Thermodynamic Study of the Binding of Mercury Ion to Human Growth Hormone at Different Temperatures

The interaction of human growth hormone (hGH) with the divalent mercury ion was studied by isothermal titration calorimetry at two temperatures of 27 °C and 37 °C in aqueous solutions. We found that there is a set of two identical and non-interacting binding sites for Hg²⁺ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 4.2 mmol⋅L⁻¹ and −14.8 kJ⋅mol⁻¹ at 27 °C and 5.1 mmol⋅L⁻¹ and −14.2 kJ⋅mol⁻¹ at 37 °C, respectively. The results obtained indicate that the stability of the protein increases due to the binding of mercury ions using the extended solvation theory.     

Application of an extended solvation theory to study on the binding of magnesium ion with myelin basic protein

Binding properties of myelin basic protein (MBP) from bovine central nervous system due to the interaction by divalent magnesium ion (Mg²⁺) was investigated at 27°C in aqueous solution using isothermal titration calorimetry (ITC) technique. An extended solvation model was used to reproduce the enthalpies of Mg²⁺-MBP interaction over the whole Mg²⁺ concentrations. It was found that there is a set of two identical and noninteracting binding sites for Mg²⁺ ions. The dissociation equilibrium constant is K _d=45.5 μM. The molar enthalpy of binding site is identical for both sites; ΔH=−15.24 kJ mol⁻¹. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction.     

Thermodynamic Study on the Interaction of Copper Ion with Human Growth Hormone

A thermodynamic study on the interaction between the Cu²⁺ ion and human growth hormone (hGH) was studied at the temperatures 300.15 and 310.15 K in NaCl solution using isothermal titration calorimetry. The new solvation model was used to reproduce the enthalpies of Cu²⁺+hGH interaction over the whole range of Cu²⁺ concentrations. It was found that there is a set of three identical and non-interacting binding sites for Cu²⁺ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 1313.4 μmol⋅L⁻¹ and −16.80 kJ⋅mol⁻¹ at 300.15 K, and 1648.2 μmol⋅L⁻¹ and −16.40 kJ⋅mol⁻¹ and 310.15 K, respectively. The binding parameters recovered from the new equation are attributed to a structural change of hGH and its biological activity due to metal ion interaction.     

Thermodynamics of Binding 2,2′-Bipyridineglycinato Palladium (II) Chloride on Human Serum Albumin

The interaction of human serum albumin (HSA) with 2,2′-bipyridineglycinato palladium (II) chloride was studied by isothermal titration microcalorimetry at 27°C and equilibrium dialysis and UV-Vis. spectrophotometry techniques at temperatures of 27 & 37°C in 2.5 mM phosphate buffer solution at pH = 7.0. The enthalpy of binding was calculated from binding data, which were obtained from equilibrium dialysis in terms of the Wyman binding potential theory related to the van't Hoff relation. The enthalpy of HSA unfolding was determined by subtraction of the microcalorimetric enthalpy (binding and unfolding enthalpies) and the enthalpy of binding. The enthalpy of HSA unfolding, due to the binding of that ligand, was 491.43 kJ mol^?1.     

A Structural and Calorimetric Study on the Interaction Between Jack Bean Urease and Cyanide Ion

The cyanide ion was studied as an effecter of Jack bean urease at 300 K in 30 mmol⋅L⁻¹ Tris buffer, pH=7. The inhibition was investigated by isothermal titration calorimetry (ITC). The extended solvation model was used for CN⁻+JBU interaction over the whole range of CN⁻ concentrations. The binding parameters recovered from the solvation model were attributed to the interaction with cyanide ion. It was found that cyanide ion acted as a noncooperative inhibitor of urease, and there is a set of 12 identical and independent binding sites for CN⁻ ions. The dissociation equilibrium constant is 749.99 μmol⋅L⁻¹. The molar enthalpy of binding is ΔH=−13.60 kJ⋅mol⁻¹.     

Study on the thermodynamic properties of cholesterol

The standard molar enthalpy of combustion of cholesterol was measured at constant volume. According to value of Δ_r U _m^θ(−14358.4±20.65 kJ mol⁻¹), Δ_r H _m^θ(−14385.7 kJ mol⁻¹) of combustion reaction and Δ_f H _m^θ(2812.9 kJ mol⁻¹) of cholesterol were obtained from the reaction equation. The enthalpy of combustion reaction of cholesterol was also estimated by the average bond enthalpies. By design of a thermo-chemical recycle, the enthalpy of combustion of cholesterol were calculated between 283.15∼373.15 K. Besides, molar enthalpy and entropy of fusion of cholesterol was obtained by DSC technique.     

