Polar Binary Mixtures Research Articles

Development of Soave–Redlich–Kister Equation of State and Vapor–Liquid Equilibrium Modeling For Polar Pure Compounds and Binary Mixtures

Development of Soave–Redlich–Kister Equation of State and Vapor–Liquid Equilibrium Modeling For Polar Pure Compounds and Binary Mixtures

Fmoc-Removal with Pyrrolidine Expands the Available Solvent Space in Green Solid-Phase Peptide Synthesis

Green binary solvent mixtures with a polarity and viscosity close to that of DMF perform similarly in solid-phase peptide synthesis (SPPS). However, while coupling reactions readily proceed in solvents of significantly lower polarity than that of DMF, a high solvent polarity is essential for Fmoc-removal using piperidine, which limits the options for green SPPS solvents. Herein, we report our efforts to expand the available solvent polarity space for green SPPS. We identified pyrrolidine as an efficient base to enable Fmoc-removal in less polar solvent mixtures that also favor coupling reactions, such as dimethyl sulfoxide/ethyl acetate (1:9) and N-butylpyrrolidone/1,3-dioxolane (2:8 and 4:6). Employing less polar binary solvent mixtures in combination with pyrrolidine gave crude peptide purities comparable to or better than for DMF with piperidine in the SPPS of challenging peptide targets. An evaluation of base-dependent side reactions such as diketopiperazine (DKP) and aspartimide formation showed increased side-product formation when using pyrrolidine on DKP- and aspartimide-prone sequences. However, the scaled-up syntheses (5 and 7.5 mmol, respectively) of the peptide therapeutics dasiglucagon (29-mer) and bivalirudin (20-mer) gave good crude peptide purities and purity profiles amenable to SPPS optimization. Pyrrolidine therefore represents a useful alternative to piperidine for Fmoc-removal in an expanded solvent space for green SPPS.

Physico-chemical properties of binary systems involving modifier (methanol or propionic acid) and an acidic extractant di (2-ethylhexyl) phosphoric acid (DEHPA): volumetric, acoustic and viscometric routes

In solvent extraction, a suitable modifier, basically polar liquid is used with extractant like DEHPA, TBP, TOPO and MIBK to enhance the efficiency in extraction processes. This paper is related to the study of physico-chemical properties of polar – polar binary mixtures at 303.15K and 0.1 MPa. Molar volume, free volume, isentropic compressibility, intermolecular free length, specific acoustic impedance, relaxation time, Rao’s constant, Wada’s constant, absorption coefficient have been calculated from the experimentally measured data of density, ultrasonic velocity and viscosity of pure components and binary mixtures of methanol/ propionic acid + DEHPA. In addition, excess molar volume, excess Gibb’s energy of activation of viscous flow, deviations in viscosity, isentropic compressibility, free volume, intermolecular free length and acoustic impedance were also computed from the experimental data. The observed variations of excess/deviation functions with the composition of DEHPA have been discussed in terms of molecular interaction between unlike molecules in two binary mixtures due to chemical, physical and structural effects. It is found that the molecular interaction of methanol with extractant DEHPA is better than that of propionic acid and so methanol may be used as a suitable modifier with DEHPA in the solvent extraction process.

Dielectric studies of binary mixtures of ethylene glycol mono phenyl ether with 1-butanol at different temperatures

Static permittivity ([Formula: see text]), refractive index ([Formula: see text]) and density ([Formula: see text]) of binary mixtures of ethylene glycol mono phenyl ether (EGMPE) with 1-butanol (1-BuOH) over the entire range of mole fraction and at temperatures ([Formula: see text], 313.15 and 323.15[Formula: see text]K) have been measured. From the experimental data, parameters such as excess static permittivity ([Formula: see text]), excess permittivity at optical frequency ([Formula: see text]), effective Kirkwood correlation factor ([Formula: see text]), corrective Kirkwood correlation factor ([Formula: see text]) and Bruggeman factor ([Formula: see text]) have been calculated to obtain qualitative and quantitative information about the complex formation through H-bond in binary system. In order to predict the static permittivity of polar–polar binary mixtures six mixing rules were applied and for refractive index five mixing rule were applied. Experimental results of permittivity ([Formula: see text]) and refractive index (n) are compared with those obtained from theoretical calculations. Excess parameters were fitted to the Redlich–Kister type polynomial equation.

