Standard Molar Gibbs Energy Research Articles

Thermodynamic Properties of Moldy-Musty Contaminants of Wine

This paper reports thermodynamic properties of phase transitions of 2,4,6-trichloro and 2,4,6-tribromo anisoles and of 2,4,6-tribromophenol. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of the three compounds were measured, respectively, in the temperature ranges T = (297.1 to 368.3) K, T = (330.7 to 391.7) K, and T = (336.5 to 401.7) K, using a static method based on capacitance diaphragm manometers. Moreover, the sublimation vapor pressures of 2,4,6-tribromophenol were also measured in the temperature interval (307.2 to 329.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies, and Gibbs energies of sublimation and of vaporization, at reference temperatures, were derived from the experimental results as well as the (p,T) values of the triple point of each compound. The temperatures and molar enthalpies of fusion of the three benzene derivatives were determined using differential scanning calorimetry and were compared with...

Interaction of aloe active compounds with calf thymus DNA.

Natural anthraquinone compounds have emerged as potent anticancer chemotherapeutic agents because of their promising DNA-binding properties. Aloe vera is among one of the very well-known medicinal plants, and the anthraquinone derivatives like aloe emodin (ALM), aloins (ALN), and aloe emodin-8-glucoside (ALMG) are known to have immense biological activities. Here, we have used biophysical methods to elucidate the comparative DNA-binding abilities of these three molecules. Steady-state fluorescence study indicated complexation between calf thymus DNA (ctDNA) and both the molecules ALM and ALMG whereas ALN showed very weak interaction with DNA. Displacement assays with ctDNA-bound intercalator (ethidium bromide) and a groove binder (Hoechst 33258) indicated preferential binding of both ALM and ALMG to minor groove of DNA. Isothermal titration calorimetric (ITC) data suggested spontaneous exothermic single binding mode of both the molecules: ALM and ALMG. Entropy is the most important factor which contributed to the standard molar Gibbs energy associated with relatively small favorable enthalpic contribution. The equilibrium constants of binding to ctDNA were (6.02±0.10)×104 M-1 and (4.90±0.11)×104 M-1 at 298.15K, for ALM and ALMG, respectively. The enthalpy vs temperature plot yielded negative standard molar heat capacity value, and a strong negative correlation between enthalpy and entropy terms was observed which indicates the enthalpy entropy compensation behavior in both systems. All these thermodynamic phenomena indicate that hydrophobic force is the key factor which is involved in the binding process. Moreover, the enhancement of thermal stability of DNA helix by ALM and ALMG fully agreed to the complexation of these molecules with DNA.

Solubility of acetaminophen in 1-propanol + water mixtures at T = 293.2–313.2 K

ABSTRACT The mole fraction solubilities of acetaminophen (ACP) were measured in the binary solvent mixtures of {1-propanol + water} at T = 293.2–313.2 K. The Jouyban–Acree, Jouyban–Acree–van’t Hoff, combined nearly ideal binary solvent/Redlich–Kister (CNIBS/R-K) and modified Wilson models as well as a non-linear model presented by Machatha et al. were used to correlate the measured equilibrium solubilities. Furthermore, the experimental data were predicted with five predictive models, i.e. Yalkowsky, extended Yalkowsky as well as trained versions of Yalkowsky, Jouyban–Acree and Jouyban–Acree–Hansen models. Moreover, the apparent standard molar Gibbs energy, enthalpy, and entropy of dissolution and mixing (, , , , , ) of ACP in {1-propanol (1) + water (2)} mixtures were calculated at mean harmonic temperature T hm = 303 K based on van’t Hoff and Gibbs free energy equations. Additionally, preferential solvation parameters of ACP in the mixtures were also analysed based on the inverse Kirkwood–Buff integrals.

Determination of thermodynamic properties of the ternary oxides in the Y-Ru-O system by electromotive force measurements and differential scanning calorimetric measurements

