Standard Molar Gibbs Energy Research Articles

Calorimetric investigation on the interaction of proflavine with human telomeric G-quadruplex DNA

The interaction of an acridine dye, proflavine, with human telomeric G-quadruplex DNA was characterized by isothermal titration calorimetry and differential scanning calorimetry. The equilibrium constant of binding was deduced to be (1.36±0.09)·106M−1 at T=298.15K. The binding reaction was driven by both negative enthalpy and positive entropy contributions. The equilibrium constant decreased and the reaction became increasingly enthalpy driven with rise in temperature. However, the standard molar Gibbs energy change exhibited only marginal alterations suggesting the occurrence of enthalpy–entropy compensation. Negative heat capacity values were also obtained from the temperature dependence of enthalpy change. Parsing of the standard molar Gibbs energy using the salt dependent calorimetric data revealed that the binding was dominated by non-polyelectrolytic forces which remained virtually unaltered with changing salt concentration. Proflavine binding also significantly enhanced the thermal stability of G-quadruplex DNA against thermal unfolding.

A microcalorimetric study on the binding of proflavine with tRNAphe

The interaction of proflavine with tRNAphe was studied using isothermal titration calorimetry to gain insights into thermodynamics of the binding reaction. Isothermal titration calorimetric studies revealed the association to be exothermic and favored by both negative enthalpy and positive entropy changes. The equilibrium constant for the complexation process was calculated to be (2.85±0.09) 105M−1 at T=293.15K. The equilibrium constant decreased with increasing temperature suggesting that the complexation is less favored at higher temperatures. The standard molar enthalpic contribution enhanced in magnitude while the standard molar entropic contribution decreased with increasing temperature. The complexation was further characterized by negative standard molar heat capacity and (enthalpy+entropy) compensation. Salt dependent ITC studies and parsing of the standard molar Gibbs energy revealed that the complexation process was largely dominated by non-polyelectrolytic forces which remained almost unaltered at all the salt concentrations studied.

Studying the sublimation thermodynamics of ethionamide and pyridinecarbothioamide isomers by transpiration method

Temperature dependences of saturated vapor pressure for crystalline phases of 2-ethyl-4-pyridinecarbothioamide (ethionamide) and two parent compounds 2- and 4-pyridinecarbothioamide isomers were measured by the transpiration method. The results were used to determine the standard molar enthalpies, entropies and Gibbs energies of sublimation at T=298.15K. HYBOT descriptors application has shown an increase in the donor–acceptor ability of the molecules of the studied compounds to form hydrogen bonds to result in their crystal lattice energy growth. The obtained standard molar sublimation enthalpies have been compared with the literature results for 2- and 4-substituted pyridine isomers.

Size-Dependent Thermodynamic Properties of the Reaction of Nano-ZnO with Benzoic Acid

Studying the thermodynamic properties of the reaction of nanoparticle with organic substance is significant for the application of nanomaterial in organic fields. In this work, by using the reaction of nano- ZnO with different particle sizes with benzoic acid as a research system, the size-dependent standard equilibrium constant and reaction thermodynamic properties were analyzed theoretically, and the influence regularities of the particle size on the standard equilibrium constant and the reaction thermodynamic properties were studied. The excellent agreement between the experimental results and theoretical analysis shows that the particle size has remarkable influence on the standard equilibrium constant and the thermodynamic properties of the reaction; with the decrease of the particle size, the standard equilibrium constant increases, while the standard molar reaction Gibbs energy, the standard molar reaction enthalpy and the standard molar reaction entropy decrease. Furthermore, the logarithm of the standard equilibrium constant and the thermodynamic properties present linear relations with the reciprocal of the particle diameter, respectively. The theory and the influence regularities will provide useful tools to lead better and broader application of nanomaterial in organic fields.

The influence of the halogen atoms and acetyl group on vapour pressures and related properties of the p-haloacetophenones

This work reports experimental vapour pressures at different temperatures of four halogenated acetophenones. The liquid phase vapour pressures of p-fluoro and p-chloro acetophenones were measured, respectively, across the temperatures ranges (255.1 to 310.2)K and (271.6 to 335.0)K, using a static method based on capacitance diaphragm manometers. This experimental technique was also used to measure the vapour pressures of both (crystalline and liquid) condensed phases of p-bromo- and p-iodoacetophenones, respectively, through the temperature intervals (295.3 to 378.4)K and (313.1 to 402.0)K. The temperatures and molar enthalpies and entropies of fusion of the four p-halogenated acetophenones were determined using differential scanning calorimetry. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporisation, at selected reference temperatures, were derived from the experimental results. The contributions of the acetyl group and of the constituent halogen atoms to these thermodynamic properties were also predicted through correlation equations.

