Showing papers on "Solvation published in 2014"
TL;DR: This work implements an implicit solvation model that has a firm theoretical foundation into the widely used density-functional code Vienna ab initio Software Package and finds that solvation reduces the surface energies of the nanocrystals and increases the energy barrier of the SN2 reaction.
Abstract: Solid-liquid interfaces are at the heart of many modern-day technologies and provide a challenge to many materials simulation methods. A realistic first-principles computational study of such systems entails the inclusion of solvent effects. In this work, we implement an implicit solvation model that has a firm theoretical foundation into the widely used density-functional code Vienna ab initio Software Package. The implicit solvation model follows the framework of joint density functional theory. We describe the framework, our algorithm and implementation, and benchmarks for small molecular systems. We apply the solvation model to study the surface energies of different facets of semiconducting and metallic nanocrystals and the SN2 reaction pathway. We find that solvation reduces the surface energies of the nanocrystals, especially for the semiconducting ones and increases the energy barrier of the SN2 reaction.
1,378 citations
TL;DR: In this paper, Raman data analysis supported by DFT calculations on Na+-TFSI complexes, allow to determine the sodium ion solvation and charge carrier nature as a function of salt concentration.
240 citations
TL;DR: In this paper, the dissolution of microcrystalline cellulose in 1-butyl-3-methylimidazolium acetate [C4C1Im][OAc] was studied using a solid-liquid equilibrium method based on polarized-light optical microscopy from 30 to 100 °C.
222 citations
TL;DR: In this article, special attention is paid to ions relevant in cement chemistry likely to interact with tricalcium silicate (C3S) in order to determine whether specific effects occur at the interface C3S-water, particular efforts have been made to model ion activities using Pitzer's model.
169 citations
TL;DR: This work uses single-molecule Förster resonance energy transfer to probe the temperature-induced chain collapse of five unfolded or intrinsically disordered proteins and finds that each of the proteins undergoes a collapse with increasing temperature, with the most hydrophobic one, λ-repressor, undergoing a reexpansion at the highest temperatures.
Abstract: For disordered proteins, the dimensions of the chain are an important property that is sensitive to environmental conditions. We have used single-molecule Forster resonance energy transfer to probe the temperature-induced chain collapse of five unfolded or intrinsically disordered proteins. Because this behavior is sensitive to the details of intrachain and chain–solvent interactions, the collapse allows us to probe the physical interactions governing the dimensions of disordered proteins. We find that each of the proteins undergoes a collapse with increasing temperature, with the most hydrophobic one, λ-repressor, undergoing a reexpansion at the highest temperatures. Although such a collapse might be expected due to the temperature dependence of the classical “hydrophobic effect,” remarkably we find that the largest collapse occurs for the most hydrophilic, charged sequences. Using a combination of theory and simulation, we show that this result can be rationalized in terms of the temperature-dependent solvation free energies of the constituent amino acids, with the solvation properties of the most hydrophilic residues playing a large part in determining the collapse.
159 citations
TL;DR: In this paper, the solvent polarity parameter E-T(30) was measured from the solvatochromism of the betaine dye 30 for 84 solvents and re-measured for 186 additional ones.
153 citations
TL;DR: The results show that HMF solvation by DMSO increases its LUMO energy, which reduces its susceptibility to nucleophilic attack and minimizes undesirable hydration and humin-formation reactions, which provide an explanation for the enhanced HMF stability in D MSO/water mixtures observed experimentally.
Abstract: In the present work, we combined vibrational spectroscopy with electronic structure calculations to understand the solvation of HMF in DMSO, water, and DMSO/water mixtures and to provide insights into the observed hindrance of HMF rehydration and aldol condensation reactions if it is dissolved in DMSO/water mixtures. To achieve this goal, the attenuated total reflection FTIR spectra of a wide composition range of binary and ternary mixtures were measured, analyzed, and compared to the findings of ab initio DFT calculations. The effect of solvent on the HMF C-O and O-H vibrational modes reveals significant differences that are ascribed to different intermolecular interactions between HMF and DMSO or water. We also found that DMSO binds to HMF more strongly than water, and interactions with the HMF hydroxyl group are stronger than those with the HMF carbonyl group. We also showed the preferential solvation of HMF C-O groups by DMSO if HMF is dissolved in DMSO/water mixed solvent. Frontier molecular orbital theory was used to examine the influence of the solvent on side reactions. The results show that HMF solvation by DMSO increases its LUMO energy, which reduces its susceptibility to nucleophilic attack and minimizes undesirable hydration and humin-formation reactions. This result, together with the preferential solvation of HMF by DMSO, provide an explanation for the enhanced HMF stability in DMSO/water mixtures observed experimentally.
