Partial Molar Heat Capacities Research Articles

Effect of the Temperature on the Process of Preferential Solvation of 1,4-Dioxane, 12-Crown-4, 15-Crown-5 and 18-Crown-6 Ethers in the Mixture of N-Methylformamide with Water: Composition of the Solvation Shell of the Cyclic Ethers.

The aim of the work was to analyze the preferential solvation process, and determine the composition of the solvation shell of cyclic ethers using the calorimetric method. The heat of solution of 1,4-dioxane, 12-crown-4, 15-crown-5 and 18-crown-6 ethers in the mixture of N-methylformamide with water was measured at four temperatures, 293.15 K, 298.15 K, 303.15 K, and 308.15 K, and the standard partial molar heat capacity of cyclic ethers has been discussed. 18-crown-6 (18C6) molecules can form complexes with NMF molecules through the hydrogen bonds between -CH3 group of NMF and the oxygen atoms of 18C6. Using the model of preferential solvation, the cyclic ethers were observed to be preferentially solvated by NMF molecules. It has been proved that the molar fraction of NMF in the solvation shell of cyclic ethers is higher than that in the mixed solvent. The exothermic, enthalpic effect of preferential solvation of cyclic ethers increases with increasing ring size and temperature. The increase in the negative effect of the structural properties of the mixed solvent with increase in the ring size in the process of preferential solvation of the cyclic ethers indicates an increasing disturbance of the mixed solvent structure, which is reflected in the influence of the energetic properties of the mixed solvent.

Composition of the Solvation Shell of the Selected Cyclic Ethers (1,4-Dioxane, 12-Crown-4, 15-Crown-5 and 18-Crown-6) in a Mixture of Formamide with Water at Four Temperatures

The solution enthalpy of 15-crown-5 and 18-crown-6 ethers in the mixture of formamide (F) and water (W) was measured at four temperatures: 293.15 K, 298.15 K, 303.15 K, 308.15 K. The standard molar enthalpy of solution, ΔsolHo, depends on the size of cyclic ethers molecules and the temperature. With increasing temperature, the values of ΔsolHo become less negative. The values of the standard partial molar heat capacity Cp,2o of cyclic ethers at 298.15 K have been calculated. The Cp,2o=f(xW) curve shape indicates the hydrophobic hydration process of cyclic ethers in the range of a high-water content in the mixture with formamide. The enthalpic effect of preferential solvation of cyclic ethers was calculated and the effect of temperature on the preferential solvation process was discussed. The process of complex formation between 18C6 molecules and formamide molecules is observed. The cyclic ethers molecules are preferentially solvated by formamide molecules. The mole fraction of formamide in the solvation sphere of cyclic ethers has been calculated.

Thermochemistry of solution of methylpheophorbide a, dioxidine and their conjugate in chloroform from 298.15 K to 318.15 K

This paper focuses on the study of thermochemistry of solution and transfer of potential hydrophobic photosensitizers, viz. 9-ethenyl-14-ethyl-21-(methoxycarbonyl)-3-{(O-methylcarbamoyl)ethyl}-4,8,13,18-tetramethyl-20-oxo-phorbine (Methylpheophorbide a, comp. 1), [3-(hydroxymethyl)-1-oxido-4-oxoquinoxalin-4-ium-2-yl]methanol (Dioxidine, comp. 2) and their conjugate 9-ethenyl-14-ethyl-3-{[2-(3-hydroxymethyl)]-1-oxido-4-oxoquinoxalin-4-ium-2-methyleneoxy}carbamoyl}ethyl)-4,8,13,18-tetramethyl-20-oxo-phorbine (Conjugate, comp. 3), in liquid chloroform (CHCl3) and N,N-dimethylformamide (DMF) between the temperatures of 298.15 K and 318.15 K. The standard enthalpies and heat capacities of solution as well as partial molar heat capacities of these species and some non-electrolytes modeling their side-chains have been computed from experimental enthalpies of solution and compared with previously reported quantities to highlight several important features of solvation of potential drugs in H-donor and H-acceptor media.