Study of di-hydrogen (Na; K or NH4) orthophosphates in aqueous solutions at temperatures from 298.15 K to 353.15 K

In this investigation, the thermodynamic properties of aqueous solutions Na, K or NH4 dihydrogenphosphate were determined at various temperatures ranging from 298.15 K to 353.15 K. The measurements of water activity were performed in the molality range from dilution to saturation using the hygrometric method. The modeling approach based on the ion interaction model was developed to determine the thermodynamic properties. From these measurements of phosphate salts, mixing parameters in binary solutions were evaluated at various temperatures, without considering formation of aqueous complexes. The osmotic and activity coefficients were determined for these aqueous solutions of orthophosphate salts. The measurements of the binary systems were combined with reference pure water, NaH2PO4(s), KH2PO4(s) and (NH4)H2PO4(s) solubility data to construct a chemical model that calculates solute and solvent activities from dilute to saturated solution concentration from 298.15 to 353.15 K respectively up to mmax(NaH2PO4(s)) = 7.90–18.29 mol kg−1; mmax(KH2PO4(s)) = 1.83–5.10 mol kg−1; and mmax((NH4)H2PO4(s)) = 4.93–12.62 mol kg−1. The thermodynamic characteristics, solubility products Ksp° and the standard molar Gibbs energy of dissolution ΔGdiss° were also given.

Vapor pressure and sublimation thermodynamics of aminobenzoic acid, nicotinic acid, and related amido-derivatives

The inert gas transpiration technique was used for measuring the vapor pressures of the following biologically active compounds: 4-aminobenzoic acid, nicotinic acid, 4-aminobenzamide, 4-pyridinecarboxamide, N-(2-chloro-3-pyridinyl)-benzenesulfonamide, 4-nitro-N-2-thiazolyl-benzenesulfonamide, and 4-amino-N-(5-methyl-3-isoxazolyl)-benzenesulfon-amide in the appropriate temperature ranges. Differential scanning calorimetric analysis was applied to obtain the temperature and molar enthalpy of melting of the compounds studied. Standard molar enthalpies, entropies, and Gibbs energies of sublimation were derived at T = 298.15 K from the temperature dependences of the vapor pressure of the compounds. The obtained results allowed the estimation of the relationship between the sublimation thermodynamic parameters and the thermophysical properties of the substances. Correlation equations were used for calculating the saturated vapor pressures on the basis of the melting temperatures, sublimation enthalpies, and physicochemical HYBOT descriptors.

Studies on the interaction of the food colorant tartrazine with double stranded deoxyribonucleic acid

Interaction of the food additive tartrazine with double-stranded DNA was studied by spectroscopic and calorimetric techniques. Absorbance studies revealed that tartrazine exhibited hypochromism in the presence of DNA without any bathochromic effects. Minor groove displacement assay of DAPI and Hoechst 33258 suggested that tartrazine binds in the minor groove of DNA. The complexation was predominantly entropy driven with a smaller but favorable enthalpic contribution to the standard molar Gibbs energy. The equilibrium constant was evaluated to be (3.68 ± .08) × 104 M−1 at 298.15 K. The negative standard molar heat capacity value along with an enthalpy–entropy compensation phenomenon proposed the involvement of dominant hydrophobic forces in the binding process. Tartrazine enhanced the thermal stability of DNA by 7.53 K under saturation conditions.

Measurement and Correlation of the Solubility for 4,4′-Diaminodiphenylmethane in Different Solvents

In this experiment, the solubility data of 4,4′-diaminodiphenylmethane in different pure solvents, including methanol, ethanol, 2-propanol, 1-butanol, toluene, chloroform, and benzene, were measured by a synthetic method from (293.15 to 333.15) K at atmospheric pressure. It is indicated that the solubility of 4,4′-diaminodiphenylmethane in each solvent increases with increasing temperature. The modified Apelblat, λh, and van’t Hoff equations were employed to correlate experimental solubility data, and each selected correlation equation could give a good fitting result of the relationship between solubility and temperature. The modified Apelblat equation shows the best agreement, in general. Furthermore, the standard molar enthalpy, standard molar Gibbs energy, and standard molar entropy of 4,4′-diaminodiphenylmethane in the dissolution process were calculated based on the van’t Hoff analysis and Gibbs equation.

