Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

Structural studies of cyclic ureas: 2. Enthalpy of formation of parabanic acid

Thermophysical and thermochemical studies have been carried out for crystalline parabanic acid. The thermophysical study was made by differential scanning calorimetry, DSC, over the temperature interval between T = (263 and 473) K. Two phase transitions were found: at T = (392.3 ± 1.6) K with the enthalpy of transition of (2.1 ± 0.4) kJ · mol⁻¹ and at T = (509.8 ± 1.5) K, when the compound was scanned to its fusion temperature. The standard (p = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for crystalline parabanic acid was determined using static-bomb combustion calorimetry as −(590.2 ± 1.0) kJ · mol⁻¹. The standard molar enthalpy of sublimation, at T = 298.15 K, was derived from the variation of their vapour pressures, measured by the Knudsen-effusion method, with the temperature. These two thermochemical parameters yielded the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, as −(470.8 ± 1.2) kJ · mol⁻¹.     

Dinitrogen and carbon monoxide hydrogen bonding in protonic zeolites: Studies from variable-temperature infrared spectroscopy

Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-Y results in hydrogen bonding of the adsorbed N₂ molecules with the zeolite Si(OH)Al Brønsted-acid groups. This hydrogen-bonding interaction leads to activation, in the infrared, of the fundamental N–N stretching mode, which appears at 2334 cm⁻¹. From infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH···N₂ complex was found to be ΔH⁰ = −15.7(±1) kJ mol⁻¹. Similarly, variable-temperature infrared spectroscopy was used to determine the standard enthalpy change involved in formation of H-bonded CO complexes for CO adsorbed on the zeolites H-ZSM-5 and H-FER; the corresponding values of ΔH⁰ were found to be −29.4(±1) and −28.4(±1) kJ mol⁻¹, respectively. The whole set of results was analysed in the context of other relevant data available in the literature.     

Enthalpies of combustion and formation of 2-acetylpyrrole, 2-acetylfuran and 2-acetylthiophene

The combustion energies for 2-acetylpyrrole (cr) and 2-acetylfuran (cr) were determined using a static bomb calorimeter, whereas the combustion energy of 2-acetylthiophene (l) was determined with a rotating bomb calorimeter; both calorimeters have been recently described. The molar combustion energies obtained were: −(3196.1 ± 0.6) kJ mol⁻¹ for 2-acetylpyrrole, −(2933.8 ± 0.7) kJ mol⁻¹ for 2-acetylfuran, and −(3690.4 ± 0.8) kJ mol⁻¹ for 2-acetylthiophene. From these combustion energy values, the standard molar enthalpies of formation in the condensate phase were obtained as: −(163.51 ± 0.97) kJ mol⁻¹, −(283.50 ± 1.06) kJ mol⁻¹ and −(123.93 ± 1.15) kJ mol⁻¹, respectively. The obtained values of combustion and formation enthalpies of 2-acetylthiophene are in concordance with the reported previously. For the two last compounds, polyethene bags were used as an auxiliary material in the combustion experiments. The heat capacities and purities of the compounds were determined using a differential scanning calorimeter.     

Standard molar enthalpies of formation of 2-, 3- and 4-cyanobenzoic acids

The standard (p = 0.1 MPa) molar enthalpies of formation of 2-, 3- and 4-cyanobenzoic acids were derived from their standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpies of sublimation of 2- and 3-cyanobenzoic acids. The standard molar enthalpies of formation of the three compounds, in the gaseous phase, at T = 298.15 K, have been derived from the corresponding standard molar enthalpies of formation in the condensed phase and standard molar enthalpies for phase transition. The results obtained are −(150.7 ± 2.0) kJ · mol⁻¹, −(153.6 ± 1.7) kJ · mol⁻¹ and −(157.1 ± 1.4) kJ · mol⁻¹ for 2-cyano, 3-cyano and 4-cyanobenzoic acids, respectively. Standard molar enthalpies of formation were also estimated by employing two different methodologies: one based on the Cox scheme and the other one based on several different computational approaches. The calculated values show a good agreement with the experimental values obtained in this work.     

