Excess Molar Heat Capacities Research Articles

Energetic domains analysis of bovine α-lactalbumin upon interaction with copper and dodecyl trimethylammonium bromide

Domain analysis of the dialyzed form of α-lactalbumin (m-α-LA) with varying concentrations of Cu +2 and DTAB has been carried out by differential scanning calorimetry (DSC), circular dichroism (CD) and resonance Rayleigh scattering (RLS) to elucidate the effect of the ligands on the thermal and structural properties of m-α-LA. The DSC profile displayed two dissimilar temperature-induced heat-absorption peaks as well as two melting points ( T m = 305 K, T m = 333 K). The m-α-LA is not a new form of α-LA, but rather contains a mixture of the apo- and holo-forms of α-LA (i.e., a-α-LA and h-α-LA) at low and high temperatures, respectively. The presence of Cu +2 as the metal ion and DTAB as the non-metal ion altered the two heat-absorption peaks in such a manner that, with the addition of Cu +2 to m-α-LA, the excess molar heat capacity profile showed three sub-peaks, i.e., one sub-peak for a-α-LA at 303.2 K and two other sub-peaks for h-α-LA at 325 K and 334 K. The presence of these peaks was due to the molecular population of the a-α-LA form changing into h-α-LA. Contrarily, when it came to the interaction between DTAB and m-α-LA, the DSC thermogram showed two sub-peaks, i.e., one sub-peak for a-α-LA and another sub-peak for h-α-LA, resulting from the molecular population of the h-α-LA form changing into a-α-LA. The CD experiments on m-α-LA upon interaction with Cu +2 and DTAB demonstrated an increment and a decrement, respectively, of the α-helix content relative to that of the protein in the absence of the ligands. However, the α-helix induced by Cu +2 as a metal ion inspired one energetics domain in m-α-LA, wherefore it could be deduced that the helicity content caused an increment of the energetics content of α-LA. Hence, Cu +2 and DTAB at various concentrations played important roles as good probes for defining the electrostatic moiety for domains of m-α-LA initiated through a dissimilarity with regard to the α-helicity of these domains. The RLS intensity of m-α-LA upon interaction with Cu +2 and DTAB determine the DSC and CD results for inducing h-α-LA and a-α-LA respectively.

Molar heat capacities of the (water + acetonitrile) mixtures at T = (283.15, 298.15, 313.15, and 328.15) K

The molar heat capacities of the (water + acetonitrile) mixtures have been measured at T = (283.15, 298.15, 313.15, and 328.15) K as a function of mole fraction. The excess molar heat capacities, C p E , limiting partial molar heat capacities of water and acetonitrile C ¯ p ∘ have been calculated. The excess molar heat capacities are positive over the whole mole fraction range and increase with increasing temperatures from (283.15 to 328.15) K. The excess molar heat capacities have been fitted to the Redlich–Kister equation.

Measurements of Density and Heat Capacity for Binary Mixtures {x Benzonitrile + (1 −x) (Octane or Nonane)}

Densities and isobaric heat capacities per unit volume have been measured for binary mixtures {x benzonitrile + (1 − x) octane} and {x benzonitrile + (1 − x) nonane} in the temperature ranges of (283.15 to 318.15) K and (283.15 to 313.15) K, respectively. Measurements covered the whole composition range at the ambient pressure. From these measured data, the excess molar volumes, excess isobaric thermal expansivities, and excess isobaric molar heat capacities were calculated and fitted with the Redlich−Kister equation. The excess molar volumes, excess isobaric thermal expansivities, and excess isobaric molar heat capacities of both systems were found to exhibit the S-shaped curves against the composition and the feature of the nonrandomness mixing. The dependences of these properties on the temperature and composition were analyzed and discussed in terms of the natures of the two pure components and the molecular interactions in the mixtures.

