Influence of temperature on thermodynamic properties of acid–base liquid mixtures

Ultrasonic velocity, u density, ?? and viscosity, ?? of mixtures of N,N-dimethyl acetamide with equimolar mixture of ethanol?+?isopropyl alcohol/isobutyl alcohol/isoamyl alcohol, including those of pure liquids over the entire composition have been measured at T?=?308.15, 313.15, and 318.15?K. Using this data, various thermo-acoustic parameters such as deviations in ultrasonic velocity, ?u, isentropic compressibility, ?k _s , viscosity, ????, excess molar volume, $ V_{\text{m}}^{\text{E}} $ and excess Gibb??s free energy of activation for viscous flow, ??G ^*E have been calculated at different temperatures. The calculated deviation and excess functions have been fitted to the Redlich?CKister type polynomial equation. The influence of temperature on the observed negative and positive values of deviation and excess thermodynamic properties has been explained in terms of molecular interactions present in the investigated acid?Cbase liquid mixtures. The experimental data of ultrasonic velocity have been used to check the applicability of velocity models of Nomoto, Van Dael and Vangeel and Junjie and viscosity data have also been availed to test the applicability of standard viscosity models of Grunberg-Nissan, Hind-Mc Laughlin, and Katti-Chaudhary for all the systems investigated at various temperatures.     

Thermo-physical properties of the binary mixture of benzaldehyde with bromobenzene at 303.15, 308.15, and 313.15?K

The values of density, viscosity, and ultrasonic velocity for the binary liquid mixture of benzaldehyde with bromobenzene have been measured over the entire range of composition at 303.15, 308.15, and 313.15?K. These values have been used to calculate the excess molar volume (V ^E), deviation in viscosity (????), deviation in velocity (?U), deviation in isentropic compressibility (??? _s), excess internal pressure (???), excess intermolecular free length (?L _f), and excess acoustic impedance (?Z). McAllister??s three-body-interaction model is used for correlating kinematic viscosity of binary mixtures. The excess values were correlated using the Redlich?CKister polynomial equation to obtain their coefficients and standard deviations. The thermo-physical properties (density, viscosity, and ultrasonic velocity) under the study were fitted to the Jouyban?CAcree model.     

Influence of the composition of aqueous dimethylsulfoxide solvent on thermodynamics of complexing between 18-crown-6-ether and D,L-alanine

Standard thermodynamic parameters (logK ^o, ??_r H ^o, T??_r S ^o) of complexing 18-crown-6 ether (18C6) with D,L-alanine (Ala) in mixed water-dimethysulfoxide (H₂O-DMSO) solvents are calculated on the basis of calorimetric titration results. A rise in the DMSO concentration in mixed solvent is found to increase stability and increase the exothermicity of the formation of [Ala-18C6] molecular complex. Changes in the reaction energetic are shown to be determined by changes in the solvation state of 18C6 that is the characteristic of the reactions of molecular complex formation between 18C6 and D,L-alanine or glycine in water-organic solvents.     

Spectroscopic Study of the Interactions of Buflomedil to Serum Albumin and β-Cyclodextrin

The effects of buflomedil (BFM), a novel cerebrovascular medicine, on serum albumin and the feasibility of ??-cyclodextrin (??-CD) acting as a controlled releaser for BFM were investigated by molecular spectroscopy methods, including fluorescence emission, UV?Cvisible absorption, Fourier transform infrared (FT-IR), synchronous and three-dimensional fluorescence spectroscopies. The interaction of BFM with bovine serum albumin (BSA) was analyzed by fluorescence quenching and it was found that BFM had reacted with BSA in the ground state and had affected the secondary structure of BSA. The observed binding constant K _b, the number of binding sites n, the distance r between donor (BSA) and acceptor (BFM), the enthalpy change (??H ^?? ), Gibbs energy change (??G ^?? ) and entropy change (??S ^?? ) at different temperatures were calculated. The inclusion reaction between ??-CD and BFM was explored by the Lineweaver?CBurk equation. The inclusion constants and the thermodynamic parameters were determined. The mechanism of the inclusion reaction was discussed and the controlled release characteristics of ??-CD to BFM were considered at the molecule level.     

