牛血清蛋白在盐酸胍和尿素体系中变性的微量热研究

在30 ℃时用恒温微量热法研究了不同pH值下盐酸胍、尿素诱导牛血清蛋白变性的过程. 并用Privalov提出的简单键合模型对量热数据进行了分析, 计算了表观键合常数K, 简单键合的单个表观键合自由能ΔG和总吉布斯能ΔG(a), 用变性中点的直线外推方法求出了表观变性焓ΔH_d. 实验结果表明, 牛血清蛋白与盐酸胍的键合在碱性条件下更易进行, 牛血清蛋白在盐酸胍溶液中的变性焓ΔH_d在牛血清蛋白的pH＝6.97和7.05时为350 kJ•mol^－1, 在pH＝9.30时为275 kJ•mol^－1, 表明牛血清蛋白在接近中性时较稳定. 而牛血清蛋白与尿素的键合在酸性条件下更易进行, 此变性焓ΔH_d在牛血清蛋白的pH＝6.97时为295 kJ•mol^－1, 在pH＝7.05和9.30时为230 kJ•mol^－1. 此结果说明牛血清蛋白在两种变性剂溶液中的展开程度是不同的.     

Studies of the interaction between apigenin and bovine serum albumin by spectroscopic methods

The interaction between apigenin (Ap) and bovine serum albumin (BSA) in physiological buffer (pH = 7.4) is investigated by fluorescence quenching technique and UV-vis absorption spectra. The results reveal that Ap could strongly quench the intrinsic fluorescence of BSA. The quenching mechanism of Ap for BSA varies with the change of Ap concentration. when Ap concentration is lower, it is a static quenching procedure, when Ap concentration is higher, a combined quenching (both static and dynamic) would operate. The apparent binding constants Ka and number of binding sites n of Ap with BSA are obtained by fluorescence quenching method. The thermodynamic parameters, enthalpy change (Δ_r H ^m and entropy change (Δ_r S ^m ), are calculated to be −15.382 kJ mol⁻¹ K⁻¹ < 0 and 104.888 J mol⁻¹ K⁻¹ > 0, respectively, which indicate that the interaction of Ap with BSA is driven mainly by hydrogen bonding and hydrophobic interactions. The distance r between BSA and Ap is calculated to be 1.89 nm based on F?rster’s non-radiative energy transfer theory. The results of synchronous fluorescence spectra show that binding of Ap with BSA cannot induce conformational changes in BSA.     

Investigation of the Interaction Between Ofloxacin and Bovine Serum Albumin: Spectroscopic Approach

Ofloxacin is an antibacterial compound that belongs to the fluoroquinolone family. In this paper, the interaction between ofloxacin and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy and UV-Vis absorbtion spectroscopy under approximately the human physiological conditions. The thermodynamic parameters were calculated according to the dependence of enthalpy change on the temperature as follows: ΔH has a small negative value (−9.96 kJ⋅mol⁻¹), whereas ΔS has a positive value (54.77 J⋅mol⁻¹⋅K⁻¹). In this work, it was proved that the fluorescence quenching of BSA by ofloxacin is a result of the formation of an ofloxacin–BSA complex. Binding studies concerning the number of binding sites (n=1.14) and apparent binding constant were performed by Scatchard’s procedure. The binding distance r between donor (BSA) and acceptor (ofloxacin) was obtained according to the fluorescence resonance energy transfer (FRET) method.     

The thermal decomposition of N , N -dimethyl-3-oxaglutaramic acid and the kinetics of its second-stage thermal decomposition reaction

N,N-dimethyl-3-oxa-glutaramic acid was purified and characterized by ¹H-NMR, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis. The thermal decomposition of the title compound was studied by means of thermogravimetry differential thermogravimetry (TG-DTG) and FT-IR. The kinetic parameters of its second-stage decomposition reaction were calculated and the decomposition mechanism was discussed. The kinetic model function in a differential form, apparent activation energy and pre-exponential constant of the reaction are 3/2 [(1−α)^1/3−1]⁻¹, 203.75 kJ·mol⁻¹ and 10^17.95s⁻¹, respectively. The values of ΔS ^≠, ΔH ^≠ and ΔG ^≠ of the reaction are 94.28 J·mol⁻¹·K⁻¹, 203.75 kJ·mol⁻¹ and 155.75 kJ·mol⁻¹, respectively. Supported by the National Natural Science Foundation of China (Grant No. 20106009)     

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.     