Standard Partial Molar Heat Capacities and Volumes of Aqueous N,N-Dimethylethanolamine and N,N-Dimethylethanolammonium Chloride from 283.15 to 393.15 K, and Ionization Constants to 598.15 K

Standard Partial Molar Heat Capacities and Volumes of Aqueous <i>N</i>,<i>N</i>-Dimethylethanolamine and <i>N</i>,<i>N</i>-Dimethylethanolammonium Chloride from 283.15 to 393.15 K, and Ionization Constants to 598.15 K

Origin of heat capacity increment in DNA folding: The hydration effect

BackgroundUnderstanding DNA folding thermodynamics is crucial for prediction of DNA thermal stability. It is now well established that DNA folding is accompanied by a decrease of the heat capacity ∆cp, F, however its molecular origin is not understood. In analogy to protein folding it has been assumed that this is due to dehydration of DNA constituents, however no evidence exists to support this conclusion. MethodsHere we analyze partial molar heat capacity of nucleic bases and nucleosides in aqueous solutions obtained from calorimetric experiments and calculate the hydration heat capacity contribution ∆cphyd. ResultsWe present hydration heat capacity contributions of DNA constituents and show that they correlate with the solvent accessible surface area. The average contribution for nucleic base dehydration is +0.56 J mol−1 K−1 Å−2 and can be used to estimate the ∆cp, F contribution for DNA folding. ConclusionsWe show that dehydration is one of the major sources contributing to the observed ∆cp, F increment in DNA folding. Other possible sources contributing to the overall ∆cp, F should be significant but appear to compensate each other to high degree. The calculated ∆cphyd for duplexes and noncanonical DNA structures agree excellently with the overall experimental ∆cp, F values. By contrast, empirical parametrizations developed for proteins result in poor ∆cphyd predictions and should not be applied to DNA folding. General significanceHeat capacity is one of the main thermodynamic quantities that strongly affects thermal stability of macromolecules. At the molecular level the heat capacity in DNA folding stems from removal of water from nucleobases.

HEAT CAPACITY PROPERTIES OF AQUEOUS BUFFER SOLUTIONS OF L-HISTIDINE IN A WIDE TEMPERATURE RANGE

The influence of temperature and concentration of L-histidine on the heat capacity properties of its aqueous buffer solutions was studied by differential scanning calorimetry. The investigations were carried out in aqueous buffer solutions (pH 7.4) containing monobasic sodium phosphate and dibasic sodium phosphate, which brings the environment closer to the conditions of real biological systems. The pH values of the solutions were fixed with a digital pH meter Mettler Toledo, model Five-Easy (Switzerland). The differential scanning microcalorimeter SCAL-1 (Biopribor, Pushchino, Russia) was used for measure the specific heat capacity of the system under study. It was equipped with Peltier thermoelectric elements, two measuring glass cells with an internal volume of 0.377 cm3, as well as a computer terminal and software for calculating heat capacity. The standard error of measurement of the specific heat for the studied solutions was within ±7·10-3 J·K-1·g-1. The experimental values of the specific heat of solutions of the amino acid in a phosphate buffer solvent in the temperature range (283.15 – 343.15) K were obtained. The concentration of histidine was varied from (0.00215 to 0.03648) mol·kg-1. All the studied solutions were prepared by the gravimetric method using Sartorius-ME215S scales (with a weighing accuracy of 1·10-5 g). The apparent molar heat capacities of L-histidine in the buffer solution, as well as its partial molar heat capacities at infinite dilution, were determined. The calculated molar parameters increase with an increase in both temperature and amino acid concentration. It was shown that the partial molar heat capacities transfers of L-histidine from water to the buffer solution have positive values in the temperature range studied. The results are discussed on base of the Gurney model.

