Thermodynamic investigations on derivatives of pyrimidine nucleic acid bases: Joint use of calorimetric, volumetric and structural data for the description of properties of pyrimidine nucleic acid bases and their derivatives

The experimental enthalpies of solution Δ_solH_m^∞, van’t Hoff enthalpies of sublimation Δ_s^gH_m⁰ of solid compounds, partial molar volumes V₂⁰, and partial molar heat capacities C_p,2⁰ of aqueous solutions of pyrimidine nucleic acid bases and their derivatives, determined previously and collected here, are discussed in terms of calculated structural parameters. Relations have been established between the calorimetric and volumetric properties. Correlations have been developed to relate both the enthalpies of solvation and the partial molar heat capacities to the polar and apolar parts of the accessible molecular surface areas.     

Protonation Curves of the D10N Variant of Endoglucanase Cel45 Catalytic Domain From Humicola Insolens. Isothermal calorimetry and combined isoelectric focusing-electrophoresis

Titration of ionizable groups of D10N variant catalytic domain has been performed by isothermal calorimetric technique and by combined isoelectric focusing-electrophoresis in the range of pH 3–9. pK ₀ ⁱ andΔH ⁰ _i related to the ionizable groups have been estimated using Lindestrøm–Lang equation. Both experimental techniques are in agreement and confirm the validity of the applied theory. Slight differences in protonation enthalpies of carboxyl groups are caused by Asp10 interaction with the other part of the macromolecule.

     

Thermodynamic investigation of the moderately dilute liquid Bi-Fe-Sb alloys

The molar enthalpies of formation of liquid ternary Bi-Fe-Sb alloys have been determined at 1065 K by direct reaction calorimetry using the drop method. Measurements were performed along two sections: X_Bi/X_Sb = 1/9 and 1/4. The experimental calorimetric data and estimated values with a Redlich-Kister formulation are compared.     

Analysis of {α,ω-Dichloroalkane or α,ω-Dibromoalkane] + Benzene and α,ω-Dichloroalkane + Tetrachloromethane} Mixtures in Terms of Group Contributions

Abstract

Molar excess enthalpies, H ^E _m, at 298.15K and atmospheric pressure have been determined for three binary liquid mixtures [x{1,3-dichloropropane or 1,4-dichlorobutane and 1,6-dichlorohexane} + (1 - x) tetrachloromethane]. These experimental results along with the data available in the literature on molar excess Gibbs energies, G ^E _m, activity coefficients at infinite dilution, In γ^∞ _i , and molar excess enthalpies, H ^E _m, for α,ω-dihaloalkanes + benzene or + tetrachloromethane mixtures are examined on the basis of the DISQUAC group contribution model.     

Thermochemical Study of Solutions of Copper(II) Chloride in Methanol-Rich Water + Methanol Mixtures

The calorimetric enthalpies of dilution of water + methanol solutions of CuCl₂ (m < 3.3 mol/kg; methanol mole fractions of 0.5–1.0) with corresponding water + alcohol solutions at 298. 15 K are studied. These data are used to calculate the enthalpies of dilution and the relative partial molar enthalpies for the entire solution and its components (solvent and solute). The data are considered in terms of the structural evolution of the solution and copper(II) chloride complexing; these factors influence the dissolution energy of the electrolyte and its state in solution.     

Thermochemical parameters of dimethyl and di-iso-propyl dithiocarbamate complexes of palladium(II)

The standard molar enthalpy of formation of crystalline dialkyldithiocarbamate chelates, [Pd(S₂CNR₂)₂], with R=CH₃ and i-C₃H₇, was determined through reaction-solution calorimetry in 1,2-dichloroethane, at 298 K. Using the standard molar enthalpies of formation of the gaseous chelates, the homolytic (526±18 and 666±10) and heterolytic (2693±18 and 2957±10 kJ mol^-1) mean enthalpies of palladium-sulphur bond dissociation were calculated. This revised version was published online in August 2006 with corrections to the Cover Date.     

