Neutron Diffraction Study of Indole Solvation in Deep Eutectic Systems of Choline Chloride,Malic Acid,and Water |
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| Authors: | Dr Oliver S Hammond Ria Atri Dr Daniel T Bowron Prof Karen J Edler |
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| Institution: | 1. Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath Claverton Down, Bath, BA2 7AY U.K.;2. Centre for Sustainable Chemical Technologies and Department of Chemical Engineering, University of Bath Claverton Down, Bath, BA2 7AY U.K.;3. ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, OX11 0QX U.K. |
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| Abstract: | Deep eutectic systems are currently under intense investigation to replace traditional organic solvents in a range of syntheses. Here, indole in choline chloride-malic acid deep eutectic solvent (DES) was studied as a function of water content, to identify solute interactions with the DES which affect heterocycle reactivity and selectivity, and as a proxy for biomolecule solvation. Empirical Potential Structure Refinement models of neutron diffraction data showed Cholinium]+ cations associate strongly with the indole π-system due to electrostatics, whereas malic acid is only weakly associated. Trace water is sequestered into the DES and does not interact strongly with indole. When water is added to the DES, it does not interact with the indole π-system but is exclusively in-plane with the heterocyclic rings, forming strong H-bonds with the -NH group, and also weak H-bonds and thus prominent hydrophobic hydration of the indole aromatic region, which could direct selectivity in reactions. |
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| Keywords: | deep eutectic solvents green chemistry heterocycles neutron diffraction pi interactions |
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