Hydrogen-bonded Mixtures Research Articles

Modeling Mixtures with PCP-SAFT: Insights from Large-Scale Parametrization and Group-Contribution Method for Binary Interaction Parameters

Vapor/liquid equilibria of mixtures are of utmost importance in the design of chemical processes. Because of the combinatorial complexity of mixtures, the available experimental data are small when considering the large molecular space. To fill this knowledge gap, molecular equations of state like PCP-SAFT show promise due to their explicit consideration of intermolecular interactions that can be transferred to mixtures. In this work, we comprehensively assess and exploit PCP-SAFT for modeling phase equilibria of mixtures. First, we provide binary interaction parameters for 7861 binary systems for which pure-component parameters and experimental data are available. Bubble and dew point pressures are described with a median deviation of 2.3 %. Secondly, we adjust a matrix of binary group/group interaction parameters for the homosegmented and heterosegmented group-contribution (GC) methods for PCP-SAFT. Among 1389 mixtures that can be described with the GC methods, the median deviation in bubble and dew point pressures are 6.4 % for the homosegmented approach and 5.1 % for the heterosegmented approach. The detailed analysis shows the importance of hydrogen bonds in mixtures of non-self-associating components with self-associating components. The parametrization is only possible by introducing a fast numerical method to calculate the derivative of bubble and dew point pressures with respect to arbitrarily many model parameters. The approach leverages reverse mode automatic differentiation (backpropagation), the same method used in machine learning to regress millions of model parameters to large datasets.

COSMO-RS Exploration of Highly CO2-Selective Hydrogen-Bonded Binary Liquid Absorbents under Humid Conditions: Role of Trace Ionic Species.

It is critical to improve carbon capture efficiency while reducing costs to popularize carbon capture and storage. Considering the green chemistry and engineering objectives, this study theoretically explores the CO2 absorption capacity of 1,533,528 hydrogen-bonded mixtures, i.e., deep eutectic solvents in a broad sense. Exhaustive statistical thermodynamic calculations well explain the experimental reports; it is confirmed that deep eutectic solvents containing ionic compounds have higher CO2 selective absorption capacity than those composed of non-ionic species. Quantitative evaluation of hydrogen-bonding interaction also predicts that the capacity is higher when the ionic compounds work as hydrogen-bonding donors. This is because the trace ionic species weaken the hydrogen-bonding network in the mixtures to improve CO2 physisorption.

Quantification and Distribution of Three Types of Hydrogen Bonds in Mixtures of an Ionic Liquid with the Hydrogen-Bond-Accepting Molecular Solvent DMSO Explored by Neutron Diffraction and Molecular Dynamics Simulations.

The concept of hydrogen bonding is celebrating its 100th birthday. Hydrogen bonds (H-bonds) play a key role in the structure and function of biological molecules, the strength of materials, and molecular binding. Herein, we study H-bonding in mixtures of a hydroxyl-functionalized ionic liquid with the neutral, H-bond-accepting molecular liquid dimethylsulfoxide (DMSO) using neutron diffraction experiments and molecular dynamics simulations. We report the geometry, strength, and distribution of three different types of H-bond OH···O, formed between the hydroxyl group of the cation and either the oxygen atom of another cation, the counteranion, or the neutral molecule. Such a variety of different strengths and distributions of H-bonds in one single mixture could hold the promise of providing solvents with potential applications in H-bond-related chemistry, for example, to alter the natural selectivity patterns of catalytic reactions or the conformation of catalysts.

Mixed Networks of Hydrogen Bonds in an Ethylene Glycol–Ethylenediamine System

Networks of hydrogen bonds in mixtures of ethylene glycol (EG) and ethylenediamine (ED) are studied and described via molecular dynamics, graph theory, and Delaunay simplices. Results are compared to data on EG–H2O and ED–H2O systems.

Completely Computational Model Setup for Spectroscopic Techniques: The Ab Initio Molecular Dynamics Indirect Hard Modeling Approach.