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.     

Hydrogen-bonding interaction of urea with DNA bases: A density functional theory study

This work deals with the interaction between urea and DNA bases (adenine, thymine, guanine, and cytosine). The optimized geometries, binding energies, and harmonic vibrational frequencies are calculated using the DFT/B3LYP functional combined with the 6–31+G(d,p) basis set. Their interactions are studied aiming to understand more about the nature of the intercalation binding forces between urea and DNA. Fourteen stable complexes are found on the potential energy surface. The structures are cyclic; they are stabilized by NH...O/N and CH...O interactions. The binding energies range from −19.9 kJ·mol⁻¹ to −74.0 kJ·mol⁻¹. The obtained formation energies indicate that Urea:G and Urea:C are more favorable than Urea:T and Urea:A. In addition, the Atoms in Molecules theory is performed to study the hydrogen bonds in the complexes.     

Bioelectrochemical response of a choline biosensor fabricated by using polyaniline

On the basis of the isoelectric point of an enzyme and the doping principle of conducting polymers, choline oxidase was doped in a polyaniline film to form a biosensor. The amperometric detection of choline is based on the oxidation of the H₂O₂ enzymatically produced on the choline biosensor. The response current of the biosensor as a function of temperature was determined from 3 to 40°C. An apparent activation energy of 22.8 kJ·mol⁻¹ was obtained. The biosensor had a wide linear response range from 5 × 10⁻⁷ to 1 × 10⁻⁴ M choline with a correlation coefficient of 0.9999 and a detection limit of 0.2 μM, and had a high sensitivity of 61.9 mA·M⁻¹·cm⁻² at 0.50 V and at pH 8.0. The apparent Michaelis constant and the optimum pH for the immobilized enzyme are 1.4 mM choline and 8.4, respectively, which are very close to those of choline oxidase in solution. The effect of selected organic compounds on the response of the choline biosensor was studied.     

Thermochemistry of copper complex of 6-benzylaminopurine

The copper(II) complex of 6-benzylaminopurine (6-BAP) has been prepared with dihydrated cupric chloride and 6-benzylaminopurine. Infrared spectrum and thermal stabilities of the solid complex have been discussed. The constant-volume combustion energy, Δ_c U, has been determined as −12566.92±6.44 kJ mol⁻¹ by a precise rotating-bomb calorimeter at 298.15 K. From the results and other auxiliary quantities, the standard molar enthalpy of combustion, Δ_c H _m ^θ, and the standard molar of formation of the complex, Δ_f H _m ^θ, were calculated as −12558.24±6.44 and −842.50±6.47 kJ mol⁻¹, respectively.     

Catalytic and Thermodynamic Characterization of Endoglucanase (CMCase) from <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> cmc-1

Monomeric extracellular endoglucanase (25 kDa) of transgenic koji (Aspergillus oryzae cmc-1) produced under submerged growth condition (7.5 U mg⁻¹ protein) was purified to homogeneity level by ammonium sulfate precipitation and various column chromatography on fast protein liquid chromatography system. Activation energy for carboxymethylcellulose (CMC) hydrolysis was 3.32 kJ mol⁻¹ at optimum temperature (55 °C), and its temperature quotient (Q ₁₀) was 1.0. The enzyme was stable over a pH range of 4.1–5.3 and gave maximum activity at pH 4.4. V _max for CMC hydrolysis was 854 U mg⁻¹ protein and K _m was 20 mg CMC ml⁻¹. The turnover (k _cat) was 356 s⁻¹. The pK _a1 and pK _a2 of ionisable groups of active site controlling V _max were 3.9 and 6.25, respectively. Thermodynamic parameters for CMC hydrolysis were as follows: ΔH* = 0.59 kJ mol⁻¹, ΔG* = 64.57 kJ mol⁻¹ and ΔS* = −195.05 J mol⁻¹ K⁻¹, respectively. Activation energy for irreversible inactivation ‘E _a(d)’ of the endoglucanase was 378 kJ mol⁻¹, whereas enthalpy (ΔH*), Gibbs free energy (ΔG*) and entropy (ΔS*) of activation at 44 °C were 375.36 kJ mol⁻¹, 111.36 kJ mol⁻¹ and 833.06 J mol⁻¹ K⁻¹, respectively.     

