Molecular Approach toward Gases Absorption by Ionic Liquids

This thesis reports the theoretical studies of gas absorption in complex systems. These systems, namely ionic liquids, are considered to be promising candidates to substitute conventional gas capture systems which violate principles of Green Chemistry. The primary focus of this work is to understand gas absorption in ionic liquids on the molecular level using first principles methods such as ab initio molecular dynamics simulations and static quantum chemical calculations combined with statistical thermodynamics and predictive thermodynamic models. These methods allow for the derivation of predictive estimates for the knowledge-based design and tuning of ionic liquids for gas capture. A simple protocol is suggested in the first part of the thesis to distinguish physical from chemical absorption of carbon dioxide (CO2) in ionic liquids with varying anion basicity. This protocol includes a simple geometric optimization with a continuum solvation model of anion-CO2 complexes. A value of the O-C-O angle in these optimized structures defines the possible kind of CO2 absorption in the ionic liquid with the corresponding anion. The anions showing chemical absorption are further narrowed down to those promising for reversible chemical absorption based on the calculated reaction Gibbs free energies. The suggested approaches are easily transferable to other systems if the possible reactions are known. In case of complex reaction mechanisms such as the absorption of CO2 in amino acid ionic liquids, the application of ab initio molecular dynamics simulations allows for the determination of the possible reactions in the system. The subsequent variation of the structure of the cation and the anion reveals the change of Gibbs free energies and barriers in the reactions. These small structural changes affecting the kinetics and energetics of the CO2 absorption can be used as recipes for the precise tuning of the absorption rate and the total CO2 capacity in ionic liquids. The solvation mechanisms of CO2 and sulfur dioxide (SO2) gases in ionic liquids are analyzed in the second part of the thesis. The solvation shells of both gases contain groups donating weak interactions, e.g., a $pi$-system of the cation or alkyl hydrogen atoms, indicating the high importance of the weak interactions in the CO2 and SO2 solvation. The essential difference between the solvation mechanisms of CO2 and SO2 is the interaction with an extended cation-anion network of an ionic liquid. CO2 molecules do not incorporate into the cation-anion network, tending to be solvated by nonpolar groups of an ionic liquid. Instead, SO2 acts as a linker and incorporates into the cation-anion network, which corresponds to the formation of anion-solute-cation structures. From this qualitative picture, the significantly higher solubility of SO2 than CO2 in ionic liquids can be explained. The last part of the thesis deals with the chemical absorption of CO2 by carbenes available in some ionic liquids. The ability of the 1-ethyl-3-methylimidazolium acetate ionic liquid to form a carbene varies from gas to bulk phases in presence or absence of CO2. While CO2 suppresses the carbene formation in the gas phase, the opposite effect is observed in the bulk phase. This occurs due to an inverse ionic liquid effect, when an introduction of the neutral molecules in the pure ionic liquid might induce the formation of neutral species like carbenes. The detailed insight into the subsequent reactions of CO2 with carbene and the transformation of the formed carbene-CO2 adduct into an isomeric adduct has been performed theoretically in close collaboration with experimentalists. The experimental evidence supported by static quantum chemical calculations and ab initio molecular dynamics simulations allows for the establishment of a possible generalized mechanism of the isomerization of the carbene-CO2 adduct. The driving force for such isomerization is the high basicity of the system. The presented theoretical approaches from the combination of first principles methods can be routinely applied to investigate the absorption of other gases in unstudied ionic liquids. The gathered knowledge can be further used for the optimization and precise tuning of the ionic liquids for gas absorption

Ab initio kinetics predictions for H-atom abstraction from diethoxymethane by hydrogen, methyl, and ethyl radicals and the subsequent unimolecular reactions