Generalized Quasi-Random Lattice model for electrolyte solutions: Apparent and partial molal heat capacities

Ionic solutions play an important role in many areas of technology and science, therefore understanding and predicting their thermodynamic behavior has been an essential research topic for an extended period of time. However, complexity and variety of real systems and the need for accurate representation of thermodynamic data hamper the development of models that are truly predictive over wide ranges of concentration, temperature and pressure conditions. In this regard, predictive potentialities of the Quasi-Random Lattice (QRL) model seem worthy of consideration.The QRL model, originally proposed for mean-activity/osmotic coefficients, was recently presented in a generalized form inclusive of formulae for partial/apparent molal enthalpies and volumes. This article follows and presents some further developments concerning partial and apparent molal heat capacities with application to various aqueous 1:1, 2:1, and 3:1 electrolytes. The semi-predictive character of QRL will be confirmed by present results and an improved procedure that yields the main QRL parameterization within a few steps will be illustrated. As a general remark, the experimental information required by QRL is very modest compared to the number of data points typically used with regression analysis.

Thermodynamically Traceable Calorimetric Results for Dilute Aqueous Potassium Chloride Solutions at Temperatures from 273.15 to 373.15 K. Part 2. The Quantities Associated with the Partial Molar Heat Capacity

In previous articles (Partanen J. Chem. Eng. Data 2019, 64, 16−33 and Partanen J. Chem. Eng. Data 2019, 64, 2519–2535), we presented traceable and transparent two-parameter Hückel equations (with parameters B and b1) for the activity coefficients of the salt and for the osmotic coefficients of water in aqueous KCl solutions in the temperature range of 273.15–383.15 K. The latter article is the first part (Part 1) of the calorimetric study. We showed in these articles that our equations for these solutions explain within experimental error the literature data on almost all thermodynamic quantities including the partial molar enthalpies at least up to a molality of 0.2 mol·kg–1 and up to 373 K. In this model, parameter B is regarded as a constant but parameter b1 has a quadratic temperature dependence. No calorimetric data were needed in the parameter estimation. In the second part (Part 2) of the calorimetric study, now, the results obtained for the heat capacity quantities of KCl (aq.) are considered. We show here that all heat capacity literature available for KCl solutions at least up to 0.5 mol·kg–1 is possible to explain within experimental error using exactly the same Hückel equations as those considered previously in our studies for dilute KCl solutions from 273 to 373 K. Because of the success of the used model, we supplement the existing thermodynamic tables with new values for the relative apparent and partial molar heat capacities for KCl solutions. It is likely that the new tables contain the most reliable values available for these heat capacity quantities.

Enthalpies and heat capacities of solution of 3,5-diamino-1,2,4-triazole and 3,5-diamino-1-phenyl-1,2,4-triazole in water

This paper focuses on the thermochemical behavior of two derivatives of 1,2,4-triazole which is often considered as a potential synthetic platform to develop novel antitumor or antimicrobial drugs, i.e., 3,5-diamino-1,2,4-triazole (compound 1) and 3,5-diamino-1-phenyl-1,2,4-triazole (compound 2). Experimental enthalpies of solution in water have been determined calorimetrically over the physiological temperature range. These quantities are used to compute standard enthalpies and heat capacities of solution. Standard partial molal heat capacities of solution are calculated from the heat capacities of solution and experimentally determined heat capacities of solid heterocycles. The results obtained are compared with those for hydrophilic urea and hydrophobic benzene and briefly discussed.

Heat Capacity and Volume Properties of Ammonium Thiocyanate in N-Methylpyrrolidone Solution at 298.15 K

The heat capacity and volumetric properties of ammonium thiocyanate solutions in N-methylpyrrolidone are measured at 298.15 K by calorimetric and densimetric means. Concentration dependences of the partial and apparent molar heat capacities and volumes of the investigated systems are discussed. The standard partial molar heat capacity and volume of NH4CNS, and the standard heat capacity and volume of ammonium and thiocyanate ions in N-methylpyrrolidone at 298.15 K are calculated.