The spectroscopic quantification of mixture compositions usually requires pure compounds and mixtures of known compositions for calibration. Since they are not always available, methods to fill such gaps have evolved, which are, however, not generally applicable. Therefore, calibration can be extremely challenging, especially when multiple unstable species, for example, intermediates, exist in a system. This study presents a new calibration approach that uses ab initio molecular dynamics (AIMD)-simulated spectra to set up and calibrate models for the physics-based spectral analysis method indirect hard modeling (IHM). To demonstrate our approach called AIMD-IHM, we analyze Raman spectra of ternary hydrogen-bonding mixtures of acetone, methanol, and ethanol. The derived AIMD-IHM pure-component models and calibration coefficients are in good agreement with conventionally generated experimental results. The method yields compositions with prediction errors of less than 5% without any experimental calibration input. Our approach can be extended, in principle, to infrared and NMR spectroscopy and allows for the analysis of systems that were hitherto inaccessible to quantitative spectroscopic analysis.

Pressure-Dependent Structure of Methanol-Water Mixtures up to 1.2 GPa: Neutron Diffraction Experiments and Molecular Dynamics Simulations.

Total scattering structure factors of per-deuterated methanol and heavy water, CD3OD and D2O, have been determined across the entire composition range as a function of pressure up to 1.2 GPa, by neutron diffraction. The largest variations due to increasing pressure were observed below a scattering variable value of 5 Å−1, mostly as shifts in terms of the positions of the first and second maxima. Molecular dynamics computer simulations, using combinations of all-atom potentials for methanol and various water force fields, were conducted at the experimental pressures with the aim of interpreting neutron diffraction results. The peak-position shifts mentioned above could be qualitatively reproduced by simulations, although in terms of peak intensities, the accord between neutron diffraction and molecular dynamics was much less satisfactory. However, bearing in mind that increasing pressure must have a profound effect on repulsive forces between neighboring molecules, the agreement between experiment and computer simulation can certainly be termed as satisfactory. In order to reveal the influence of changing pressure on local intermolecular structure in these “simplest of complex” hydrogen-bonded liquid mixtures, simulated structures were analyzed in terms of hydrogen bond-related partial radial distribution functions and size distributions of hydrogen-bonded cyclic entities. Distinct differences between pressure-dependent structures of water-rich and methanol-rich composition regions were revealed.

Hydrogen bonding and the design of twist-bend nematogens

The phase properties of equimolar mixtures consisting of a hydrogen bond donor, a 4-alkoxybenzoic acid (nOBA), and one of two different stilbazole-based hydrogen bond acceptors, either 4-[(E)-2-(4-{[6-(4′-methoxy[1,1′-biphenyl]-4-yl)hexyl]oxy}phenyl)-ethenyl]-pyridine (1OB6OS) or 4-[(E)-4′-(6-{4-[(E)-2-(pyridin-4-yl)ethenyl]phenoxy}hexyl)-[1,1′-biphenyl]-4-carbonitrile (CB6OS) are reported. Neither hydrogen bond acceptor exhibits liquid crystal behaviour whereas the nOBA compounds show smectic and/or nematic behaviour depending on the length of the alkyloxy chain. For the complexes of an nOBA with n = 1–5, both conventional nematic and twist-bend nematic phases were observed, while for n ≥ 6 smectic phases emerged and the twist-bend nematic phase was extinguished. The CB6OS-nOBA mixtures may exhibit the heliconical smectic CTB phase. The local molecular arrangement in the two sets of mixtures are similar and changes on increasing n but this is not reflected in the nematic-isotropic transition temperatures. Birefringence studies of the mixtures are reported. In general the behaviour of the hydrogen-bonded mixtures is similar to that of their covalently bonded counterparts.