Thermodynamic investigations of oxyfluoride of thorium and uranium

The standard molar Gibbs energy of formation of ThOF2(s) and UO2F2(s) has been determined using an e.m.f. technique. For this purpose, separate fluoride cell has been constructed using CaF2(s) as the solid electrolyte. From the measured e.m.f. values and required Gibbs energy data available in the literature, ΔfGom(T) for these oxyfluorides has been calculated. The enthalpy of formation of ThOF2(s) and UO2F2(s) at 298.15 K has been calculated from the experimentally measured Gibbs energy data using the second and the third law methods. To determine the stability domains of ThOF2(s) and UO2F2(s), the phase diagram and chemical potential diagrams of Th–F–O and U–F–O systems were calculated by the CALPHAD method and FactSage software. These calculations can be used to predict the oxygen partial pressures and the temperature domains in which thorium and uranium oxyfluorides might be formed in the molten salt medium.

Solubilities of Phosphoramidic Acid, N-(phenylmethyl)-, Diphenyl Ester in Selected Solvents

Phosphoramidic acid, N-(phenylmethyl)-, diphenyl ester (PANDE) was synthesized, and its thermostability was measured by thermogravimetric analysis. The melting temperature and the fusion enthalpy of PANDE were evaluated by a differential scanning calorimeter. The solubilities of PANDE in chloroform, tertrahydrofuran, dichloromethane, acetone, methyl acetate, ethyl acetate, acetonitrile, methanol, and toluene were measured by a gravimetric method at different temperatures. The solubilities of PANDE in different solvents at low temperatures are in the order of chloroform > tetrahydrofuran > dichloromethane > acetone > methyl acetate > ethyl acetate > acetonitrile > methanol > toluene. At higher temperatures the order is the same except that acetonitrile now becomes the least soluble. The solubility data of PANDE in nine selected solvents were well fitted by the Wilson, nonrandom two-liquid (NRTL), and universal quasichemical equations. The Wilson model and the NRTL model show better agreement in general. Finally, the solubility parameters of PANDE were evaluated by the Scatchard–Hildebrand model, and meanwhile, the standard dissolution enthalpy, the standard dissolution entropy, and the standard molar Gibbs energy of PANDE in the selected solvents were also calculated by the van’t Hoff model and the Gibbs–Helmholtz equation. The results show that the dissolution process is endothermic and entropy-driven.

Thermodynamic properties of bromine fluorene derivatives: An experimental and computational study

This report presents a comprehensive experimental and computational study of the thermodynamic properties of two bromine fluorene derivatives: 2-bromofluorene and 2,7-dibromofluorene. The standard (p°=0.1MPa) molar enthalpies of formation in the crystalline phase of these compounds were derived from the standard molar energies of combustion, in oxygen, at T=298.15K, measured by rotating bomb combustion calorimetry. The vapour pressures of the crystalline phase of the two compounds were measured using the Knudsen effusion method and a static method that has also been used to measure the liquid vapour pressures of 2-bromofluorene. From these results the standard molar enthalpies, entropies and Gibbs energies of sublimation of the two compounds studied and of vapourisation of 2-bromofluorene were derived. The enthalpies and temperatures of fusion were determined from DSC experiments. Derived results of standard enthalpies and Gibbs energies of formation, in both gaseous and crystalline phases, were compared with the ones reported in the literature for fluorene.The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates based on density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with the 6-311++G(d,p) basis set.