Two-point scaling analysis of the isobaric heat capacity of dodecyltrimethylammonium bromide aqueous solutions in the presence of the n-hexan-1-ol as a co-surfactant

The specific heat capacities at constant pressure cp of aqueous solutions of cationic surfactant: dodecyltrimethylammonium bromide, with addition of co-surfactant: n-hexan-1-ol with the molar ratio of surfactant to co-surfactant 1:1 have been measured within temperature range (278.15–328.15) K over wide concentration range. The apparent and partial molar heat capacities of the surfactant/co-surfactant were calculated to analyse the aggregation process taking place in the solution. In order to study some additional information on the solution structure and verify the shape of the aggregates the two-point scaling theory was used for the first in the case of the surfactant/co-surfactant system in which prolate micelles are formed.

Unusual behavior of temperature-dependent solvent H/D isotope effects in the enthalpy and heat capacity of hexamethylenetetramine (urotropine) hydration

Based on the identified inconsistencies in the existing literature data on the enthalpies and heat capacities of dissolution (solvation) of hexamethylenetetramine (HMTA) in ordinary (H2O) and heavy (D2O) water, we carried out carefully the calorimetric study of these two binary systems at seven temperatures from (278.15 to 318.15) K. It is established that the considered D2O–H2O enthalpy-isotopic effect exhibits a pronounced exothermic maximum between two sign-inversion points near 293 K and 318 K. The same goes the negative (up to ~305 K) solvent isotope effect (IE) in the partial molar heat capacity of HMTA in water. Such an unusual temperature-dependent behavior of the thermodynamic IEs points out the dualistic character of the HMTA hydration process which is dependent on the initial structure state of the solvent.

Properties of Micellar Solutions of Sodium Decyl Sulfate at Relatively High Concentrations

Heat capacities of aqueous solutions of anionic surfactant sodium decyl sulfate in the 0.28–0.42 mol kg−1 range of molar concentrations and the 278–363 K range of temperatures are studied via precision adiabatic differential scanning microcalorimetry. Specific and apparent heat capacities of solutions at intervals of 0.01 mol kg−1, partial molar heat capacities of the solute and the solvent, and excess partial molar heat capacities are plotted as functions of concentration and temperature. The Kraft boundary is determined. Analysis of the characteristic changes in the above properties reveals structural changes in sodium decyl sulfate micelles that correspond to their shape transforming from cylindrical to plate-like in the region of the third critical micelle concentration.

Standard Partial Molar Heat Capacity and the Volume of the Cadmium Ion in Acetonitrile at 298.15 K

The heat capacity and volumetric properties of cadmium iodide solutions in acetonitrile (AN) are measured at 298.15 K by calorimetric and densimetric means. Standard partial molar heat capacity $$\bar {C}_{{p,2}}^{^\circ }$$ and volume $$\bar {V}_{2}^{^\circ }$$ of CdI2 in AN are calculated. Standard heat capacity $$\bar {C}_{{p,i}}^{^\circ }$$ and volume $$\bar {V}_{i}^{^\circ }$$ of the cadmium ion in AN at 298.15 K are determined. The effect produced by the nature of such solvents as AN, DMF, DMSO, and MP on $$\bar {C}_{{p,i}}^{^\circ }$$ and $$\bar {V}_{2}^{^\circ }$$ of the cadmium ion is analyzed, and a substantial contribution from the electrostatic component is discovered.

Standard Partial Molar Heat Capacities and Volumes of Barium and Cadmium Ions in Dimethylformamide at 298.15 K

The heat capacity and bulk properties of barium and cadmium iodide solutions in dimethylformamide (DMF) at 298.15 K are measured via calorimetry and densimetry. Standard partial molar heat capacities $$\bar {C}_{{p,2}}^{^\circ }$$ and volumes $$\bar {V}_{2}^{^\circ }$$ ВаI2 and CdI2 in DMF are calculated. The standard values of heat capacity $$\bar {C}_{{p,i}}^{^\circ }$$ and volume $$\bar {V}_{i}^{^\circ }$$ of barium and cadmium in DMF at 298.15 K were determined.

