Gibbs Energy Change Research Articles

Synthetic, Structural, and Computational Studies on Heavier Tetragen and Chalcogen Triazenide Complexes.

The syntheses of the triazenide complexes [{N(NDipp)2}2M] (Dipp = 2,6-di-isopropylphenyl; M = Ge(II) (1), Sn(II) (2), Pb(II) (3), and Te(II) (5)) are described for the first time. These compounds have been characterized by single-crystal X-ray diffraction and heteronuclear NMR spectroscopy. Density functional theory calculations were employed to confirm the presence and nature of the stereochemically active lone pairs in 1-5, alongside the Gibbs energy changes for their general synthesis, which enable the rationalization of observed reactivities.

Adsorption of metformin from an aqueous solution by Fe-ZSM-5 nano-adsorbent: Isotherm, kinetic and thermodynamic studies

Metformin (MET) is one of the anti-diabetic drugs which is widely used in the world and found abundantly in pharmaceutical wastewater. The purpose of this study, the adsorption of MET from aqueous solution by Fe-ZSM-5 (Fe-Z) zeolite as an adsorbent. The zeolite characterization was analyzed using FTIR, FE-SEM, TEM, XRD, and N2 adsorption-desorption Techniques. The adsorption was performed in a batch system, and the effect of parameters such as solution pH, initial concentration of MET, adsorbent dose, temperature, and contact time was investigated to optimize the adsorption process. Adsorption isotherms were studied by Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models. The Langmuir model with a high correlation coefficient (R2 = 0.999) and the maximum monolayer adsorption capacity (qmax = 14.992 mg g−1) at T = 25 °C showed the highest consistent with MET adsorption on the Fe-Z zeolite. The kinetic data were best represented by the pseudo-second-order model. Also, thermodynamic parameters such as enthalpy changes (ΔH), Gibbs energy changes (ΔG), and entropy changes (ΔS) were investigated. The highest adsorption efficiency was 95.7% at the optimum operating conditions: pH = 8.33, t = 25 °C, 1.1 g L−1 Fe-Z and C0 = 10 mg L−1. The developed nano-adsorbent had high reusability including only 4.4% drop in the removal efficiency. The results showed that the Fe-Z zeolite could be a promising adsorbent for the MET removal.

Unfolding of CBP21, a lytic polysaccharide monooxygenase, without dissociation of its copper ion cofactor.

Chitin-binding protein 21 (CBP21) from Serratia marcescens is a lytic polysaccharide monooxygenase that contains a copper ion as a cofactor. We aimed to elucidate the unfolding mechanism of CBP21 and the effects of Cu2+ on its structural stability at pH 5.0. Thermal unfolding of both apo- and holoCBP21 was reversible. ApoCBP21 unfolded in a simple two-state transition manner. The peak temperature of the DSC curve, tp , for holoCBP21 (74.4°C) was about nine degrees higher than that for apoCBP21 (65.6°C). The value of tp in the presence of excess Cu2+ was around 75°C, indicating that Cu2+ does not dissociate from the protein molecule during unfolding. The unfolding mechanism of holoCBP21 was considered to be as follows: N∙Cu2+ ⇌ U∙Cu2+ , where N and U represent the native and unfolded states, respectively. Urea-induced equilibrium unfolding analysis showed that holoCBP21 was stabilized by 35 kJ mol-1 in terms of the Gibbs energy change for unfolding (pH 5.0, 25°C), compared with apoCBP21. The increased stability of holoCBP21 was considered to result from the structural stabilization of the protein-Cu2+ complex itself.

Synthesis of Quaternary Carbon-Centered Benzoindolizidinones via Novel Photoredox-Catalyzed Alkene Aminoarylation: Facile Access to Tylophorine and Analogues

Photoredox-catalyzed aminoarylation and thioamination of unactivated alkenes have been developed, providing novel synthetic routes to access synthetically challenging quaternary carbon-centered ben...