Molecular interactions in β-alanine-water-methanol solutions at 308.15 K on volumetric, viscometeric, and acoustic data

The density, viscosity and ultrasonic velocity for β-alanine solutions in aqueous and aqueous methanol medium at different concentrations has been determined at 308.15 K. The experimentally obtained data were used to evaluate the apparent molal volume and apparent molal adiabatic compressibility. The related thermodynamic parameters like partial molal volume as well as partial molal adiabatic compressibility at infinite dilution along with their corresponding constants S _v and S _k , respectively, give an insight to the nature of molecular interactions. The viscosity coefficient has also been calculated using Jones-Dole equation.     

Temperature dependence of density, viscosity, ultrasonic velocity, and other properties of substituted pyrazoles in acetone-water mixtures

The density, viscosity and ultrasonic velocity of some substituted pyrazoles viz. 5-(2-hydroxyphenyl)-3-(pyridin-3-yl)-4-benzoylpyrazol, 5-(2-hydroxyphenyl)-3-(3-nitrophenyl)-4-(3-pyridinoyl)-pyrazol, 5-(2-hydroxyphenyl)-3-(3-nitrophenyl)-4-benzoylpyrazol and 5-(2-hydroxyphenyl)-3-phenyl-4-(3-pyridinoyl)-pyrazole have been measured in 70: 30 (vol/vol) acetone-water mixture at 298, 303, 308, and 313 K for 0.01 mol dm^?3 concentration of pyrazoles. The acoustical parameters such as adiabatic compressibility (??_s), relative association (R _A), specific acoustic impedance (Z), apparent molar volume (?_v), apparent molar adiabatic compressibility (?_K), and intermolecular free length (L _f) were calculated from the experimental densities and velocities. The changes in acoustical properties have been used to interpret the molecular interactions in solutions. The activation energies of viscous flow of pyrazole solutions were determined from the data of viscosity at different temperature.     

Intermolecular/interionic interactions in l-leucine-, l-asparagine-, and glycylglycine-aqueous electrolyte systems

Ultrasonic velocity and density values have been measured for ternary systems (amino acid/di-peptide + salt + water): l-leucine/l-asparagine/glycylglycine each in 1.5 M aqueous solutions of NaCl or NaNO₃ or KNO₃ used as solvents for several concentrations of amino acids/di-peptide at different temperatures in the range of 298.15-323.15 K. The ultrasonic velocity values have been found to increase with increase in amino acids/di-peptide concentration and temperature in all the systems. The increase in ultrasonic velocity with increase in concentration has been discussed in terms of electrostatic interactions occurring between terminal groups of zwitterions (NH₄⁺ and COO⁻) and Na⁺, K⁺, Cl⁻, NO₃⁻ ions. The interactions of water dipoles with cations/anions and with zwitterions have also been taken into consideration. It has been observed that the ion-zwitterion and ion-dipole attractive forces are stronger than those of ion-hydrophobic repulsive forces. These interactions comprehensively introduce the cohesion into solutions under investigation. The cohesive forces are further enhanced on successive increases in solute concentration. Using ultrasonic velocity and density data, the parameters such as isentropic compressibility (κ_s), change (Δκ_s) and relative change (Δκ_s/κ₀) in isentropic compressibility, specific acoustic impedance (Z) and relative association (RA) have been computed. The isentropic compressibility values decrease with increase in the concentration of solutes as well as with temperature. The decrease in κ_s values with increase in concentration of l-leucine, l-asparagine and glycylglycine in 1.5 M aqueous solutions of NaCl, NaNO₃ and KNO₃ have been explained in terms of an increase in the number of incompressible molecules/zwitterions in solutions and the formation of compact zwitterions-water dipole and zwitterions-ions structures in solutions. The decrease in κ_s values with increase in temperature has been attributed to the corresponding decrease of κ_relax. (relaxational part of compressibility)_, which is dominant over the corresponding increase of κ_∞ (instantaneous part of compressibility). The trends of variations of Δκ_s, Δκ_s/κ₀, Z and RA with change of concentration and temperature have also been interpreted in terms of various intermolecular/interionic interactions existing in the systems.     