A thermodynamic study on the interaction of nickel ion with myelin basic protein by isothermal titration calorimetry

The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent nickel ion was studied by isothermal titration calorimetry at 37 and 47 °C in Tris buffer solution at pH = 7. The new solvation model was used to reproduce the heats of MBP + Ni²⁺ interaction over the whole Ni²⁺ concentrations. It was found that MBP has three identical and independent binding sites for Ni²⁺ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 89.953 μM, −14.403 kJ mol⁻¹ and 106.978 μM, −14.026 kJ mol⁻¹ at 37 and 47 °C, respectively. The binding parameters recovered from the new solvation model were correlated to the structural changes of MBP due to its interaction with nickel ion interaction. It was found that in the low and high concentrations of the nickel ions, the MBP structure was destabilized.     

Denaturation study of bovine serum albumin induced by guanidine chloride or urea by microcalorimetry

The denaturation of bovine serum albumin (BSA) induced by guanidine chloride or urea at different pH values was studied by isothermal microcalorimetry measurements at 30°C. The simple bonding model, which was developed by Privalov, was employed to obtain the apparent bonding constant K, the apparent singular bonding Gibbs bonding energy ΔG and the total Gibbs energy ΔG(a) between the protein and denaturant, from analysis of the calorimetric data. Furthermore, linear extrapolation at the midpoint of transition was employed to determine the apparent denaturation enthalpy ΔH _d. The results showed that for guanidine chloride, the bonding between BSA and guanidine chloride could proceed more easily in an alkaline condition, and the apparent denaturation enthalpy ΔH _d of BSA due to guanidine chloride was 350 kJ·mol⁻¹ at pH 6.97 and 7.05, while it was 275 kJ·mol⁻¹ at pH 9.30, which indicated that BSA was more stabilized in a neutral condition. However, for urea, the bonding between BSA and urea could proceed more easily in an acidic condition, and the apparent denaturation enthalpy ΔHd of BSA due to urea was 295 kJ · mol⁻¹ at pH 6.97, while it was 230 kJ · mol⁻¹ at pH 7.05 and 9.30. The results indicate that the degree of expansion of BSA in the two denaturants is different. __________ Translated from Acta Chimica Sinica, 2008, 66(5) (in Chinese)     

Application of a simple calorimetric data analysis on the binding study of calcium ions by human growth hormone

A simple graphical linear method was introduced for isothermal titration calorimetric data analysis in the protein-ligand interaction. The number of binding sites, the dissociation binding constant and the molar enthalpy of binding site can be obtained by using this new isothermal titration calorimetric data analysis method. The method was applied to the study of the interaction of human growth hormone (hGH) with divalent calcium ion at 27°C in NaCl solution, 50 mM. hGH has a set of three identical and independent binding sites for Ca ²⁺ . The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 52 μMand -17.4, respectively. Results obtained by this new calorimetric data analysis are in good agreement with results obtained using our previous method.     

Thermal Decomposition of Strontium and Barium Malonates

The thermal decomposition of strontium and barium malonates has been studied isothermally and non-isothermally employing simultaneous TG-DTG-DTA, DSC, XRD and IR spectroscopic techniques. DSC of these malonates has been recorded both in oxygen and nitrogen atmospheres. The decomposition is a single step process and the end product formed is carbonate. The energy of activation and frequency factor values for the decomposition of strontium malonate are 547 kJ mol⁻¹ and 10⁴¹ s⁻¹ respectively. The activation energy and frequency factor values for isothermal dehydration of barium malonate sester-hydrate are 57–111 kJ mol⁻¹ and 10⁷–10¹² s⁻¹ respectively and the corresponding values for decomposition from DSC are 499.5 kJ mol⁻¹ and 10⁴⁴ s⁻¹ respectively. The higher thermal stability of strontium malonate as compared to that of barium salt is ascribed to its being anhydrous so that decomposition proceeds without restructuring. Their thermal stabilities have also been compared with that of respective oxalate salts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Analysis Studies on Isopropylnitrate