Corrosion mechanism investigation of TiN/Ti coating and TC4 alloy for aircraft compressor application

It is imperative to develop multifunctional erosion and corrosion resistant coatings for compressor blades of aircraft engines in harsh environment. PVD (Physical Vapor Deposition) technology has the advances in processing erosion-resistant coatings; however, the performance of PVD coatings to combat corrosion depends on various coating defects. Determining and comparing the corrosion performances of PVD TiN/Ti coating and uncoated TC4 alloy was the main objective of present work. The 960 h salt spray corrosion and 116 h hot corrosion tests were conducted to simulate the grounding and working environments of the aircraft compressors. The corrosion mechanisms due to the coating defects such as pinhole, columnar boundary and large grain were analyzed based on the OM, Confocal microscope, electrochemical measurements, SEM, XRD and EDS results. Owing to the disordered state associated with the columnar boundary and the coating defect, nitrogen could be easily replaced by oxygen in the hot corrosion process, these structures were channels for fast diffusion of oxygen. Moreover, the Gibbs energy changes of Ti oxidation and TiN oxidation were thermodynamically calculated according to the working condition of aircraft compressors, and considerable research effort was focused on mapping out the phase diagram of Ti, TiN and high pressure gases. The findings of this research can provide insights into developing multifunctional coatings for future aircraft engines.

Method of UV-Metric and pH-Metric Determination of Dissociation Constants of Ionizable Drugs: Valsartan

Valsartan is used for treating high blood pressure, congestive heart failure and to increase the chances of living longer after a heart attack and to reduce the mortality rate for people with left ventricular dysfunction following a heart attack. Regression analysis of the pH-spectra with REACTLAB and of the pH-titration curve with ESAB determined two close consecutive dissociation constants. MARVIN and ACD/Percepta predicted two protonation sites. In water a soluble anion L2− forms two sparingly soluble species LH−, LH2. Although adjusted pH less affected the spectral changes in the chromophore, $${\text{p}}K_{a1}^{\text{T}}$$ = 3.70 ± 0.12, $${\text{p}}K_{a2}^{\text{T}}$$ = 4.82 ± 0.08 at 25 °C and $${\text{p}}K_{a1}^{\text{T}}$$ = 3.44 ± 0.08, $${\text{p}}K_{a2}^{\text{T}}$$ = 4.67 ± 0.02 at 37 °C in an aqueous phosphate buffer were determined. By regression analysis of potentiometric pH-titration curves and $${\text{p}}K_{a1}^{\text{T}}$$ = 3.51 ± 0.01, $${\text{p}}K_{a2}^{\text{T}}$$ = 4.63 ± 0.01, at 25 °C and $${\text{p}}K_{a1}^{\text{T}}$$ = 3.44 ± 0.03, $${\text{p}}K_{a2}^{\text{T}}$$ = 4.51 ± 0.03 at 37 °C in an aqueous medium were estimated. Positive enthalpy values ΔH0(pKa1) = 10.33 kJ·mol−1, ΔH0(pKa2) = 17.70 kJ·mol−1 showed that the dissociation process was endothermic. The standard state Gibbs energy changes are ΔG0(pKa1) = 20.03 kJ·mol−1, ΔG0(pKa2) = 26.43 kJ·mol−1 at 25 °C and the ΔS0 at 25 °C and 37 °C are (ΔS0(pKa1) = − 32.56 J·K−1·mol−1, ΔS0(pKa2) = − 29.26 J·K−1·mol−1 at 25 °C and ΔS0(pKa1) = − 30.01 J·K−1·mol−1, ΔS0(pKa2) = − 25.92 J·K−1·mol−1 at 37 °C.

