Interaction and dynamics of (alkylamide + electrolyte) deep eutectics: dependence on alkyl chain-length, temperature, and anion identity.
13 Mar 2014-Journal of Chemical Physics (American Institute of Physics)-Vol. 140, Iss: 10, pp 104514-104514
TL;DR: Representative all-atom molecular dynamics simulations of (CH3CONH2 + LiX) DEs at different temperatures reveal strongly stretched exponential relaxation of wavevector dependent acetamide self dynamic structure factor with time constants dependent both on ion identity and temperature, providing justification for explaining the fluorescence results in terms of temporal heterogeneity and amide clustering in these multi-component melts.
Abstract: Here we investigate the solute-medium interaction and solute-centered dynamics in (RCONH2 + LiX) deep eutectics (DEs) via carrying out time-resolved fluorescence measurements and all-atom molecular dynamics simulations at various temperatures. Alkylamides (RCONH2) considered are acetamide (CH3CONH2), propionamide (CH3CH2CONH2), and butyramide (CH3CH2CH2CONH2); the electrolytes (LiX) are lithium perchlorate (LiClO4), lithium bromide (LiBr), and lithium nitrate (LiNO3). Differential scanning calorimetric measurements reveal glass transition temperatures (Tg) of these DEs are ∼195 K and show a very weak dependence on alkyl chain-length and electrolyte identity. Time-resolved and steady state fluorescence measurements with these DEs have been carried out at six-to-nine different temperatures that are ∼100–150 K above their individual Tgs. Four different solute probes providing a good spread of fluorescence lifetimes have been employed in steady state measurements, revealing strong excitation wavelength dependence of probe fluorescence emission peak frequencies. Extent of this dependence, which shows sensitivity to anion identity, has been found to increase with increase of amide chain-length and decrease of probe lifetime. Time-resolved measurements reveal strong fractional power dependence of average rates for solute solvation and rotation with fraction power being relatively smaller (stronger viscosity decoupling) for DEs containing longer amide and larger (weaker decoupling) for DEs containing perchlorate anion. Representative all-atom molecular dynamics simulations of (CH3CONH2 + LiX) DEs at different temperatures reveal strongly stretched exponential relaxation of wavevector dependent acetamide self dynamic structure factor with time constants dependent both on ion identity and temperature, providing justification for explaining the fluorescence results in terms of temporal heterogeneity and amide clustering in these multi-component melts.
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TL;DR: A detailed review of the current literature reveals the lack of predictive understanding of the microscopic mechanisms that govern the structure-property relationships in deep eutectic solvents, and highlights recent research efforts to elucidate the next steps needed to develop a fundamental framework needed for a deeper understanding.
Abstract: Deep eutectic solvents (DESs) are an emerging class of mixtures characterized by significant depressions in melting points compared to those of the neat constituent components. These materials are promising for applications as inexpensive "designer" solvents exhibiting a host of tunable physicochemical properties. A detailed review of the current literature reveals the lack of predictive understanding of the microscopic mechanisms that govern the structure-property relationships in this class of solvents. Complex hydrogen bonding is postulated as the root cause of their melting point depressions and physicochemical properties; to understand these hydrogen bonded networks, it is imperative to study these systems as dynamic entities using both simulations and experiments. This review emphasizes recent research efforts in order to elucidate the next steps needed to develop a fundamental framework needed for a deeper understanding of DESs. It covers recent developments in DES research, frames outstanding scientific questions, and identifies promising research thrusts aligned with the advancement of the field toward predictive models and fundamental understanding of these solvents.
911 citations
12 Nov 2018
TL;DR: An all-atom molecular dynamics simulation study to investigate the influence of water on the molecular level arrangement of reline deep eutectic solvent for different hydration levels reveals that at and above 41 wt % of water, the molecular arrangement of Reline drastically changes and set to transition from reline to an aqueous solution of relines components with further increase in the hydration level.
Abstract: In this article, we have performed an all-atom molecular dynamics simulation study to investigate the influence of water on the molecular level arrangement of reline deep eutectic solvent for different hydration levels ranging from 3.4 to 58.1 wt % of water and complemented the observations of recently measured neutron scattering experimental data. This study is particularly important because water is being introduced as a second hydrogen bond donor/acceptor in reline, wherein the structure is primarily governed by hydrogen bonding and electrostatic interactions. We have analyzed the simulated X-ray scattering structure functions, their partial components, and hydrogen bonding interactions to understand the effects of water on various intermolecular interactions in reline–water mixtures. It is observed that at lower hydration level, reline structure is qualitatively retained. At higher hydration level, most water molecules preferentially solvate chloride anions and ammonium group of choline cations mostly...
111 citations
TL;DR: It is demonstrated that nanoscale spatial heterogeneity is exhibited profoundly by the segregated domains of the constituent electrolyte, and the principal peak in S(q) is because of all sorts of close-contact correlations.
Abstract: In this article, we report a molecular dynamics simulation study on the X-ray and neutron scattering structures of deep eutectic solvents (DESs) and show that the DESs studied possess unique spatial heterogeneity on molecular length scales. The simulated X-ray and neutron scattering structure functions (S(q)s) of the DESs made of alkylamide + Li(+)/ClO4(-) display two peaks in the intermolecular region of the S(q)s. As a signature of nanoscale structural organization/heterogeneity, a prepeak is observed at 0.1 < q/A(-1) < 0.4. The principal peak observed at around 1.2 < q/A(-1) < 2 is rendered by short-distance inter- and intraspecies correlations. For the DESs studied, we demonstrate that nanoscale spatial heterogeneity is exhibited profoundly by the segregated domains of the constituent electrolyte, and the principal peak in S(q) is because of all sorts of close-contact correlations. The extent of nanoscale morphology as well as the strength of ion pairing is enhanced for the longer-tail alkylamide DES.
110 citations
TL;DR: This work discusses metal-free DESs, focusing on their preparation, characterization of physical properties, and considerations for their application, and highlights inconsistencies or omissions in literature reports, as well as factors to consider when investigating these systems.
Abstract: In the past decade, reports detailing the preparation, characterization, and application of deep eutectic solvents (DESs) have grown in number significantly, showing signs of increased interest and...
89 citations
TL;DR: Ab initio molecular dynamic simulations reveal significantly reduced ion charges in several choline-based deep eutectic solvents, which are cheap and eco-friendly alternatives to ionic liquids.
Abstract: Ab initio molecular dynamic simulations reveal significantly reduced ion charges in several choline-based deep eutectic solvents, which are cheap and eco-friendly alternatives to ionic liquids. Increasing hydrogen bond strength between the anion and the organic compound enhances charge spreading from the anion to the organic compound while the positive charge is stronger located at the cation. Nonetheless, the negative charge transferred from chloride to urea in choline chloride urea mixtures is negligible. Thus, it seems questionable if charge delocalization occurring through hydrogen bonding between the halide anion and the organic compound is responsible for the deep eutectic melting point.
83 citations
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