Standard Gibbs Free Energy Change Research Articles

Effect of Nonionic Surfactants on the Kinetics of Disproportion of Copper Sulfide Nanoparticles in the Aqueous Sols

The effect of nonionic surfactants on the disproportion kinetics of copper sulfide nanoparticles (aqueous sols) from the golden brown, copper-rich phase (Q-Cu2S) to the green covellite phase (Q-CuS) has been presented. The transformation follows a first-order rate law. There is a substantial decrease in the rate of transformation in the presence of nonionic surfactants, viz. TX-100, NP-9.5, and NP-40. An attempt has been made to explain the phenomenon based on a surface state catalyzed transformation that is sensitive to the adsorption. The surface coverage (θ), estimated from the dependence of the rate constant on surfactant concentration, fitted the Langmuir adsorption isotherm. From these, the equilibrium constants and standard Gibbs free energy change of adsorption have been estimated.

Solubilities and surface activities of phthalates investigated by surface tension measurements

Aqueous solutions of DEP (di-ethyl), DnBP (di-n-butyl), DnH(6)P (di-n-hexyl), and DEHP (di-[2-ethyl-hexyl]) phthalates have been investigated by use of surface tension measurements at temperatures between 10 and 35 degrees C. A tensiometric approach allows for the determination of unimeric solubilities and delta G degree, which is the standard Gibbs free energy change, for the dissolution of phthalates in water. The unimeric solubility of the phthalates increase with decreasing temperature. The delta G degree shows a linear increase with increasing phthalate alkyl chain length. The contribution of enthalpy (delta H degree) and entropy (delta S degree) to delta G degree were calculated from the temperature-dependent solubilities. The contributions of both delta H degree and delta S degree are negative and increase in magnitude with increasing alkyl chain length, suggesting hydrophobic interactions between phthalates and water. The ability of different phthalates to lower the surface tension decreases with increasing alkyl chain length, whereas the relative affinity for adsorption in the air-water interface increases drastically for long-chain phthalates. Despite the low surface activity of phthalates compared with that of common surfactants, they show significant affinity for adsorption in air-water interfaces of natural surface waters. This property, combined with their low solubilities, may affect the fate of these compounds within the natural environment, because they form emulsions above unimeric saturation in aqueous media.

Helicobacter pylori eradication with tetracycline, furazolidone and bismuth (TFB), and rate of reinfection one year after successful treatment

In the current study we have investigated the interaction of newly approved kinase inhibitors namely Cabozantinib (CBZ) and Tofacitinib (TFB) with human Alpha-1 acid glycoprotein (AAG) under simulated physiological conditions using fluorescence quenching measurements, circular dichroism, dynamic light scattering and molecular docking methods. CBZ and TFB binds to AAG with significant affinity and the calculated binding constant for the drugs lie in the order of 104. With the increase in temperature the binding constant values decreased for both CBZ and TFB. The fluorescence resonance energy transfer (FRET) from AAG to CBZ and TFB suggested the fluorescence intensity of AAG was quenched by the two studied drugs via the formation of a non-fluorescent complex in the static manner. The molecular distance r value calculated from FRET is around 2 nm for both drugs, fluorescence spectroscopy data was employed for the study of thermodynamic parameters, standard Gibbs free energy change at 300K was calculated as − 5.234 kcal mol− 1 for CBZ-AAG interaction and − 6.237 kcal mol− 1 for TFB-AAG interaction, standard enthalpy change and standard entropy change for CBZ-AAG interaction are − 9.553 kcal mol− 1 and − 14.618 cal mol− 1K− 1 respectively while for AAG-TFB interaction, standard enthalpy and standard entropy change was calculated as 4.019 kcal mol− 1 and 7.206 cal mol− 1K− 1 respectively. Protein binding of the two drugs caused the tertiary structure alterations. Dynamic light scattering measurements demonstrated the reduction in the hydrodynamic radii of the protein. Furthermore molecular docking results suggested the Hydrophobic interaction and hydrogen bonding were the interactive forces in the binding process of CBZ to AAG while in case of TFB only hydrophobic interactions were found to be involved, overlap of the binding site for two studied drugs on the AAG molecule was revealed by docking results.

Thermodynamics of anion exchange on a chloride-intercalated zinc–aluminum layered double hydroxide: a microcalorimetric study

The thermodynamic properties of anion exchange on a chloride-intercalated zinc–aluminium layered double hydroxide have been studied at 298.15 K. The heats for total exchange of Cl− for F−, Br−, I−, OH−, NO3−, and SO42− have been determined by microcalorimetry and the standard molar enthalpies of these exchange reactions have been estimated. For the processes involving OH− and NO3−, the exchange isotherms have been determined using potentiometry in the former case and capillary ion analysis in the latter. The standard molar Gibbs free energy and entropy changes upon exchange of Cl− for OH− and exchange of Cl− for NO3− have been calculated as a function of the fraction of exchanged Cl−. These exchange processes appear to be entropy-driven, but the selectivity is controlled by the enthalpic contribution.