Adsorption selectivity of cubic nano-CeO2 and effect of particle size on adsorption thermodynamics

Nanoparticles can effectively remove organic dyes from wastewater due to their excellent adsorption performances which are closely related to particle size. Herein, the relations between the thermodynamic properties and the particle size were deduced, and the influence mechanisms were also discussed. Then the adsorptions of four dyes on cubic nano-CeO2 were investigated. We found that cubic nano-CeO2 has strong adsorption selectivity for four dyes and the size dependence of the adsorption thermodynamic properties. This strong selectivity is attributed to electrostatic interaction and hydrogen bonding. Furthermore, with the particle size decreasing, the logarithm of standard adsorption equilibrium constant (lnKo) increase, while the standard molar Gibbs energy change of adsorption (ΔadsGmθ), the standard molar adsorption enthalpy change (ΔadsHmθ) and the standard molar adsorption entropy change (ΔadsSmθ) decrease, and there are good linear relationships between this thermodynamic properties and the reciprocal of the particle size. The essences of effect of particle size on adsorption thermodynamics are that lnKθ and ΔadsGmθ are influenced by both the molar surface area and the difference in surface tensions after adsorption, ΔadsHmθ by the molar surface area, the differences in surface tensions and in temperature coefficients of surface tensions, ΔadsSmθ by the molar surface area and the difference in temperature coefficients of the surface tensions.

Production of silumins using silicon production waste

The paper presents a review of existing methods to produce silumins. The possibility of obtaining foundry alloys using amorphous microsilica is shown. Different methods of adding SiO 2 particles into molten aluminum are studied: in the form of aluminum powder — SiO 2 master alloy tablets, particle mixing in the melt at the liquidus temperature and introducing SiO 2 together with a stream of argon. The paper provides calculations of Gibbs energy formation and change enthalpy for silicon reduction by aluminum from its oxide. Calculations demonstrated the thermodynamic possibility of silumin production using amorphous microsilica. The effect of alloying additives and impurities on the silicon reduction behavior is determined. It is found that magnesium can be used as a surface-active additive to remove oxygen from dispersed particle surfaces and reduce silicon from its oxide. It is determined that the method of aluminum-silicon alloy production by introducing amorphous microsilica preheated to 300 °С into the aluminum melt (t = = 900 °С) together with argon stream (with subsequent intensive mixing) features higher efficiency since it ensures producing aluminum-silicon alloys containing more than 6 wt.% of silicon and microstructure of pre-eutectic foundry silumins. Industrial application of the proposed method will improve the efficiency of the existing silumin production process due to savings on purchasing commercial crystalline silicon. Moreover, this technology will minimize the environmental impact by reducing the volume and subsequent eliminating sludge fields used as landfills for storing dust from silicon gas treatment systems containing up to 95 wt.% of amorphous microsilica.

Characterization of the interactions between apple condensed tannins and biologically important metal ions [Fe2+ (3d6), Cu2+ (3d9) and Zn2+ (3d10)

To provide information regarding the mechanisms of interactions between apple condensed tannins (ACT) and biologically important metal ions (Fe2+, Cu2+, Zn2+) as well as characterize ACT-metal ion coprecipitates, spectroscopy methods, inductively coupled plasma mass spectrometry (ICP-MS), thermogravimetry analysis (TGA) and field emission scanning electron microscopy (FE-SEM) studies were utilized in the present study. Our results showed that ACT from unripe apple (cv. Golden Delicious) fruits were a mixture of B-type procyanidin oligomers with tetramers and pentamers as the main components. The (−)-epicatechin was the dominant unit of oligomer structures. Metal ions quenched the fluorescence of ACT via a static mechanism, while ACT interacted with metal ions mainly via catechol group-ion exchange. The binding constants, binding sites, the absolute values of Gibbs energy changes and effectiveness of precipitation of metal ions by ACT followed the order of Fe2+ > Cu2+ > Zn2+. Besides, the characteristics of ACT-metal ion coprecipitates confirmed the interactions of ACT with metal ions. The metal content of ACT-Fe2+, ACT-Cu2+ or ACT-Zn2+ coprecipitates was approximately 1.94%, 1.71% or 1.25%, respectively. Therefore, the findings of our investigation were able to help in the developments of ACT-metal nanoparticles, ACT-based sensors and sorption materials for metal ions.