Electrolytic conductivity and molar heat capacity of two aqueous solutions of ionic liquids at room-temperature: Measurements and correlations

As part of our systematic study on physicochemical characterization of ionic liquids, in this work, we report new measurements of electrolytic conductivity and molar heat capacity for aqueous solutions of two 1-ethyl-3-methylimidazolium-based ionic liquids, namely: 1-ethyl-3-methylimidazolium dicyanamide and 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate, at normal atmospheric condition and for temperatures up to 353.2 K. The electrolytic conductivity and molar heat capacity were measured by a commercial conductivity meter and a differential scanning calorimeter (DSC), respectively. The estimated experimental uncertainties for the electrolytic conductivity and molar heat capacity measurements were ±1% and ±2%, respectively. The property data are reported as functions of temperature and composition. A modified empirical equation from another researcher [1] was used to correlate the temperature and composition dependence of the our electrolytic conductivity results. An excess molar heat capacity expression derived using a Redlich–Kister type equation was used to represent the temperature and composition dependence of the measured molar heat capacity and calculated excess molar heat capacity of the solvent systems considered. The correlations applied represent the our measurements satisfactorily as shown by an acceptable overall average deviation of 6.4% and 0.1%, respectively, for electrolytic conductivity and molar heat capacity.

Heat Capacities of Binary Mixtures of Acetic Acid with Acetic Anhydride and Methenamine at Different Temperatures

Heat capacities of binary mixtures of acetic acid with acetic anhydride and methenamine were measured by a cooling method with a simple calorimeter from (308.15 to 333.15) K at atmospheric pressure with different compositions. The excess molar heat capacities of the binary mixture of acetic acid with acetic anhydride were calculated from the experimental data and were fitted to the Redlich−Kister equation.

Measurements of the Molar Heat Capacities and Excess Molar Heat Capacities for Water + Organic Solvents Mixtures at 288.15 K to 303.15 K and Atmospheric Pressure

Experimental molar heat capacity data (Cpm) and excess molar heat capacity data (\(\mathit{Cp}^{\mathrm{E}}_{\mathrm{m}}\)) of binary mixtures containing water + (formamide or N,N-dimethylformamide or dimethylsulfoxide or N,N-dimethylacetamide or 1,4-dioxane) at several compositions, in the temperature range 288.15 K to 303.15 K and atmospheric pressure, have been determined using a modified 1455 PAAR solution calorimeter. The excess heat capacities are positive for aqueous solutions containing 1,4-dioxane, N,N-dimethylformamide or dimethylsulfoxide, negative for solutions containing water + formamide and show a sigmoid behavior for mixtures containing water + N,N-dimethylacetamide, over the whole composition range. The experimental excess molar heat capacities are discussed in terms of the influence of temperature and of the organic solvent type present in the binary aqueous mixtures, as well as in terms of the existing molecular interactions and the organic solvent’s molecular size and structure.

Liquid heat capacity of the solvent system (piperazine + 2-amino-2-methyl-l-propanol + water)

This report presents a new set of heat capacity data for the system piperazine {(PZ) + 2-amino-2-methyl-1-propanol (AMP) + water (H 2O)}, measured using the differential scanning calorimetry technique, over the temperature range 303.2 K to 353.2 K and at fourteen (14) different concentrations in which the water mole fractions, x 3’s, were fixed at 0.60, 0.70, 0.80, and 0.90. Heat capacity for the binary system {PZ (1) + AMP (2)} at x 1 = 0.05, 0.10, 0.15, and 0.20 were, likewise, measured to generate parameters necessary in the Redlich–Kister-type model, which was used to estimate excess molar heat capacities. Such estimates were then used to predict the values of the molar heat capacity at the corresponding sets of temperature and concentration. The predicted values were subsequently compared against the measured values and the results are satisfactory.