Microwave dielectric relaxation spectroscopy studies on associative polar binary mixtures of nitrobenzene with primary alcohols

The microwave dielectric relaxation behavior of binary mixtures of nitrobenzene with primary alcohols namely ethanol, 1-propanol and 1-butanol has been studied at different temperatures using Time Domain Reflectometry method. The measured complex dielectric spectra of pure and mixture solutions have been fitted with Debye model using least square method. The obtained static dielectric and relaxation time constant values are plotted against mole fraction of solute. The important dielectric parameters such as excess dielectric constant, excess inverse relaxation time and effective Kirkwood correlation factors are computed and the same has been used to interpret the intermolecular interaction and dynamic change in the solution. Furthermore, the mixing effect of nitrobenzene in different chain length alcohols has been explored by concentration dependent excess dielectric constant values. The positive molar enthalpy values of mixtures indicate that the heat energy is absorbed owing to the process of dipole reorientation. Moreover, the heterogeneous interaction between solute and solvent molecular functional groups has been confirmed by equi-molar FT-IR spectra analysis.

Relaxation phenomena of nicotinamide and benzamide with 1-propanol and 1-butanol in C6H6 under static and 9.385 GHz electric field

Dielectric relaxation behaviors of nicotinamide+1-propanol, benzamide+1-propanol, and nicotinamide+1-butanol dissolved in C6H6 at 0.990, 0.985, 0.980, 0.975, 0.970; 0.990, 0.985, 0.980, and 0.980 mol fraction xj of 1-propanol or 1-butanol at temperature 30 °C and 30, 40, 50, and 60 °C, respectively, are studied using the Debye model of binary polar–non-polar liquid mixture to predict double relaxation times τ2 and τ1 and dipole moments μ2 and μ1 from susceptibility measurement of concentration variation solution data under static and 9.385 GHz electric fields. Nineteen systems exhibit τ2, τ1 and μ2, μ1. τ2 are found to increase with temperature for all the binary polar mixtures, whereas τ1, most probable τ0, and measured τ from slope methods are almost the same. They agree well with the τ reported by Higasi. The plots of τjk–xj and μjk–xj curves reveal solute–solute and solute–solvent molecular association through H-bonding, and variation of μ with t (°C) is noted from the μjk–t curve. The associational aspects are taken into consideration from theoretical μtheo from the standpoint of inductive, mesomeric, and electromeric effects within the polar groups of the molecules. The estimated Debye factor τjkT/η and Kalman factor τjkT/ηγ reveal that the polar mixture obeys the Debye relaxation mechanism.

Peroxyoxalate chemiluminescence efficiency in polar medium is moderately enhanced by solvent viscosity

Abstract The peroxyoxalate reaction is one of the most efficient chemiluminescence transformations and the only system which is believed to occur by an intermolecular Chemically Initiated Electron Exchange Luminescence (CIEEL) mechanism with proven high efficiency. Although this reaction system is utilized in a variety of analytical applications, its exact reaction mechanism is still unknown, specifically with respect to the structure of the high-energy intermediate, the mechanism of its interaction with a chemiluminescence activator, as well as the reason for the extraordinarily high chemiexcitation efficiency. The solvent viscosity influence on the singlet quantum yields of the peroxyoxalate reaction is studied in this work, using the polar binary solvent mixture of ethyl acetate and dimethyl phthalate spanning a viscosity range of 0.42–14.4 cP. The viscosity increase of about forty times leads to a quantum yield increase of a factor of around five. Although the viscosity effect on the quantum yields is significant, it is considerably lower than that obtained before in less polar media. The quantum yield dependency on the viscosity can be described with both the collisional and the frictional model, with good correlation coefficients ( R 2 > 0.95). However, the α values obtained from the frictional model would be more compatible with an intramolecular transformation than with the intermolecular interaction of a high-energy intermediate with an external activator. This apparent contradiction is thought to be due to stabilization of the charge-transfer complex between the high-energy intermediate and the activator by the polar medium, avoiding solvent cavity escape and increasing chemiexcitation efficiency. The high stability of the charge-transfer complex in the peroxyoxalate reaction might be due to the high planarity of the possible high-energy intermediate in this transformation, 1,2-dioxetanedione, the peroxidic carbon dioxide dimer.

