47% of their original size in 24 h and 13 min, respectively, whereas Eudragit does not undergo dimensional change. The TPI technique was used to measure the ingress of water into HPMC tablets over a period of 24 h and it was observed that water penetrates into the tablet by anomalous diffusion. X-ray microtomography was used to measure tablet porosity alongside helium pycnometry and was linked to the results obtained by TPI. Our results highlight a new application area of TPI in the pharmaceutical sciences that could be of interest in the development and quality testing of advanced drug delivery systems as well as immediate release formulations.We would like to thank Huxley Bertram Engineering Ltd.,Cambridge, UK for making time available on the compactionsimulator and Martin Bennett from Huxley Bertram for helppreparing samples. We would also like to acknowledge EvonikIndustries, Germany for providing Eudragit RSPO. S.Y. wouldlike to thank the UK Engineering and Physical Sciences Re-search Council for financial support.This is the final version of the article. It was originally published online in the Journal of Pharmaceutical Sciences, 2015, doi: 10.1002/jps.24376
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