Microcalorimetry and spectroscopic studies on the binding of dye janus green blue to deoxyribonucleic acid

The interaction of the phenazinium dye janus green blue (JGB) with deoxyribonucleic acid was investigated using isothermal titration calorimetry and thermal melting experiments. The calorimetric data were supplemented by spectroscopic studies. Calorimetry results suggested the binding affinity of the dye to DNA to be of the order of 105 M−1. The binding was predominantly entropy driven with a small negative favorable enthalpy contribution to the standard molar Gibbs energy change. The binding became weaker as the temperature and salt concentration was raised. The temperature dependence of the standard molar enthalpy changes yielded negative values of standard molar heat capacity change for the complexation revealing substantial hydrophobic contribution in the DNA binding. An enthalpy–entropy compensation behavior was also observed in the system. The salt dependence of the binding yielded the release of 0.69 number of cations on binding of each dye molecule. The non-polyelectrolytic contribution was found to be the predominant force in the binding interaction. Thermal melting studies revealed that the DNA helix was stabilized against denaturation by the dye. The binding was also characterized by absorbance, resonance light scattering and circular dichroism spectral measurements. The binding constants from the spectral results were close to those obtained from the calorimetric data. The energetic aspects of the interaction of the dye JGB to double-stranded DNA are supported by strong binding revealed from the spectral data.

Thermodynamic properties of sublimation of the ortho and meta isomers of acetoxy and acetamido benzoic acids

This paper reports vapour pressures measured at several different temperatures using the Knudsen effusion method of ortho-acetoxybenzoic acid (aspirin) (341.1 to 361.1)K, meta-acetoxybenzoic acid (344.2 to 362.2)K, ortho-acetamidobenzoic acid (367.2 to 389.2)K, and meta-acetamidobenzoic acid (423.2 to 441.1)K. The experimental results enabled the determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T=298.15K, of the four compounds studied. DSC experiments yield results of the temperature and enthalpy of fusion. The experimental results were compared with literature ones for the para isomers of the acids acetoxybenzoic and acetamidobenzoic. Correlations involving temperature of fusion, and standard molar enthalpy and Gibbs energy of sublimation of several substituted benzoic acids were proposed. Those correlation equations allow a good estimative of volatility of benzoic acid derivatives from their enthalpies of sublimation and temperatures of fusion.

Vapor pressures and thermodynamic sublimation of antitubercular drugs

The temperature dependencies of the saturated vapor pressure for antituberculous drug compounds: pyrazinecarboxamide and three isonicotinic acid hydrazides were obtained using the method of inert gas-carrier transfer. The standard sublimation molar enthalpies, entropies and Gibbs energies were derived at T = 298.15 K. The temperature and fusion molar enthalpy of the compounds were measured using the differential scanning calorimetry technique. The influence of the structure of the studied compounds on the crystal lattice energy and volatility was analyzed. It was estimated that the saturated vapor pressure of the studied substances decreases when the molecule polarizability and donor–acceptor ability increase.

Thermochemistry of the Ga-Se System

Solid state electrochemical cells were employed to obtain standard Gibbs energy of formation of Ga2Se3 as well as the temperature and enthalpy of the α to β-Ga2Se3 transformation in the Ga-Se system. The reversible Emfs of the following solid-state electrochemical cells were measured: Pt, Ga(l), Ga2O3(s)||YSZ||Ga2O3(s), GaSe(s), Liquid1, C, Pt I; Pt, Ga(l), Ga2O3(s)‖YSZ‖Ga2O3(s), GaSe(s), Ga2Se3(s), C, Pt II; Pt, Ga(l), Ga2O3(s)||YSZ||Ga2O3(s), Ga2Se3(s), Liquid2, C, Pt III. The standard molar Gibbs energy of formation of Ga2Se3, which was calculated by analysis of measured data, is given by: ΔGof(Ga2Se3, α) ± 1.00(kJ/mol) = −442.65 + 0.11816 T(K) (823 − 962 K); ΔGof(Ga2Se3, β) ± 0.48(kJ/mol) = −425.46 + 0.10086 T(K (986 − 1100 K). The thermodynamic and phase diagram data in the Ga-Se system were critically assessed. A self consistent set of thermochemistry and phase diagram data was obtained with the help of thermochemical measurements. The liquid phase was modeled by the associated solution model with two associates of GaSe and Ga2Se3. The α-Ga2Se3 phase was described by the sublattice model with two sublattices according to the formula (Ga,Va)2 (Se,Va)3. The other two intermediate phases, GaSe and β-Ga2Se3 were treated as line compounds.

