Thermodynamic properties of potassium metasilicate (K2SiO3)

The standard enthalpy of formation of potassium metasilicate (K₂SiO₃), determined by hydrofluoric acid solution calorimetry, was found to be ΔH^o_f,298 = −363.866±0.421 kcal mol⁻¹ (−1522.415±1.762 kj mol⁻¹). The standard enthalpy of formation from the oxides was found to beΔH^o₂₉₈ = −64.786±0.559 kcal mol⁻¹ (−271.065±2.339 kJ mol⁻¹).These experimentally determined data were combined with data from the literature to calculate the Gibbs energies of formation and equilibrium constants of formation over the temperature range of the literature data. The standard enthalpies of formation and Gibbs energies of formation are given as functions of temperature. The standard Gibbs energy of formation is ΔG_f,298.15⁰ = −341.705 kcal mol⁻¹ (−1429.694 kJ mol⁻¹).     

Kinetics of D,L–Lactide Polymerization Initiated with Zirconium Acetylacetonate

The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol⁻¹. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy E_a=44.51±5.35 kJ mol⁻¹, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol⁻¹ K⁻¹. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown.     

基于支撑向量机方法的有机化合物的生成Gibbs自由能的预测

基于支撑向量机方法的有机化合物的生成Gibbs自由能的预测;支撑向量机;多元线形回归;吉布斯自由能     

Thermodynamics of the adsorption of different dyes onto bentonite modified with hexadecyltrimethylammonium cation

Removal of two different dyes: Acid Orange 10 (AO10) and Reactive Black 5 (RB5) from their aqueous solutions using organobentonite as adsorbent was investigated. The experiments were carried out at different temperatures (298, 313, 323, and 333 K) in order to obtain thermodynamic parameters for adsorbate/adsorbent system i.e., activation energy, Gibbs free energy, enthalpy and entropy. The results of thermodynamic studies indicated that the adsorption of both dyes onto organobentonite is an endothermic process, while the values for activation energies (76 kJ mol^?1 for AO10 and 51 kJ mol^?1 for RB5) indicated that chemisorption occurred.     

Thermal properties of seed proteins

The sample of LiCoO₂ was synthesized, and the heat capacity was measured by adiabatic calorimetry between 13 and 300 K. The smoothed values of the heat capacity were calculated from the data. The thermodynamic functions, standard enthalpy, entropy and Gibbs energy, of LiCoO₂ were calculated from the heat capacity and the numerical values are tabulated at selected temperatures from 15 to 300 K. The heat capacity, enthalpy, entropy, and Gibbs energy at T=298.15 K are 71.57 J K^–1mol^–1, 9.853 kJ mol^–1, 52.45 J K^–1 mol^–1, –5.786 kJ mol^–1, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Time‐Resolved Thermodynamic Profile upon Photoexcitation of a Nitrospiropyran in Cycloalkanes and of the Corresponding Merocyanine in Aqueous Solutions

The photoconversion of 2′,3′‐dihydro‐6‐nitro‐1′,3′,3′‐trimethylspiro[2H‐1‐benzopyran‐2,2′‐indole] ( Sp ) to its open merocyanine form ( Mc ) in a series of aerated cycloalkanes (cyclopentane, cyclohexane, and trans‐ and cis‐decalin) and of the protonated merocyanine ( McH ⁺ ) to Sp in aqueous solution were studied by laser‐induced optoacoustic spectroscopy (LIOAS). The +(11±2) ml mol⁻¹ expansion determined for the ring closure is due to deprotonation of McH ⁺ plus the reaction of the ejected proton with the monoanion of malonic acid (added to stabilize Mc ), an intrinsic expansion and a small electrostriction term. The energy difference between Sp and initial McH ⁺ is (282±110) kJ mol⁻¹. An intrinsic contraction of −(47±15) ml mol⁻¹ occurs upon ring opening, forming triplet ³Mc in the cycloalkanes, whereas no volume change was detected for the ³Mc to Mc relaxation. Electrostriction decreases the ³Mc energy, (165±18) kJ mol⁻¹, to 135 kJ mol⁻¹. The difference in the values of the ring‐opening ( Sp to Mc ) reaction enthalpy in cycloalkanes as derived from the temperature dependence of the Sp ⇌ Mc equilibrium, (29±8) kJ mol⁻¹, and from the LIOAS data, −(9±25) kJ mol⁻¹, is due to the formation of Mc‐Sp aggregates during steady‐state measurements. The Sp ‐sensitized singlet molecular oxygen, O₂(¹Δ_g), quantum yield (average Φ_Δ=0.58±0.03) derived from the near‐IR emission of O₂(¹Δ_g), was taken as a measure of Mc production in the cycloalkanes. These solvents, albeit troublesome in their handling, provide an additional series for the determination of structural volume changes in nonaqueous media, besides the alkanes already used.     