Sorption of Cu2+ and Zn2+ Ions by Humic Acids of Tundra Peat Gley Soils (Histic Reductaquic Cryosols)

Sorption properties of humic acid (HA) preparations extracted from the peaty horizon of peat gley tundra soil (Histic Reductaquic Cryosols) are characterized. The kinetic and thermodynamic sorption parameters of Cu2+ and Zn2+ ions by HAs are calculated. The sorption of the study heavy metal ions by HA preparations is estimated to be truly approximated by the pseudo-first-order response equation. The negative values of the Gibbs energy change at temperatures of 298.0 К and 314.3 К for Сu2+ (–26.2 and –24.5 kJ/mol, respectively) and Zn2+ ions (–22.2 and –22.0 kJ/mol, respectively) attest to the possibility of self-sorption of the study ions within the considered temperature range. Changes in the sorption enthalpy values (–33.1 kJ/mol for Cu2+ ions and –4.5 kJ/mol for Zn2+ ions) characterize both reactions as exothermal reactions. As the temperature rises, the sorption equilibrium constant for Сu2+ ions considerably decreases, whereas it does not change significantly for Zn2+ ions. The decreasing sorption equilibrium constants with the rise in temperature point to the equilibrium shift towards desorption. This is a characteristic feature of physical sorption that indicates possible existence of two fixation mechanisms of ions on the surface of HA preparations, namely, physical sorption and сhemisorption.

Temperature and methyl substitution effect on copper(II) complexes with biorelevant ligands and species distribution in aqueous solution

ABSTRACT In the present work, the stability constants of copper(II) complexes with 1,10-phenanthroline (phen), its methyl derivatives [4-methyl-1,10-phenanthroline (4-mphen) and 4,7-dimethyl-1,10-phenanthroline (dmphen)] and L-tryptophan (trp) were investigated using potentiometric method in 0.1 mol⋅L−1 KCl aqueous ionic media at 298.15 K, 308.15 K and 318.15 K. ‘BEST’ software package was applied to the potentiometric data for the calculation of the protonation constants of the ligands and the stability constants of the copper(II) binary and ternary complexes. The concentration distributions of the various complex species formed in solution were also evaluated as a function of pH using the ‘SPE’ software package. The thermodynamic parameters, enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs energy change (ΔG°) were determined from the stability constants using Gibbs and van’t Hoff equations. The complexation of copper(II) with the ligands in this work is spontaneous, exothermic and favourable at lower temperatures.

Microstructure and thermodynamic properties of aqueous alumina nanofluids

In this work, an assessment of the shear-thinning behaviour of alumina colloidal suspensions based on thermodynamics parameters was carried out. For this purpose, two activation kinetic models, based on the dependence of viscosity with temperature, were analyzed. The first was a modified version of the Andrade-Eyring equation, while the second considered the stress contributing to the activation energy, resulting in a modified version of the Arrhenius relationship. In both models, the activation Gibbs energy change was determined, and a decrease of the activation Gibbs energy change in the Newtonian region compared to the shear-thinning zone was obtained. The stress assisted activation kinetic model indicated a very high increase of the activation volume in the shear-thinning flow compared to the Newtonian regime. This parameter consisted of two contributions: enthalpic and entropic, respectively, from which the enthalpy and entropy changes of distinct flow zones were estimated. The decrease in the entropy change (and entropic forces too) as a consequence of small changes in the suspension microstructure was in agreement with the results obtained by other authors. The determination of thermodynamic parameters from rheological measurements has demonstrated to be an effective method for the analysis and assessment of non-Newtonian behaviours.