Studies of Thermochemical Properties of a New Ionic Liquid Prepared by Mixing 1-Methyl- 3-Pentylimidazolium Chloride with InCl3

A new ionic liquid, PMIInCl₄, was prepared by mixing 1-methyl-3-pentylimidazolium chloride (PMIC) with InCl₃. The molar enthalpies of solution of PMIC and PMIInCl₄ in water to form solutions at various molalities were determined at 298.15 K using an isoperibol calorimeter. Using Pitzer's electrolyte solution model, the molar enthalpies of solution of PMIC and PMIInCl₄ at infinite dilution, Δ_sol H^_m, and Pitzer's ion-interaction parameters β_MX ^(0)L, β_MX ^(1)L and C_MX ^ϕL, were derived. The values of the apparent relative molar enthalpy L and relative partial molar enthalpy of the solutes (PMIC and PMIInCl₄), , were subsequently calculated. Using the values of Δ_sol H^_m of PMIC, PMIInCl₄ and InCl₃, the enthalpy change, Δ_r<H=−38.19kJ·;mol^-1, was calculated for the reaction PMIC + InCl₃ → PMIInCl₄     

Equilibrium and kinetics study of Gd(III) and U(VI) adsorption from aqueous solutions by modified Sorrel’s cement

Modified Sorrel’s cement was prepared by the addition of ferric chloride. The modified cement (MF5) was analyzed and characterized by different methods. Adsorption of Gd(III) and U(VI) ions in carbonate solution has been studied separately as a function of pH, contact time, adsorbent weight, carbonate concentration, concentration of Gd(III) and U(VI) and temperature. From equilibrium data obtained, the values of Δ H, Δ S and Δ G were found to equal −30.9 kJ ⋅ mol⁻¹, −85.4 J ⋅ mol⁻¹ ⋅,K⁻¹, and −5.4 KJ ⋅ mol⁻¹, respectively, for Gd(III) and 18.9 kJ ⋅ mol⁻¹, 67.8 J ⋅ mol⁻¹ K⁻¹ and −1.3 KJ ⋅ mol⁻¹, respectively, for U(VI). The equilibrium data obtained have been found to fit both Langmuir and Freundlich adsorption isotherms. The batch kinetic of Gd(III) and U(VI) on modified Sorrel’s cement (MF5) with the thermodynamic parameters from carbonate solution were studied to explain the mechanistic aspects of the adsorption process. Several kinetic models were used to test the experimental rate data and to examine the controlling mechanism of the adsorption process. Various parameters such as effective diffusion coefficient and activation energy of activation were evaluated. The adsorption of Gd(III) and U(VI) on the MF5 adsorbent follows first-order reversible kinetics. The forward and backward constants for adsorption, k ₁and k ₂ have been calculated at different temperatures between 10 and 60^∘C. Form kinetic study, the values of Δ H ^* and Δ S ^* were calculated for Gd(III) and U(VI) at 25^∘C. It is found that Δ H ^* equals −14.8 kJmol⁻¹ and 7.2 kJmol⁻¹ for Gd(III) and U(VI), respectively, while Δ S ^* were found equal −95.7 Jmol⁻¹K⁻¹ and −70.5 Jmol⁻¹K⁻¹ for Gd(III) and U(VI), respectively. The study showed that the pore diffusion is the rate limiting for Gd(III) and (VI).     

