title: Molecular and ionic diffusion in aqueous - deep eutectic solvent mixtures: probing inter-molecular interactions using PFG NMR.
abstract: Pulsed field gradient (PFG) NMR has been used to probe self-diffusion of molecular and ionic species in aqueous mixtures of choline chloride (ChCl) based deep eutectic solvents (DESs), in order to elucidate the effect of water on motion and inter-molecular interactions between the different species in the mixtures, namely the Ch(+) cation and hydrogen bond donor (HBD). The results reveal an interesting and complex behaviour of such mixtures at a molecular level. In general, it is observed that the hydroxyl protons ((1)H) of Ch(+) and the hydrogen bond donor have diffusion coefficients significantly different from those measured for their parent molecules when water is added. This indicates a clear and significant change in inter-molecular interactions. In aqueous Ethaline, the hydroxyl species of Ch(+) and HBD show a stronger interaction with water as water is added to the system. In the case of Glyceline, water has little effect on both hydroxyl proton diffusion of Ch(+) and HBD. In Reline, it is likely that water allows the formation of small amounts of ammonium hydroxide. The most surprising observation is from the self-diffusion of water, which is considerably higher that expected from a homogeneous liquid. This leads to the conclusion that Reline and Glyceline form mixtures that are inhomogeneous at a microscopic level despite the hydrophilicity of the salt and HBD. This work shows that PFG NMR is a powerful tool to elucidate both molecular dynamics and inter-molecular interactions in complex liquid mixtures, such as the aqueous DES mixtures.
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK. cd419@hermes.cam.ac.uk.
authors.forename: Carmine
authors.initials: C
authors.lastname: D'Agostino
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK. cd419@hermes.cam.ac.uk.
authors.forename: Lynn F
authors.initials: LF
authors.lastname: Gladden
authors.affiliation: Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK. cd419@hermes.cam.ac.uk.
authors.forename: Mick D
authors.initials: MD
authors.lastname: Mantle
authors.affiliation: Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK. apa1@le.ac.uk.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Abbott
authors.affiliation: Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK. apa1@le.ac.uk.
authors.forename: Essa I
authors.initials: EI
authors.lastname: Ahmed
authors.affiliation: Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK. apa1@le.ac.uk.
authors.forename: Azhar Y M
authors.initials: AYM
authors.lastname: Al-Murshedi
authors.affiliation: Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK. apa1@le.ac.uk.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Harris