135 citations
TL;DR: An accurate and general solvation model that includes a cavity that is a nonlocal functional of both solute electron density and potential, local dielectric response on this nonlocally determined cavity, and nonlocal approximations to the cavity-formation and dispersion energies is developed.
Abstract: Many important applications of electronic structure methods involve molecules or solid surfaces in a solvent medium. Since explicit treatment of the solvent in such methods is usually not practical, calculations often employ continuum solvation models to approximate the effect of the solvent. Previous solvation models either involve a parametrization based on atomic radii, which limits the class of applicable solutes, or based on solute electron density, which is more general but less accurate, especially for charged systems. We develop an accurate and general solvation model that includes a cavity that is a nonlocal functional of both solute electron density and potential, local dielectric response on this nonlocally-determined cavity, and nonlocal approximations to the cavity-formation and dispersion energies. The dependence of the cavity on the solute potential enables an explicit treatment of the solvent charge asymmetry. With only three parameters per solvent, this `CANDLE' model simultaneously reproduces solvation energies of large datasets of neutral molecules, cations and anions with a mean absolute error of 1.8 kcal/mol in water and 3.0 kcal/mol in acetonitrile.
134 citations
TL;DR: It is shown that 3D-RISM is relatively accurate at predicting the electrostatic component of the HFE without correction but requires a modification of the nonpolar contribution that originates in the formation of the cavity created by the solute in water.
Abstract: We show that an Ng bridge function modified version of the three-dimensional reference interaction site model (3D-RISM-NgB) solvation free energy method can accurately predict the hydration free energy (HFE) of a set of 504 organic molecules. To achieve this, a single unique constant parameter was adjusted to the computed HFE of single atom Lennard-Jones solutes. It is shown that 3D-RISM is relatively accurate at predicting the electrostatic component of the HFE without correction but requires a modification of the nonpolar contribution that originates in the formation of the cavity created by the solute in water. We use a free energy functional with the Ng scaling of the direct correlation function [Ng, K. C. J. Chem. Phys. 1974, 61, 2680]. This produces a rapid, reliable small molecule HFE calculation for applications in drug design.
127 citations
TL;DR: Free energy simulations for electrostatic and charging processes in complex molecular systems encounter specific difficulties owing to the long-range, 1/r Coulomb interaction, but these issues can be handled with established computational protocols and illustrated for several small ions and three solvated proteins.
Abstract: Free energy simulations for electrostatic and charging processes in complex molecular systems encounter specific difficulties owing to the long-range, 1/r Coulomb interaction. To calculate the solvation free energy of a simple ion, it is essential to take into account the polarization of nearby solvent but also the electrostatic potential drop across the liquid-gas boundary, however distant. The latter does not exist in a simulation model based on periodic boundary conditions because there is no physical boundary to the system. An important consequence is that the reference value of the electrostatic potential is not an ion in a vacuum. Also, in an infinite system, the electrostatic potential felt by a perturbing charge is conditionally convergent and dependent on the choice of computational conventions. Furthermore, with Ewald lattice summation and tinfoil conducting boundary conditions, the charges experience a spurious shift in the potential that depends on the details of the simulation system such as the volume fraction occupied by the solvent. All these issues can be handled with established computational protocols, as reviewed here and illustrated for several small ions and three solvated proteins.
122 citations
TL;DR: The data suggest that contact ion-pairs are a common feature in multivalent electrolytes in monovalent and multivalent TFSI salts in diglyme.
Abstract: By analysing X-ray pair distribution function data using a multivariate statistical approach, we isolate the cation solvation structure for monovalent (Li+/Na+/K+) and multivalent (Mg2+/Ca2+/Zn2+) electrolytes based on TFSI salts in diglyme. Parallel molecular dynamics simulations provide enhanced structural details. The data suggest that contact ion-pairs are a common feature in multivalent electrolytes.