110th Anniversary: From Solubility Parameters to Predictive Equation-of-State Modeling

A simple predictive molecular thermodynamic model for bulk phases and interfaces is presented. The model combines features of the quantitative structure–property relationships (QSPR) approach, the equation-of-state approach, and quantum-chemical calculations. Simple formalisms on a sound thermodynamic basis have been developed for the main thermodynamic quantities of pure components and mixtures while the required parameters for the calculations are rather easily obtained from common databases in the public domain. The widely available solubility parameters or the linear solvation energy relationships (LSER) molecular descriptors are exploited for the extraction of the required information. The predictive capacity of the model with a variety of properties and types of systems including highly nonideal hydrogen-bonded mixtures is reviewed. Emphasis is given in this work on predictions of solvation free energies and the results are rather satisfactory. The strength and weakness of the model and its perspect...

Calorimetric investigations of hydrogen-bonded liquid crystal binary mixtures

Double hydrogen-bonded liquid crystals formed between methyl malonic acid (MM) and p-n-alkyloxy benzoic acids (nBAO) are characterized. Variation in the molar proportion of MM + nBAO (n = 8, 11 and 12) exhibiting good phase polymorphism yields two different sets of binary mixtures labeled as X and Y (where X = MM + 8BAO and Y = MM + 11BAO, MM + 12BAO) which yields 18 hydrogen-bonded binary mixtures as a result. The molar proportions of X and Y are varied in steps of 0.1–0.9 to obtain 18 binary mixtures. Chemical, optical and thermal analysis are carried out for all the 18 binary mixtures formed. Hydrogen bond existence and the chemical environment of the precursor are confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy studies, respectively. Phase variance and the corresponding transition temperatures of the binary mixtures are studied by the observation of textures through polarizing optical microscope (POM), and the same is verified by recording the differential scanning calorimetry (DSC). Phase diagram of the two binary mixtures is built from the POM and DSC data. Thermal equilibrium, odd–even effect, thermal stability factor, order of phase transition, stability of phase through enthalpy values and specific heat value possessed by the mixtures are derived from the DSC datum obtained. These investigations are performed for the prepared binary mixtures with a curiosity to understand the optical and calorimetric properties exhibited by them.

Reorientational Relaxation and Hydrogen Bonding in Mixtures of Water and Methanol

Water-methanol mixtures (with a CH3OH mole fraction, χ, ranging from 0 to 1) are investigated using Broadband Electrical Spectroscopy (BES). A relaxation mode is detected in the 2 – 20 GHz frequency range, ascribed to the collective reorientational relaxation of the molecules. The interpretation of the results is carried out with an innovative thermodynamic formalism, that is not based on the Eyring equation and allows to determine general thermodynamic parameters able to clarify the structure of the water-methanol mixtures. The thermodynamic formalism correlates: (i) the relaxation parameters determined by BES; with (ii) the local intermolecular interactions (i.e., hydrogen bonds, HBs, and van der Waals interactions) that are responsible for the formation of structurally heterogeneous aggregates at the molecular level in the mixture. In particular, the various types of HBs in the mixture play a crucial role to modulate the relative abundance of aggregates and their topology. The information obtained with the proposed thermodynamic formalism is also confirmed by the analysis of the BES relaxation parameters in the framework of the Frölich theory. Finally, the presence of heterogeneities at the subnanometric scale in the mixtures, that is consistent with the results derived by the proposed thermodynamic formalism, is further corroborated by the application of the Bruggeman equation. The latter allows for the determination the volume fraction of water and methanol aggregates as a function of χ and the temperature.

Toward a Simple Predictive Molecular Thermodynamic Model for Bulk Phases and Interfaces

A simple molecular thermodynamic model, based on the QSPR/LSER approach, is presented. The development involves a critical examination of the suitability of available LSER molecular descriptors for calculations of properties of pure-component bulk phases, concentrated solutions, and interfaces. The appropriate descriptors for these calculations are obtained by applying simple and straightforward criteria on freely available data for pure compounds. These criteria arise from a re-examination of basic elements of the solvation picture on which the LSER approach resides. Extensive tables with molecular descriptors are reported. The predictive capacity of the model is tested against a variety of experimental data for mixtures including vapor–liquid equilibria, drug solubilities, and wetting behavior of solid polymer surfaces. Emphasis is given on hydrogen-bonded mixtures. The results are rather satisfactory, in view of the breadth of applications and the nonuse of adjustable parameters. All working equations ...

