The enthalpies and kinetic of dissolution of diterpenoid derivative—paclitaxel in aqueous NaCl solutions at 309.5 K

The enthalpies of dissolution of paclitaxel in normal saline were measured using a RD496-2000 Calvet Microcalorimeter at 309.65 K under atmospheric pressure. The differential enthalpy (Δ_dif H _m ) and molar enthalpy (Δ_sol H _m) of dissolution of paclitaxel innormal saline were determined. The corresponding kinetic equation described the dissolution process was elucidated to be dα/dt = 10^?3.57(1 ? a)^1.15. Moreover, the half-life, Δ_sol H _m , Δ_sol G _m and Δ_sol S _m of the dissolution process were also obtained. This work will provide a potential reference for the clinical application of paclitaxel.     

Thermochemical characteristics of interactions of DL-alanine in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol

The method of dissolution calorimetry was used to measure the integral enthalpy of dissolution ??_sol H ^m of DL-alanine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at a concentration of organic solvent up to 0.32 mole fraction. The standard dissolution enthalpy (??_sol H ⁰) and transport enthalpy of amino acids from water to mixed solvent (??_tr H ⁰) were calculated. The calculated enthalpy coefficients of pair interactions of the DL-alanine molecules with the polyol molecules are positive and less than these values for L-alanine. The effect of interactions of different types in solution and the structural features of biomolecules and co-solvents on the enthalpy of dissolution characteristics of amino acids were considered.     

Enthalpy characteristics of L-asparagine interaction with glycerol, ethylene glycol, and 1,2-propylene glycol in aqueous solutions

Integral dissolution enthalpies ??_sol H ^m of L-asparagine in the mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at the concentration of organic solvents up to 0.24 mole fraction were measured by the calorimetry method. The standard enthalpies of dissolution (??_sol H ⁰) and transport (??_tr H ⁰) of amino acids from water to the mixed solvents were derived. The calculated enthalpy coefficients of the molecule pair interactions of L-asparagine-cosolvent are positive, except for the amino acid-glycerol-water system. The data obtained are interpreted in terms of prevalence of different types of interactions in solution and effect of the cosolvent nature on the thermochemical characteristics of the L-asparagine dissolution.     

Dissolution properties of oxymatrine in citric acid solution

In this article, the enthalpy of dissolution for oxymatrine in 0.15 M citric acid solution is measured using a RD496-2000 Calvet Microcalorimeter at 36.5 °C under atmospheric pressure. The differential enthalpy (Δ _dif H _m) and molar enthalpy (Δ _sol H _m) were determined for oxymatrine dissolution in 0.15 M citric acid solution. On the basis of these experimental data and calculated results, the kinetic equation, half-life, Δ _sol H _m, Δ _sol G _m, and Δ _sol S _m of the dissolution process were also obtained.     

Dissolution properties of N-guanylurea dinitramide (GUDN) in dimethyl sulfoxide and N-methyl pyrrolidone

The enthalpies of dissolution of N-guanylurea dinitramide (GUDN) in dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP) were measured using an RD496-2000 Calvet microcalorimeter at 298.15 K under atmospheric pressure, respectively. Empirical formulae for the calculation of the enthalpy of dissolution (Δ_diss H), relative partial molar enthalpy (Δ_diss H _partial), and relative apparent molar enthalpy (Δ_diss H _apparent) were obtained from the experimental data of the dissolution processes of GUDN in DMSO and NMP. Furthermore, the corresponding kinetic equations describing the two dissolution processes were dα/dt = 10^?3.39(1 ? α)^0.70 for the dissolution of GUDN in DMSO, and dα/dt = 10^?4.06(1 ? α)^1.11 for the dissolution of GUDN in NMP.     

Saturation molalities and standard molar enthalpies of solution of cytidine(cr), hypoxanthine(cr), thymidine(cr), thymine(cr), uridine(cr), and xanthine(cr) in H2O(l)

Saturation molalities m(sat) in H₂O(l) have been measured for the substances cytidine(cr), hypoxanthine(cr), thymidine(cr), thymine(cr), uridine(cr), and xanthine(cr) by using h.p.l.c. The states of hydration were established by performing Karl-Fischer analyses on samples of these substances, which had been allowed to equilibrate with their respective aqueous saturated solutions for several days at T≈298 K and then dried with air at T≈296 K for ≈24 h. The crystalline forms of the substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Also, molar enthalpies of solution Δ_solH_m(cal) for these substances were measured by using an isoperibol solution calorimeter. A self-association (stacking) model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies L_φ for these substances. These γ and L_φ values were used to adjust the measured values of m(sat) and Δ_solH_m(cal) to the standard state and thus obtain values of the standard molar Gibbs free energy Δ_solG^∘_m and enthalpy changes Δ_solH_m^∘ for the dissolution reactions of these substances. The values of the pKs and of the standard molar enthalpies of the ionization reactions were also used to account for speciation of the substances in the calculations of Δ_solG_m^∘ and Δ_solH_m^∘. Values of standard molar enthalpies of formation Δ_fH_m^∘, standard molar Gibbs free energies of formation Δ_fG_m^∘, and standard partial molar entropies S_2,m^∘ for the aqueous species of hypoxanthine and xanthine were calculated. A detailed summary and comparison of thermodynamic results from the literature for these substances is presented.     