Dielectric study of molecular association of polar–polar binary mixtures (Benzyl alcohol + Aliphatic alcohols) at 298.2 K

Dielectric constants of the polar–polar binary mixtures (1-butanol + benzyl alcohol), (3-methyl-1-butanol + benzyl alcohol), (2-methyl-2-butanol + benzyl alcohol) were investigated experimentally with various mole fractions at 298.2 K to determine their dielectric behavior and molecular association. The corrective correlation factor, excess permittivity and Bruggman dielectric factor were also calculated in order to obtain information about the heterogeneous intermolecular interactions in these binary mixtures. The deviation of Bruggeman factor (f B) from linearity and corrective correlation factor (g f ) from unity indicates the existence of intermolecular interaction and parallel and anti-parallel orientations of molecules between the aromatic and aliphatic alcohols. The excess permittivity provides qualitative information about multimer formation in the binary mixture, which increases the total number of parallel aligned effective dipoles that contributes to the mixture dielectric polarization. The outcome of this study could be helpful in investigation of possible intermolecular interaction within various binary mixtures.

Solvent sorting in (mixed solvent + electrolyte) systems: Time-resolved fluorescence measurements and theory

In this manuscript we explore electrolyte-induced modification of preferential solvation of a dipolar solute dissolved in a binary mixture of polar solvents. Composition dependence of solvation characteristics at a fixed electrolyte concentration has been followed. Binary mixtures of two different polarities have been employed to understand the competition between solute-ion and solute-solvent interactions. Time-resolved fluorescence Stokes shift and anisotropy have been measured for coumarin 153 (C153) in moderately polar (ethyl acetate + 1-propanol) and strongly polar (acetonitrile + propylene carbonate) binary mixtures at various mixture compositions, and in the corresponding 1.0 M solutions of LiClO4. Both the mixtures show red shifts in C153 absorption and fluorescence emission upon increase of mole fraction of the less polar solvent component in presence of the electrolyte. In addition, measured average solvation times become slower and rotation times faster for the above change in the mixture composition. A semi-molecular theory based on solution density fluctuations has been developed and found to successfully capture the essential features of the measured Stokes shift dynamics of these complex multi-component mixtures. Dynamic anisotropy results have been analyzed by using both Stokes-Einstein-Debye (SED) and Dote-Kivelson-Schwartz (DKS) theories. The importance of local solvent structure around the dissolved solute has been stressed.

A study of internal pressures of ternary and sub-binary liquid mixtures at various temperatures

Internal pressures of the ternary and sub-binary mixtures of Benzene (1) +Hexane (2) + n-Butanol (3) have been computed from ultrasonic velocity measurements at different mole fractions in the temperature range of 300C-450C. The present work has been carried out to study the variation of internal pressure with temperature and composition of polar binary mixtures. The equation proposed by Andiappan et.al, for evaluating internal pressures of binary liquid mixtures has been modified and extended in the present work for the Ternary systems. The internal pressures computed with the help of the modified relation shows close agreement with observed values. The absolute deviation between the calculated and observed values from 1.15% to 1.9% for the ternary system studied.

Molecular interaction studies in hydrogen bonded polar binary mixtures

The molecular interactions between the polar systems of propan-1-ol (1PN) with alkyl benzoates (methyl benzoate and ethyl benzoate) for various mole fractions at different temperatures are studied by determining the dielectric permittivity in radio, microwave and optic frequency regions, respectively. Dipole moment, excess dipole moment, excess Helmholtz free energy, excess permittivity, relaxation time, excess inverse relaxation time and excess thermodynamical values are calculated using experimental data. Hamiltonian quantum mechanical calculations are performed on both pure and equimolar binary systems of 1PN with alkyl benzoates for the measurement of dipole moment from the ab initio Hartree–Fock and density functional theory (B3LYP) methods with 6-31 + G* and 6-311 + G** basis sets using Spartan 08 modelling software and these theoretical values are in good agreement with the experimental values.

