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.     

A thermodynamic study of nickel ion interaction with bovine carbonic anhydrase II molecule

A thermodynamic study on the interaction of bovine carbonic anhydrase II (CAII) with nickel ions was performed by using isothermal titration calorimetry (ITC) at 27 °C in Tris buffer solution at pH = 7.5. The enthalpies of Ni²⁺ + CAII interaction are reported and analysed in terms of the new solvation theory. It was indicated that there are three identical and non-cooperative sites for Ni²⁺. The binding of a nickle ion is exothermic with dissociation equilibrium constants of 81.306 and 99.126 μM at 27°C and 37°C, respectively. The binding of nickel ions can cause some changes in the stability of the enzyme at low and high Ni²⁺ concentrations.     

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.     

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.     

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.     

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.     

A New Approach for Titration Calorimetric Data Analysis on the Binding of Magnesium Ion with Myelin Basic Protein

The interaction of the myelin basic protein (MBP) from the bovine central nervous system with divalent magnesium ion was studied by isothermal titration calorimetry at 27 °C in aqueous solution. A simple rapid method for determination of the dissociation binding constants for Mg²⁺-MBP interaction was introduced using the isothermal titration calometric data. The binding isotherm for Mg²⁺-MBP interaction is easily obtained by carrying out a titration calorimetric experiment using only one set of concentrations of MBP. There are two identical independent intrinsic association constants equal to 0.021 μmol⋅L⁻¹ in the first- and second-binding sites, respectively.     

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.     

Kinetic and mechanistic studies on the reaction of thiosemicarbazide with [(H<Subscript>2</Subscript>O)(tap)<Subscript>2</Subscript>RuORu(tap)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]<Superscript>2+</Superscript> {tap = 2-(m-tolylazo)pyridine}

The interaction of thiosemicarbazide with the title complex has been studied spectrophotometrically in aqueous medium as a function of [complex], [thiosemicarbazide], pH and temperature at constant ionic strength. At pH 7.4, the reaction shows two distinct paths; both of which are [thiosemicarbazide] dependent. A parallel reaction scheme fits well with the experimental findings. An associative interchange mechanism is proposed for both the paths; the activation parameters calculated from Eyring plots are ΔH₁^≠ = 14.2 ± 0.8 kJ mol⁻¹, ΔS₁^≠ = −241 ± 2 JK⁻¹ mol⁻¹, ΔH₂^≠ = 30.8 ± 1.4 kJ mol⁻¹ and ΔS₂^≠ = −236 ± 4 JK⁻¹ mol⁻¹. From the temperature dependence of the outer sphere association complex equilibrium constants, the thermodynamic parameters calculated are ΔH₁^° = 34.25 ± 1.9 kJ mol⁻¹, ΔS₁^° = 146 ± 6 J K⁻¹ mol⁻¹ and ΔH₂^° = 9.4 ± 1.1 kJ mol⁻¹, ΔS₂^° = 71 ± 3 JK⁻¹ mol⁻¹, which gives a negative ΔG° at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex.     

Thermodynamic Study of Myelin Basic Protein upon Interaction with [Hg2+] Using Extension Solvation Model

Mercury ion interaction with myelin basic protein (MBP) was studied at 300 K in 30 mmol/L tris buffer, pH=7 by isothermal titration calorimetry (ITC). An extended solvation model was used for Hg²⁺+MBP interaction over the whole range of Hg²⁺ concentrations. The binding parameters recovered from the solvation model were attributed to the structural changes of MBP due to its interaction with mercury ion. It was found that mercury ion acted as a noncooperative effector of MBP, and there is a set of two identical and independent binding sites for Hg²⁺ ions. The dissociation equilibrium constant is 97.6 µmol/L. The molar enthalpy change of binding is ?11.25 kJ·mol^?1.     

What is the enthalpy of formation of acrylonitrile?

Acrylonitrile is a key industrial compound with numerous uses. Despite its importance, its enthalpy of formation is still contentious. There is a 12 kJ mol⁻¹ range of values reported for the gas phase quantity: 173–185 kJ mol⁻¹. Quantum chemical calculations, using current methodologies and defining reactions, suggest values between 185 and 191 kJ mol⁻¹: the recommended value, an average, is 188 ± 7 kJ mol⁻¹.     

Effects of Temperature and Common Ions on Binding of Puerarin to BSA

The effects of temperature and common ions on binding of puerarin to bovine serum albumin (BSA) are investigated. The binding constants (K _a) between puerarin and BSA are 1.13×10⁴ L⋅mol⁻¹ (20 °C) and 1.54×10⁴ L⋅mol⁻¹ (30 °C), and the number of binding sites (n) is (0.95±0.02). However, at a higher temperature (40 °C) the stability of the puerarin–BSA system decreases, which results in a lower binding constant (1.58×10³ L⋅mol⁻¹) and number of binding sites (n=0.73) of the puerarin–BSA system. However, the presence of Cu²⁺ and Fe³⁺ ions increases the binding constants and the number of binding sites in the puerarin–BSA complex.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

