Gibbs Free Energy Of Activation Research Articles

Kinetic and Thermodynamic Characteristics of Thermal Degradation of Anthocyanins from Strawberry and Blueberry Commercial Juices

Thermal stabilities of anthocyanins in strawberry and blueberry commercial juices were studied over the temperatures 75, 85 and 95 oC. Results indicated that the thermal degradation of anthocyanins followed the first-order reaction kinetics. The temperature-dependent degradation was adequately modeled on the Arrhenius equation. During heating, anthocyanins in the strawberry juice degraded faster than in blueberry juice, with the activation energies of 74.16 kJ/mol and 65.75 kJ/mol, respectively. Cyanidin-3-glucoside (cyd-3-glu) was more susceptible to the thermal treatment than pelargonidin glycosides in strawberry juice. Delphinidin glycosides were more susceptible to the thermal treatment than cyanidin glycosides in blueberry juice. However, cyd-3-glu in strawberry juice was more sensitive to the thermal treatment than in blueberry juice. Obtained results for activation enthalpies indicated that the degradation process was endothermic and Gibbs free energy of activation indicated that they were not spontaneous.

Proton Coupled Electron Transfer in the Reaction of Hydroxybenzenes with Hydrazyl Radical in Aqueous Media

Possible electron transfer mechanisms have been studied for the reaction of 2,2′-diphenyl-1-picrylhydrazyl with a number of natural hydroxybenzenes in aqueous buffer solutions at pH = 2–9 using the methods of spectrophotometry and quantum chemical calculations. In acidic media, electron transfer occurs from the molecular form of hydroxybenzene to the radical with subsequent loss of proton, whereas in alkaline media the electron is transferred from the phenolate ion to the radical, preceded by the proton elimination step. Realization of a specific mechanism is indicated by the dependence of the reaction rate constant on the pH of the media and by the presence of correlation between the Gibbs free activation energy, calculated using the Marcus equation and that determined experimentally.

Corrosion Inhibition and Adsorption Properties of <i>Commelina benghalensis</i> Leaves Extract on Mild Steel in 1M H<sub>2</sub>SO<sub>4</sub> Solution

The corrosion inhibition of mild steel in 1M sulphuric acid solution by the ethanol extract of Commelina benghalensis (C. B) leaves was determined using gravimetric technique. Phytochemical analysis was carried out on the extract and the effect of extract concentration, temperature, immersion time and acid concentration on the corrosion process was determined. The corrosion inhibition efficiency of the extract increased with increase in the concentration of the extract and decreased with increase in temperature. Increase in temperature also increased the corrosion rate of mild steel in 1M sulphuric acid in the absence and presence of different concentrations of the extract. The adsorption of the plant extract obeyed Langmuir and Freundlich adsorption isotherms. The process of physical adsorption was proposed for the extract from the trends of inhibition efficiency with temperature and from calculated values of Gibbs free energy, activation energy and enthalpy of adsorption. Gibbs free energy values for the reactions were less than 20kJ/mol, indicating physical adsorption process and were also found to be negative, indicating that the adsorption process was spontaneous. The corrosion inhibition efficiency (% IE) of the plant extract was attributed to the phytochemical constituents (alkaloids, flavonoids, tannins, saponins, phenolics, steroids and cardiac glycosides) present in them. The results showed that Commelina benghalensis can serve as a good corrosion inhibitor of mild steel in acid medium, since it reached a corrosion inhibition efficiency (% IE) of 91.91% at 2.0g/L extract concentration.

ИССЛЕДОВАНИЕ МЕХАНИЗМА АДСОРБЦИИ ДИОКСИДА СЕРЫ ИЗ ГАЗОВЫХ ВЫБРОСОВ ПРОИЗВОДСТВА БИСУЛЬФИТА НАТРИЯ

It is proposed to purify industrial gas emissions from sulfur dioxide by the adsorption method. Waste from the power industry - sludge from the chemical water treatment of Kazan CHPP-1 - was used as an adsorption material. Its chemical composition is presented. Experimental studies of a new sorption material based on energy waste for gas purification from sulfur dioxide have been carried out. The kinetic dependence and isotherm of the adsorption process are obtained. The mechanism of the process of adsorption of sulfur dioxide by sorption material at different temperatures has been studied. The Gibbs free energy, differential heat, and activation energy of adsorption are determined. The economic and environmental impact of modernization of procedure for cleaning gas emissions from sulfur dioxide in sodium bisulfite production at JSC “Chemical factory named after L.Ya. Karpov” was measured.