Acoustic and volumetric studies of uracil in aqueous urea solution at different temperatures

Volumetric, viscometric and ultrasonic studies of uracil in an aqueous urea solution in varying concentration of 2, 3 and 5?M have been carried out at 298, 308 and 318?K. The uracil concentration in the aqueous urea solution varies from 0.05% to 0.4%. Density (ρ), viscosity (η) and sound speed (u) have been measured. The experimental data are used for computing various thermodynamic and acoustic parameters, namely apparent molar volume, isentropic compressibility, apparent isentropic compressibility, relative association, intermolecular free length, acoustic impedance, viscous relaxation time, hydration number, Gibb's free energy, classical absorption coefficient of the solution and viscosity data have been further analysed in the light of Masson's equation and Jones–Dole's equations, respectively. The results have been discussed in terms of solute–solute and solute–solvent interaction and the structural changes of the solutes in solutions. The effect of variation of temperature on these interactions has also been investigated.     

Exploring antibiotic resistant mechanism by microcalorimetry

In an effort to probe the reaction of antibiotic hydrolysis catalyzed by B3 metallo-??-lactamase (M??L), the thermodynamic parameters of penicillin G hydrolysis catalyzed by M??L L1 from Stenotrophomonas maltophilia were determined by microcalorimetric method. The values of activation free energy ??G _?? ^?? are 88.26, 89.44, 90.49, and 91.57?kJ?mol^?1 at 293.15, 298.15, 303.15, and 308.15?K, respectively, activation enthalpy ??H _?? ^?? is 24.02?kJ?mol^?1, activation entropy ??S _?? ^?? is ?219.2511?J?mol^?1?K^?1, apparent activation energy E is 26.5183?kJ?mol^?1, and the reaction order is 1.0. The thermodynamic parameters reveal that the penicillin G hydrolysis catalyzed by M??L L1 is an exothermic and spontaneous reaction.     

Studies on thermo-acoustic parameters of poly(ethylene glycol)- 400 at different temperatures

The ultrasonic velocity and density have been measured at different temperatures between 299 and 363 K for the pure liquid sample, poly(ethylene glycol) with average molecular mass 400 g mol^?1 (PEG 400). From these, isentropic compressibility (β), intermolecular free length (L _f), acoustic impedance (Z), molar volume (V _m), Schaff’s available volume V _a(s), molar sound velocity (R _a), and molar compressibility (W) have been evaluated. The variations of these parameters with the temperature of the sample have been studied. Data so obtained are employed to compute other thermodynamic parameters. Variations in various parameters with respect to temperature are discussed in the light of the results obtained.     

Excess Acoustical and Volumetric Properties and Theoretical Estimation of Ultrasonic Velocities in Binary Liquid Mixtures of 2-Chloroaniline with Acrylic Esters at 308.15 K

The ultrasonic velocities (u) and densities (??) for three binary mixture systems of 2-chloroaniline (CA) with ethyl acrylate (EA), butyl acrylate (BA), and 2-ethylhexyl acrylate (EHA) were measured over the entire mole fraction range at the temperature 308.15?K, including those of pure liquids. From these data, the deviations in ultrasonic velocity (??u), the excess molar volumes ( $V_{\mathrm{m}}^{\mathrm{E}}$ ), deviations in excess molar volume ( $\delta V_{\mathrm{m}}^{\mathrm{E}}$ ), deviations in isentropic compressibility (??k _S), excess intermolecular free lengths ( $L_{\mathrm{f}}^{\mathrm{E}}$ ), and excess acoustic impedances (Z ^E) have been calculated. The variations of these properties with solution composition are discussed in terms of molecular interactions among unlike molecules of the mixtures. The excess and deviation functions have been fitted to Redlich-Kister type polynomials and the corresponding standard deviations ??(Y ^E) have been calculated. The deviations and excess values were plotted against the mole fraction of CA over the whole composition range. The $V_{\mathrm{m}}^{\mathrm{E}}$ and ??k _S values are negative in the EA + CA and BA + CA systems but are positive in the EHA + CA system, which indicates the presence of specific interactions between unlike molecules. Further, theoretical values of the sound velocity in these mixtures have been evaluated using various theories and have been compared with experimental sound velocities to verify the applicability of such theories to the investigated systems. Two types of polynomial equations, f(x) and g(x), have been fitted to experimental values of ultrasonic velocities. The sound velocities obtained by these polynomials have extremely small deviations from the experimental values.     