TL;DR: The use of the high resolution phenol hydroxyl group 1H-NMR spectral region provides a general method for the analysis of complex plant extracts without the need for the isolation of the individual components.
Abstract: Experimental parameters that influence the resolution of 1H-NMR phenol OH signals are critically evaluated with emphasis on the effects of pH, temperature and nature of the solvents. Extremely sharp peaks (Δν1/2 ≤ 2 Hz) can be obtained under optimized experimental conditions which allow the application of 1H-13C HMBC-NMR experiments to reveal long range coupling constants of hydroxyl protons and, thus, to provide unequivocal assignment of the OH signals even in cases of complex polyphenol natural products. Intramolecular and intermolecular hydrogen bonds have a very significant effect on 1H OH chemical shifts which cover a region from 4.5 up to 19 ppm. Solvent effects on –OH proton chemical shifts, temperature coefficients (Δδ/ΔT), OH diffusion coefficients, and nJ(13C, O1H) coupling constants are evaluated as indicators of hydrogen bonding and solvation state of phenol –OH groups. Accurate 1H chemical shifts of the OH groups can be calculated using a combination of DFT and discrete solute-solvent hydrogen bond interaction at relatively inexpensive levels of theory, namely, DFT/B3LYP/6-311++G (2d,p). Excellent correlations between experimental 1H chemical shifts and those calculated at the ab initio level can provide a method of primary interest in order to obtain structural and conformational description of solute-solvent interactions at a molecular level. The use of the high resolution phenol hydroxyl group 1H-NMR spectral region provides a general method for the analysis of complex plant extracts without the need for the isolation of the individual components.
TL;DR: In this article, the solubility of CO2 in three kinds of deep eutectic solvents, (choline chloride+phenol, choline chloride + diethylene glycol, and choline glycol+triethylene glycol), were determined at temperatures ranging from 293.15 k to 323.15k under pressures up to 600 kPa using isochoric saturation method.
TL;DR: In this paper, the solubility of CO2 in eutectic mixtures containing choline chloride and dihydric alcohols (including 1,4-butanediol, 2,3-butaniol, and 1,2-propanediol) with a molar ratio of choline to di hydric alcohol of 1:3 and 1:4 were measured at 293.15 K, 303.15 k, 313.15k, and 323.0 kPa using an isochoric saturation method.
Abstract: The solubilities of CO2 in eutectic mixtures containing choline chloride and dihydric alcohols (including 1,4-butanediol, 2,3-butanediol, and 1,2-propanediol) with a molar ratio of choline chloride to dihydric alcohol of 1:3 and 1:4 were measured at 293.15 K, 303.15 K, 313.15 K, and 323.15 K under pressures up to 600.0 kPa using an isochoric saturation method. Henry’s constant and the dissolution Gibbs free energy, enthalpy, and entropy changes of CO2 solvation were obtained by correlating the experimental data. The solubility of CO2 in the mixtures increased linearly with the increasing pressure or the decreasing temperature. The enthalpies of solution were negative at all conditions.
TL;DR: In this article, the authors evaluated the performance of electrolytes with the salt lithium bis(fluorosulfonyl)imide (LiFSI) compared to comparable electrolyte with other lithium salts.
Abstract: Electrolytes with the salt lithium bis(fluorosulfonyl)imide (LiFSI) have been evaluated relative to comparable electrolytes with other lithium salts. Acetonitrile (AN) has been used as a model electrolyte solvent. The information obtained from the thermal phase behavior, solvation/ionic association interactions, quantum chemical (QC) calculations and molecular dynamics (MD) simulations (with an APPLE&P many-body polarizable force field for the LiFSI salt) of the (AN)n-LiFSI mixtures provides detailed insight into the coordination interactions of the FSI- anions and the wide variability noted in the electrolyte transport property (i.e., viscosity and ionic conductivity).
TL;DR: The atomic electrostatic potentials calculated by the CHELPG method have been shown to be sensitive indicators of the gas phase and solution properties of the statins and suggest that clinical definitions of statins as either "hydrophilic" or "lipophilic" based on experimental partition coefficients are misleading.
TL;DR: For the first time, this multiscale approach links metal-ion coordination with nanoscale structure to reveal the free-energy balance that drives the phase transfer of neutral metal salts.