The solvation of L-serine in mixtures of water with some aprotic solvents at 298.15 K

The integral enthalpies of solution Δ_sol H ^m of L-serine in mixtures of water with acetonitrile, 1,4-dioxane, dimethylsulfoxide (DMSO), and acetone were measured by solution calorimetry at organic component concentrations up to 0.31 mole fractions. The standard enthalpies of solution (Δ_sol H°), transfer (Δ_tr H°), and solvation (Δ_solv H°) of L-serine from water into mixed solvents were calculated. The dependences of Δ_sol H°, Δ_solv H°, and Δ_tr H° on the composition of aqueous-organic solvents contained extrema. The calculated enthalpy coefficients of pair interactions of the amino acid with cosolvent molecules were positive and increased in the series acetonitrile, 1,4-dioxane, DMSO, acetone. The results obtained were interpreted from the point of view of various types of interactions in solutions and the influence of the nature of organic solvents on the thermochemical characteristics of solutions.     

Saturation molalities and standard molar enthalpies of solution of adenosine(cr), guanosine · 2H2O(cr), inosine(cr), and xanthosine · 2H2O(cr) in H2O(l)

Saturation molalities m(sat) in H₂O(l) have been measured for the substances adenosine(cr), guanosine · 2H₂O(cr), inosine(cr), and xanthosine · 2H₂O(cr) over the temperature range T=287.91 K to T=308.18 K by using h.p.l.c. The indicated states of hydration of these substances were established by performing Karl–Fischer analyses of samples of these substances which had been equilibrated over H₂O(l) and of samples obtained by passing air over the wet crystals (air dried samples). The crystalline phases of these substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Molar enthalpies of solution Δ_solH_m for adenosine(cr) and inosine(cr) were measured by using an isoperibol solution calorimeter. A “stacking” or “self-association” model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies L_φ for these substances. These γ and L_φ values were used to adjust the measured values of m(sat) and Δ_solH_m to the standard state and obtain values of the standard molar Gibbs free energy and enthalpy changes Δ_solG^∘_m and Δ_solH^∘_m, respectively, for the dissolution reactions of these substances. Values of Δ_solH^∘_m calculated from the temperature dependence of values of Δ_solG^∘_m were in good agreement with the values of Δ_solH^∘_m obtained by using calorimetry.     

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.     

Thermodynamic properties of laburnine in saline and glucose solutions

Laburnine’s dissolution behaviors in glucose and saline solution were studied by a micro-calorimetry method. The measured integral and differential heats of solution were utilized to build equations of the solute and the heat, so that dissolution thermodynamic equations and half-time periods, Δ_sol H _m, Δ_sol G _m, and Δ_sol S _m were obtained. The results show that this study does not only provide a simple method for the determination of the half-life period for a drug but also offer a theoretical reference for the clinical application of laburnine.     

Enthalpy pair coefficients of interaction for DL-valine in aqueous solutions of polyatomic alcohols at 298 K

Integral enthalpies of dissolution Δ_sol H ^m of DL-valine are measured via calorimetry of dissolution in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol. Standard values of the enthalpies of dissolution (Δ_sol H ^○) and transfer (Δ_tr H ^○) of amino acid from water to mixed solvent are calculated from the resulting experimental data. The enthalpy coefficients for pair interactions h_xy of amino acid with polyatomic alcohol molecules are calculated using the McMillan-Meyer theory and have positive values. The obtained results are discussed in light of the theory of the predomination of various types of interactions in mixed solutions and the effect of structural features of interacting biomolecules on the thermochemical parameters of the dissolution of amino acids.     

Thermochemistry of aqueous solutions of nucleic acid bases and their alkylated derivatives

Enthalpy of solution, ΔH _sol ^o , enthalpy of sublimation, ΔH _subl ^o , apparent partial molar volume and heat capacities,V ₂ ^o andC _p,2 ^o were determined for aqueous solutions of thirty alkylated derivatives of uracyl and adenine, eight derivatives of cytosine and guanine. Calculated accessible surface areas and molar volumes are presented, too. The values of enthalpy of solution, enthalpy of sublimation can be useful in the studies on the nature of interaction between these compounds and water molecules. Apparent partial molar volume and heat capacity give a new aspect on hydrophob properties of the examined nucleic acid base derivatives.     