298.15 K时斯蒂芬酸钾盐和铯盐在水和DMF中的溶解热

在298.15 K时, 采用微热量热仪测定斯蒂芬酸钾盐[K₂(TNR)(H₂O)]_n和斯蒂芬酸铯盐[Cs₂(TNR)(H₂O)₂]_n两种含能配合物在水和N,N-二甲基甲酰胺(DMF)溶剂中的溶解热, 研究其溶解过程和溶解热化学性质. 结果表明, 两种配合物溶解于水是吸热过程, 而溶解于DMF则为放热过程, 这主要是由于溶质和溶剂的分子结构及其极性不同而导致的. 通过对实验数据计算拟合, 求得这两种配合物的溶解焓(Δ_solH)、相对表观摩尔焓(ФL_i)、相对偏摩尔焓(L_i)及稀释焓(Δ_dilH_1,2)的经验公式和标准溶解焓值(Δ_solH_m^θ).     

Thermochemical Properties of Palladium(II) Chelates Involving Dialkyldithiocarbamates

The standard molar enthalpies of formation of crystalline dialkyldithiocarbamates chelates, [Pd(S₂CNR₂)₂], with R=C₂H₅, n-C₃H₇, n-C₄H₉ and i-C₄H₉, were determined through reaction-solution calorimetry in acetone, at 298.15 K. From the standard molar enthalpies of formation of the gaseous chelates, the homolytic (172.4±3.8, 182.5±3.2,150.9±3.1 and 162.6±3.1 kJ mol⁻¹) and heterolytic (745.0±3.8, 803.7±3.3,834.3±3.1 and 735.2±3.0 kJ mol⁻¹) mean palladium-sulphur bond-dissociation enthalpies were calculated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Measurement and Correlation of Excess Molar Enthalpy of Binary Mixtures Containing Butyl Acetate + 1-Alkanols (C1–C6) at 298.15 K

Excess molar enthalpies, ?H _m ^E , for the binary mixtures of butyl acetate + 1-alkanols, namely (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol), were measured over the whole range of composition at 298.15 K using a Parr 1455 solution calorimeter. The excess partial molar enthalpies, ?H _m,i ^E , were calculated from the experimental excess molar enthalpies using the Redlich–Kister polynomial equation. The sign of ?H _m ^E for all systems are positive because of the disruption of hydrogen bonding and dipole–dipole interactions in the alkanols and esters, respectively. The magnitude of the ?H _m ^E values increases with increasing alkyl chain length. The behavior of ?H _m ^E was analyzed in terms of the length of the alkanol chain, the nature and type of intermolecular interactions and the balance between positive and negative effects on deviations from ideality. The experimental excess molar enthalpy data have also been correlated using the Redlich–Kister and SSF equations and two local composition models (UNIQUAC and NRTL).     

Proximity effects and cyclization in oxaalkanes+CCl4 mixtures DISQUAC characterization of the Cl–O interactions. Comparison with Dortmund UNIFAC results

Thermodynamic properties, vapor–liquid equilibria (VLE), molar excess Gibbs energies (G^E), molar excess enthalpies (H^E) and natural logarithms of activity coefficients at infinite dilution (ln γ_i^∞) or partial molar excess enthalpies at infinite dilution (H_i^E,∞) of mixtures of oxaalkanes, linear or cyclic monoethers, diethers or acetals, and CCl₄ are studied in the framework of DISQUAC. The oxygen/CCl₄ contacts are characterized by dispersive (DIS) and quasichemical (QUAC) interaction parameters, which are reported. Contacts of the type (polar group)/CCl₄ are usually characterized by DIS parameters only. The effects of proximity and cyclization on the interchange coefficients are examined. In comparison with systems of oxaalkanes and n-alkanes, some differences exist; e.g., linear monoethers and diethers+CCl₄ mixtures are represented by different interaction parameters due to proximity effects of oxygen atoms (i.e., –O–C–C–O–) in diethers. In solutions with cyclic molecules, ring strain seems to be now more important. DISQUAC results are compared with those obtained using the Dortmund version of UNIFAC. From this comparison, it is concluded that it is necessary to distinguish at least between monoethers, diethers and acetals when treating mixtures with oxaalkanes and that each cyclic molecule should be characterized by its own set of interaction parameters.     

Thermodynamic properties of binary mixtures containing n-alkylamines: I. Isothermal vapour–liquid equilibrium and excess molar enthalpy of n-alkylamine+toluene mixtures. Measurement and analysis in terms of group contributions

Molar excess enthalpies, H^E, at 303.15 K and atmospheric pressure, of n-propyl-, n-butyl-, n-pentyl-, n-octyl- or n-decylamine+toluene, as well as the isothermal vapour–liquid equilibria, VLE, of n-butylamine+toluene and of n-butylamine+benzene at 298.15 K have been determined. These experimental results, along with the data available in the literature on molar excess Gibbs energies, G^E, activity coefficients at infinite dilution, γ_i^∞, and molar excess enthalpies, H^E, for n-alkylamine+toluene mixtures are examined on the basis of the DISQUAC group contribution model. The modified UNIFAC is also used to describe the mixtures.     