In this study, the standard molar Gibbs energy of formation of Y2Ru2O7(s) and Y3RuO7(s) was determined using calcia-stabilized zirconia (CSZ) as an electrolyte and air as a reference electrode. The cells can be represented by: (−)Pt/{Y2O3(s) + Y2Ru2O7(s) + Ru(s)}//CSZ//O2(p(O2) = 21.21 kPa)/Pt(+), (−)Pt/{Y3RuO7(s) + Y2Ru2O7(s) + Y2O3(s)}//CSZ//O2(p(O2) = 21.21kPa)/Pt(+). The electromotive force was measured in the temperature range from 981 to 1155 K and 932 to 1186 K, respectively. The standard molar Gibbs energy of formation of Y2Ru2O7(s) and Y3RuO7(s) from elements in their standard state was calculated by the least squares regression analysis of the data obtained in the present study and can be given, respectively, by: {ΔfG(Y2Ru2O7, s)/(kJmol−1) ± 2.22} = − 2554.1 + 0.625 ⋅ (T/K) and {ΔfG(Y3RuO7, s)/(kJmol−1) ± 2.45} = − 3249.5 + 0.635 ⋅ (T/K). The standard molar heat capacity Cop,m(T) of Y2Ru2O7(s) was measured using a heat flux–type differential scanning calorimeter (DSC) in the temperature range, from 307 to 780 K. The heat capacity was fitted into a mathematical expression and can be represented by: Cp, m(Y2Ru2O7, s, T)(JK−1mol−1) = 256.1 + 5.88 ∙ 10−2T(K) − 34.75 ∙ 105/T2(K). (307 ≤ T (K) ≤ 780). The heat capacity of Y2Ru2O7(s) was used along with the data obtained from the electrochemical cell to determine its decomposition temperature and stability in air and to calculate other thermodynamic parameters.

Thermodynamic properties of Pr7O12

To explore the potential of Pr7O12 in a biphasic oxygen buffer in automobile exhaust control systems, thermodynamic data for Pr7O12 are required. Since there is no information on Pr7O12 in thermodynamic data compilations, its Gibbs energy of formation has been determined relative to that of Pr2O3 as a function of temperature in the range from 850 to 1200 K using a solid-state electrochemical technique. The standard molar Gibbs energy of formation of Pr7O12 from elements can be represented by two equations. In the range from 850 to 1068 K, ΔGf°Jmol-1=-6454317+1085.52T/K. From 1068 to 1204 K, ΔGf°Jmol-1=-6467695+1097.77T/K.

Lamotrigine solubility in 1-propanol + water mixtures at different temperatures: experimental data and mathematical modelling

ABSTRACT The solubility of lamotrigine (LTG) was determined in {1-propanol (1) + water (2)} mixtures over a temperature range of 293.15 to 313.15 K. The measured data were correlated to cosolvency models namely Jouyban-Acree, Jouyban-Acree-van’t Hoff, combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K), modified Wilson and Machatha models. Among the models, Jouyban-Acree with temperature and solvent composition dependencies has more accuracy rather than Jouyban-Acree-van’t Hoff model and CNIBS/R-K model with solvent composition dependency is more compatible with the experimental solubility data. Furthermore, the apparent standard molar Gibbs energy, entropy, and enthalpy of dissolution and mixing , , , , and for LTG in the studied binary mixtures were calculated based on the van’t Hoff and Gibbs free energy equations which suggest that the dissolution process is more favourable in 1-propanol-rich mixtures and proceeds entropically. Finally, preferential solvation parameters of LTG by 1-propanol were also calculated by means of the inverse Kirkwood-Buff integrals.

Preparation of Nano‐bismuth with Different Particle Sizes and the Size Dependent Electrochemical Thermodynamics

AbstractNano‐bismuth has excellent electrochemical properties. However, it is still unclear how the particle size of nano‐bismuth influences its electrochemical thermodynamic properties. In this paper, spherical bismuth nanoparticles with different particle sizes were prepared by solvothermal method; the electrode potentials, the temperature coefficients of the electrode potentials and the thermodynamic functions of reaction for nano‐bismuth electrodes with different particle sizes at different temperatures were determined; and the effects of particle size on the electrode potential, the temperature coefficient and the thermodynamic functions were discussed. The experimental results show that particle size of bismuth nanoparticles has a significant influences on the electrochemical thermodynamic properties. The standard electrode potential of the nano‐bismuth electrode with a diameter of 39.9 nm was 0.009 V lower than that of the ordinary standard electrode (0.308 V); the temperature coefficient of the electrode potential with a diameter of 39.9 nm was nearly double that of 85.9 nm. With the particle sizes decrease, the standard molar Gibbs energy of reaction, the standard molar enthalpy of reaction, the standard molar entropy of reaction, the molar reversible reaction heat and the temperature coefficient increase; and these quantities are linearly related to the reciprocal of the particle diameter.