Temperature dependence vapour pressure measurements of Mg(tmhd)2(tmeda) [(tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione, tmeda = N,N,N′,N′-tetramethylethylenediamine]

The reaction between the magnesium β-diketonate complex Mg(tmhd)₂(H₂O)₂ and 1 equiv. of N,N,N′,N′-tetramethylethylenediamine (tmeda = Me₂NCH₂CH₂NMe₂) in hexane at room temperature yielded Mg(tmhd)₂(tmeda). The standard enthalpy of sublimation (83.2 ± 2.3 kJ mol⁻¹) and entropy of sublimation (263 ± 6.3 J mol⁻¹ K⁻¹) of Mg(tmhd)₂(tmeda) were obtained from the temperature dependence vapour pressure, determined by adopting a horizontal dual arm single furnace thermogravimetric analyser as a transpiration apparatus. From the observed melting point depression DTA, the standard enthalpy of fusion (58.3 ± 5.2 kJ mol⁻¹) was evaluated, using the ideal eutectic behaviour of Mg(tmhd)₂(tmeda) as a solvent with bis(2,4-pentanedionato)magnesium(II), Mg(acac)₂ as a non-volatile solute.     

Vapor pressure, kinetics and enthalpy of sublimation of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II)

The kinetics of sublimation of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II), [Cu(tmhd)₂] was studied by non-isothermal and isothermal thermogravimetric (TG) methods. The non-isothermal sublimation activation energy values determined following the procedures of Friedman, Kissinger, and Flynn–Wall methods yielded 93 ± 5, 67 ± 2, and 73 ± 4 kJ mol⁻¹, respectively and the isothermal sublimation activation energy was found to be 97 ± 3 kJ mol⁻¹ over the temperature range of 375–435 K. The dynamic TG run proved the complex to be completely volatile and the equilibrium vapor pressure (p_e)_T of the complex over the temperature range of 375–435 K determined by a TG-based transpiration technique, yielded a value of 96 ± 2 kJ mol⁻¹ for its standard enthalpy of sublimation (Δ_subH°).     

The standard partial molar entropy of the aqueous tetra-n-butylammonium cation

The standard partial molar entropy of the aqueous tetrabutylammonium cation, not known previously, has now been obtained, based on the molar entropy of two of its crystalline salts, the iodide and the tetraphenylborate, recently determined experimentally for this purpose. The calculation required also published molar enthalpies of solution and solubilities of these two salts as well as of the perchlorate. The choice of the anions depended mainly on the limited solubilities of the examined salts in water, facilitating the estimation of the relevant activity coefficients. The result is S^∞(Bu₄N⁺, aq) = (380 ± 20) J · K⁻¹ · mol⁻¹ at T = 298.15 K, on the mol · dm⁻³ scale and based on S^∞(H⁺, aq) = (−22.2 ± 1.2) J · K⁻¹ · mol⁻¹ (yielding the ‘absolute’ value). The molar entropy of this cation in the ideal gas standard state, S(Bu₄N⁺, g) = (798 ± 8) J · K⁻¹ · mol⁻¹ then yielded the molar entropy of hydration Δ_hydS^∞ (Bu₄N⁺) = (−418 ± 23) J · K⁻¹ · mol⁻¹.     

Diffusion of Sr and Zr in BaTiO3 single crystals

The diffusion of strontium and zirconium in single crystal BaTiO₃ was investigated in air at temperatures between 1000 °C and 1250 °C. Thin films of SrTiO₃, deposited by spin coating a precursor solution and thin films of zirconium, deposited onto the sample surfaces by sputtering, were used as diffusion sources. The diffusion profiles were measured by SIMS depth profiling on a time-of-flight secondary ion mass spectrometer (ToF-SIMS). The diffusion coefficients of strontium and zirconium were given by D_Sr = 3.6 × 10^2.0±4.4 exp[−(543 ± 117) kJ mol⁻¹/(RT)] cm² s⁻¹ and D_Zr = 1.1 × 10^1.0±2.1 exp[−(489 ± 56) kJ mol⁻¹/(RT)] cm² s⁻¹. The results are discussed in terms of different diffusion mechanisms in the perovskite structure of BaTiO₃.     