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     

Enthalpy characteristics of dissolution of <Emphasis Type="SmallCaps">l</Emphasis>-cysteine and <Emphasis Type="SmallCaps">l</Emphasis>-asparagine in aqueous solutions of acetonitrile and dimethyl sulfoxide at 298.15 K

The integral enthalpies of dissolution Δ_sol H ^m of l-cysteine and l-asparagine in mixtures of water with acetonitrile and dimethyl sulfoxide at the concentration of organic solvent up to 0.32 molar fractions were measured by means of dissolution calorimetry. The standard enthalpies of dissolution (Δ_sol H°) and transfer (Δ_trans H°) of the amino acids from water to a mixed solvent were calculated. The enthalpy coefficients of pair interactions for L-cysteine and L-asparagine with cosolvent molecules are positive, except for the L-asparagine-water-acetonitrile system. The concepts on the prevailing effect of specific interactions in solutions and the influence of the nature of the cosolvents and lateral substituents of the amino acids on the thermochemical characteristics of dissolution were used to explain the data obtained.     

Critical micelle concentration and self-aggregation of hexadecyltrimethylammonium bromide in aqueous glycine and glycylglycine solutions at different temperatures

Conductivities, densities and ultrasonic speeds measurements of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions of glycine (Gly) and glycylglycine (Gly-Gly) have been made at various temperatures. The critical micelle concentration (CMC), the degree of ionization (??) of the micelles, standard free energy, enthalpy, and entropy of the micellization process (??G _m ^° , ??H _m ^° , and ??S _m ^° ) for the present systems were estimated at different temperatures. The CMC values of HTAB in aqueous Gly and Gly-Gly were also evaluated by density and ultrasonic speed measurements. Apparent molar volumes, (V _?), apparent molar volumes at infinite dilution, (V _? ^° ), apparent molar compressibilities, (K _?), of HTAB in the pre- and post-micellar regions, and volume change on micellization (??V _? ^m ) were also estimated. Large positive values of T??S _m ^° and small negative values of ??H _m ^° suggest that micellization process is driven primarily by entropy increase. The increase in ??V _? ^m and K _? with rise in temperature is indicative of less compact micellar structure of HTAB in presence of amino acid additives. These data suggest that amino acids are solubilised probably in the palisade layer of the micelle.     

Energetics of the molecular interactions of L-alanine and L-serine with xylitol, D-sorbitol, and D-mannitol in aqueous solutions at 298.15 K

Integral enthalpies of dissolution Δ_sol H ^m of L-alanine and L-serine are measured via the calorimetry of dissolution in aqueous solutions of xylitol, D-sorbitol, and D-mannitol. Standard enthalpies of dissolution (Δ_sol H ^○) and the transfer (Δ_tr H ^○) of amino acids from water to binary solvent are calculated from the experimental data. Using the McMillan-Mayer theory, enthalpy coefficients of pairwise interactions h _xy of amino acids with molecules of polyols are calculated that are negative. The obtained results are discussed within the theory of the prevalence of different types of interactions in mixed solutions and the effect of the structural features of interacting biomolecules on the thermochemical parameters of dissolution of amino acids.     

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.     

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).     

Effect of the composition of a solution on the enthalpies of solvation of piperidine in methanol-acetonitrile and dimethylsulfoxide-acetonitrile mixed solvents

Heat effects of dissolution of piperidine (ppd) are measured by calorimetry at 298.15 K over the range of composition of acetonitrile-methanol (AN-MeOH) mixed solvents. Based on the Δ_sol H ^○(ppd)_AN-MeOH values obtained using the literature data on Δ_sol H ^○ (ppd) in acetonitrile-dimethylsulfoxide (AN-DMSO) mixed solvents and the vaporization enthalpy of ppd, the enthalpies of solvation of amine in AN-MeOH and AN-DMSO binary mixtures are calculated. A rise in the exothermicity of solvation of piperidine is observed upon the transition from AN to DMSO and MeOH, due mainly to the enhanced solvation of the amino group of ppd as a result of changes in the acid-base properties of the mixed solvent.     

Thermochemical properties of RE (Gly)4 Im (ClO4) 3 2H2O (RE = La,Pr, Nd,Sm, Eu)

The enthalpies of solution in water for five new light rare earth ternary complexes RE(Gly)₄Im(ClO₄)₃ 2H₂O (RE = La, Pr, Nd, Sm, Eu; Gly‐glycine; Im‐imidazole) were measured by means of a Calvet microcalorimeter. The empirical formula of enthalpy of solution (Δ_solH), relative apparent molar enthalpy (πL_i), relative partial molar enthalpy (L_i) and enthalpy of dilution (Δ_dllH_1,2) were drawn up by the data of enthalpies of solution of these complexes. From three plots of the values of standard enthalpy of solution Δ_sol H?, πL_i, L_i) versus the values of ionic radius (r) of the light rare earth elements, the grouping effect of lanthanide was observed, showing that the coordination bond between rare earth ion and ligand possesses a certain extent of the property of a covalent bond. The standard enthalpies of solution in water of similar complexes, Ce(Gly)₄Im(ClO₄)₃.2H₂O were estimated according to the plot of Δ_solH?, versus r.