Effect of Molecular Composition of Head Group and Temperature on Micellar Properties of Ionic Surfactants with C12 Alkyl Chain

The paper analyses influences of the temperature and hydrophilic groups on micellar properties of ionic surfactants with 12-carbonic hydrophobic chains. The aim is to assess the impact of hydrophilic groups and temperature on thermodynamic parameters and micellization. This knowledge is indispensable for the formulation of new dosage forms. The method uses conductometric measurements. The following hydrophilic groups are analyzed: trimethylammonium bromide, trimethylammonium chloride, ethyldimethylammonium bromide, didodecyldimethylammonium bromide, pyridinium chloride, benzyldimethyl-ammonium chloride, methylephedrinium bromide, cis and trans-[(2-benzyloxy)-cyclohexyl-methyl]-N, N-dimethylammonium bromide, sodium sulphate and lithium sulphate. Except for a few cases, there is a good agreement between values of critical micellar concentrations (CMC) and critical vesicle concentration (CVC) obtained here and those which were obtained by other authors and/or by other physicochemical methods. Values of the CMC are compared with respect to the molar masses of hydrophilic groups. It was found that CMC values increased non-linearly with increasing system temperature. The degrees of counterion binding and thermodynamic parameters, like the standard molar Gibbs energy, enthalpy and entropy of micellization are determined and discussed in detail. The results obtained will be incorporated into in silico processes of modeling and design of optimal dosage forms, a current interdisciplinary research focus of the team.

A calorimetric characterization of the interaction of quinacrine with poly(I).poly(C) and its comparison to proflavine

Thermodynamics of the interaction of quinacrine with poly(I).poly(C) was studied in comparison to proflavine using microcalorimetry. Isothermal titration calorimetry results suggested that the binding of quinacrine to poly(I).poly(C) was enthalpy dominated with a smaller but favourable entropic contribution at 298.15 K. For proflavine, the binding was predominantly entropy dominated at 298.15 K. The equilibrium constant for quinacrine-poly(I).poly(C) complexation was calculated to be (5.11 ± 0.88)·105 M−1 while for proflavine the equilibrium constant was (3.45 ± 0.85)·105 M−1 at 298.15 K. With increasing temperature the equilibrium constant decreased, the standard molar enthalpic contribution increased in magnitude, the positive standard molar entropic contribution decreased while standard molar Gibbs energy remained almost invariant for both the systems. An enthalpy-entropy compensation phenomenon was observed for the complexation of both quinacrine and proflavine with poly(I).poly(C). Negative standard molar heat capacity values were also observed for the complexation of both quinacrine and proflavine with poly(I).poly(C) which suggested the involvement of hydrophobic forces in the binding reaction. Salt dependent calorimetric data and the dissection of the standard molar Gibbs energy suggested the involvement of a dominant non-electrostatic component in the binding reaction for both quinacrine and proflavine.

Thermodynamic stability of CaThF6(cr) by transpiration and e.m.f. techniques

In the present paper, we report the standard molar Gibbs energy of formation for CaThF6 measured by gas equilibration and e.m.f. methods. The HF(g) vapour pressure over the equilibrium reaction: $${\text{CaThF}}_{6} \left( {\text{cr}} \right) + 2 {\text{H}}_{ 2} {\text{O}}\left( {\text{g}} \right) = {\text{CaF}}_{2} \left( {\text{cr}} \right) + {\text{ThO}}_{2} \left( {\text{cr}} \right) + 4{\text{HF}}\left( {\text{g}} \right)$$ has been measured using transpiration technique. The above reaction mechanism has been established employing TG and XRD techniques. A fluoride e.m.f. cell: (−)Pt, CaF2(cr) + ThOF2(cr) + CaThF6(cr) |CaF2(cr)| NiO(cr) + NiF2(cr), Pt(+) has been constructed to measure Gibbs energy of formation of CaThF6 (cr) using CaF2 (cr) as a solid electrolyte. The isobaric heat capacity $${\text{Cp}}_{\text{m}}^{{\circ }} \left( T \right)$$ of the compound has been measured using differential scanning calorimetric technique. Based on the experimental results, thermodynamic functions for CaThF6 have been generated.

Thermodynamic properties of phase transitions of phenyl derivatives of maleic anhydride and oxazole

An experimental study of the vapour pressures and related thermodynamic properties of three phenyl derivatives of maleic anhydride and oxazole is reported. The vapour pressures of the crystalline phase of these compounds were measured at different temperatures using the Knudsen mass-loss effusion method, enabling the determination of the standard (p° = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation. The enthalpies and temperatures of fusion were determined from DSC experiments. Quantum chemical calculations were used to calculate gas-phase isobaric heat capacities and absolute entropies.