Diethoxymethane (DEM) is a promising oxygenated fuel and fuel additive, which has similar positive combustion characteristics as dimethoxymethane. DEM contains C-C bonds and can form ethylene via beta-scission, which potentially increases its sooting tendency. Since DEM is rarely studied, however, kinetic modeling attempts are forced to rely on rate constant analogies. Therefore, we employ high level CCSD(T)/aug-cc-pV(T+D)Z//B2PLYPD3BJ/6-311++(d,p) theory along with transition state theory to predict reaction rate constants for H-abstraction by H and CH3 and the subsequent unimolecular reactions. We further prove that the DLPNO approximation to CCSD(T) leads to a deviation of less than 0.25 k/mol in barrier heights for the presently studied open-shell electronic structures and use it for the prediction of reaction rate constants for H-abstraction by C2H5 radicals. We find that H-abstraction by ethyl radicals might denote a significant pathway, which should not be neglected in kinetic modeling studies of DEM. It is also shown that reaction pathways leading to ethylene formation are of minor importance and give thereby a first insight into the fate of the C-C bonds. To the best of our knowledge, this study represents the first high-level ab-initio study of DEM, which makes the reaction kinetics and thermochemistry data provided by this study vital for future comprehensive kinetic modeling of DEM. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Peer reviewe

Prediction of the enthalpies of vaporization for roomerature ionic liquids: Correlations and a substitution-based additive scheme

© 2015 Elsevier B.V. All rights reserved. The literature data on the enthalpies of vaporization for aprotic ionic liquids (ILs) published by the end of May 2014 were analyzed and the most reliable ΔlgHm values were derived for 68 ILs. The selected enthalpies of vaporization were correlated with density and surface tension using symbolic regression and a number of effective correlation equations were proposed. The substitution-based incremental scheme for prediction of the enthalpies of vaporization of imidazolium, pyridinium and pyrrolidinium ILs was developed. The standard error of the regression for the developed scheme is significantly lower than that for the atom-based group-contribution schemes proposed earlier

The furan microsolvation blind challenge for quantum chemical methods: First steps

© 2018 Author(s). Herein we present the results of a blind challenge to quantum chemical methods in the calculation of dimerization preferences in the low temperature gas phase. The target of study was the first step of the microsolvation of furan, 2-methylfuran and 2,5-dimethylfuran with methanol. The dimers were investigated through IR spectroscopy of a supersonic jet expansion. From the measured bands, it was possible to identify a persistent hydrogen bonding OH-O motif in the predominant species. From the presence of another band, which can be attributed to an OH-π interaction, we were able to assert that the energy gap between the two types of dimers should be less than or close to 1 kJ/mol across the series. These values served as a first evaluation ruler for the 12 entries featured in the challenge. A tentative stricter evaluation of the challenge results is also carried out, combining theoretical and experimental results in order to define a smaller error bar. The process was carried out in a double-blind fashion, with both theory and experimental groups unaware of the results on the other side, with the exception of the 2,5-dimethylfuran system which was featured in an earlier publication

Comprehensive study of the thermodynamic properties for 2-methyl-3-buten-2-ol

© 2015 Elsevier Ltd. All rights reserved. The heat capacity of 2-methyl-3-buten-2-ol over the interval T = (5 to 370) K was measured in an adiabatic calorimeter. The standard entropy and heat capacity of the liquid phase at a reference temperature 298.15 K were found to be Som = (232.6 ± 1.0) J·K-1·mol-1 and Cs,m = (237.4 ± 0.9) J·K-1·mol-1. The triple-point temperature Tfus = (245.03 ± 0.03) K and the corresponding enthalpy of fusion ΔcrlHom = (5.199 ± 0.012) kJ·mol-1 were also determined. The enthalpy of vaporisation was determined with a Calvet-type calorimeter to be ΔlgHmo(305.1K) = (46.9 ± 1.6) kJ·mol-1. The vapour pressure over the temperature interval (280 to 328) K was measured with a static technique. The standard entropy of vaporisation at T = 298.15 K was found to be ΔlgSom = (132.7 ± 0.2) J·K-1·mol-1. The standard enthalpy of combustion for liquid 2-methyl-3-buten-2-ol ΔcHmo(l, 298.15 K) = -(3145.1 ± 2.7) kJ·mol-1 was measured with two static-bomb isoperibol combustion calorimeters. From the experimental data, the standard enthalpies of formation for liquid and gaseous 2-methyl-3-buten-2-ol were found to be ΔfHom(l, 298.15 K) = -(251.6 ± 2.8) kJ·mol-1 and ΔfHom (g, 298.15 K) = -(203.3 ± 2.8) kJ·mol-1, respectively. The latter value was confirmed by high-level quantum chemical calculations. Molecular association in the gas phase and its effect on thermodynamic properties of the compound were discussed