Segregation Structures and Miscellaneous Diffusions for Ethanol/Water Mixtures in Graphene-Based Nanoscale Pores

Molecular dynamics simulation was conducted to study ethanol–water mixtures and the corresponding pure species, confined within slit-shaped graphene nanopores. Extensive structural and dynamical properties of the confined fluids, including hydrogen-bonding behavior, were investigated. The effects of pore width and mixture composition on the confined behavior were illustrated. It is observed that a layered structure is formed within the confined spaces and the ethanol–water mixtures show segregation at larger pores, with ethanol molecules preferentially adsorbing on graphene surfaces. This microphase demixing behavior stems from the competitive effect of the solid–fluid and fluid–fluid interactions. Moreover, miscellaneous diffusion mechanisms have been revealed for the hydrogen-bonding mixtures within the graphene pores. In the mixtures, water and ethanol generally display analogous diffusion mechanism due to ethanol–water association, converting from short-time subdiffusion to long-time Fickian diffusion...

New insights into the liquid crystal behaviour of hydrogen-bonded mixtures provided by temperature-dependent FTIR spectroscopy

The phase behaviour of equimolar mixtures of 6-(4ʹ-cyanobiphenyl-4-yl)hexyloxybenzoic acid (CB6OBA) with either 1-(4-butylazobenzene-4ʹ-oxy)-5-(4-oxypyridine)pentane (BuABO5OPyr) or 1-(4-butylazobenzene-4ʹ-oxy)-6-(4-oxypyridine)hexane (BuABO6OPyr) is reported. CB6OBA shows a monotropic twist-bend nematic phase and an enantiotropic nematic phase whereas the two pyridyl-based components do not exhibit liquid crystallinity. Both equimolar mixtures (CB6OBA/BuABOnOPyr) show enantiotropic nematic phases. The nematic-isotropic transition temperature and associated entropy change are higher for the CB6OBA/BuABO6OPyr mixture than for the CB6OBA/BuABO5OPyr mixture. This may be accounted for in terms of the average shapes of the hydrogen-bonded 1:1 complexes formed between the two differing components in the mixtures. However, Fourier transform infrared spectroscopy reveals that this complex is not formed quantitatively, but instead a complex mixture exists over the complete temperature range studied, involving the 1:1 complex, both cyclic and open acid dimers, free acid and hence, free BuABOnOPyr molecules.

Non-ideal mixing behaviour of hydrogen bonding in mixtures of protic ionic liquids.

Ionic liquids (ILs) attract interest in science and technology as a result of their unique properties. Binary and ternary mixtures of ILs significantly increase the number of possible cation/anion combinations, resulting in targeted physical and chemical properties. In this work, we study the mixing behaviour of two protic ILs: triethyl ammonium methylsulfonate [Et3 NH][CH3 SO3 ] and triethylammonium triflate [Et3 NH][CF3 SO3 ]. We find a characteristic deviation from ideal mixing by means of low-frequency infrared spectroscopy. By using molecular dynamics simulations, we explain this behaviour as being the result of different strengths of anion/cation hydrogen bonding. This non-ideality of non-random H-bond mixing is also reflected in macroscopic properties such as the viscosity. Mixing suitable ILs may, thus, result in new ILs with targeted physical properties.

ChemInform Abstract: Hydrogen Bonding in Mixtures of Dimethyl Sulfoxide and Cosolvents

AbstractReview: 85 refs.