Differential scanning calorimetric measurements and thermodynamic functions of YbRhO3(s)

Abstract

Determination of the thermodynamic properties of the Li2CaThF8 in Li-Ca-Th-F system by the solid-state electrochemical cell method

In the present paper, we have reported the standard molar Gibbs energy of formation for Li2CaThF8(s) measured by solid electrolyte galvanic cell technique with CaF2 as solid electrolyte. The heat capacity, Cp, of the compound has been measured using the differential scanning calorimetric technique. Based on the experimentally obtained thermodynamic parameters, thermodynamic functions for Li2CaThF8(s) have been generated.

Thermodynamics on the Bi-Fe-Ti System and the Gibbs Energy of Bi9Ti8

Partial isothermal sections of the Bi-Fe-Ti system at 700 °C and 900 °C were constructed to investigate the reactivity of Fe with Bi-Ti liquid alloy. In the ternary system, three-phase equilibria such as liquid-Fe-Fe2Ti, liquid-Fe2Ti-Bi2FeTi4, and liquid-Bi9Ti8-Bi2FeTi4 were confirmed at both temperatures. The solubility of Fe in liquid Bi at these temperatures is negligibly small. On the other hand, it is notable that the solubility of Fe in liquid Bi containing Ti at 900 °C is much larger and reaches 2.3 mol pct. Then, we measured the electromotive force (emf) between Bi-20 mol pct Ti alloy and pure Ti at 700 °C in equimolar NaCl-KCl where 1 mol pct TiCl2 was added. From the result, the interaction parameter of the liquid phase in the Bi-Ti system and the standard molar Gibbs energies of formation of Bi9Ti8 and Bi2FeTi4 at 700 °C were estimated.

Vapour pressures and thermodynamic stability of the three aminophenol isomers

The Knudsen mass-loss effusion method was used to determine the sublimation vapour pressures, at different temperatures, of ortho and para aminophenols in the temperature intervals T = (321.1 to 343.3) K and T = (337.2 to 359.2) K, respectively. The vapour pressures of crystalline meta-aminophenol were measured using the referred to above technique, between (321.4 and 343.3) K, and a static method, based on capacitance diaphragm manometers, between (354.4 and 391.8) K. The latter technique was also used to measure the liquid vapour pressures of this isomer over the temperature range T = (370.0 to 423.3) K. The experimental results enabled the determination of the standard (po = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the three compounds, and of vaporization of the meta isomer. The standard enthalpies of formation in the gaseous phase were calculated using quantum chemical calculations and also by combining literature results of enthalpies of formation in the crystalline phase with the sublimation enthalpies results determined in this work. Gas-phase absolute entropies and heat capacities of the three compounds studied were also calculated using theoretical methods. The standard Gibbs energies of formation in crystalline and gaseous phases were determined and used to evaluate the thermodynamic stability of the three isomers in standard conditions. DSC analysis enabled the determination of the temperature and molar enthalpies of fusion of the compounds studied.

Volatility and thermodynamic stability of vanillin

Vanillin is a naturally occurring phenolic aldehyde that is world-wide known for its flavouring properties. This work reports an extensive experimental and computational study of its thermodynamic properties. The vapour pressures of crystalline and liquid phases of vanillin were measured in the following temperature ranges T = (321.0–350.7) K and (324.9–382.3) K respectively, using a static method based on diaphragm capacitance gauge. Additionally, the crystalline vapour pressures were also measured in the temperature interval T = (303.1–325.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization, at selected reference temperatures, were derived from the vapour pressure measurements. The enthalpies of vaporization and of sublimation, at T = 298.15 K, were also determined using Calvet microcalorimetry and the standard (p° = 105 Pa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, was calculated and compared with the values estimated by employing quantum chemical calculations. To analyse the thermodynamic stability of vanillin, the standard Gibbs energies of formation in crystalline and gaseous phases were calculated. The molar enthalpy of fusion determined using DSC is compared with indirect results determined using Calvet microcalorimetry and vapour pressure measurements.