Abstract: Combining experiment with theory reveals the role of self-assembly and complexation in metal-ion transfer through the water-oil interface. The coordinating metal salt Eu(NO3)3 was extracted from water into oil by a lipophilic neutral amphiphile. Molecular dynamics simulations were coupled to experimental spectroscopic and X-ray scattering techniques to investigate how local coordination interactions between the metal ion and ligands in the organic phase combine with long-range interactions to produce spontaneous changes in the solvent microstructure. Extraction of the Eu(3+)-3(NO3(-)) ion pairs involves incorporation of the "hard" metal complex into the core of "soft" aggregates. This seeds the formation of reverse micelles that draw the water and "free" amphiphile into nanoscale hydrophilic domains. The reverse micelles interact through attractive van der Waals interactions and coalesce into rod-shaped polynuclear Eu(III) -containing aggregates with metal centers bridged by nitrate. These preorganized hydrophilic domains, containing high densities of O-donor ligands and anions, provide improved Eu(III) solvation environments that help drive interfacial transfer, as is reflected by the increasing Eu(III) partitioning ratios (oil/aqueous) despite the organic phase approaching saturation. For the first time, this multiscale approach links metal-ion coordination with nanoscale structure to reveal the free-energy balance that drives the phase transfer of neutral metal salts.
TL;DR: In this paper, the preferential solvation parameters of sulfadiazine, sulfamerazine and sulfamethazine in ethanol+water binary mixtures were derived from their thermodynamic properties by means of the inverse Kirkwood-Buff integrals (IKBI) method.
TL;DR: In this article, charged-slab first principles calculations integrated with a periodic continuum solvation model is utilized to analyze the initiating steps of water splitting on the two most common TiO2 surfaces, namely, rutile (110) and anatase (101), at the solid-water interface.
Abstract: Photocatalytic water splitting is regarded as an important route for generating renewable energy. Here, charged-slab first principles calculations integrated with a periodic continuum solvation model is utilized to analyze the initiating steps of water splitting on the two most common TiO2 surfaces, namely, rutile (110) and anatase (101), at the solid–water interface. It is found that the first proton removal of water (H2O + hole+ → OH + H+) is sensitive to the crystalline phase and surface. The rutile (110) surface is more active for water splitting, with the calculated barrier of O–H bond breaking being 0.2 eV lower compared to that on anatase (101). The higher activity of rutile is not due to the redox level of the hole (the position of the valence band maximum), but caused by the more favorable local bonding geometry of the surface. Unexpectedly, the photogenerated hole does not promote O–H bond breaking, and the charge transfer occurs after the H2O dissociation when the surface O nearby the dissociated OH anion traps the hole. The solvation plays an important catalytic role to stabilize and remove protons from the reaction site, which effectively inhibits the charge-recombination of the dissociated OH anion with the proton. The theory presented here shows that the chemical properties of the surface play a significant role in the photocatalytic process, and a strategy based on simple structural parameters is proposed towards the design of new photocatalysts.
TL;DR: In this article, the authors give calculations of dispersion interactions of ions with other ions and with water molecules via symmetry adapted perturbation theory with density functional theory (DFT-SAPT).
TL;DR: In this article, the authors introduce the methods available for predicting gas phase acidity and pKas in aqueous and non-aqueous solvents including high-level electronic structure methods, empirical linear free energy relationships (LFERs), implicit solvent methods, explicit solvent statistical free energy methods, and hybrid implicit-explicit approaches.
Abstract: Computational prediction of condensed phase acidity is a topic of much interest in the field today. We introduce the methods available for predicting gas phase acidity and pKas in aqueous and non-aqueous solvents including high-level electronic structure methods, empirical linear free energy relationships (LFERs), implicit solvent methods, explicit solvent statistical free energy methods, and hybrid implicit–explicit approaches. The focus of this paper is on implicit solvent methods, and we review recent developments including new electronic structure methods, cluster-continuum schemes for calculating ionic solvation free energies, as well as address issues relating to the choice of proton solvation freeenergytousewithimplicitsolvationmodels,andwhetherthermodynamiccyclesarenecessaryforthecomputationof pKas. A comparison of the scope and accuracy of implicit solvent methods with ab initio molecular dynamics free energy methods is also presented. The present status of the theory and future directions are outlined.