Molar Heat Capacity of Aqueous Sulfolane, 4-Formylmorpholine, 1-Methyl-2-pyrrolidinone, and Triethylene Glycol Dimethyl Ether Solutions from (303.15 to 353.15) K

The present study has focused on the experimental measurements of the molar heat capacities of four aqueous physical solvents of importance in natural gas sweetening: (1) tetramethylene sulfone (sulfolane), (2) 4-formylmorpholine (NFM), (3) 1-methyl-2-pyrrolidinone (NMP), and (4) triethylene glycol dimethyl ether (TEGDME). The measurements of the molar heat capacities were carried out in the temperature range of (303.15 to 353.15) K and for the entire range of mole fractions. Fractional deviations of the measured molar heat capacities from literature data were less than 1 %, and at worst 2 %. Molar excess heat capacities were calculated from the measurements and correlated as a function of mole fraction and temperature employing the Redlich−Kister equation. The excess partial molar quantities (Cio − Ci*) were calculated by extrapolating the reduced excess heat capacity (CpE/x1x2) function at x1 = 0 and x1 = 1.

Speed of sound, density, and heat capacity for (2-methyl-2-butanol + heptane) at pressures up to 100 MPa and temperatures from (293 to 318) K. Experimental results and theoretical investigations

In this paper, some new physicochemical properties of (2-methyl-2-butanol + heptane) are investigated using an acoustic method. Of clear interest to us is the study of the effect of branched structure of alcohol on association in mixtures with heptane and consequently, the effect of temperature and pressure on deviations from ideal solution behaviour. Thus, this work presents experimental properties and theoretical study of (2-methyl-2-butanol + heptane) as functions of temperature and pressure over the entire composition range. The densities and speeds of sound in (2-methyl-2-butanol + heptane) have been measured for temperatures ranging from (293 to 318) K under atmospheric pressure and under elevated pressures up to 101 MPa, respectively. The densities, heat capacities and appropriate excesses of these binaries were calculated for the same temperatures and for pressures up to 100 MPa. The acoustic method was applied in the calculations. The effects of pressure and temperature on the excess molar volume and the excess molar heat capacity of (2-methyl-2-butanol + heptane) are explained in terms of the influence of the molecular size and configuration of the alcohols on their self-association capability, packing effect, and the non-specific interactions between the 2-methyl-2-butanol and heptane basing on the results obtained from the modified ERAS model.

Heat capacities of the mixtures of ionic liquids with acetonitrile

Isobaric specific heat capacities were measured for {1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF 4) + acetonitrile (MeCN)} and {1-methyl-3-octylimidazolium tetrafluoroborate (OMIMBF 4) + acetonitrile} within the whole range of composition and temperatures from (283.15 to 323.15) K. The excess molar heat capacities were calculated from the experimental results and satisfactorily fitted to Redlich–Kister type polynomials for several selected temperatures. Negative deviations from the additivity of molar heat capacities were observed within the whole composition range of (HMIBMF 4 + MeCN) and (OMIMBF 4 + MeCN). The results obtained have been interpreted in terms of interactions between ionic liquids and acetonitrile.

Molar heat capacity and electrolytic conductivity of aqueous solutions of [Bmim][MeSO 4] and [Bmim][triflate

Here we report the new measurements of molar heat capacity, C P and electrolytic conductivity, σ for aqueous solutions of 1-butyl-3-methylimidazolium methylsulfate, [Bmim][MeSO 4] and 1-butyl-3-methylimidazolium trifluoromethanesulfonate, [Bmim][triflate]. Heat capacities were measured from 303.2 to 353.2 K with a differential scanning calorimeter. Electrolytic conductivities were measured from 293.2 to 353.2 K with a commercial conductivity meter. The estimated uncertainties of C P and σ measurements were ±2 and ±1%, respectively. The present measurements of C P and σ were presented as a function of temperature and composition. An excess molar heat capacity C P E expression using the Redlich–Kister equation for the temperature and composition dependence was used to represent the measured C P and a modified empirical equation was used to correlate the temperature and composition dependence of the measured σ of the studied systems. The applied correlations represent the C P and σ measurements satisfactorily. The C P and σ values presented in this work are, in general, of sufficient accuracy for most engineering-design calculations.