Isopropylnitrate (IPN) is described as a detonable material used in propellants and explosives. While there is considerable information available on its sensitivity and compatibility with other materials, very little is known about its thermochemical properties. This paper will describe the results obtained from some DSC, heat flux calorimetry (HFC) and accelerating rate calorimetry (ARC) measurements. The ASTM DSC method using a hermetic aluminum pan having a lid with a laser-produced pin hole was used to determine the vapour pressure of IPN₁. Results calculated from an Antoine equation are in substantial agreement with those determined from DSC measurements. From the latter measurements, the enthalpy of vaporization was determined to be 35.32±0.62 kJ mol⁻¹. Attempts to determine vapour pressures above about 0.8 MPa resulted in significant decomposition of IPN_g. The enthalpy change for decomposition in sealed glass systems was found to be -3.43±0.09 kJ g⁻¹ and -3.85±0.03 kJ g⁻¹, respectively from DSC and HFC measurements on IPN₁ samples loaded in air. Slightly larger exotherms were observed for the HFC results in air than those in inert gas, suggesting some oxidation occurs. In contrast, no significant difference in the observed onset temperature of about 150°C was observed for both the HFC and ARC results. From DSC measurements, an Arrhenius activation energy for decomposition of 126±4 kJ mol⁻¹ was found. These measurements were also conducted in sealed glass systems and decomposition appeared to proceed primarily from the liquid phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Thermodynamic Study on the Binding of Calcium Ion with Myelin Basic Protein

The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent calcium ion was studied by isothermal titration calorimetry at 27 °C in aqueous solution. The extended solvation model was used to reproduce the enthalpies of Ca²⁺-MBP interaction over the whole range of Ca²⁺ concentrations. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction. It was found that there is a set of two identical and non-interacting binding sites for Ca²⁺ ions. The association equilibrium constant is 0.021 μmol⋅dm⁻³. The molar enthalpy of binding is ΔH=−15.10 kJ⋅mol⁻¹.     

Phase transitions of K<Subscript>2</Subscript>TaF<Subscript>7</Subscript> within 680–800°C

Three thermal effects on heating/cooling of K₂TaF₇ in the temperature interval of 680–800°C were investigated by the DSC method. The values determined for the enthalpy change of the individual processes are: Δ_transIIH_m(K₂TaF₇; 703°C) = 1.7(2) kJ mol⁻¹, Δ_transIH_m(K₂TaF₇; 746°C) = 19(1) kJ mol⁻¹ and Δ_transIIIH_m(K₂TaF₇; 771°C) = 13(1) kJ mol⁻¹. The first thermal effect was attributed to a solid-solid phase transition; the second to the incongruent melting of K₂TaF₇ and the third to mixing of two liquids. These findings are supported by in situ neutron powder diffraction experiments performed in the temperature interval of 654–794°C.      

Thermal behavior study and decomposition kinetics of salbutamol under isothermal and non-isothermal conditions

The thermal decomposition of salbutamol (β₂ — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage of the thermal decomposition process. For isothermal experiments the average values were E _act=130 kJ mol⁻¹ (for standard sample) and E _act=252 kJ mol⁻¹ (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min⁻¹). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min⁻¹). The calculated values were E _act=134 kJ mol⁻¹ (for standard sample) and E _act=139 kJ mol⁻¹ (for pharmaceutical sample).     

What is the enthalpy of formation of acrylic acid?

Acrylic acid is a key industrial compound with numerous uses. Despite its importance, its enthalpy of formation is still contentious—even ignoring “ancient” determinations, there is a 12 kJ mol⁻¹ range of values reported for the gas phase quantity, −320 to −332 kJ mol⁻¹. Our quantum chemical calculations using current methodology suggest the value of −321 ± 3 kJ mol⁻¹.     

Thermodynamic Aspects of the Vaterite-Calcite Phase Transition

Although vaterite is the least stable anhydrous calcium carbonate polymorph, it is formed as a metastable phase in some normal and pathological biomineralisation processes. In this work, thermodynamic aspects of the vaterite-calcite phase transition were comprehensively studied. Vaterite samples were prepared by different methods and characterised for the composition, crystal structure, specific surface and grain size. All products were identified to be pure vaterite by careful X-ray diffraction measurements. The enthalpy and Gibbs energy of transition were determined by precise calorimetric and potentiometric measurements. The reliability of the thermodynamic data for the vaterite-calcite phase transition derived from this work was shown by the use of different calorimetric methods to determine the enthalpy of transition and the independent measurements of heat capacity and entropy of vaterite. Our recommended values are Δ_trs G*=−2.9±0.2 kJ mol⁻¹ , Δ _trs H *=−3.4±0.2 kJ mol−1 and Δ _trs S *=−1.7±0.9 J K⁻¹ mol⁻¹ , where the uncertainties are given as twice the standard deviations. This revised version was published online in August 2006 with corrections to the Cover Date.     