Temperature-dependent microwave dielectric relaxation studies of hydrogen bonded polar binary mixtures of propan-1-ol and propionaldehyde

The molecular interaction between the polar systems of propan-1-ol and propionaldehyde for various mole fractions at different temperatures were studied by determining the frequency dependent complex dielectric permittivity by using the open-ended coaxial probe technique method in the microwave frequency range from 20MHz to 20GHz. The geometries are optimized at HF, B3LYP and MP2 with 6-311G and 6-311G+ basis sets. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi’s method and compared with the theoretical results. Conformational analysis of the formation of hydrogen bond between the propan-1-ol and propionaldehyde is supported by the FT-IR and molecular polarizability calculations. The average relaxation times are calculated from their respective Cole–Cole plots. The activation entropy, activation enthalpy and Kirkwood correlation ‘g’ factor, excess permittivity (εE), excess inverse relaxation time (1/τ)E, Bruggeman parameter (fB) have also been determined for propan-1-ol and propionaldehyde and the results were correlated.

Dielectric and excess dielectric constants in non polar + polar binary liquid mixtures of toluene with alcohols at 303, 313 and 323 K

The dielectric constants and excess dielectric constants in non-polar+polar binary liquid mixtures of toluene with alkanols (methyl alcohol, ethyl alcohol, propyl alcohol and isopropyl alcohol) have been studied at 303, 313 and 323K temperatures and over the complete mole fraction range. The dielectric constants for these mixtures were measured using a microcontroller based system. The results are negative over the entire range of composition. Symmetrical curves were observed for the systems in which the minimum occurs approximately at 0.5-mole fraction of toluene. The results are discussed in terms of intermolecular interactions. In order to predict the dielectric data for non-polar+polar binary liquid mixtures, five mixing rules were applied and the results indicate that the predictions of the five mixing rules are satisfactory. The investigation of dielectric constant of mixed solvents bearing alcohols aims at better comprehension of their biological, chemical, pharmaceutical, technological and laboratory applications.

Microwave dielectric relaxation studies of hydrogen bonded polar binary mixtures of isobutanol and aniline

The molecular interaction between the polar systems of isobutanol and aniline for various mole fractions at different temperatures were studied by determining the frequency dependent complex dielectric permittivity by using the open-ended coaxial probe technique method in the microwave frequency range from 20MHz to 20GHz. The geometries are optimized at HF and B3LYP with 6-31G and 6-31G+ basis sets. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi’s method and compared with the theoretical results. Conformational analysis of the formation of hydrogen bond between the isobutanol and aniline is supported by the FT-IR and molecular polarizability calculations. The average relaxation times are calculated from their respective Cole–Cole plots. The activation entropy, activation enthalpy and Kirkwood correlation ‘g’ factor, excess permittivities (εE), Bruggeman parameters (fB) have also been determined for isobutanol and aniline and the results were correlated.

Study of molecular interactions in the polar binary mixtures of N-methyl aniline and alcohols, using excess dielectric and thermodynamic parameters

Molecular interactions between the polar systems N-methyl aniline and alcohols (propan-1-ol/propan-2-ol) for various mole fractions at different temperatures are studied by determining the dielectric permittivity using LF impedance analyzer, Microwave bench and Abbe’s refractometer in radio, microwave and optic frequency regions respectively. The dipole moment, excess dipole moment, excess Helmholtz energy, excess permittivity, excess inverse relaxation time and excess thermodynamic values are calculated using experimental results. The optimized geometry, harmonic vibrational wave numbers and dipole moments of pure and equimolar binary mixtures have been calculated theoretically from the ab initio Hartree–Fock (HF) and Density Functional Theory (DFT – B3LYP) methods with 6-31+G ∗ and 6-311+G ∗∗ basis sets using Spartan 08 modelling software. Conformational analysis of the formation of hydrogen bond in the equimolar binary mixture systems of N-methyl aniline and alcohols (propan-1-ol/propan-2-ol) is supported by experimental FT-IR spectra. The calculated wave numbers and dipole moments agree well with the experimental values. Further, the correlations among the parameters are discussed in detail.

Correlation studies on dielectric and thermodynamic parameters in the binary mixtures of N-methyl aniline and alcohols

The dielectric and thermodynamic studies on polar binary mixtures of N- methyl aniline with alcohols — propan-1-ol and propan-2-ol have been carried out, at different temperatures and mole fractions. LF impedance analyzer, Microwave bench and Abbe’s refractometer are used respectively in radio, microwave (X-Band) and high frequency regions to determine the dielectric data. The experimental data is used to correlate the dielectric and thermodynamic parameters — static permittivity, high frequency permittivity, Kirkwood effective correlation factor, corrective Kirkwood correlation factor, excess permittivity, excess Helmholtz free energy, dipole moment, excessive dipole moment, relaxation time, excess inverse relaxation time and the excess thermodynamic parameters. These parameters are used to interpret the molecular interactions between the molecular species of the liquid mixtures.