Heat capacity and phase behaviour of {pentaethylene glycol monoheptyl ether + water} system. Two-point scaling approach

The miscibility in the {pentaethylene glycol monoheptyl ether (C7E5) + water} system was investigated by differential scanning calorimetry (DSC). The specific heat capacities cp of chosen nonionic amphiphile (C7E5) aqueous solutions have been measured within temperature range 273.15–338.15 K over wide concentration range. The apparent and partial molar heat capacities were calculated to analyze the aggregation process taking place in the solution. In order to study some additional information on the solution structure two-point scaling theory was used. On the base of temperature dependences of differential heat flow, phase coexistence curve was determined.

Standard Partial Molar Heat Capacities and Volumes of Barium and Cadmium Ions in Dimethylsulfoxide at 298.15 K

The heat capacities and volumes of dimethylsulfoxide (DMSO) solutions of barium and cadmium iodides at 298.15 K were measured by calorimetry and densimetry. The standard partial molar heat capacities $$\bar {C}_{{p,2}}^{^\circ }$$ and volumes $$\bar {V}_{2}^{^\circ }$$ of BaI2 and CdI2 in DMSO were calculated. The standard heat capacities $$\bar {C}_{{p,i}}^{^\circ }$$ and volumes $$\bar {V}_{i}^{^\circ }$$ of barium and cadmium ions in DMSO at 298.15 K were determined.

The energetics of solvation and ion-ion interactions in prospidium chloride aqueous solutions

This paper focuses on the first accurate thermochemical study of hydration and interactions of the well-established cytostatics “Prospidine” (prospidium chloride) in water. Enthalpies of solution of the drug have been determined with the isoperibol solution calorimeter at 298 and 313 K and heat capacities of solid prospidine have been obtained with the NETZSCH DSC calorimeter at 275–355 K. Standard enthalpies and heat capacities of solution, partial molal heat capacities at an infinite dilution as well as enthalpic parameters of solute-solute pair interactions have been computed using the Redlich-Rosenfeld-Meyer-type equation and discussed in terms of solute-solvent and solute-solute interactions in a liquid phase.

Traceable Thermodynamic Quantities for Dilute Aqueous Sodium Chloride Solutions at Temperatures from (0 to 80) °C. Part 2. The Quantities Associated with the Partial Molar Heat Capacity

In Part 1 of this two-part study (J. Chem. Eng. Data 2017, 62, 2617–2632), we presented fully traceable two-parameter Hückel equations (with parameters B and b1) for the activity and osmotic coefficients in dilute aqueous NaCl solutions in the temperature range (0 to 80) °C, and these equations apply within experimental error to almost all thermodynamic data existing in the literature and used in the tests at least up to a molality of 0.2 mol·kg–1. These data include also molar enthalpies of the components in the solutions. In our model, parameter B is treated as a constant whereas parameter b1 depends in a quadratic way on the temperature. No calorimetric data were used in the parameter estimation of the model. In this second part (Part 2) of the study, the results of the quantities associated with the heat capacity of NaCl solutions are considered. All heat capacity data available for NaCl solutions at least up to 0.2 mol·kg–1 can be predicted within experimental error using the same Hückel equations as those determined in Part 1 in dilute NaCl solutions from (0 to 80) °C. For comparison, also other parametrization (obtained in Part 1 for higher temperatures) was here considered and it applies better to less dilute solutions in the higher temperatures than the model recommended now primarily. Following the success of the new models, we supplement the thermodynamic tables of Part 1 with the relative apparent and partial molar hear capacities for NaCl solutions. We have good reason to believe that the new tables contain the most reliable values available for the heat capacity quantities in dilute NaCl solutions.

Thermodynamics of solution of L-valine in water

This paper focuses on the accurate thermodynamic study of solution of L-valine in water in a wide temperature range. Enthalpies of solution of L-valine in water have been calorimetrically determined between T=279K and T=323 К. Standard enthalpies and heat capacities of solution as well as standard partial molal heat capacities have been calculated and compared with available literature values. The free energy of solution and its enthalpic and entropic terms have been computed using the combination of solubility and calorimetric data via the Gibbs-Helmholtz equation from T=280K to T=360K. The temperature dependence of solubility of the amino acid has been also computed and compared with experimental quantities. The satisfactory agreement is found between experimental and predicted solubility values.