Liquid heat capacity of the solvent system (piperazine + n-methyldiethanolamine + water)

A new set of values for the heat capacity of aqueous mixtures of piperazine (PZ) and n-methyldiethanolamine (MDEA) at different concentrations and temperatures are reported in this paper. The differential scanning calorimetry technique was used to measure the property over the range T = 303.2 K to T = 353.2 K for mixtures containing 0.60 to 0.90 mole fraction water with 15 different concentrations of the system (PZ + MDEA + H 2O). Heat capacity for four concentrations of the binary system (PZ + MDEA) was also measured. A Redlich–Kister-type equation was adopted to estimate the excess molar heat capacity, which was used to predict the value of the molar heat capacity at a particular concentration and temperature, which would then be compared against the measured value. A total of 165 data points fit into the model resulted in a low overall average absolute deviation of 4.6% and 0.3% for the excess molar heat capacity and molar heat capacity, respectively. Thus, the results presented here are of acceptable accuracy for use in engineering process design.

Heat capacities of aqueous solutions containing diethanolamine and N-methyldiethanolamine

In this work, we present new results for heat capacities of aqueous mixtures of diethanolamine with N-methyldiethanolamine over the temperature range (303.2 to 353.2) K with a differential scanning calorimeter. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the (DEA + MDEA + water) systems were investigated. For the binary system, (DEA + MDEA), heat capacities of nine concentrations were also measured. A Redlich–Kister-type equation for representing excess molar heat capacity was applied to correlate the measured C p of aqueous alkanolamine solutions. For a total of 176 data points for the (DEA + MDEA + water) system, the overall average absolute percentage deviation of the calculations are 16.5% and 0.2% for the excess molar heat capacity and the molar heat capacity, respectively. The heat capacities presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.

Measurements of excess molar enthalpy and excess molar heat capacity of (1-heptanol or 1-octanol)+(diethylamine or s-butylamine) mixtures at 298.15 K and 0.1 MPa

Abstract Experimental data of excess molar enthalpy (H mE) and excess molar heat capacity (C pmE) of binary mixtures containing (1-heptanol or 1-octanol)+(diethylamine or s-butylamine) have been determined as a function of composition at 298.15 K and at 0.1 MPa using a modified 1455 Parr solution calorimeter. The excess molar enthalpy data are negative and show parabolic format over the whole composition range; however, the excess molar heat capacity values, whose curves show a S-shape, are positive in the 0.0 to 0.7 molar fraction range and negative between the molar fraction values 0.7 to 1.0. The applicability of the ERAS-model to correlate the excess molar enthalpy data was tested. The calculated data values are in good agreement with the experimental ones. The experimental behavior of H mE is interpreted in terms of specific interactions between 1-alkanol and amine molecules.

Solution thermodynamics near the liquid–liquid critical point. II. Excess second-order derivatives

We present a comprehensive study of the behaviour of excess second-order derivatives of binary mixtures near the liquid–liquid critical point. Specifically, excess (isobaric and isochoric) molar heat capacities ( c p , x E and c V , x E ), excess (isothermal and isentropic) compressibilities ( κ T , x E and κ S , x E ), and excess isobaric thermal expansivities ( α p , x E ) have been determined over the whole composition ( x) range at atmospheric pressure and in the homogeneous region within (293.15–323.15) K. Results are consistent with the predictions of the current theory of critical phenomena. Remarkably, anomalous α p , x E ( x ) and κ T , x E ( x ) curves in the critical region are observed. Such anomalies, which are reported here for the first time, are of significant size for α p , x E and very mild in the case of κ T , x E ( x ) , thereby indicating that volumetric effects at near-liquid–liquid criticality are, as expected, very small.