Thermal behavior and thermal safety on 3,3-dinitroazetidinium salt of perchloric acid

3,3-Dinitroazetidinium (DNAZ) salt of perchloric acid (DNAZ·HClO₄) was prepared, it was characterized by the elemental analysis, IR, NMR, and a X-ray diffractometer. The thermal behavior and decomposition reaction kinetics of DNAZ·HClO₄ were investigated under a non-isothermal condition by DSC and TG/DTG techniques. The results show that the thermal decomposition process of DNAZ·HClO₄ has two mass loss stages. The kinetic model function in differential form, the value of apparent activation energy (E _a) and pre-exponential factor (A) of the exothermic decomposition reaction of DNAZ·HClO₄ are f(α) = (1 − α)⁻¹/2, 156.47 kJ mol⁻¹, and 10^15.12 s⁻¹, respectively. The critical temperature of thermal explosion is 188.5 °C. The values of ΔS ^≠, ΔH ^≠, and ΔG ^≠of this reaction are 42.26 J mol⁻¹ K⁻¹, 154.44 kJ mol⁻¹, and 135.42 kJ mol⁻¹, respectively. The specific heat capacity of DNAZ·HClO₄ was determined with a continuous C _p mode of microcalorimeter. Using the relationship between C _p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic time-to-explosion) was evaluated as 14.2 s.     

Probing the Interaction Between a Surfactant–Cobalt(III) Complex and Bovine Serum Albumin

The mechanism of binding of the surfactant–cobalt(III) complex, cis-[Co(phen)₂(C₁₄H₂₉NH₂)Cl](ClO₄)₂⋅3H₂O (phen = 1,10-phenanthroline, C₁₄H₂₉NH₂ = tetradecylamine) with bovine serum albumin (BSA) was investigated by UV–vis absorption, circular dichroism (CD) and fluorescence spectroscopic techniques. The results of fluorescence titration revealed that the surfactant–cobalt(III) complex quenched the intrinsic fluorescence of BSA through a combination of static and dynamic quenching. The apparent binding constant (K _a) and number of binding sites (n) were calculated below and above the critical micelle concentration (CMC). The thermodynamic parameters determined by the van’t Hoff analysis of the constants (ΔH ^∘=14.87 kJ⋅mol⁻¹; ΔS ^∘=152.88 J⋅mol⁻¹⋅K⁻¹ below the CMC and 25.70 kJ⋅mol⁻¹ and 243.14 J⋅mol⁻¹⋅K⁻¹, respectively, above the CMC) clearly indicate that the binding is entropy-driven and enthalpically disfavored. Based on F?rster’s theory of non-radiation energy transfer, the binding distance, r, between donor (BSA) and the acceptor (surfactant–cobalt(III) complex) was evaluated. UV–vis, CD and synchronous fluorescence spectral results showed that the binding of the surfactant–cobalt(III) complex to BSA induced conformational changes in BSA.     

Thermochemical study of the solid complex Ho(PDC)3 (o-phen)

A novel solid complex, formulated as Ho(PDC)₃ (o-phen), has been obtained from the reaction of hydrate holmium chloride, ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen·H₂O) in absolute ethanol, which was characterized by elemental analysis, TG-DTG and IR spectrum. The enthalpy change of the reaction of complex formation from a solution of the reagents, Δ_rH_m^θ (sol), and the molar heat capacity of the complex, c_m, were determined as being –19.161±0.051 kJ mol^–1 and 79.264±1.218 J mol^–1 K^–1 at 298.15 K by using an RD-496 III heat conduction microcalorimeter. The enthalpy change of complex formation from the reaction of the reagents in the solid phase, Δ_rH_m^θ(s), was calculated as being (23.981±0.339) kJ mol^–1 on the basis of an appropriate thermochemical cycle and other auxiliary thermodynamic data. The thermodynamics of reaction of formation of the complex was investigated by the reaction in solution at the temperature range of 292.15–301.15 K. The constant-volume combustion energy of the complex, Δ_cU, was determined as being –16788.46±7.74 kJ mol^–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_cH_m^θ, and standard enthalpy of formation, Δ_fH_m^θ, were calculated to be –16803.95±7.74 and –1115.42±8.94 kJ mol^–1, respectively.     