Oxidation mechanisms of SiC‐fiber–reinforced Si eutectic alloy matrix composites at elevated temperatures

AbstractSiC‐fiber–reinforced binary Si eutectic alloy composites have been developed for aerospace applications using the melt infiltration method. In this study, the oxidation mechanisms of various binary Si eutectic alloys were evaluated at elevated temperatures. We suggest that the oxidation resistance of eutectic alloys could be predicted using the Gibbs energy change for the oxidation reaction. Based on these calculations, eutectic alloys of Si‐16at%Ti, Si‐17at%Cr, Si‐22at%Co, Si‐38at%Co, and Si‐27at%Fe were prepared. These alloys produced uniform SiO2 layers and showed the same oxidation resistance as Si at 1000°C under humid conditions. Therefore, SiC composites using Si alloys with excellent oxidation resistance can be predicted using thermodynamic calculations.

Treatment of soil washing wastewater via adsorption of lead and zinc using graphene oxide.

In the present work, graphene oxide (GO) was synthesized via the modified Hummers method and utilized in treating real soil washing wastewater via adsorptive removal of lead (Pb) and zinc (Zn). Characterization analysis of GO was performed using X-ray diffraction, Brunauer-Emmett-Teller method, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and zeta potential analysis. The Van't Hoff, Eyring, and Arrhenius equations were applied to determine the activation and thermodynamic parameters namely activation energy (Ea), standard Gibbs energy change (ΔG°), standard enthalpy change (ΔH°), standard entropy change (ΔS°), change in activation Gibbs energy (ΔG#), change in activation enthalpy (ΔH#), and change in activation entropy (ΔS#). Based on the high coefficient of determination values (0.8882 ≥ R2 ≥ 0.9094) and low values of SSE (0.0292 ≤ SSE ≤ 0.0511) and ARE (0.8014 ≤ ARE ≤ 0.8822), equilibrium data agreed well with the Freundlich isotherm. The maximum adsorption capacity for Pb(II) and Zn(II) was determined to be 11.57 and 4.65mg/g, respectively. Kinetic studies revealed that pseudo-second-order equation fitted well with the experimental data, which indicates that chemisorption is the rate-determining step of the adsorption system. Results have shown the possibility of GO as a potential adsorbent material in the treatment of soil washing wastewater.

Solubility and Dissolution Properties of Zaltoprofen in Alcohol, Acid, and Ester Solvents at Atmospheric Pressure and Different Temperatures

In this paper, by the polythermal method, the solubility values of zaltoprofen in alcohols, carboxylic acid, and esters were evaluated from 278.15 to 346.15 K under atmospheric pressure. The results show that the solubilities of zaltoprofen in lower polarity alcohols are higher than that in corresponding higher polarity alcohols. Moreover, the solubility of zaltoprofen increases with the increase in temperature, to expand the industrial application of the experimental solubility data of zaltoprofen in recrystallization, the solubility values measured in selected fifteen pure solvents were correlated using the modified Apelblat equation, the Buchowski–Ksiazczak (λh) equation, the van’t Hoff equation, the Wilson model and the NRTL model. In addition, the van′t Hoff equation was used to calculate the enthalpy change (ΔsolH°), the Gibbs energy change (ΔsolG°), the entropy change (ΔsolS°), the enthalpy %ζH, and entropy %ζTS during the dissolution process. According to the calculation results, the dissolution of zaltoprofen in the fifteen pure solvents is an endothermic and entropy-driven process.

DFT studies of the electron density distribution and donor-acceptor interactions in water-soluble aminohydroximate metallamacrocyclic CaII and YIII complexes

The topology of the electron density and the nature of donor-acceptor interactions in copper-based glycinehydroximate metallamacrocycles bearing calcium(ii) and yttrium(iii) have been studied for the first time in terms of the density functional theory (DFT). The DFT calculations at the M06/Def2-TZVP level were performed taking into account non-specific (PCM) and specific solvation. Quantitative estimations of the donor-acceptor interactions and topological properties of the electron density were obtained. According to them, the thermodynamic stability of the yttrium complex is higher than that of the calcium analog. The calculated values of the Gibbs energy changes indicate the spontaneous substitution of Ca2+ by Y3+ in the metallamacrocycle in an aqueous medium.