TL;DR: The physical interpretation of the electrostatic potential difference between the region near the cavity and the bulk and its calculation are clarified and will have direct consequences toward the understanding of the thermodynamics of ion solvation through the cavity charging process.
Abstract: Insertion of a hard sphere cavity in liquid water breaks translational symmetry and generates an electrostatic potential difference between the region near the cavity and the bulk. Here, we clarify the physical interpretation of this potential and its calculation. We also show that the electrostatic potential in the center of small, medium, and large cavities depends very sensitively on the form of the assumed molecular interactions for different classical simple point-charge models and quantum mechanical DFT-based interaction potentials, as reflected in their description of donor and acceptor hydrogen bonds near the cavity. These differences can significantly affect the magnitude of the scalar electrostatic potential. We argue that the result of these studies will have direct consequences toward our understanding of the thermodynamics of ion solvation through the cavity charging process.
TL;DR: The results reveal that at high hydration level, where the contribution from internal water is dominant, the temperature dependence of the Boson peak intensity shows an inflection point at about 225 K.
Abstract: The Boson peak of deeply cooled water confined in the pores of a silica xerogel is studied by inelastic neutron scattering at different hydration levels to separate the contributions from matrix, water on the pore surfaces and "internal" water. Our results reveal that at high hydration level, where the contribution from internal water is dominant, the temperature dependence of the Boson peak intensity shows an inflection point at about 225 K. The complementary use of differential scanning calorimetry to describe the thermodynamics of the system allows identifying the inflection point as the signature of a water liquid-liquid crossover.
TL;DR: Electronic structure theory and vibrational spectroscopy are employed to study molecular interactions in the room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and the results are compared with experimental observations from Raman scattering and IR absorption spectroscopies.
Abstract: Electronic structure theory (density functional and Moller-Plesset perturbation theory) and vibrational spectroscopy (FT-IR and Raman) are employed to study molecular interactions in the room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Different conformers of a cation-anion pair based on their molecular interactions are simulated in the gas phase and in a dielectric continuum solvent environment. Although the ordering of conformers in energy varies with theoretical methods, their predictions for three lowest energy conformers in the gas phase are similar. Strong C-H---N interactions between the acidic hydrogen atom of the cation imidazole ring and the nitrogen atom of the anion are predicted for either the lowest or second lowest energy conformer. In a continuum solvent, different theoretical methods yield the same ion-pair conformation for the lowest energy state. In both phases, the density functional method predicts that the anion is in a trans conformation in the lowest energy ion pair state. The theoretical results are compared with experimental observations from Raman scattering and IR absorption spectroscopies and manifestations of the molecular interactions in the vibrational spectra are discussed. The directions of the frequency shifts of the characteristic vibrations relative to the free anion and cation are explained by calculating the difference electron density coupled with electron density topography.
TL;DR: The overall picture indicates that the solvation of [Li](+) cations in this amphiphilically nanostructured environment takes place by means of a sort of inhomogeneous nanostructureural solvation, which could be a universal solvation mechanism in ionic liquids.
Abstract: The structure of solutions of lithium nitrate in a protic ionic liquid with a common anion, ethylammonium nitrate, at room temperature is investigated by means of molecular dynamics simulations. Several structural properties, such as density, radial distribution functions, hydrogen bonds, spatial distribution functions, and coordination numbers, are analyzed in order to get a picture of the solvation of lithium cations in this hydrogen-bonded, amphiphilically nanostructured environment. The results reveal that the ionic liquid mainly retains its structure upon salt addition, the interaction between the ammonium group of the cation and the nitrate anion being only slightly perturbed by the addition of the salt. Lithium cations are solvated by embedding them in the polar nanodomains of the solution formed by the anions, where they coordinate with the latter in a solid-like fashion reminiscent of a pseudolattice structure. Furthermore, it is shown that the average coordination number of [Li]+ with the anions...
TL;DR: This study examines combinations of chloride, acetate, and dimethylphosphate anions paired with cations of increasing tail length to elucidate the precise role of the cation in solvating cellulose and shows how decreased concentration of anions in the bulk affects hydrogen bond formation with cellulose.