Kinetic and Thermodynamic Study of Syn−Anti Glycosyl Isomerization in Aqueous Solutions of AMP, ADP, and ATP by Ultrasonic Relaxation Methods

Ultrasonic absorption coefficients in aqueous solutions of adenosine 5‘-triphosphate (ATP) were measured at 25 °C as a function of concentration and pH in the frequency range from 0.8 to 220 MHz. An ultrasonic relaxational absorption with two relaxation frequencies was observed near pH 3. However, above pH 12, only a single relaxational absorption was detected at around 100 MHz, and this relaxation is the focus of this report. The relaxation frequency is independent of the concentration and pH at around pH 12, and the maximum absorption per wavelength increases linearly with concentration. From these results, the cause of the relaxation was attributed to a syn−anti glycosyl isomerization reaction of ATP. The rate of the rotational motion in ATP was found to be smaller than that for ADP and greater than those for AMP and adenosine. These results are discussed in relation to the charge distribution and the effect of the size of the phosphate group of the nucleotides. To examine the reaction mechanism further, ultrasonic absorption measurements were carried out for aqueous solutions of adenosine 5‘-monophosphate (AMP), adenosine 5‘-diphosphate (ADP), and ATP at 15, 20, and 25 °C above pH 12 from which activation enthalpies were determined. Furthermore, the detailed temperature dependence of the absorption in AMP was investigated at several concentrations in order to determine the standard Gibbs free energy, enthalpy, entropy, and volume changes of the reaction, revealing the thermodynamic properties of the syn−anti conformational isomerization process of the nucleotides.

Thermodynamic evaluation of water splitting by a cation-excessive (Ni, Mn) ferrite

Water-splitting potential by cation-excessive (Ni, Mn) Ferrite, Ni 0.5(1+ ε )Mn 0.50(1+ ε )Fe 1.99(1+ ε )O 4 was evaluated using the standard Gibbs free energy change (Δ G°) for the cation-excessive ferrite formation in different O 2 partial pressures. The cation-excessive degree ε ranged from 0.026 to 0.16 in pO 2 values of 7.9×10 −7 to 1.0×10 −1. From the relation between ε value of (Ni, Mn) ferrite and oxygen partial pressure, equilibrium constant K( th) was determined. Furthermore Δ H°s for O 2 releasing and water-splitting reactions with cation-excessive (Ni, Mn) ferrite were evaluated from the vant Hoff plot and compared with that for magnetite-wüstite system; where Δ H°s were assumed to be the same values for both (Ni, Mn) ferrite and magnetite–wüstite system: +300 kJ for O 2 releasing and −35 ∼ −63 kJ for water-splitting. Δ G°s evaluated for water-splitting with cation-excessive (Ni, Mn) ferrite and wüstite were −38 kJ and −35 kJ, respectively, at 298K. It suggests that water splitting with cation-excessive (Ni, Mn) ferrite proceed easily compared with that with wüstite. Δ S°s for water-splitting are −0.93 kJ K −1 for the former and −0.83 kJ K −1 for the latter. H 2 generation rates by reaction with H 2O for (Ni, Mn) ferrite were studied at temperatures of 573 K–1073 K. It reached the maximum at 1000 K while it proceeds preferentially below 830 K from thermodynamics.

Thermodynamic and Quantum Chemical Study of the Conversion of Chorismate to (Pyruvate + 4-Hydroxybenzoate)

A thermodynamic investigation of the conversion of chorismate2-(aq) to {pyruvate-(aq) + 4-hydroxybenzoate-(aq)} has been performed by using microcalorimetry and high-performance liquid chromatography. The study used a genetically engineered sample of chorismate lyase that was prepared with the Escherichia coli ubiC gene. The calorimetric measurements led to a standard molar enthalpy change = −(144 ± 7) kJ mol-1 for this reaction at the temperature T = 298.15 K and ionic strength Im = 0. An estimated value of the standard molar entropy change = 222 J K-1 mol-1 for the above reaction was used together with the experimental value of to obtain a standard molar Gibbs free energy change ≈ −210 kJ mol-1 and an equilibrium constant K ≈ 1037 for the conversion of chorismate2-(aq) to {pyruvate-(aq) + 4-hydroxybenzoate-(aq)} at T = 298.15 K and Im = 0. Quantum mechanics (Gaussian 94 with a B3LYP functional and a 6-31G* basis set) was used to calculate values of absolute energies for the neutral and ionic species per...

