title: Structural studies on choline-carboxylate bio-ionic liquids by x-ray scattering and molecular dynamics.
abstract: We report a X-ray diffraction and molecular dynamics study on three choline-based bio-ionic liquids, choline formate, [Ch] [For], choline propanoate, [Ch][Pro], and choline butanoate, [Ch][But]. For the first time, this class of ionic liquids has been investigated by X-ray diffraction. Experimental and theoretical structure factors have been compared for each term of the series. Local structural organization has been obtained from ab initio calculations through static models of isolated ion pairs and dynamic simulations of small portions of liquids through twelve, ten, and nine ion pairs for [Ch][For], [Ch][Pro], and [Ch][But], respectively. All the theoretical models indicate that cations and anions are connected by strong hydrogen bonding and form stable ion pairs in the liquid that are reminiscent of the static ab initio ion pairs. Different structural aspects may affect the radial distribution function, like the local structure of ion pairs and the conformation of choline. When small portions of liquids have been simulated by dynamic quantum chemical methods, some key structural features of the X-ray radial distribution function were well reproduced whereas the classical force fields here applied did not entirely reproduce all the observed structural features.
authors.affiliation: Department of Physical and Chemical Sciences, University of L'Aquila, Via Vetoio, L'Aquila I-67100, Italy.
authors.forename: Luana
authors.initials: L
authors.lastname: Tanzi
authors.affiliation: Department of Physical and Chemical Sciences, University of L'Aquila, Via Vetoio, L'Aquila I-67100, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Ramondo
authors.affiliation: Department of Chemistry, University of Rome 'La Sapienza', P.le Aldo Moro 5, I-00185 Rome, Italy.
authors.forename: Ruggero
authors.initials: R
authors.lastname: Caminiti
authors.affiliation: Department of Chemistry, University of Rome 'La Sapienza', P.le Aldo Moro 5, I-00185 Rome, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Campetella
authors.affiliation: Department of Chemistry, University of Rome 'La Sapienza', P.le Aldo Moro 5, I-00185 Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Di Luca
authors.affiliation: Department of Chemistry, University of Rome 'La Sapienza', P.le Aldo Moro 5, I-00185 Rome, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Gontrani
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D002794:Choline / Q000737:chemistry*; D006860:Hydrogen Bonding; D052578:Ionic Liquids / Q000737:chemistry*; D008962:Models, Theoretical; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D011789:Quantum Theory; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D002264:Carboxylic Acids; D052578:Ionic Liquids; D002794:Choline