Crystal Structure and Thermal Decomposition of 5-Aminotetrazole Trinitrophloroglucinolate

5-Aminotetrazole trinitrophloroglucinolate ((ATZ)TNPG) was prepared and characterized by elemental analysis and FT-IR spectroscopy. The crystal structure was determined by X-ray diffraction analysis and it belonged to orthorhombic system and Pbca space group with a=0.6624(2) nm, b=1.7933(4) nm, c=2.3117(5) nm, V=2.7458(9) nm³, Z=4, and D_c=1.849 g·cm⁻³. The molecular formula was confirmed to be (ATZ)TNPG·2H₂O. 5-Aminotetrazole cation (ATZ⁺) and trinitrophloroglucinol anion (TNPG⁻) were linked into 2-D layers along b-axis and c-axis by hydrogen bonds. Then the layers were linked along a-axis by hydrogen bonds between the water molecules belonging to different layers. The thermal decomposition mechanism of the compound was studied by differential scanning calorimetry (DSC), thermogravimetry-thermogravimetric analysis (TG-DTG), and Fourier transform-infrared (FT-IR) spectroscopy techniques. Under nitrogen atmosphere with a heating rate of 10 °C·min⁻¹, the compound experienced one endothermic process with peak temperature of 76 °C and one exothermal process with peak temperature of 203 °C. The former was confirmed to be a dehydrate process. The latter was the decomposition of TNPG⁻ and ATZ⁺ in the compound. The exothermic enthalpy change of this process was −212.10 kJ·mol⁻¹. The kinetic parameter calculation from Kissinger's method were, E=132.1 kJ·mol⁻¹, ln(A/s⁻¹)=12.54 with r=0.9990, and the calculation results from Ozawa-Doyle's method were, E=133.1 kJ·mol⁻¹ with r=0.9992.     

Equilibrium, kinetics and thermodynamic aspects of Promethazine hydrochloride sorption by iron rich smectite

Equilibrium, kinetics and thermodynamic aspects of sorption of Promethazine hydrochloride (PHCl) onto iron rich smectite (IRS) from aqueous solution were investigated. The effect of pH on sorption of PHCl onto IRS was also found out. Experimental data were evaluated by using Langmuir, Freundlich and Dubinin–Raduschkevich (DR) isotherm equations. Freundlich and DR equations provided better compatibility than Langmuir equation. Besides, it was determined that the maximum sorption of PHCl takes place at about pH 5. From kinetic studies, it was obtained that sorption kinetics follow pseudo-second-order kinetic model for PHCl sorption onto IRS. When thermodynamic studies are concerned, the values of activation energy (E_a), ΔG°, ΔH° and ΔS° were obtained. ΔG° values are in the range of −8.84 and −9.45 kJ mol⁻¹ indicating spontaneous nature of physisorption. The negative value of the ΔH° (−3.20 kJ mol⁻¹) indicates exothermic nature of adsorption. FTIR analysis and SEM observations of IRS and PHCl adsorbed IRS were also carried out. Sorption experiments indicate that IRS may be used effectively for the adsorption of PHCl.     

Total phase change entropies and enthalpies. An update on fusion enthalpies and their estimation

This compendium summarizes the fusion enthalpies of approximately 1000 new measurements. A group additivity method developed to estimate the total phase change entropies and enthalpies of organic solids is updated, applied to the new data and the results are compared. The uncertainties associated with the 1016 new measurements, ±18.5 J mol⁻¹ K⁻¹ and ±7.6 kJ mol⁻¹ for total phase change entropies and enthalpies, respectively, are similar in magnitude to those reported previously. Experimental and estimated fusion entropies and fusion enthalpies along with references are available as supplementary material.     

Study on the interaction between antibacterial drug and bovine serum albumin: A spectroscopic approach

The binding of sulfamethoxazole (SMZ) to bovine serum albumin (BSA) was investigated by spectroscopic methods viz., fluorescence, FT-IR and UV–vis absorption techniques. The binding parameters have been evaluated by fluorescence quenching method. The thermodynamic parameters, ΔH°, ΔS°and ΔG° were observed to be −58.0 kJ mol⁻¹, −111 J K⁻¹ mol⁻¹ and −24 kJ mol⁻¹, respectively. These indicated that the hydrogen bonding and weak van der Waals forces played a major role in the interaction. Based on the Forster's theory of non-radiation energy transfer, the binding average distance, r, between the donor (BSA) and acceptor (SMZ) was evaluated and found to be 4.12 nm. Spectral results showed the binding of SMZ to BSA induced conformational changes in BSA. The effect of common ions and some of the polymers used in drug delivery for control release was also tested on the binding of SMZ to BSA. The effect of common ions revealed that there is adverse effect on the binding of SMZ to BSA.     