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.     

Thermal behavior of 3,4,5-triamino-1,2,4-triazole dinitramide

The thermal decomposition behavior of 3,4,5-triamino-1,2,4-triazole dinitramide was measured using a C-500 type Calvet microcalorimeter at four different temperatures under atmospheric pressure. The apparent activation energy and pre-exponential factor of the exothermic decomposition reaction are 165.57 kJ mol⁻¹ and 10^18.04 s⁻¹, respectively. The critical temperature of thermal explosion is 431.71 K. The entropy of activation (ΔS ^≠), enthalpy of activation (ΔH ^≠), and free energy of activation (ΔG ^≠) are 97.19 J mol⁻¹ K⁻¹, 161.90 kJ mol⁻¹, and 118.98 kJ mol⁻¹, respectively. The self-accelerating decomposition temperature (T _SADT) is 422.28 K. The specific heat capacity of 3,4,5-triamino-1,2,4-triazole dinitramide was determined with a micro-DSC method and a theoretical calculation method. Specific heat capacity (J g⁻¹ K⁻¹) equation is C _p = 0.252 + 3.131 × 10⁻³  T (283.1 K < T < 353.2 K). The molar heat capacity of 3,4,5-triamino-1,2,4-triazole dinitramide is 264.52 J mol⁻¹ K⁻¹ at 298.15 K. The adiabatic time-to-explosion of 3,4,5-triamino-1,2,4-triazole dinitramide is calculated to be a certain value between 123.36 and 128.56 s.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

Thermodynamic properties of Ni-Ga melts

The partial mixing enthalpies of the components (Δ_m $ \bar H $ \bar H _i ) of the Ni-Ga melts were measured using the high-temperature isoperibolic calorimetry at 1770 ± 5 K in wide concentration interval. The limiting partial mixing enthalpy of gallium in a liquid nickel (Δ_m $ \bar H $ \bar H _Ga^∞) is −95.5 ± 19.8 kJ mol⁻¹, and similar function of nickel in liquid gallium (Δ_m $ \bar H $ \bar H _Ni^∞) is −74.5 ± 16.4 kJ mol⁻¹. The integral mixing enthalpy of liquid alloys of this system was calculated from partial enthalpies for the whole concentration area (Δ_m H _min = −32.1 ± 2.7 kJ mol⁻¹ at x _Ni = 0.5). The Δ_m H value of liquid nickel-gallium alloys independence of the temperature is confirmed. Enthalpies of formation of liquid (Δ_m H) phases of Ni-Ga system were compared with ones for solid (Δ_f H) phases of this system. An analysis of d-metals influence on formation energy of Ga-d-Me melts was made using the values of Δ_f H for intermediate phases of these systems. The article was translated by the authors.     

Studies on Thermodynamics Features of the Interaction between Imidacloprid and Bovine Serum Albumin

At different temperatures, the interactions between imidacloprid （IMI） and bovine serum albumin （BSA） were investigated with a fluorescence quenching spectrum, a synchronous fluorescence spectrum, a three-dimensional fluorescence spectrum and an ultraviolet-visible spectrum. The average values of bonding constants （KLB： 3.424 × 10^4 L,mol^-1）, thermodynamic parameters （△H： 5.188 kJ,mol^-1, △G^（○—）：-26.36 kJ,mol^-1, △S： 103.9 J,K^-1,mol^-1） and the numbers of bonding sites （n： 1.156） could be obtained through Stern-Volmer, Lineweaver-Burk and ther- modynamic equations. It was shown that the fluorescence of BSA could be quenched for its reactions with IMI to form a certain kind of new compound. The quenching belonged to a static fluorescence quenching, with a non-radiation energy transfer happening within a single molecule. The thermodynamic parameters agree with △H〉 0, △S〉0 and△G^（○-）〈0, suggesting that the binding power between IMI and BSA should be mainly a hydrophobic interaction.