Experimental standard molar enthalpies of formation of crystalline 3,5-dimethylpyrazole, 3,5-dimethyl-4-nitrosopyrazole, 1,3,5-trimethyl-4-nitrosopyrazole,and 3,5-dimethyl-1-phenyl-4-nitrosopyrazole

The standard (p^o =  0.1 MPa) molar enthalpies of combustion in oxygen, at T =  298.15 K, for crystalline 3,5-dimethylpyrazole (Me₂Pyr), 3,5-dimethyl-4-nitrosopyrazole (Me₂PyrNO), 1,3,5-trimethyl-4-nitrosopyrazole (Me₃PyrNO), and 3,5-dimethyl-1-phenyl-4-nitrosopyrazole (Me₂PhPyrNO) were measured by static-bomb calorimetry. These values were used to derive the standard molar enthalpies of formation of the crystalline compounds. The standard molar enthalpies of sublimation for these four compounds were measured by microcalorimetry.The experimental results obtained allow us to derive the values of the standard molar enthalpies of formation, in the gaseous state, for the monomeric compounds involved in this work. These last values are discussed comparatively with results previously obtained for some aromatic nitroso derivatives.     

Interactions of Peptides and Lysozyme with Aqueous Tetraethylammonium Bromide at 298.15 K

The apparent molar volumes, V _{ø, 2}, of gly-leu, gly-gly-leu and the partial specific volume ν^° of hen-egg-white lysozyme have been determined in aqueous of TEAB solutions by density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volumes V _2,m ^o for the peptides in aqueous TEAB solutions and the standard partial molar volumes of transfer Δ_tr V _2,m ^o of the peptides from water to aqueous TEAB solutions. The results on Δ_tr V _2,m ^o of peptides from water to aqueous TEAB solutions have been interpreted in terms of ion-ion, ion-polar, hydrophilic-hydrophilic and hydrophobic-hydrophobic group interactions. In order to supplement this information, enthalpies of transfer of aqueous peptides from water to TEAB solution have been determined at 298.15 K using a VP-ITC titration calorimeter. The data on partial molar volumes and enthalpies of transfer have been discussed in light of various interactions operating in the ternary system of peptides, water and TEAB. The partial specific volume of transfer of lysozyme from water to aqueous TEAB solutions also indicates the predominance of hydrophobic interactions.     

The standard enthalpies of formation of alkoxy-NNO-azoxy compounds

The standard enthalpies of combustion Δ_c H ^o and formation Δ_f H ^o of seven alkoxy-NNO-azoxy compounds containing the-N⁺(O^?)=NO-characteristic group were determined by combustion in a calorimetric bomb in the atmosphere of oxygen. The contribution of this group to the Δ_f H ^o enthalpies of the substances studied was calculated. The Δ_f H ^o enthalpies found by the method of group contributions were in satisfactory agreement with experimental data.     

Thermochemical study of 2- and 3-alkyl substituted thiophenes

The standard (p ⁰=0.1 MPa) molar enthalpies of formation, in the condensed phase, of nine linear-alkyl substituted thiophenes, six in position 2- and three in position 3-, at T=298.15 K, were derived from the standard massic energies of combustion, in oxygen, to yield CO₂(g) and H₂SO₄·115H₂O(aq), measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of vaporization of these compounds were measured by high temperature Calvet Microcalorimetry, so their standard molar enthalpies of formation, in the gaseous phase, were derived. The results are discussed in terms of structural contributions to the energetics of the alkyl-substituted thiophenes, and empirical correlations are suggested for the estimation of the standard molar enthalpies of formation, at T=298.15 K, for 2- and 3-alkyl-substituted thiophenes, both in the condensed and in the gaseous phases.     

Ternary excess molar enthalpies for the mixtures of methanol and ethanol with tetrahydropyran or 1,4-dioxane at 298.15 K

Ternary excess molar enthalpies, H_m^E, at 298.15 K and atmospheric pressure measured by using a flow microcalorimeter are reported for the (methanol+ethanol+tetrahydropyran) and (methanol+ethanol+1,4-dioxane) mixtures. The pseudobinary excess molar enthalpies for all the systems are found to be positive over the entire range of compositions. The experimental results are correlated with a polynomial equation to estimate the coefficients and standard errors. The results have been compared with those calculated from a UNIQUAC associated solution model in terms of the self-association of alcohols as well as solvation between unlike alcohols and alcohols with tetrahydropyran or 1,4-dioxane. The association constants, solvation constants and optimally fitted binary parameters obtained solely from the pertinent binary correlation predict the ternary excess molar enthalpies with an excellent accuracy.     