Hydrogen Bonding in Mixtures of Dimethyl Sulfoxide and Cosolvents

Hydrogen Bonding in Mixtures of Dimethyl Sulfoxide and Cosolvents

Hydrogen Bonding in Mixtures of Dimethyl Sulfoxide and Cosolvents

Abstract: Dimethyl sulfoxide (DMSO) represents a dipolar aprotic solvent which incorporates a strongly polar sulfoxide group and two hydrophobic methyl moieties. Owing to its beneficial properties including low toxicity and environmental compatibility, DMSO has been and still is widely used as a solvent in industry as well as research. Applications can be found in many different areas ranging from medicine and biotechnology to electrochemistry and laser physics. In practical systems, DMSO is usually accompanied by other substances with whom it interacts at molecular scale. These interactions include, for instance, hydrogen bonds and van der Waals forces and determine the microscopic dissolution properties as well as the macroscopic solution behavior. Moreover, such interactions exert influence on the molecular structures of the involved molecules. In turn, this means that analyzing the molecular structure by means of theoretical and experimental approaches can shed light on the nature of interactions and help to achieve better understanding of the phenomena observed. In this article we review the literature reporting DMSO hydrogen bonding interactions with cosolvent molecules. In this context, theoretical as well as experimental studies are considered and compared in order to get a clear picture of this important solvent. Special attention is paid to the DMSO/water system which is well known for exhibiting a strongly nonideal mixing behavior. In addition, mixtures of DMSO with alcohols and other organic solvents are discussed.

Molecular dynamics and neutron scattering study of glucose solutions confined in MCM-41.

Glucose aqueous solutions confined in MCM-41 cylindrical pores of diameter 3.2 nm have been studied by molecular dynamics (MD) simulations and quasielastic neutron scattering (QENS). MD simulations reveal a strong preferential interaction of glucose molecules with the silica walls, which induces significant concentration gradients within the pore. The influence of glucose on the structural and dynamical properties of water strongly depends on the region of the pore considered. The distortion of the hydrogen bond network (HBN) and of the tetrahedral organization of interfacial water molecules induced by silica is much stronger than that induced by glucose molecules. The interfacial glucose molecules diffuse about 1 order of magnitude slower than those in the core region. Differences in affinities for silica of the different species in confined hydrogen-bonded mixtures induce significant structural and dynamical heterogeneities not present in bulk solutions.

Dielectric relaxation dynamics in glass-forming mixtures of propanediol isomers

The relaxation dynamics of 1,2-propanediol-1,3-propanediol mixtures is studied in supercooled liquid regions across a wide composition range. The composition dependences of liquid fragility and nonexponential parameter β(KWW) are presented in the hydrogen-bonded mixtures with ideal mixing. The fragility index and glass transition temperature are shown to develop inversely with β(KWW), in analogy to the dynamic behaviors in mixtures of van der Waals liquids. Negative mixing effects on liquid fragility and β(KWW) are observed, and the strongest dependence of β(KWW on relaxation dynamics is revealed at the equimolar concentration. The glass formation in isomeric liquids is also addressed.

Extension of the Cubic-plus-Association (CPA) Equation of State to Amines

The cubic-plus-association (CPA) equation of state has been extended to modeling mixtures containing amines. Special focus was given to primary and secondary amines, which are known to self-associate, thus forming hydrogen bonds in mixtures with alkanes. Pure-compound parameters have been determined from vapor pressure and liquid density data, but phase equilibrium data were also used as guidance for selecting the optimum sets among those which best represent the pure-compound properties. Diethylamine was modeled as a two-site molecule, whereas the two primary amines considered (methylamine, ethylamine) were modeled using both the two-site and three-site schemes. Both schemes perform overall equally well, when care is exercised in the parameter estimation, by giving more weight on the vapor pressures rather than the liquid densities. Thus, only results using the two-site scheme are shown. Excellent binary vapor−liquid equilibria have been obtained for amine + aliphatic hydrocarbons with a low value of the binary interaction parameter. Satisfactory results are obtained also for cross-associating systems with alcohols but less so with water, using, moreover, a rather high value of the interaction parameter.