Kinetics of the R + HBr RH + Br (CH3CHBr, CHBr2 or CDBr2) equilibrium. Thermochemistry of the CH3CHBr and CHBr2 radicals

The kinetics of the reaction of the CH₃CHBr, CHBr₂ or CDBr₂ radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH₃CHBr (or CHBr₂ or CDBr₂) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH₃CHBr₂ (or CHBr₃ or CDBr₃). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH₃CHBr + HBr) and from 288 to 477 K (CHBr₂ + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm³ molecule⁻¹ s⁻¹, no error limits for the third reaction): k(CH₃CHBr + HBr) = (1.7 ± 1.2) × 10⁻¹³ exp[+ (5.1 ± 1.9) kJ mol⁻¹/RT], k(CHBr₂ + HBr) = (2.5 ± 1.2) × 10⁻¹³ exp[−(4.04 ± 1.14) kJ mol⁻¹/RT] and k(CDBr₂ + HBr) = 1.6 × 10⁻¹³ exp(−2.1 kJ mol⁻¹/RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH₃CHBr and CHBr₂ radicals and an experimental entropy value at 298 K for the CH₃CHBr radical were obtained using a second-law method. The result for the entropy value for the CH₃CHBr radical is 305 ± 9 J K⁻¹ mol⁻¹. The results for the enthalpy of formation values at 298 K are (in kJ mol⁻¹): 133.4 ± 3.4 (CH₃CHBr) and 199.1 ± 2.7 (CHBr₂), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol⁻¹): 415.0 ± 2.7 (CH₃CH₂Br) and 412.6 ± 2.7 (CH₂Br₂), respectively.     

Calorimetric determination of enthalpy changes for the proton ionization of N-tris(hydroxymethyl)methyl-4-aminobutanesulfonic acid (TABS), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS) and 3-[N-tris(hydroxymethyl)methylamino]-2-hyroxypropane sulfonic acid (TAPSO) in water–methanol mixtures

Enthalpies for the two proton ionizations of the biochemical buffers N-tris(hydroxymethyl)methyl-4-aminobutanesulfonic acid (TABS), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS) and 3-[N-tris(hydroxymethyl)methylamino]-2-hyroxypropane sulfonic acid (TAPSO) were obtained in water–methanol mixtures with methanol mole fraction (X_m) from 0 to 0.360. The ionization enthalpy for the first proton (ΔH₁) of all three buffers was small and exhibited slight changes upon methanol addition. The ionization enthalpy of the second proton (ΔH₂) of TABS increased from 39.6 to 49.8 kJ mol⁻¹ and for TAPS from 40.1 to 43.2 kJ mol⁻¹, with a minimum of 38.2 kJ mol⁻¹ at X_m = 0.059. For TAPSO the increase was from 33.1 to 35.6 kJ mol⁻¹ at X_m = 0.194, with measurements at higher X_m precluded by low solubility of TAPSO in methanol rich solvents. The solvent composition was selected so as to include the region of maximum structure enhancement of water by methanol. The results were interpreted in terms of solvent–solvent and solvent–solute interactions.     

Equilibrium constant for the reaction Xe + 2Ar XeAr + Ar in the temperature range 150–300 k and the dissociation energy of XeAr

The equilibrium Xe + 2Ar has been investigated in the temperature range 150–300 K using a selected ion flow tube appratus. From the temperature variation of the equilibrium constant the standrad enthalpy change for the reaction is determined to be −25 ± 5 kj mol⁻¹ and the dissociation energy of XeAr⁺ is estimated to be 24 ±5 kj mol⁻¹ (0.25 ± 0.05 eV). At ≈ 150 K the approach to equilibrium is consistent with a rate coefficent of (5 ± 3) × 10⁻²¹ cm ⁶ s⁻¹ for the forward three-body association reaction.     

Thermochemistry of the mixed calcium phosphate Ca8P2O7(PO4)4

The calcium mixed phosphate Ca₈P₂O₇(PO₄)₄ has been synthesized by thermal decomposition of octacalcium phosphate previously prepared by precipitation in ammoniacal phosphate solution. The enthalpy of formation at 298.15 K referenced to β-tricalcium phosphate and calcium pyrophosphate is determined. β-Tricalcium phosphate was prepared by two methods: precipitation in ammoniacal aqueous medium and high temperature solid-state reaction. Calcium pyrophosphate was prepared by high temperature solid-state reaction. All the compounds are characterized by chemical analysis, X-rays diffraction and IR spectroscopy. The enthalpy of formation +10.83 ± 0.63 kJ mol⁻¹ is obtained by solution calorimetry at 298.15 K in nitric acid.     