Study of complex formation between ��-cyclodextrin and benzene

In this work study of complex formation of ??-cyclodextrin with benzene was performed both experimentally and theoretically. Interaction of benzene with ??-cyclodextrin in aqueous solutions was investigated by means of UV spectroscopy at temperatures in the range 291?C303 K. The stoichiometric composition, stability constant, and thermodynamic parameters of ????-cyclodextrin-benzene?? supramolecular structures formation were calculated from spectroscopic data. It was proved that 1:1 inclusion complex is mainly formed in aqueous solutions. The calculations of a spatial structure, formation energy, and vibration spectra in IR range for the complex of ??-cyclodextrin with benzene were performed by Hartree?CFock?CRoothaan method within PM3 semiempirical approximation with quantum chemistry package GAMESS (version 6.4). The calculated energy parameters for ????-cyclodextrin-benzene?? inclusion complex are in agreement with experimental data.     

Effect of Temperature and Solvent on the Ultrasonic Velocity and Allied Acoustical Parameters of the Epoxy Oleate of 9,9′-Bis(4-hydroxyphenyl) Anthrone-10 Solutions

Density (ρ), viscosity (η) and ultrasonic velocity (U) (2 MHz) of the pure solvents (chloroform, THF and 1,4-dioxane) and solutions of the epoxy oleate of 9,9′-bis(4-hydroxyphenyl) anthrone-10 (EBANO) have been investigated at 303, 308 and 313 K. Acoustical parameters such as specific acoustical impedance (Z), adiabatic compressibility (κ _a ), intermolecular free path length (L _f ), classical absorption coefficient (α/f ²)_cl and viscous relaxation time (τ) have been determined from the ρ, η and U data and are correlated with concentration. A fairly good to excellent correlation between a given parameter and concentration is observed at all temperatures and solvent systems studied. Linear or nonlinear increases or decreases of acoustical parameters with concentration and temperature indicated the existence of strong molecular interactions.     

Viscosities of Binary Liquid Mixtures of 2-Methylpropane Nitrile and Some Aromatic Hydrocarbons at 303.15 K and 308.15 K

Viscosities, ??, of five binary mixtures of 2-methylpropane nitrile with aromatic hydrocarbons, viz. benzene, methylbenzene, 1,4-dimethylbenzene, chlorobenzene and 1,2-dichlorobenzene, have been measured at temperatures 303.15 and 308.15?K. Deviations in viscosities, ????, from the linear mixing rule have been determined for all of the binary mixtures studied at both experimental temperatures. The ???? values are negative for all the five systems at both experimental temperatures. Parameters of the Redlich?CKister and Myers and Scott equations have been fitted to the ???? values and standard deviations, ??(????), have also been evaluated. The correlating performances of several viscosity models have been evaluated. The Hind?CMcLaughlin?CUbbelohde viscosity model gives fairly constant interaction parameters with composition. Results are discussed in terms of unlike molecular interactions between the components of the binary mixtures.     

Thermoanalysis of binary condensed eutectic phases evincing molecular interactions

This article discusses the thermoanalytical model developed in the current work to study the influence of the molecular interactions between binary condensed eutectic phases in terms of excess thermodynamic functions that exhort the ability of providing quantitative idea of the interactions. Non-ideality of binary eutectic systems over the entire range of mole fraction composition is ascertained by subjecting the experimentally determined solidus?Cliquidus equilibrium data to thermodynamic analysis and thereby, apprehending quantitative idea about the nature of molecular interactions. The estimation of molecular interactions model of binary naphthalene?Co-nitrophenol, ??-naphthol?Cnaphthalene, diphenylamine?C??-naphthol, benzil?Cdiphenyl, acenaphthene?Cantimonytrichloride and cadmium?Cbismuth eutectic systems authenticates the reliability of the excess functions, since the mixing of the eutectic phases either side of solidus?Cliquidus equilibrium curves of the systems is found to follow the criteria of spontaneity and Planck formulation S?=?klnw; where S, k and w, respectively, are the configurational entropy, Boltzmann constant and complexion number of constituent phase molecules. Moreover, the Guggenheim lattice theory applied to solidus mixtures at their liquidus temperatures offers supporting evidence to the essence of the excess functions and hence the thermomolecular interactions model.     