High temperature enthalpies and heat capacities of YbMnO 3 and YMnO 3

Heat capacities of YbMnO 3 and YMnO 3 were measured by differential scanning calorimetry (DSC) from room temperature to 850 K. Enthalpy changes of YbMnO 3 and YMnO 3 were measured by drop calorimeter in the temperature range 573 to 1373 K and heat capacity equations were also estimated. The heat capacity equations were determined by combining the data from both calorimeters and the equations derived for YbMnO 3 from 298 K to 1373 K were Cp,m (J K −1 mol −1)=125.3+11.5×10 −3· T−1.78×10 6· T −2 and for YMnO 3 Cp,m( J K −1 mol −1)=120.8+15.8·10 −3· T−2.41·10 6· T −2. The standard Gibbs free energy changes of formation for YbMnO 3 and YMnO 3 at 298 K were also calculated by using above data. The values were determined to be −1317.6 kJ mol −1 and −1367.1 kJ mol −1, respectively.

Temperature, stability, and the hydrophobic interaction

Changes in free energy are normally used to track the effect of temperature on the stability of proteins and hydrophobic interactions. Use of this procedure on the aqueous solubility of hydrocarbons, a standard representation of the hydrophobic effect, leads to the conclusion that the hydrophobic effect increases in strength as the temperature is raised to approximately 140 degrees C. Acceptance of this interpretation leads to a number of far-reaching conclusions that are at variance with the original conception of the hydrophobic effect and add considerably to the complexity of interpretation. There are two legitimate thermodynamic functions that can be used to look at stability as a function of temperature: the standard Gibbs free energy change, deltaG degrees, and deltaG degrees/T. The latter is proportional to the log of the equilibrium constant and is sometimes called the Massieu-Planck function. Arguments are presented for using deltaG degrees/T rather than deltaG degrees for variations in stability with temperature. This makes a considerable difference in the interpretation of the hydrophobic interaction, but makes little change in the stability profile of proteins. Protein unfolding and the aqueous solubility of benzene are given as examples. The contrast between protein unfolding and the hydration of nonpolar molecules provides a rough estimate of the contribution of other factors that stabilize and destabilize protein structure.

Thermodynamics of the Conversion of Chorismate to Prephenate: Experimental Results and Theoretical Predictions

A thermodynamic investigation of the Claisen rearrangement of chorismate2-(aq) to prephenate2-(aq) has been performed using microcalorimetry and high-performance liquid chromatography. The study used a well-characterized monofunctional chorismate mutase from Bacillus subtilis that was devoid of prephenate dehydrogenase and prephenate dehydratase activities. The calorimetric measurements led to a standard molar enthalpy change = −(55.4 ± 2.3) kJ mol-1 at 298.15 K for this reaction. An estimated value of the standard molar entropy change = 3 J K-1 mol-1 for the above reaction was used together with the experimental value of to obtain a standard molar Gibbs free energy change ≈ −56 kJ mol-1 and an equilibrium constant K ≈ 7 × 109 for the conversion of chorismate2-(aq) to prephenate2-(aq) at 298.15 K. Thus, for all practical purposes, this reaction can be considered to be “irreversible”. Quantum mechanics (Gaussian 94 with a B3LYP functional and a 6-31G* basis set) was used to calculate values of absolute and...

Decomposition behavior of Ln2Mn4/3W2/3O7 (Ln = Eu and Er) in reducing atmosphere and their thermodynamic properties

Decomposition behavior of Ln2Mn4/3W2/3O7 (Ln = Eu and Er) in reducing atmosphere at 1273 K was determined. These compounds decomposed to LnMnO3 and Ln2MnWO7 at PO2 = 10−8.46 atm for Ln = Eu and 10−7.46 atmosphere for Ln = Er, respectively. Decomposition product Eu2MnWO7 decomposed to Eu2MnWO6 at PO2 = 10−15.67 atm, while Er2MnWO7 decomposed to Er2O3, MnO, and W less than 10−17 atm. The standard Gibbs free energy changes of decomposition for Eu2Mn4/3W2/3O7, Eu2MnWO7, and Er2Mn4/3W2/3O7 at 1273 K were determined to be 34.4 kJ · mol−1, 191.9 kJ · mol−1, and 44.8 kJ · mol−1, respectively. The standard Gibbs free energy changes of formation of Er2Mn4/3W2/3O7 and Er2MnWO7 were also determined to be −2429.5 and −2463.2 kJ · mol−1 at 1273 K, respectively.