Molecular modeling and spectroscopic studies on binding of 2,6-bis[4-(4-amino-2-trifluoromethylphenoxy)benzoyl] pyridine to human serum albumin

BAFP (2,6-bis[4-(4-amino-2-trifluoromethylphenoxy)benzoyl] pyridine), a synthesized polyimide compound, was exploited for the first time to analyze its interaction with human serum albumin (HSA) by molecular modeling, fluorescence and Fourier transform infrared attenuated total reflection spectroscopy (FTIR ATR) with drug concentrations of 3.3 × 10⁻⁶ to 3.0 × 10⁻⁵ mol L⁻¹. Molecular docking was performed to reveal the possible binding mode. The results suggested that BAFP can strongly bind to human serum albumin (HSA) and the primary binding site of BAFP is located in site II of HSA, which is supported by the results from the competitive experiment. The binding constants for the interaction of BAFP with HSA have been evaluated from relevant fluorescence data at different temperatures (296, 303, 310 and 308 K). The alterations of the protein secondary structure in the presence of BAFP in aqueous solution were quantitatively calculated by the evidences from FTIR ATR spectroscopes. The binding process was exothermic and spontaneous, as indicated by the thermodynamic analyses, and the major part of the binding energy is hydrophobic interaction, which is also in good agreement with the results of molecule modeling study. The enthalpy change ΔH⁰, the free energy change ΔG⁰ and the entropy change ΔS⁰ of 296 K were calculated to be −7.75, −27.68 kJ mol⁻¹ and 67.33 J mol⁻¹ K⁻¹, respectively.     

Phosphate desorption kinetics from goethite as induced by arsenate

The kinetics of the arsenate-induced desorption of phosphate from goethite has been studied with a batch reactor system and ATR-FTIR spectroscopy. The effects of arsenate concentration, adsorbed phosphate, pH and temperature between 10 and 45 °C were investigated. Arsenate is able to promote phosphate desorption because both oxoanions compete for the same surface sites of goethite. The desorption occurs in two steps: a fast step that takes place in less than 5 min and a slow step that lasts several hours. In the slow step, arsenate ions exchange adsorbed phosphate ions in a 1:1 stoichiometry. The reaction is first order with respect to arsenate concentration and is independent of adsorbed phosphate under the experimental conditions of this work. The rate law is then r = k_r[As], where r is the desorption rate, k_r is the rate constant and [As] is the arsenate concentration in solution. The values of k_r at pH 7 are 1.87 × 10⁻⁵ L m⁻² min⁻¹ at 25 °C and 7.95 × 10⁻⁵ L m⁻² min⁻¹ at 45 °C. The apparent activation energy of the desorption process is 51 kJ mol⁻¹. Data suggest that the rate-controlling process is intraparticle diffusion of As species, probably As diffusion in pores. ATR-FTIR spectroscopy suggests that adsorbed phosphate species at pH 7 are mainly bidentate inner-sphere surface complexes. The identity of these complexes does not change during desorption, and there is no evidence for the formation of intermediate species during the reaction.     

Kinetic and thermodynamic characterization of camptothecin hydrolysis at physiological pH in the absence and presence of human serum albumin

To accurately derive the kinetic and thermodynamic parameters governing the hydrolysis of the lactone ring at physiological pH, a derivative spectrophotometric technique was used for the simultaneous estimation of lactone and carboxylate forms of camptothecin (CPT). The hydrolysis of the CPT‐lactone and the lactonization of CPT‐carboxylate at 310.15 K followed a first‐order decay with apparent rate constants equal to 0.0279 ± 0.0016 min^?1 and 0.0282 ± 0.0024 min^?1, respectively. The activation energy associated with the hydrolysis of the CPT‐lactone and the lactonization of the CPT‐carboxylate as calculated from the Arrhenius equation was 89.18 ± 0.84 and 86.49 ± 2.7 kJ mol^?1, respectively. The enthalpy and entropy of the thermodynamically favored hydrolysis reaction were on average 10.49 kJ mol^?1 and 48.00 J K^?1 mol^?1, respectively. The positive enthalpy and entropy values of the CPT‐lactone hydrolysis indicate that the reaction is endothermic and entropically driven. The stability of CPT‐lactone in the presence of human serum albumin (HSA) was also analyzed. Notwithstanding the much faster hydrolysis of the CPT‐lactone in the presence of HSA at various temperatures, the energy of activation was determined to be similar to the one estimated in the absence of HSA, suggesting that HSA does not catalyze the hydrolysis reaction, but it merely binds, sequesters, and stabilizes the CPT‐carboxylate species. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 704–715, 2009