The critical behavior of the dielectric constant in the polar + polar binary liquid mixture nitromethane + 3-pentanol: An unusual sign of its critical amplitude in the one-phase region

Dielectric constant measurements have been carried out in the one- and two-phase regions near the critical point of the polar + polar binary liquid mixture nitromethane + 3-pentanol. In the two-phase region, evidence for the |t|(2β) singularity in the coexistence-curve diameter has been detected, thus confirming the novel predictions of complete scaling theory for liquid-liquid criticality. In the one-phase region, an "unusual" negative sign for the amplitude of the |t|(1-α) singularity has been encountered for the first time in an upper critical solution temperature type of binary liquid mixture at atmospheric pressure. Mass density measurements have also been carried out to provide additional information related to such experimental finding, which entails an increase of the critical temperature T(c) under an electric field.

Solvation effects in phase transitions in soft matter

Phase transitions in polar binary mixtures can be drastically altered by even a smallamount of salt. This is because the preferential solvation strongly depends on the ambientcomposition. Together with a summary of our research on this problem, we presentsome detailed results on the role of antagonistic salt composed of hydrophilic andhydrophobic ions. These ions tend to segregate at liquid–liquid interfaces andselectively couple to water-rich and oil-rich composition fluctuations, leading tomesophase formation. In our two-dimensional simulation, the coarsening of the domainstructures can be stopped or slowed down, depending on the interaction parameter (orthe temperature) and the salt density. We realize stripe patterns at the criticalcomposition and droplet patterns at off-critical compositions. In the latter case,charged droplets emerge with considerable size dispersity in a percolated region.We also give the structure factors among the ions, accounting for the Coulombinteraction and the solvation interaction mediated by the composition fluctuations.

Phase Transitions in Soft Matter Induced by Selective Solvation

Abstract We review our recent studies on selective solvation effects in phase separation in polar binary mixtures with a small amount of solutes. Such hydrophilic or hydrophobic particles are preferentially attracted to one of the solvent components. We discuss the role of antagonistic salt composed of hydrophilic and hydrophobic ions, which undergo microphase separation at water–oil interfaces leading to mesophases. We then discuss phase separation induced by a strong selective solvent above a critical solute density np, which occurs far from the solvent coexistence curve. We also give theories of ionic surfactant systems and weakly ionized polyelectrolytes including solvation among charged particles and polar molecules. We point out that the Gibbs formula for the surface tension needs to include an electrostatic contribution in the presence of an electric double layer.

Excited state charge transfer reaction in (mixed solvent + electrolyte) systems: Role of reactant–solvent and reactant–ion interactions

Fluorescence spectroscopic techniques have been used to study the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in two sets of mixed solvents, (1-propanol + ethyl acetate) and (propylene carbonate + acetonitrile), in the absence and presence of a strong electrolyte, lithium perchlorate. These two sets of mixed solvent systems represent binary solvent mixtures of low and high polarities, respectively. Density, sound velocity and viscosity measurements indicate that these two mixed solvent systems are structurally different. Stronger ion-reactant interaction is evidenced in the mole fraction independence of emission frequencies in electrolyte solutions of low polar binary solvent mixtures. For both these mixtures, the reaction driving force (− ΔG r ) decreases with increase in mole fraction of the relatively less polar solvent component of the mixture. Interestingly, − ΔG r increases significantly on addition of electrolyte in low polar mixtures and exhibits mixture composition dependence but, in contrast, − ΔG r in high polar mixtures does not sense variation in mixture composition in presence of electrolyte. This insensitivity to mixture composition for high polar mixtures is also observed for the measured reaction time constant. In addition, the reaction time constant does not sense the presence of electrolyte in the high polar solvent mixtures. The reaction time constant in low polar mixtures, which becomes faster on addition of electrolyte, lengthens on increasing the mole fraction of the relatively less polar solvent component of the mixture. These observations have been qualitatively explained in terms of the measured solvent reorganization energy and reaction driving force by using expressions from the classical theory of electron transfer reaction.