Thermodynamics of the interaction of the food additive tartrazine with serum albumins: A microcalorimetric investigation

The thermodynamics of the interaction of the food colourant tartrazine with two homologous serum proteins, HSA and BSA, were investigated, employing microcalorimetric techniques. At T=298.15K the equilibrium constants for the tartrazine-BSA and HSA complexation process were evaluated to be (1.92±0.05)×105M−1 and (1.04±0.05)×105M−1, respectively. The binding was driven by a large negative standard molar enthalpic contribution. The binding was dominated essentially by non-polyelectrolytic forces which remained largely invariant at all salt concentrations. The polyelectrolytic contribution was weak at all salt concentrations and accounted for only 6–18% of the total standard molar Gibbs energy change in the salt concentration range 10–50mM. The negative standard molar heat capacity values, in conjunction with the enthalpy–entropy compensation phenomenon observed, established the involvement of dominant hydrophobic forces in the complexation process. Tartrazine enhanced the stability of both serum albumins against thermal denaturation.

Determination of the solubility and thermodynamic properties of wedelolactone in a binary solvent of ethanol and water

Experimental solubility data of wedelolactone in a binary system of ethanol and water from 278.15K to 323.15K were measured using a thermostatted reactor by static method and HPLC analysis. The effects of binary solvents composition and temperature on the solubility were discussed and it was found that wedelolactone solubility in (water+ethanol) mixed solvents presented a monotonic effect in the studied region. The measured data were regressed by the modified Apelblat equation, Wilson model, nonrandom two-liquid (NRTL) model and the binary solvent (CNIBS)/Redlich–Kister model, and the maximum ∑(%D) values were 0.75, 1.90, 4.34 and 0.38, respectively. The correlation results showed that calculated values by the four models agree well with the experimental data. Using the experimentally measured solubility values, the thermodynamic properties of dissolution of the wedelolactone, including Gibbs energy change (ΔGd), molar enthalpy change (ΔHd) and molar entropy change (ΔSd) of dissolution, were calculated. The values of the standard molar Gibbs energy change and standard enthalpy molar change of solution were both positive, which indicated that the dissolution of wedelolactone in the binary system of ethanol and water was endothermic and no-spontaneous process.

Targeting proteins with toxic azo dyes: a microcalorimetric characterization of the interaction of the food colorant amaranth with serum proteins.

The interaction of amaranth with two homologous serum albumins from human and bovine (HSA and BSA) was studied by microcalorimetry. The binding stoichiometry for the complexation of amaranth to both BSA and HSA was around 1, and the equilibrium constants were (5.79 ± 0.07) × 10(5) and (1.76 ± 0.05) × 10(5) M(-1), respectively. The binding reaction to HSA at 298.15 K was driven by a large negative enthalpic contribution and a small but positive entropic contribution, while to BSA, it was entirely enthalpy-driven and the entropic contribution was unfavorable. Parsing of the standard molar Gibbs energy revealed that the complexation was dominated by non-polyelectrolytic forces. Temperature-dependent isothermal titration calorimetry studies revealed that the enthalpic contribution increased and the entropic contribution decreased with the rise in the temperature but the Gibbs energy change remained almost unaltered. Differential scanning calorimetry results revealed that the binding reaction stabilized the serum albumins significantly against thermal unfolding.

Calorimetry and thermal analysis studies on the binding of 13-phenylalkyl and 13-diphenylalkyl berberine analogs to tRNAphe

The interaction of 13- monophenylalkyl and diphenylalkyl berberine analogs with tRNAphe has been investigated using various thermochemical techniques like thermal melting, isothermal titration calorimetry, and differential scanning calorimetry experiments. Thermal melting studies revealed that all the analogs stabilized the tRNAphe better than berberine. The binding affinity for the analogs was of the order of 105 M−1. Calorimetry results suggested that the binding of these analogs was predominantly entropy driven with small negative enthalpy contribution to the standard molar Gibbs energy. The temperature dependence of the standard molar enthalpy changes yielded negative values of standard molar heat capacity changes for the complexation revealing substantial hydrophobic contribution in the RNA binding of these analogs. An enthalpy–entropy compensation behavior was also seen in all the systems. The diphenylalkyl analogs were found to be more effective tRNAphe binders compared to the monophenylalkyl analogs. The utility of the present work lies in understanding the structural and energetic aspects of the interaction of these berberine analogs with tRNA, which may be useful in the development of RNA-targeted drugs.