Ingemar Wadsö

Standards in isothermal microcalorimetry (IUPAC Technical Report)

The main calorimetric principles used in isothermal microcalorimetry are briefly discussed. Different chemical calibration and test reactions are discussed, with a focus on reactions suitable for ambient conditions: reactions initiated by mixing of liquids (including titration microcalorimetry), dissolution of solid compounds and of slightly soluble gases, a photochemical process, and thermal power signals released over an extended period of time. Guidelines on the use of standardized chemical test and calibration reactions in isothermal microcalorimetry are presented. A standardized terminology in reporting characteristics of isothermal microcalorimeters is proposed.

Isothermal microcalorimetry in applied biology

Techniques of isothermal microcalorimetry have been much improved during the past two decades. In addition to their use in fundamental research, applications of practical importance have been established in some areas. However, no significant use of isothermal microcalorimetry has yet been seen in practical applications of biology, despite many methodological studies reported from that area. The main problem appears to be that the sample throughput of isothermal microcalorimeters is low compared to other techniques used in that field. Further, the non-specificity of calorimetric signals is in some cases a serious limitation. Significant progress has recently been made in the design of multi-channel isothermal microcalorimeters and in techniques where specific analytical methods have been combined with isothermal microcalorimeters. Some conclusions will be drawn with respect to the use of these techniques in applied work on living materials.

Calorimetric determination of enthalpies of solution of slightly soluble liquids II. Enthalpy of solution of some hydrocarbons in water and their use in establishing the temperature dependence of their solubilities

Abstract Enthalpies of solution in water of D 6 -benzene, toluene, ethylbenzene, propylbenzene, and cyclohexane have been determined in the temperature range 288 to 308 K by a flow-microcalorimetric technique. Measurements have also been made for pentane and hexane (at 288 and 298 K) and for benzene (at 308 K). From the results ΔC p values and the partial molar heat capacities for the solutes at infinite dilution have been calculated. Minimum solubility temperatures have also been calculated. Comparison is made between results from solubility measurements and calorimetric measurements for benzene.

Thermochemical results for “tris” as a test substance in solution calorimetry

Abstract Various thermochemical results are reported supporting the use of “tris” (tris(hydroxymethyl) aminomethane, also known as “tham”) as a test substance for solution calorimetry. The enthalpy change for the reaction of tris with 0.1 M hydrochloric acid has been determined at 0, 15, 25, and 50 °C; −ΔH = 33.942, 31.482, 29.744, and 25.335 kJ mol−1 respectively. Mean ΔCp values have been calculated for the temperature ranges 0 to 15 °C, 15 to 25 °C, and 25 to 50 °C: −ΔCp = 164.0, 173.8, and 176.3 J K−1 mol−1 respectively. The (positive) enthalpy of solution of tris in aqueous sodium hydroxide solution has been measured at 25 °C for various hydroxyl ion concentrations (0.01 to 1 M). The enthalpy of protonation of tris in dilute aqueous solution has subsequently been derived: ΔHprot. = −47.50 kJ mol−1.

Test and calibration processes for microcalorimeters, with special reference to heat conduction instruments used with aqueous systems

Calorimeters are normally calibrated by use of electrical heaters, but the calibration values derived may not always be representative for the chemical or biological process investigated. It is therefore important to have available chemical test processes by which the electrical calibration values can be controlled. In some cases, electrical calibration should be replaced by chemical calibrations. With particular reference to needs in work with thermophile heat conduction microcalorimeters, a number of test and calibration processes are presented. Some calibration problems for various types of reaction vessel are discussed.

Additivity relations for the heat capacities of non-electrolytes in aqueous solution☆

A simple additivity scheme is derived for the partial molar heat capacities of non-ionic compounds in infinitely dilute aqueous solution at 298.15 K. Calculated group parameters are based on several homologous series of compounds of the type H(CH2)nX and the internal agreement of the system is shown. The effects of branching and cyclization are discussed. Predicted partial molar heat capacities are compared with experimental results.

Enthalpies and heat capacities for n-alkan-1-ols in H2O and D2O☆

Enthalpies of dissolution of n-alkan-1-ols in H2O and in D2O have been determined calorimetrically at different temperatures. For the C1 to C4 compounds, measurements were performed with both H2O and D2O as solvent, whereas for C5 to C8 only H2O was used. Results of dilution experiments with the C1 to C4 compounds were expressed in terms of second and third virial coefficients. Experiments were performed in the temperature range 284 to 318 K. Enthalpies and heat capacities were derived for the infinitely dilute solutions.

Calorimetric measurements on slightly soluble gases in water. Enthalpies of solution of helium, neon, argon, krypton, xenon, methane, ethane, propane, n-butane, and oxygen at 288-15, 298-15, and 308.15 K

Abstract Calorimetric measurements have been made of enthalpies of solution Δ sol H m ∞ in water of helium, neon, argon, krypton, xenon, methane, ethane, propane, n -butane, and oxygen at 288.15, 298.15, and 308.15 K. Values of the heat-capacity changes Δ sol C p ,m ∞ have been derived. The found values for both the enthalpy and heat-capacity changes for the rare gases and for oxygen fully confirm the values derived by Benson and Krause, Jr. (1976) , and Benson, Krause, Jr., and Peterson (1979) from the results of their very careful gas-solubility measurements. The partial molar heat capacities C p , 2 ∞ of the hydrocarbons studied were derived. The group-additivity schemes that have been used successfully for the estimation of values for C p , 2 ∞ for various non-ionic organic compounds do not correctly predict values of C p , 2 ∞ for the hydrocarbons in the present study.

Thermochemistry of solutions of biochemical model compounds. 2. Alkoxyethanols and 1, 2-dialkoxyethanes in water

Enthalpies of solution in water have been determined calorimetrically at 293.15, 298.15, and 303.15K, at different final concentrations, for a number of alkoxyethanols, ROCH 2 CH 2 OH (R = Me, Et, Pr, i -Pr, Bu) and 1,2-dialkoxyethanes, ROCH 2 CH 2 OR′ (R,R′ = Me,Me; Me,Et; Et,Et; Me,Pr; Me,Bu; Pr,Pr). Heat capacities have been determined for the pure compounds at 298.15 K by use of a novel micro drop calorimeter. From the experimental results enthalpies of solution in water at infinite dilution, enthalpies of solvation at 298.15 K, and partial molar heat capacities in aqueous solution at 298.15 K have been derived. The thermodynamic results obtained are correlated with structural parameters and are compared with corresponding data recently derived for carboxylic acids, amines, alcohols, and N-substituted amides.

Thermochemistry of solutions of biochemical model compounds 7. Aqueous solutions of some amides, t-butanol and pentanol☆☆☆

Abstract Enthalpies of solution in water at infinite dilution have been determined at 298.15 K for formamide, N -methylformamide, acetamide, and t -butanol. Corresponding partial molar heat capacities were determined for these compounds and for N -methylacetamide, N -butylacetamide, N -methylpentanamide, and pentanol using a drop heat-capacity calorimeter. Heat capacities for the pure compounds were also determined.