O2 Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

This paper reports the computed O₂ binding to heme, which for the first time explains experimental enthalpies for this process of central importance to bioinorganic chemistry. All four spin states along the relaxed Fe? O₂‐binding curves were optimized using the full heme system with dispersion, thermodynamic, and scalar‐relativistic corrections, applying several density functionals. When including all these physical terms, the experimental enthalpy of O₂ binding (?59 kJ mol^?1) is closely reproduced by TPSSh‐D3 (?66 kJ mol^?1). Dispersion changes the potential energy surfaces and leads to the correct electronic singlet and heptet states for bound and dissociated O₂. The experimental activation enthalpy of dissociation (～82 kJ mol^?1) was also accurately computed (～75 kJ mol^?1) with an actual barrier height of ～60 kJ mol^?1 plus a vibrational component of ～10 and ～5 kJ mol^?1 due to the spin‐forbidden nature of the process, explaining the experimentally observed difference of ～20 kJ mol^?1 in enthalpies of binding and activation. Most importantly, the work shows how the nearly degenerate singlet and triplet states increase crossover probability up to ～0.5 and accelerate binding by ～100 times, explaining why the spin‐forbidden binding of O₂ to heme, so fundamental to higher life forms, is fast and reversible.     

Oxidative thermal degradation of LDPE and the determination of some thermodynamic quantities

The pyrolysis of polyolefin wastes is one of the possible ways to obtain chemical feedstocks. In this work, the thermal degradation of low density polyethylene, (LDPE), which is a major product within plastics, was investigated in a semi-batch reactor system. First-order rate kinetics approach was chosen and reaction rate coefficients, k, and some thermodynamic quantities determined such as activation energy, reaction enthalpy, free activation enthalpy, and entropy of degradation of LDPE for different air flow rates. We found that the maximum value of some thermodynamic quantities, such as reaction rate coefficient is 0.0243 min⁻¹ at 600 mL min⁻¹ air flow rate and the free activation enthalpy (ΔG^≠) is 148.66 kJ mol⁻¹ at 450 mL min⁻¹ air flow rate and the reaction enthalpy (ΔH^≠) is 57.65 J mol⁻¹ at 623 K temperature conditions. Moreover, we found that the oxidative degradation of LDPE is not spontaneous and has lower energy necessary (for degradation) than non-oxidative degradation processes.     

Thermodynamics of Hydrophobic Interactions: Entropic Recognition of a Hydrophobic Moiety by Poly(Ethylene Oxide)–Zinc Porphyrin Conjugates

The recognition of 4‐alkylpyridines by water‐soluble poly(ethylene oxide)–zinc porphyrin conjugates was studied with a focus on the thermodynamic parameters of binding. Microcalorimetric studies indicated that binding of the alkyl group of the guest in water is driven by the entropic term (δΔH⁰=ΔH⁰(4‐pentylpyridine)? ΔH⁰(4‐methylpyridine)=+1.7 kJ mol^?1, δTΔS⁰=TΔS⁰(4‐pentylpyridine)? TΔS⁰(4‐methylpyridine)=+11.8 kJ mol^?1 at 298 K), thus showing the significance of water reorganization during host–guest interaction. The enthalpy–entropy compensation temperature of binding of 4‐alkylpyridines was as low as 38 K; only below this temperature could the enthalpic term be a driving force. The binding affinity was modulated by the addition of cations and by varying the degree of polymerization of poly(ethylene oxide), which suggests that guest binding is coupled with polymer conformation.     