Abstract: We present a systematic molecular dynamics study examining the roles of the individual ions of different alkylimidazolium-based ionic liquids in the solvation of cellulose. We examine combinations of chloride, acetate, and dimethylphosphate anions paired with cations of increasing tail length to elucidate the precise role of the cation in solvating cellulose. In all cases we find that the cation interacts with the nonpolar domains of cellulose through dispersion interactions, while interacting electrostatically with the anions bound at the polar domains of cellulose. Furthermore, the structure and dimensions of the imidazolium head facilitate the formation of large chains and networks of alternating cations and anions that form a patchwork, satisfying both the polar and nonpolar domains of cellulose. A subtle implication of increasing tail length is the dilution of the anion concentration in the bulk and at the cellulose surface. We show how this decreased concentration of anions in the bulk affects hydro...
TL;DR: It is concluded that COSMOmic can be successfully used for high-throughput computations of global thermodynamic properties, for example, partition coefficients and energy barrier heights, in phosphocholine membranes.
Abstract: The partitioning behavior of drug-like molecules into biomembranes has a crucial impact on the design and efficacy of therapeutic drugs. Thermodynamic properties connected with the interaction of molecules with membranes can be evaluated by calculating free-energy profiles normal to the membrane surface. We calculated the free-energy profiles of 25 drug-like molecules in a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membrane and free energies of solvation in water and heptane using two methods, molecular dynamics (MD) simulations with the Berger lipid force field and COSMOmic, based on a continuum conductor-like screening model for realistic solvation (COSMO-RS). The biased MD simulations (in total ∼22 μs long) were relatively computationally expensive, whereas the COSMOmic approach offered a significantly less expensive alternative. Both methods provided similar results and showed that the studied amphiphilic drug-like molecules accumulate in the membrane, with the majority localized below the head g...
TL;DR: In this paper, the exact solution theory of Kirkwood and Buff (KB) was used to explain how osmolytes affect the conformation and configuration of supramolecular assembly, such as ion channel opening and actin polymerization.
Abstract: How do osmolytes affect the conformation and configuration of supramolecular assembly, such as ion channel opening and actin polymerization? The key to the answer lies in the excess solvation numbers of water and osmolyte molecules; these numbers are determinable solely from experimental data, as guaranteed by the phase rule, as we show through the exact solution theory of Kirkwood and Buff (KB). The osmotic stress technique (OST), in contrast, purposes to yield alternative hydration numbers through the use of the dividing surface borrowed from the adsorption theory. However, we show (i) OST is equivalent, when it becomes exact, to the crowding effect in which the osmolyte exclusion dominates over hydration; (ii) crowding is not the universal driving force of the osmolyte effect (e.g., actin polymerization); (iii) the dividing surface for solvation is useful only for crowding, unlike in the adsorption theory which necessitates its use due to the phase rule. KB thus clarifies the true meaning and limitatio...
TL;DR: In this paper, the results obtained by both methods indicate that the formation of complexes with four solvent molecules around Li+, exhibiting a strong local tetrahedral order, is the most favorable.
Abstract: Classical molecular dynamics (MD) simulations and quantum chemical density functional theory (DFT) calculations have been employed in the present study to investigate the solvation of lithium cations in pure organic carbonate solvents (ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC)) and their binary (EC-DMC, 1:1 molar composition) and ternary (EC-DMC-PC, 1:1:3 molar composition) mixtures. The results obtained by both methods indicate that the formation of complexes with four solvent molecules around Li+, exhibiting a strong local tetrahedral order, is the most favorable. However, the molecular dynamics simulations have revealed the existence of significant structural heterogeneities, extending up to a length scale which is more than five times the size of the first coordination shell radius. Due to these significant structural fluctuations in the bulk liquid phases, the use of larger size clusters in DFT calculations has been suggested. Contrary to the findings of the DFT calculations on small isolated clusters, the MD simulations have predicted a preference of Li+ to interact with DMC molecules within its first solvation shell and not with the highly polar EC and PC ones, in the binary and ternary mixtures. This behavior has been attributed to the local tetrahedral packing of the solvent molecules in the first solvation shell of Li+, which causes a cancellation of the individual molecular dipole vectors, and this effect seems to be more important in the cases where molecules of the same type are present. Due to these cancellation effects, the total dipole in the first solvation shell of Li+ increases when the local mole fraction of DMC is high.
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.