Dan Hallén

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.

Microcalorimetric titration of α-cyclodextrin with some straight-chain alkan-1-ols at 288.15, 298.15 and 308.15 K

The binding of a series of alkan-1-ols, nc= 3–7, to α-cyclodextrin has been investigated by microcalorimetric titration at 288.15, 298.15 and 308.15 K. For nc⩽ 6, the results agree well with a 1 : 1 binding model but for nc= 7, contributions from the formation of 1 : 2 (one alkanol, two α-CD) complexes have to be assumed. Apparent values for changes in standard molar Gibbs energies, enthalpies, entropies and heat capacities have been derived. The values obtained are consistent with the commonly held view that hydrophobic interactions are important in the formation of alkanol–α-CD complexes. However, the results clearly indicate that other effects are also of some importance.

Characterization of Ligand Binding of a Soluble Human Insulin-like Growth Factor I Receptor Variant Suggests a Ligand-induced Conformational Change

Details of the signal transduction mechanisms of the tyrosine kinase family of growth factor receptors remain elusive. In this work, we describe an extensive study of kinetic and thermodynamic aspects of growth factor binding to a soluble extracellular human insulin-like growth factor-I receptor (sIGF-IR) variant. The extracellular receptor domains were produced fused to an IgG-binding protein domain (Z) in transfected human 293 cells as a correctly processed secreted α-β′-Z dimer. The receptor was purified using IgG affinity chromatography, rendering a pure and homogenous protein in yields from 1 to 5 mg/liter of conditioned cell media. Biosensor technology (BIAcore) was applied to measure the insulin-like growth factor-I (IGF-I), des(1-3)IGF-I, insulin-like growth factor-II, and insulin ligand binding rate constants to the immobilized IGF-IR-Z. The association equilibrium constant, Ka, for the IGF-I interaction is determined to 2.8 × 108 M−1 (25 °C). Microcalorimetric titrations on IGF-I/IGF-IR-Z were performed at three different temperatures (15, 25, and 37 °C) and in two different buffer systems at 25 °C. From these measurements, equilibrium constants for the 1:1 (IGF-I:(α-β′-Z)2) receptor complex in solution are deduced to 0.96 × 108 M−1 (25 °C). The determined heat capacity change for the process is large and negative, −(1)0.51 kcal (K mol)−1. Further, the entropy change (ΔS) at 25 °C is large and negative. Far- and near-UV circular dichroism measurements display significant changes over the entire wavelength range upon binding of IGF-I to IGF-IR-Z. These data are all consistent with a significant change in structure of the system upon IGF-I binding.

A new flow-microcalorimetric vessel for dissolution of small quantities of easily or slightly soluble liquids☆

Abstract A new flow-microcalorimetric vessel has been designed for the determination of enthalpies of solution of small quantities of easily or slightly soluble liquids. The design was a modification of a titration vessel that fitted into our four-channel microcalorimetric system. Different coil materials used for the adherence of the solutes in the sample compartment have been tested. Final concentrations of the solutes were usually low enough for the solutions to be regarded as infinitely dilute. The instrument was calibrated by dissolution of propan-1-ol in water and has been tested by dissolution of benzene in water, at four different temperatures (288.15 to 318.15 K), and by octan-1-ol, at 298.15 K in water, and by butan-1-ol in ethan-1,2-diol at 298.15 K.

The thermodynamics of the binding of benzene to β-cyclodextrin in aqueous solution

Abstract The apparent enthalpies, entropies and Gibbs energies for the binding of benzene to β-cyclodextrin in aqueous solution have been determined at 291.15, 298.15 and 308.15 K by microcalorimetry. The calorimetric data are consistent with a binding model that assumes formation of both 1:1 and 2:1 (benzene :β-cyclodextrin) adducts. The apparent change in heat capacity for the 1:1 binding, calculated from the temperature derivative of the enthalpy changes, indicates that the hydrophobic effect is the driving force for formation and stability of this complex.

A new microcalorimetric vessel for dissolution of slightly soluble gases enthalpies of solution in water of carbon tetrafluoride and sulphur hexafluoride at 288.15, 298.15, and 308.15 K

A new flow-microcalorimetric vessel has been designed for the determination of the enthalpy of solution of slightly soluble gases. The vessel was a modification of our ordinary titration vessel that fitted into our four-channel microcalorimetric system. The calorimeter was calibrated by dissolution of oxygen in water and has been tested by dissolution of helium and propane in the same solvent. Enthalpies of solution of carbon tetrafluoride and sulphur hexafluoride in water were determined at 288.15, 298.15, and 308.15 K, and values for the partial molar heat capacities in water were derived. A new calorimetric enthalpy of solution of oxygen in water at 308.15 K was determined.

Mixing enthalpy and phase separation in a poly(propylene oxide)–water system

Calorimetric measurements of the differential enthalpies of mixing a propylene oxide oligomer and water at two temperatures have been performed and the integral mixing enthalpies were found to be exothermic. The measurements were compared with the predictions of an extended Flory–Huggins model and a semiquantitative agreement was found. The model suggests that the origin of the exothermic mixing is a conformational change of the propylene oxide oligomer from less polar and higher-energy conformers to more polar and lower-energy conformers upon mixing with water.

Microcalorimetric titration of α-cyclodextrin with some straight-chain α,ω-dicarboxylates in aqueous solution at different temperatures

The complex formation of α-cyclodextrin and straight-chain aliphatic α,ω-dicarboxylates, –O2C(CH2)nCO2–(n= 6, 7, 8), in aqueous solution has been studied by titration microcalorimetry at 288.15, 298.15 and 308.15 K. Apparent Gibbs energies, enthalpies, entropies and heat capacities for the 1 : 1 complex formations were derived from the calorimetric data. The thermodynamics of binding show typical enthalpy–entropy compensation effects, which result in weak temperature dependences of the Gibbs energies. The heat capacities of binding are large and negative. This confirms the view that the binding of non-polar moieties to cyclodextrins is to a large extent a result of hydrophobic dehydration. Experimental conditions causing deviations from the 1 : 1 model, are also discussed.

Thermodynamics of binding of alpha-cyclodextrin to straight-chain alkyl derivatives in aqueous solution

Apparent standard Gibbs energy, enthalpy, entropy, and heatcapacity data of the interactions of α-cyclodextrin (αCD) to some n-carboxylatesH(CH2)nCOO- (n = 4–6), are determined by isothermal titration microcalorimetryat different temperatures in phosphate buffer, pH 9.0, assuming a 1 : 1 model indilute solution. Modelling of contributions of the thermodynamic properties of the solutionindicates that αCD undergoes conformational change upon binding to homologousseries of n-carboxylates, n-alcohols, α ,ω-alkane dicarboxylates andα ,ω-alkane diols.

Solvent activity meter based on a high sensitivity heat-flow microcalorimeter

Abstract A calorimetric solvent activity meter has been developed which allows fast and accurate measurements of the solvent activity as a function of solute concentration. By the use of the Gibbs-Duhem equation, the activity of the solute can be determined. The principle of operation is to measure the heat flow associated with the isothermal evaporation of solvent using a flow of dry nitrogen gas. The calorimeter consists of a precise thermostatic bath with a twin heat-conduction calorimetric unit. Special care has been taken to build the gas-handling system. The solvent activity is determined from the measured difference in thermal power for the evaporation from a solution and from the pure solvent. The solute concentration is changed by the stepwise addition of known amounts of concentrated solution to the calorimetric cell. The instrument has the potential of being both sensitive and precise and allows measurements to be made faster and more conveniently than by using the presently available methods.