Dissolution Properties of 3,6-Bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine in N-Methyl Pyrrolidone and Dimethyl Sulfoxide

The molar enthalpies of dissolution for 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz) were measured in N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) using an RD496-2000 Calvet microcalorimeter at 298.15 K under atmospheric pressure. Empirical formulae for the calculation of the molar enthalpies of dissolution (Δ_diss H), relative partial molar enthalpies (Δ_diss H _partial), and relative apparent molar enthalpies (Δ_diss H _apparent) were obtained from the experimental results of the dissolution processes of BTATz in NMP or DMSO. Furthermore, the corresponding kinetic equations describing the two dissolution processes are dα/dt = 10^?3.55(1 ? α)^0.57 for the dissolution of BTATz in NMP, and dα/dt = 10^?3.74(1 ? α)^0.63 for the dissolution of BTATz in DMSO, respectively.     

Relationships among strain energies of mono- and poly-cyclic cyclohexanoid molecules and strain of their component rings

The standard molar enthalpies of vaporizationΔ_l^gH_m^o of N -(hydroxyethyl)-piperazine, bis-piperidino-methane, 1,3,5-tri-methyl-hexahydro-s-triazine, and also the enthalpies of sublimation Δ_cr^gH_m^oofN,N^′ -di(hydroxyethyl)-piperazine, and hexamethylenetetramine were obtained from the temperature dependence of the vapor pressure measured in a flow system. The standard molar enthalpies of formationΔ_fH_m^o (l) at the temperatureT =  298.15 K were measured by means combustion calorimetry for bis-piperidino-methane and 1,3,5-tri-methyl-hexahydro-s-triazine. Strain enthalpies (ring-correction terms) of these cyclohexanoid molecules were derived from the experimental enthalpies of formation of the gaseous compounds. These experimental results, together with data available from the literature, provided a quantitative understanding of the interrelations of structure and energetics of a mono- and poly-cyclic cyclohexanoid molecules and strain of their component rings.     

Deintercalation and reintercalation energetics of ammoniated titanium disulfide

The deintercalation and reintercalation processes in ammoniated TiS₂ have been studied by thermogravimetric analysis, differential scanning calorimetry, vapor-pressure measurements, and powder X-ray diffraction. The enthalpies determined calorimetrically for complete NH₃ and NH⁺₄ deintercalation of (NH⁺₄)_0.24(NH₃)_0.23TiS^0.24−₂ are approximately 10.5 and 22 kcal/mole, respectively. These enthalpies are in good agreement with those reevaluated from a previous calorimetric study of ammoniated TaS₂. Ammonia vapor-pressure curves for deintercalation and reintercalation of (NH⁺₄)_0.24(NH₃)_y″TiS^0.24−₂ exhibit hysteresis, and the enthalpies for these reactions are estimated to be 15.5 and −13 kcal/mole, respectively. The absolute values of these enthalpies decrease progressively as NH₃ is deintercalated and then reintercalated. The structural changes that accompany these processes are relatively complex and involve at least two phases. Further structural studies are necessary to help elucidate the energetics of these intercalation compounds.     

Heat properties of Bu<Subscript>4</Subscript>NBr solutions in binary mixtures based on formamide

Heat effects of tetrabutylammonium bromide dissolution in mixtures of formamide with methanol and ethylene glycol at 25°C were determined. Partial molar enthalpies of the components of formamide-ethylene glycol mixtures at 25°C were measured by the calorimetric method, and the mixing enthalpies of this system were determined. Within the limits of the second approximation of the Debye-Hueckel theory the standard enthalpies of dissolution Δ_dis H ⁰ were calculated, and the enthalpies of Bu₄NBr transfer from formamide in its mixtures with water methanol and ethylene glycol were found on this basis. The enthalpy parameters of Bu₄NBr pair interactions with the components of the formamide-water, formamide-methanol, and formamide-ethylene glycol mixtures were calculated. The results obtained were compared with the data for the systems containing N-methylformamide and N,N-dimethylformamide.