Quantum Chemical Calculation of Reactions Involving C20, C60, Graphene and H2O

Calculations of chemical reactions between C20, C60, hydrogen and water molecules are carried out using the PM3 method. Reactions with a hydrogen release at room temperature and atmospheric pressure are identified by the Gibbs energy change. The hydrogen release can be raised by increasing the number of water molecules in chlorine-assisted decomposition of fullerenes. Calculations of the Gibbs energy of chemical reactions involving water molecules between two parallel curved graphene sheets are carried out using DFT with the functional UB3LYP. During pumping between plates of an electric capacitor designed from curved graphene sheets, the water vapor with the assistance of external illumination is enriched by electrically neutral hydroxyl groups (OH)0.

Solubility and solution thermodynamics of ammonium dihydrogen phosphate in the water–methanol system

Abstract The solubility of ammonium dihydrogen phosphate (MAP) in the water–methanol system is essential for antisolvent crystallization studies. To investigate the effect of methanol on the solubility of MAP in water, the solubility of MAP in the water–methanol system was determined by dynamic method and static equilibrium method at temperatures ranging from 293.2 to 343.2 K at atmospheric pressure. Results showed that the solubility of MAP increased with the increase of temperature and the increase of water mole fraction in the water–methanol system. The experimental solubility data were correlated with the modified Apelblat equation, the combined nearly ideal binary solvent/Redlich–Kister (CNIBS/R–K) model and the Jouyban–Acree model. The calculated results based on these three models were in very good agreement with the experimental data with the average relative deviations of 0.65%, 0.97%, and 5.38%, respectively. Simultaneously, the thermodynamic properties of the MAP dissolution process in the water–methanol system, including Gibbs energy change, enthalpy, and entropy were obtained by the Van't Hoff equation, which can be used to assess the crystallization process.

Effect of asphaltene content in bitumen on thermodynamic properties of light hydrocarbons dissolving in bitumen

Solvent recovery from diluted bitumen and froth treatment tailings, produced during the bitumen recovery process for mined oil sands, requires an understanding of the thermodynamic equilibrium and kinetics of solvent dissolution in bitumen. Thermodynamic properties of solvent in bitumen having various asphaltene contents are needed in order to model and improve the solvent recovery process. In this work, the thermodynamic properties of light hydrocarbons in bitumen were investigated using an inverse gas liquid chromatography (IGC) method. Bitumen containing different amounts of asphaltenes (0 wt%, 2.6 wt%, 9.9 wt%, 36.9 wt%, and 53.7 wt%) were used as the stationary phase of the chromatographic column, while light hydrocarbons were injected into mobile phase. The specific retention volumes of the hydrocarbons in bitumen, Vgo, were measured at different temperatures (333.2 K–393.2 K). Thermodynamic properties of these light hydrocarbons in bitumen, including infinite dilution activity coefficient, γ∞, enthalpy of solution, ΔHo, heat capacity changes, ΔCpo, Gibbs energy change, ΔGo, as well as entropy of solution change, ΔSo, were then calculated based on thermodynamic principles and data obtained from IGC measurements.

Evaluation of Experimental Studies in the U-Rich Region of the U-Pu Phase Diagram

Upon the re-examination of two experimental studies, additional thermophysical data pertaining to the uranium-rich portion of the uranium-plutonium binary phase diagram have been elucidated. The first study involved the analysis of solidification cooling curves following the processing of U-Pu alloys. Two phase transitions (liquidus and bcc) were evaluated and the results agreed very well with the established boundaries. The second study was actually performed over sixty years ago but still warrants recognition due to the paucity of thermodynamic data on the U-Pu system to date. From the investigation, the activity coefficients of plutonium in liquid uranium from 1813 K to 2042 K were derived assuming Henry’s law from which the partial molar excess Gibbs energy change of plutonium was obtained: \( \Delta \bar{G}^{\text{ex}} = R*T*\ln \gamma^{\text{o}}_{\text{Pu}} = - \;76694 + 39.2*T\left( {{\text{J}}/{\text{mol}}} \right). \)