Solubility of Carbon in Liquid Silicon Equilibrated with Silicon Carbide

The solubility of carbon in liquid silicon equilibrated with silicon carbide was determined in the temperature range from 1723 to 1873 K. Silicon was melted in a silicon carbide crucible with an Ar-CO mixture gas flowing. Carbon in silicon was analyzed by the combustion-IR absorption method. The temperature dependence of the carbon solubility in liquid silicon can be represented by the following equation: log (C c /mass%) = 3.63 - 9660/T(±0.02) (T : 1723-1873 K) The carbon solubility at the melting point of silicon was calculated to be 79 ppm (9.1 x 10 18 atoms cm -3 ). The level of oxygen impurities in the melt was much lower than that of liquid silicon equilibrated with solid silica. The standard Gibbs free energy change for carbon dissolution in liquid silicon can be represented as: C(s) =C(l mass%, in liquid silicon) ΔG° =7.20 x 10 4 - 11.4T log T+6.20T (J).

Mechanochemical solid-phase reactions between alkaline earth metal sulfates and alkali metal hydroxides

Room temperature grinding of nine kinds of powder mixtures prepared by the combination of alkaline earth metal sulfates (M–SO 4, M = Ca, Sr and Ba) and alkali metal hydroxides (R–OH, R = Li, Na and K) was conducted in a planetary ball mill. The ground products were characterized mainly by X-ray diffraction analysis. LiOH · H 2O powder reacts with CaSO 4 · 2H 2O, forming a mixture of Ca(OH) 2 and Li 2SO 4 powders, while LiOH · H 2O reacts with neither SrSO 4 nor BaSO 4 powders. NaOH as well as KOH powders react substitutionaly with each sulfate. The reaction and non-reaction systems are distinguished by negative and positive values in the calculated standard Gibbs free energy change, respectively. In the present systems, the standard free energy change is an indicator governing the substitution reactions. Grinding operation in the reaction systems plays a significant role to facilitate their forward reaction.

Thermodynamic analysis of trinitrotoluene biodegradation and mineralization pathways

Biodegradation of 2,4,6-trinitrotoluene (TNT) proceeds through several different metabolic pathways. However, the reaction steps which are considered rate-controlling have not been fully determined. Glycolysis and other biological pathways contain biochemical reactions which are acutely rate-limiting due to enzyme control. These rate-limiting steps also have large negative Gibbs free energy changes. Because xenobiotic compounds such as TNT can be used by biological systems as nitrogen, carbon, and energy sources, it is likely that their degradation pathways also contain acutely rate-limiting steps. Identification of these rate-controlling reactions will enhance and better direct genetic engineering techniques to increase specific enzyme levels. This article identifies likely rate-controlling steps (or sets of steps) in reported TNT biodegradation pathways by estimating the Gibbs free energy change for each step and for the overall pathways. The biological standard Gibbs free energy change of reaction was calculated for each pathway step using a group contribution method specifically tailored for biomolecules. The method was also applied to hypothetical “pathways” constructed to mineralize TNT using several different microorganisms. Pathways steps that have large negative Gibbs free energy changes are postulated to be potentially rate-controlling. The microorganisms which utilize degradation pathways with the largest overall (from TNT to citrate) negatiave Gibbs free energy changes were also determined. Such microorganisms can extract more energy from the starting substrate and are thus assumed to have a competitive advantage over other microorganisms. Results from this modeling-based research are consistent with much experimental work available in the literature. © 1996 John Wiley & Sons, Inc.

Thermodynamic analysis of trinitrotoluene biodegradation and mineralization pathways

Biodegradation of 2,4,6-trinitrotoluene (TNT) proceeds through several different metabolic pathways. However, the reaction steps which are considered rate-controlling have not been fully determined. Glycolysis and other biological pathways contain biochemical reactions which are acutely rate-limiting due to enzyme control. These rate-limiting steps also have large negative Gibbs free energy changes. Because xenobiotic compounds such as TNT can be used by biological systems as nitrogen, carbon, and energy sources, it is likely that their degradation pathways also contain acutely rate-limiting steps. Identification of these rate-controlling reactions will enhance and better direct genetic engineering techniques to increase specific enzyme levels.This article identifies likely rate-controlling steps (or sets of steps) in reported TNT biodegradation pathways by estimating the Gibbs free energy change for each step and for the overall pathways. The biological standard Gibbs free energy change of reaction was calculated for each pathway step using a group contribution method specifically tailored for biomolecules. The method was also applied to hypothetical "pathways" constructed to mineralize TNT using several different microorganisms. Pathways steps that have large negative Gibbs free energy changes are postulated to be potentially rate-controlling. The microorganisms which utilize degradation pathways with the largest overall (from TNT to citrate) negatiave Gibbs free energy changes were also determined. Such microorganisms can extract more energy from the starting substrate and are thus assumed to have a competitive advantage over other microorganisms. Results from this modeling-based research are consistent with much experimental work available in the literature.