Characterization of Bioimprinted Tannase and Its Kinetic and Thermodynamics Properties in Synthesis of Propyl Gallate by Transesterification in Anhydrous Medium

Tannase has been extensively applied to synthesize gallic acid esters. Bioimprinting technique can evidently enhance transesterification-catalyzing performance of tannase. In order to promote the practical utilization of the modified tannase, a few enzymatic characteristics of the enzyme and its kinetic and thermodynamics properties in synthesis of propyl gallate by transesterification in anhydrous medium have been studied. The investigations of pH and temperature found that the imprinted tannase holds an optimum activity at pH?5.0 and 40?°C. On the other hand, the bioimprinting technique has a profound enhancing effect on the adapted tannase in substrate affinity and thermostability. The kinetic and thermodynamic analyses showed that the modified tannase has a longer half-time of 1,710?h at 40?°C; the kinetic constants, the activation energy of reversible thermal inactivation, and the activation energy of irreversible thermal inactivation, respectively, are 0.054?mM, 17.35?kJ?mol^?1, and 85.54?kJ?mol^?1 with tannic acid as a substrate at 40?°C; the free energy of Gibbs (??G) and enthalpy (??H) were found to be 97.1 and 82.9?kJ?mol^-1 separately under the same conditions.     

Gold Nanoparticles Formation via Au(III) Complex Ions Reduction with l‐Ascorbic Acid

In this paper, the kinetics and mechanism of gold nanoparticles formation during the redox reaction between [AuCl₄]− complex and l ‐ascorbic acid under different conditions were described. It was also shown that reagent concentration, chloride ions, and pH influence kinetics of nucleation and growth. To establish rate constants of these stages, the model of Finke and Watzky was applied. From Arrhenius and Eyring dependencies, the values of activation energy (22.5 kJ mol⁻¹ for the nucleation step and 30.3 kJ mol⁻¹ for the growth step), entropy (about −228 J K⁻¹ mol⁻¹ for the nucleation step and −128 J K⁻¹ mol⁻¹ for the growth step), and enthalpy (19.8 kJ mol⁻¹ for nucleation and 27.8 kJ mol⁻¹ for particles growth) were determined. It was also shown that the disproporationation reaction had influence on the rate of nanoparticles formation and may have impact on final particles morphology.     

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.     

Interaction of Bovine Serum Albumin with N‐(4‐Ethoxyphenyl)‐N′‐(4‐Antipyrinyl)Thiourea (EPAT) Using Spectroscopies

The interaction between N‐(4‐ethoxyphenyl)‐N′‐(4‐antipyrinyl)thiourea (EPAT) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy in combination with UV absorption spectroscopy. The intrinsic fluorescence of bovine serum albumin was quenched by EPAT through a static quenching procedure. The binding constants of EPAT with BSA were estimated according to the fluorescence quenching results at different temperatures. The thermodynamic parameters: enthalpy change (ΔH) and entropy change (ΔS) were calculated to be ?10.69 kJ/mol and 42.64 J·mol^?1·K^?1 according to thermodynamic equations, respectively, and indicating that the binding force was suggested to be mainly a hydrophobic force. The effect of common ions on the binding constant was also investigated. A new fluorescence spectroscopy assay of the proteins was presented in this paper. The determination results of the proteins in bovine serum by means of this method were very close to those obtained using Coomassie Brilliant Blue G‐250 colorimetry.