Micellization and Thermodynamic Parameters of Butanediyl-1,4-bis(tetradecyldimethylammonium Bromide) Gemini Surfactant at Different Temperatures: Effect of the Addition of 2-Methoxyethanol

The effect of the addition of 2-methoxyethanol on the critical micelle concentration (cmc) and on the degree of counterion dissociation (??) of butanediyl-1,4-bis(tetradecyldimethylammonium bromide) gemini surfactant, [C₁₄H₂₉N⁺(CH₃)₂?C(CH₂)₄?CN⁺(CH₃)₂C₁₄H₂₉,2Br^?] (referred as 14?C4?C14,2Br^?), has been studied by varying the compositions of the 2-methoxyethanol + water mixed solvent media (0 to 50?%). To determine various thermodynamic parameters of micellization, on the basis of the mass?Caction model for micelle formation, the experiments were performed at selected compositions of the mixed solvent at four temperatures ranging between 25?°C and 50?°C. Furthermore, the air/bulk surface tensions of the pure and mixed media were determined, and a successful attempt was made to correlate the cohesive energy density described through the Gordon parameter with the values of Gibbs energy of micellization.     

Uranyl sensor based on a N,N′-bis(salicylidene)-2-hydroxy-phenylmethanediamine and multiwall carbon nanotube electrode

The electrochemical determination of uranyl was investigated by using carbon paste electrode modified with a Schiff base namely N,N??-bis(salicylidene)-2-hydroxy-phenylmethanediamine (SHPMD/CPE) and also in the presence of carbon nanotube (SHPMD/CNT/CPE). The both modified electrodes displayed an irreversible peak at E _pa?=?0.798?V versus Ag/AgCl. The electrocatalytic reduction of uranyl has been studied on SHPMD/CNT/CPE, using cyclic and differential pulse voltammetry, chronocoulometry and linear sweep techniques. Electrochemical parameters including the diffusion coefficient (D), the electron transfer coefficient (??), the ionic exchange current (i) and the redox reaction rate constant (K) were determined for the reduction of uranyl on the surface of the modified electrodes. Linear range concentration is 0.002?C0.6???mol?L^?1 and the detection limit of uranyl is 0.206?nmol?L^?1. The proposed method was used to detect uranyl in natural waters and good recovery was achieved.     

Dielectric relaxation study of binary mixture of sulfolane and N,N-dimethylformamide in benzene solution using microwave absorption data

The dielectric constant (???) and dielectric loss (???) for dilute solutions of the binary mixture of different molar concentrations of sulfolane and DMF in benzene solution has been measured at 9.885 GHz and different temperatures (25, 30, 35, 40°C) by using standard microwave techniques. Following the single frequency concentration variational method, the dielectric relaxation time (??) and dipole moment (??) have been calculated. It is found that dielectric relaxation process can be treated as the rate process, just like the viscous flow. The presence of solute-solute molecular associations in benzene solution has been proposed. Energy parameters (??H _?, ??F _?, ??S _?) for dielectric relaxation process of binary mixture at 50% mole fraction in benzene at 25, 30, 35, and 40°C have been calculated and compared with the corresponding energy parameters (??H _??, ??F _??, ??S _??) for the viscous flow.     

Acoustical studies of some derivatives of 4-amino antipyrene in 1,4-dioxane and dimethylformamide at 318.15 K

For three derivatives of 4-amino antipyrene, density, viscosity and ultrasonic velocity are measured at 318.15 K in 1,4-dioxane (DO) and dimethylformamide (DMF). From these experimental data, various acoustical properties such as specific impedance (Z), isentropic compressibility (κ_s), Rao’s molar sound function (R_m), the van der Waals constant (b), molar compressibility (W), intermolecular free length (L_f), relaxation strength (r), relative association (R_A), free volume (V_f), etc. and apparent molar volume and apparent molar compressibility were calculated. The results are interpreted in terms of molecular interactions occurring in the solutions. It is observed that in 1,4-dioxane solutions, solute–solute interactions exist whereas solvent–solute interactions predominant in DMF system.