Electrochemical modification of Bi2S3 coatings in a nickel plating electrolyte

The electrochemical behavior of Bi₂S₃ coatings in Watts nickel plating electrolyte was investigated using the cyclic voltammetry, electrochemical quartz crystal microbalance, X-ray diffraction, and energy dispersive X-ray analysis methods. During the bismuth sulfide coating reduction in Watts background electrolyte in the potential region from −0.4 to −0.6 V, the Bi₂S₃ and Bi(III) oxygen compounds are reduced to metallic Bi, and the decrease in coating mass is related to the transfer of S²⁻ ions from the electrode surface. When the bismuth sulfide coating is reduced in Watts nickel plating electrolyte, the observed increase in coating mass in the potential region −0.1 to −0.4 V is conditioned by Ni²⁺ ions reduction before the bulk deposition of Ni, initiated by Bi₂S₃. In this potential region, the reduction of Bi(III) oxygen compounds can occur. After the treatment of as-deposited bismuth sulfide coating in nickel plating electrolyte at E = −0.3 V, the sheet resistance of the layer decreases from 10¹³ to 500–700 Ω cm. A metal-rich mixed sulfide Ni₃Bi₂S₂–parkerite is obtained when as-deposited bismuth sulfide coating is treated in Watts nickel plating electrolyte at a potential close to the equilibrium potential of the Ni/Ni²⁺ system and then annealed at temperatures higher than 120 °C.     

Aqueous solutions of colloidal nickel: Radiation-chemical preparation, absorption spectra, and properties

Radiation-chemical reduction of Ni²⁺ ions in aqueous solutions of Ni(ClO₄)₂ containing sodium formate or isopropyl alcohol was studied, γ-Irradiation of deaerated solutions in the presence of polyethyleneimine, polyacrylate, or polyvinyl sulfate gives stable metal sols containing spherical particles 2–4 nm in diameter. The optical absorption spectra of nickel nanoparticles exhibit a band with a maximum at 215±5 nm (ε₂₁₅=4.7·10³ L mol⁻¹ cm⁻¹) and a shoulder at 350 nm. A mechanism for the radiation-chemical reduction of Ni²⁺ ions by hydrated electrons and organic radicals (CO₂- radical anions in the case of HCOONa and Me₂C·OH radicals in the case of PrⁱOH). The redox potentials of the Ni²⁺/Ni⁰ and Ni⁺/Ni⁰ pairs (Ni⁰ is a nickel atom) are approximately −2.2 and −1.7 V, respectively. The nanoparticles are readily oxidized by O₂, H₂O₂, and other oxidants. The reactions of these species with silver ions yield relatively stable nanoaggregates containing both nickel and silver in addition to silver nanoparticles. Published inIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 1733–1739, October, 2000.     

Kinetic study of crystallization of PHB in presence of hydroxy acids

Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid (TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear fitting to obtain the estimation for activation energy (E _a ) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 °C at 5 °C/min, and results obtained to the average activation energy, 73 ± 9 kJ mol⁻¹ and 63 ± 1 kJ mol⁻¹, to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain. PHB/TA show increase in the medium value of E _a, 119 ± 2 kJ mol⁻¹ and T _c = 48.2 °C (at 5 °C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E _a=73 ± 9 kJ mol⁻¹, T _c = 44.8 °C at 5 °C/min).     

Study of degradation kinetics of sunflower oil on H-Beta zeolite

In this study, were studied the degradation of pure sunflower oil and mixed with H-Beta zeolite. This zeolite was synthesized by the hydrothermal method, followed by calcination and ion exchanged. The characterization of the zeolite was performed by X-ray diffraction and nitrogen adsorption/desorption by the method of BET. The analysis showed that H-Beta zeolite presented a good crystallinity and the template was completely removed from the catalyst. The thermal and catalytic degradation study was carried out using the TG/DTG method in multiple heating rates of 5, 10, and 20 °C min⁻¹. The isoconversion method proposed by Vyazovkin was applied to determine the kinetic parameters for degradation of the sunflower oil. The activation energy for the degradation process of pure sunflower oil was 193 kJ mol⁻¹, while for sunflower oil mixed with 20% of H-Beta zeolite was equivalent to 88 kJ mol⁻¹. It was verified that for the degradation of 90% of the sunflower oil mixed with H-Beta, for a period of 1 h, a temperature of 356 °C was required, whereas for the pure vegetable oil, this value was of 387 °C, at the same time period, showing that the catalyst was effective for the degradation process of sunflower oil.     

Binding properties and structural changes of human growth hormone upon interaction with cobalt ion

Binding properties and structural changes of human growth hormone (hGH) due to the interaction by cobalt ion (Co²⁺) were done at 27°C in NaCl solution, 50 mM, using different techniques of UV-Vis spectroscopy, circular dichroism (CD), isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) techniques. There is a set of three identical and non-interacting binding sites for cobalt ions. The intrinsic association equilibrium constant and the molar enthalpy of binding obtained by ITC are 0.80 mM⁻¹ and −16.70 kJ mol⁻¹, respectively. The intrinsic association equilibrium constant obtained by a standard isothermal titration UV-Vis spectrophotometry method is also 0.79 mM⁻¹, which is in good agreement with the value obtained from ITC. The Gibbs free energy and entropy changes due to the binding of cobalt ion on hGH are −16.67 kJ mol⁻¹ and −0.1 J K⁻¹ mol⁻¹, respectively. Energetic domains analysis by DSC shows that phase transition of hGH in the presence of cobalt occurs at one main transition. Deconvolution of the main transition provides two sub-transitions with different values of the melting point and enthalpy of unfolding (33°C and 164 kJ mol⁻¹ for the first and 49°C and 177 kJ mol⁻¹ for the second, respectively). Interaction of cobalt ions with hGH prevents aggregation by an affect on the hydrophobicity of the protein macromolecule and provide useful information about its structure due to becoming reversible of protein thermal denaturation.