Heat capacity and electrical conductivity of aqueous mixtures of [Bmim][BF 4] and [Bmim][PF 6

New measurements of molar heat capacity C p and electrical conductivity σ for aqueous binary systems of 1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim][BF 4] and 1-butyl-3-methylimidazolium hexafluorophosphate, [Bmim][PF 6] are reported. Heat capacities were measured from 303.2 to 353.2 K with a differential scanning calorimeter having a measurement uncertainty of ±0.015 kJ/(kg K). Electrical conductivities were measured from 293.2 to 353.2 K with a conductivity meter having a measurement uncertainty of ±0.001 (mS/cm). An excess molar heat capacity expression using the Redlich–Kister equation for composition dependence was used to represent the measured C p of the studied systems. An empirical equation proposed by another researcher was modified to correlate the composition dependence of the measured σ of the investigated systems. The correlations yield satisfactory results. The heat capacities and electrical conductivities of the studied systems presented in this work are, in general, of sufficient accuracy for most engineering-design calculations.

Limitations of the Wilson model for describing excess molar heat capacities of binary solutions

The forms of the concentration dependences of the excess molar heat capacities of 150 homogeneous binary solutions were analyzed. Limitations of the Wilson model as a tool for reproducing the local trends of these dependences, including those related to temperature changes, were revealed.

Molar heat capacities for (2-methyl-2-butanol + heptane) mixtures and cyclopentanol at temperatures from (284 to 353) K

Isobaric specific heat capacities were measured for (2-methyl-2-butanol + heptane) mixtures and cyclopentanol within the temperature range from (284 to 353) K, and for 2-methyl-2-butanol in the (284 to 368) K temperature interval by means of a differential scanning calorimeter. The excess molar heat capacities were calculated from the experimental results. For the temperature range from (284 to 287) K, the excess molar heat capacity is S-shaped with negative values in the 2-methyl-2-butanol rich region and with small negative values at low alcohol concentrations at temperatures from (295 to 353) K. The excess molar heat capacities are positive for all compositions under test at temperatures from (288 to 294) K. The results are explained in terms of the influence of the molecular size and configuration of the alkanols on their self-association capability and of the change in molecular structure of the (2-methyl-2-butanol + heptane) mixtures. The differences between the temperature dependences of the heat capacities of the mixtures studied are qualitatively consistent with results obtained by Rappon et al. [M. Rappon, J.M. Greer, J. Mol. Liq. 33 (1987) 227–244; M. Rappon, J.A. Kaukinen, J. Mol. Liq. 38 (1988) 107–133; M. Rappon, R.M. Johns, J. Mol. Liq. 40 (1989) 155–179; M. Rappon, R.T. Syvitski, K.M. Ghazalli, J. Mol. Liq. 62 (1994) 159–179; M. Rappon, R.M. Johns, J. Mol. Liq. 80 (1999) 65–76; M. Rappon, S. Gillson, J. Mol. Liq. 128 (2006) 108–114].

Isobaric thermal expansivity of the binary system 1-hexanol + n-hexane as a function of temperature and pressure

The isobaric thermal expansivity against temperature and pressure for the system 1-hexanol + n-hexane was directly determined by means of a calorimetric method. From these data, the excess isobaric thermal expansivity is calculated at representative temperatures and pressures. The obtained results for this excess quantity are qualitatively discussed by applying well-known arguments often used for explaining the thermodynamic behavior of alcohol + alkane mixtures. In order to check the consistency of these data with those of literature, the derivative of excess molar volume against temperature and that of excess isobaric molar heat capacity against pressure are calculated and compared with those obtained from literature data. Very good coherence between both data sources is obtained.

Excess enthalpy, density, and heat capacity for binary systems of alkylimidazolium-based ionic liquids + water

Experimental measurements of excess molar enthalpy, density, and isobaric molar heat capacity are presented for a set of binary systems ionic liquid + water as a function of temperature at atmospheric pressure. The studied ionic liquids are 1-butyl-3-methylpyridinium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. Excess molar enthalpy was measured at 303.15 K whereas density and heat capacity were determined within the temperature range (293.15 to 318.15) K. From experimental data, excess molar volume and excess molar isobaric heat capacity were calculated. The analysis of the excess properties reveals important differences between the studied ionic liquids which can be ascribed to their capability to form hydrogen bonds with water molecules.