Studies on oxygen dissociation pressure of LnMnO3 (Ln = rare earth) with the e.m.f. technique

The oxygen dissociation pressure of LnMnO3 (Ln  La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y or Sc) was measured at high temperature (1170–1400 K) by means of e.m.f. using stabilized ZrO2 as a solid electrolyte. Assuming that the decomposition reaction proceeds in a stoichiometric form, a standard Gibbs free energy change of decomposition was determined from the oxygen dissociation pressure. The variation of the free energy change with change in identity of Ln was investigated. It was found that the energy change depends strongly upon both the crystal structure and the ionic radius of Ln3+. The standard Gibbs free energy change of formation for LnMnO3 compounds was obtained from the standard Gibbs free energy change for the decomposition reactions and those for the formation of the decomposition materials.

Standard Gibbs Free Energy Changes of Enzyme Reactions in Metabolic Pathway Computation

Standard Gibbs Free Energy Changes of Enzyme Reactions in Metabolic Pathway Computation

Thermodynamics of boron in a silicon melt

The activity coefficient of B in a Si melt and the interaction parameters of boron and nitrogen in molten silicon were determined by equilibrating solid BN and liquid Si in a nitrogen atmosphere from 1723 to 1923 K. The standard Gibbs free energy change of the nitrogen dissolution into silicon is also obtained. The activities of BO1.5 in the CaO-CaF2-SiO2 and CaO-MgO-SiO2 systems are estimated in relation to the removal of boron from silicon by these fluxes.

Protein stability: A problem in physical biochemistry

Introduction The factors which contribute to the stability of the structure of globular proteins are addressed in most biochemistry courses. Well prepared students can readily list the major interactions (eg salt links, hydrogen bonding, hydrophobic interactions, van der Waals forces and disulphide bonds) which stabilize the secondary, tertiary and quaternary structures of proteins. It is well known that proteins can lose their native conformations (become denatured) when subjected to extremes of pH or on heating, and also when they interact with denaturants such as ionic surfactants, or high concentrations of urea or guanidinium chloride. The heating of proteins is perhaps the simplest means of bringing about denaturation. Somewhat less well known is the process of cold denaturation. 1 In contrast to heat denaturation which is frequently irreversible, cold denaturation is reversible, so in practical terms it is not encountered as a problem in the same way that for example, the loss of enzyme activity due to inadvertant heating presents practical problems. The thermodynamic analysis of protein stability is an important research area and while many students understand the denaturation process in a qualitative way they often take less readily to the quantitative aspects of the process. The following problem considers the way in which information on the thermal unfolding process can be obtained from measurements by differential scanning calorimetry (DSC). It is an example not only of the value of the DSC technique but also of the application of the thermodynamic method to a biochemical problem. The problem is suitable for students who have had a basic course in thermodynamics and have been exposed to the relationship between standard Gibbs free energy change (AG °) for a process and the equilibrium constant K (i.e. AG ° = -RTInK) and the Gibbs-Helmholtz equation for the temperature coefficient of AG/T with respect to 1/T at constant pressure:

Thermochemical stability of BaFe12O19and BaFe2O4and phase relations in the Ba-Fe-O ternary system

The stability of BaFe12O19and BaFe2O4was studied by the oxygen coulometric titration technique between 700 °C and 1000 °C using a solid-state electrochemical cell. This temperature range is technologically important for the deposition of BaFe2O19magnetic thin films. The thermodynamic information obtained from the titration measurements was corroborated with structural identification of phases prepared under electrochemically controlled conditions. Accordingly, a section of the Ba–Fe–O ternary phase diagram around the BaFe12O19composition was constructed in this temperature range. The standard Gibbs free energy change for the decomposition of BaFe12O19into BaFe2O4, Fe3O4, and O2is given by the expression ΔG°[J/mol] = 7.23 × 105−480T. In the oxygen pressure-temperature domain, the thermodynamic stability limits of BaFe12O19and BaFe2O4are given by the expressions In[Po2(atm)] = 69.37 −1.04 × 105T−1and In[Po2(atm)] = 27.68 −7.12 × 104T−1, respectively. The stability limits determined here help define the process conditions for the successful synthesis of these phases.