Thermodynamic investigation of Hoechst 33258-poly(A).poly(U) binding through calorimetric studies

Abstract Interaction of the important minor groove binder Hoechst 33258 with poly(A).poly(U) was studied using isothermal titration calorimetry. The equilibrium constant of the association was calculated to be (4.00 ± 0.80) 106 M−1 at 298.15 K. The Hoechst RNA binding was driven by large negative enthalpy contributions. The equilibrium constant values for the binding reaction decreased with increasing [Na+] concentration. Parsing of the standard molar Gibbs energy change revealed that non-polyelectrolytic forces dominated the complexation process at all the salt concentrations studied. Temperature dependent calorimetric studies revealed that the equilibrium constant decreased in magnitude with increasing temperature in the range (288.15 ± 0.10)–(308.15 ± 0.10) K. Furthermore, there were significant alterations in the thermodynamic parameters with change in temperature; the binding became increasingly enthalpy driven and the standard molar entropic contribution decreased in magnitude and became unfavourable as the temperature was increased. Negative heat capacity change and an enthalpy-entropy compensation phenomenon were also observed. The data observed may be useful for developing structure selective RNA-based therapeutics.

Thermodynamic investigation of NaF-ThF4 system and fuel salts of Molten Salt Reactor

The standard molar Gibbs energy of formation of Na2ThF6(s) has been determined using an e.m.f. technique. The fluoride cell: (-) Pt, NiO(s) + NiF2(s)│CaF2(s)│ThOF2(s)+ Na2ThF6(s) + NaF(s), Pt (+) has been constructed to measure Gibbs energy of formation of Na2ThF6(s) using CaF2(s) as solid electrolyte. From the measured e.m.f. values of the cell and required Gibbs energy values from the literature, ΔrG°m (Na2ThF6, s, T) has been calculated as: ΔfG°m (Na2ThF6, s, T) (kJ mol−1) ± 10 = − 3378 + 0.5296·(T/K) (700 K ≤ T ≤ 945 K). The heat capacity of Na2ThF6(s) was measured with Differential Scanning Calorimeter in the temperature range 300–800 K. The enthalpy of formation of Na2ThF6(s) at 298.15 K has been calculated by the second method from the measured Gibbs energy and heat capacity data. The chemical potential diagram of Na-Th-F-O system has been computed based on measured data in this study and required data from the literature. Based on the thermodynamic data, melting points and compositions of several potential salt mixtures have been suggested for Molten Salt Reactors.

Effect of size on dissolution thermodynamics of nanoparticles: A theoretical and experimental research

Dramatic differences in dissolution thermodynamics between nanoparticles and their bulk counterparts have been observed in which the particle size plays a crucial role. However, the quantitative influences of particle size on the dissolution thermodynamic properties of nanoparticles have not been systematically investigated. In this paper, the relations between dissolution equilibrium constant and dissolution thermodynamic functions with particle size were deduced by introducing the surface variables into the Gibbs function. Then the influence regularities of size on the dissolution equilibrium constant and the dissolution thermodynamic functions were obtained by measuring the solubilities of nano-Cu with different sizes in dilute acid at different temperatures. Theoretical analysis and experimental results reveal that with particle size decreasing, the dissolution equilibrium constant (Ko) increases, while the standard molar dissolution Gibbs energy (ΔrGmo), the standard molar dissolution enthalpy (ΔrHmo) and the standard molar dissolution entropy (ΔrSmo) decrease. Furthermore, when the diameter approaches or exceeds 20 nm, lnKo, ΔrGmo, ΔrHmo, and ΔrSmo present linear relations with the reciprocal of diameter, respectively.

Experimental data and thermodynamic modelling of gallic acid solubility in a variety of pure solvents

ABSTRACTThe solubility of gallic acid (GA) in butan-1-ol, butan-2-ol, hexan-1-ol, 1,4-dioxane, ethyl acetate, methyl acetate and cyclohexanone from 293.15 to 318.15 K has been experimentally measured using a thermostatted reactor and UV/vis spectrophotometer analysis. The results demonstrate that the solubility of GA generally increased with the temperature and at a given temperature decreased with the increase of the carbon number of alcohols. The van’t Hoff model, modified Apelblat equation, h equation and the Two Local composition models of Wilson and NRTL model were used to predict the reported solubilities, resulting in a mean relative deviation of 3.47%, 3.54%, 2.90%, 3.12% and 3.18%, respectively. The obtained data showed that the h equation model is the most suitable for description of the solid–liquid equilibrium containing GA. Furthermore, the standard molar Gibbs energy and standard molar enthalpy of dissolution of GA were estimated.