Mapping the Free Energy of Lithium Solvation in the Protic Ionic Liquid Ethylammonuim Nitrate: A Metadynamics Study

Understanding lithium solvation and transport in ionic liquids is important due to their possible application in electrochemical devices. Using first-principles simulations aided by a metadynamics approach we study the free-energy landscape for lithium ions at infinite dilution in ethylammonium nitrate, a protic ionic liquid. We analyze the local structure of the liquid around the lithium cation and obtain a quantitative picture in agreement with experimental findings. Our simulations show that the lowest two free energy minima correspond to conformations with the lithium ion being solvated either by three or four nitrate ions with a transition barrier between them of 0.2 \eV. Other less probable conformations having different solvation pattern are also investigated

ПОЛИМЕРНЫЕ КОМПЛЕКСЫ ЦЕФАЛОСПОРИНОВЫХ АНТИБИОТИКОВ С СУЛЬФАТОМ АЦЕТАТОМ ЦЕЛЛЮЛОЗЫ

The state-of the-art in antibiotics modification is the development of acid resistant dosage forms for per oral treatment. This article is about the synthesis of complexes of ceftriaxone and cefotaxime, 3rd generation antibiotics of cephalosporines family, with new water-soluble cellulose derivative – acetate sulfate sodium salt. The composition of complexes was established by UV- and FTIR-spectroscopy. Stable in acid media tablet dosage form of antibiotics was prepared by the immobilization of complexes on activated carbon. Release of the major quantity of antibiotics was proved by HPLC method to be in alkaline media modeling the intestine.В настоящее время актуальна направленная модификация антибиотиков с целью создания кислоторезистентных лекарственных форм, пригодных для перорального применения. В настоящей работе были синтезированы полимерные комплексы цефалоспориновых антибиотиков третьего поколения цефтриаксона и цефотаксима с водорастворимым производным целлюлозы – сульфатом ацетатом в форме натриевой соли. Полученные комплексы охарактеризованы методами УФ- и ИК-спектроскопии. Путем иммобилизации комплекса на активированном угле получены кислотоустойчивые таблетированные лекарственные формы для перорального применения, которые могут быть предложены для проведения доклинических и клинических испытаний.

The first microsolvation step for furans : new experiments and benchmarking strategies

The site-specific first microsolvation step of furan and some of its derivatives with methanol is explored to benchmark the ability of quantum-chemical methods to describe the structure, energetics, and vibrational spectrum at low temperature. Infrared and microwave spectra in supersonic jet expansions are used to quantify the docking preference and some relevant quantum states of the model complexes. Microwave spectroscopy strictly rules out in-plane docking of methanol as opposed to the top coordination of the aromatic ring. Contrasting comparison strategies, which emphasize either the experimental or the theoretical input, are explored. Within the harmonic approximation, only a few composite computational approaches are able to achieve a satisfactory performance. Deuteration experiments suggest that the harmonic treatment itself is largely justified for the zero-point energy, likely and by design due to the systematic cancellation of important anharmonic contributions between the docking variants. Therefore, discrepancies between experiment and theory for the isomer abundance are tentatively assigned to electronic structure deficiencies, but uncertainties remain on the nuclear dynamics side. Attempts to include anharmonic contributions indicate that for systems of this size, a uniform treatment of anharmonicity with systematically improved performance is not yet in sight

Computational approaches to understanding reaction outcomes of organic processes in ionic liquids

This review considers how various computational methods have been applied to explain the changes in reaction outcome on moving from a molecular to an ionic liquid solvent. Initially, different conceptual approaches to modelling ionic liquids are discussed, followed by a consideration of the limitations and constraints of these approaches. A series of case studies demonstrating the utility of computational approaches to explain processes in ionic liquids are considered; some of these address the solubility of species in ionic liquids while others examine classes of reaction where the outcome in ionic liquids can be explained through the application of computational approaches. Overall, the utility of computational methods to explain, and potentially predict, the effect of ionic liquids on reaction outcome is demonstrated