The structure and thermochemistry of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1) and some related compounds

Condensed and gas phase enthalpies of formation of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1, (−199.1 ± 16.4), (−70.5 ± 20.5) kJ mol⁻¹, respectively) and 3,4,6,7-dibenzobicyclo[3.2.1]nona-3,6-dien-2-one (2, (−79.7 ± 22.9), (20.1 ± 23.1) kJ mol⁻¹) are reported. Sublimation enthalpies at T=298.15 K for these compounds were evaluated by combining the fusion enthalpies at T = 298.15 K (1, (12.5 ± 1.8); 2, (5.3 ± 1.7) kJ mol⁻¹) adjusted from DSC measurements at the melting temperature (1, (T _fus, 357.7 K, 16.9 ± 1.3 kJ mol⁻¹)); 2, (T _fus, 383.3 K, 10.9 ± 0.1) kJ mol⁻¹) with the vaporization enthalpies at T = 298.15 K (1, (116.1 ± 12.1); 2, (94.5 ± 2.2) kJ mol⁻¹) measured by correlation-gas chromatography. The vaporization enthalpies of benzoin ((98.5 ± 12.5) kJ mol⁻¹) and 7-heptadecanone ((94.5 ± 1.8) kJ mol⁻¹) at T = 298.15 K and the fusion enthalpy of phenyl salicylate (T _fus, 312.7 K, 18.4 ± 0.5) kJ mol⁻¹) were also determined for the correlations. The crystal structure of 1 was determined by X-ray crystallography. Compound 1 exists entirely in the enol form and resembles the crystal structure found for benzoylacetone.     

Low-temperature heat capacity and standard enthalpy of formation of neodymium glycine perchlorate complex [Nd2(Gly)6(H2O)4](ClO4)6·5H2O

Rare-earth perchlorate complex coordinated with glycine [Nd₂(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O was synthesized and its structure was characterized by using thermogravimetric analysis (TG), differential thermal analysis (DTA), chemical analysis and elementary analysis. Its purity was 99.90%. Heat capacity measurement was carried out with a high-precision fully-automatic adiabatic calorimeter over the temperature range from 78 to 369 K. A solid-solid phase transformation peak was observed at 256.97 K, with the enthalpy and entropy of the phase transformation process are 4.438 kJ mol⁻¹ and 17.270 J K⁻¹ mol⁻¹, respectively. There is a big dehydrated peak appears at 330 K, its decomposition temperature, decomposition enthalpy and entropy are 320.606 K, 41.364 kJ mol⁻¹ and 129.018 J K⁻¹ mol⁻¹, respectively. The polynomial equations of heat capacity of this compound in different temperature ranges have been fitted. The standard enthalpy of formation was determined to be −8023.002 kJ mol⁻¹ with isoperibol reaction calorimeter at 298.15 K.     

The standard enthalpy of formation of silver pivalate

The standard enthalpy of combustion of crystalline silver pivalate, (CH₃)₃CC(O)OAg (AgPiv), was determined in an isoperibolic calorimeter with a self-sealing steel bomb, Δ_c H ⁰ (AgPiv, cr)= −2786.9±5.6 kJ mol⁻¹. The value of standard enthalpy of formation was derived for crystalline state: Δ_f H ⁰(AgPiv,cr)= −466.9±5.6 kJ mol⁻¹. Using the enthalpy of sublimation, measured earlier, the enthalpy of formation of gaseous dimer was obtained: Δ_f H ⁰(Ag₂Piv₂,g)= −787±14 kJ mol⁻¹. The enthalpy of reaction (CH₃)₃CC(O)OAg(cr)=Ag(cr)+(CH₃)₃CC(O)O^.(g) was estimated, Δ_r H ⁰=202 kJ mol⁻¹.     

A Comparative Study of the Direct Calorimetric Determination of the Denaturation Enthalpy for Lysozyme in Sodium Dodecyl Sulfate and Dodecyltrimethylammonium Bromide Solutions

The complexes of lysozyme with the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB) have been investigated by isothermal titration calorimetry at pH=7.0 and 27 °C in a phosphate buffer. A new direct calorimetric method was applied to follow the protein denaturation and study the effect of surfactants on the stability of proteins. The extended solvation model was used to represent the enthalpies of lysozyme + SDS interaction over the whole range of SDS concentrations. The solvation parameters recovered from the new equation are attributed to the structural change of lysozyme and its biological activity. At low SDS concentrations, the binding is mainly electrostatic with some simultaneous interaction of the hydrophobic tail with nearby hydrophobic regions of lysozyme. These initial interactions presumably cause some protein unfolding and expose additional hydrophobic sites. The induced enthalpy of denaturation of lysozyme by SDS is 160.81±0.02 kJ⋅mol⁻¹. The lysozyme-DTAB complexes behave very differently from those of the lysozyme-SDS complexes. SDS induces a stronger unfolding of lysozyme than DTAB. The induced enthalpy of lysozyme denaturation by DTAB is 86.46±0.02 kJ⋅mol⁻¹.