Theoretical insights into the intermolecular and mechanisms of covalent interaction of Flutamide drug with COOH and COCl functionalized carbon nanotubes: A DFT approach

In this study, it is attempted to scrutinize the noncovalent interaction and two mechanisms of covalent between Flutamide anti-cancer drug (FLU) and functionalized carbon nanotubes (f-CNT) employing density functional theory (DFT) calculations regarding their geometries, binding energies and topological features of the electron density in the water solution. For designed noncovalent interactions, binding energies, natural bond orbital (NBO), atom in molecule (AIM) and quantum molecular descriptors analyses were applied for further understanding of the adsorption process. The computed theoretical results confirmed that binding of Flutamide molecule with functionalized CNT is thermodynamically suitable and among two considered systems containing COOH functionalized CNT (NTCOOH) and COCl functionalized CNT (NTCOCl), the NTCOOH revealed more binding energy value which suggests it as a favorable system as a drug delivery within biological and chemical systems (noncovalent). NTCOOH and NTCOCl can bond to the NH group of flutamide through OH (COOH mechanism) and Cl (COCl mechanism) groups, respectively. Finally, to obtain the values of activation energies, the activation enthalpies and the activation Gibbs free energies of two considered pathways different calculations were performed and the results have been compared with each other. Numerical studies for calculating activation parameters related to the COOH mechanism show higher values than those related to the COCl mechanism and therefore COOH mechanism can be suitable for noncovalent functionalization. These results could be generalized to other similar drugs.

FT-IR Spectroscopic study of excess thermodynamic and transport properties of liquid mixtures of p-chloroacetophenone with alkoxyalkanols

ABSTRACT Densities, speeds of sound and viscosities were measured for the binary mixtures para-chloroacetophenone (PCAP) with 2-alkoxyethanols (2-methoxyethanol [2-MOE], 2-ethoxyethanol [2-EOE] and 2-butoxyethanol [2-BOE]) at T = (303.15–318.15) K. These experimental data have been used to calculate excess volume (VE ), excess isentropic compressibility (KsE ), deviation in viscosity (∆η) and excess Gibbs free energy of activation of viscous flow (G*E ). The excess parameters have been fitted to the Redlich–Kister equation and the results were analysed in terms of acid–base interactions, hydrogen bond interactions and dipole–dipole interactions between unlike molecules. Further, the FTIR spectra have been recorded at 298.15 K and found to be useful for understanding the presence of hydrogen bonding between oxygen atom of carbonyl group of p-chloroacetophenone and hydrogen atom of the –OH group of 2-alkoxyethanols molecules in the present liquid mixtures. A good agreement is obtained between excess quantities and spectroscopic data.

Volumetric and Viscometric Properties for Binary and Ternary Solutions of Diethylenetriamine, N,N-Diethylethanolamine, and Water

The experimental values of density and viscosity for binary solutions diethylenetriamine (DETA) + H2O, DETA + N,N-diethylethanolamine (DEEA), and ternary solution DETA + DEEA + H2O over the entire concentration range were reported at atmospheric pressure and T = (293.15, 303.15, 313.15, 323.15, 333.15) K. The measured densities and viscosities were used to calculate the thermal expansion coefficient, excess molar volume, partial molar volume, apparent molar volume, partial molar volume at infinite dilution, viscosity deviation, and excess Gibbs free energy of activation for viscous flow. The molecular interactions in mixtures were discussed based on the volumetric and viscometric properties.

Understanding the Mechanism of Nitrobenzene Nitration with Nitronium Ion: A Molecular Electron Density Theory Study

AbstractThe nitration reaction of nitrobenzene with nitronium ion yielding ortho‐, meta‐ and para‐dinitrobenzenes has been studied within the Molecular Electron Density Theory, using DFT computational methods at the B3LYP/6‐311G(d,p) level. This electrophilic aromatic substitution (EAS) reaction takes place through a two‐step mechanism involving the formation of a tetrahedric cation intermediate. The electrophilic attack of nitronium ion on nitrobenzene is the rate‐determining step of this EAS reaction, and consequently, responsible for the composition of the reaction mixture. The subsequent proton abstraction from the cation intermediate is barrierless. From the computed activation Gibbs free energies, a relationship 11.0 (ortho) : 87.3 (meta) : 1.7 (para) of the dinitrobenzenes is estimated, in clear agreement with the experimental outcome. The similar nucleophilic activation of the ortho and meta carbons of nitrobenzene makes it possible to question the hypothesis for the orientation in EAS reactions involving nucleophilically deactivated benzenes based on the relative stability of the tetrahedric cation intermediates.

Density, viscosity and excess properties of binary mixtures of monoethanolamine and 2-alkoxyethanols at temperatures from (293.15 to 353.15) K

Densities and viscosities for the binary liquid mixtures of monoethanolamine (MEA) with 2-alkoxyethanols (2-ethoxyethanol (EGEE) and 2-butoxyethanol (EGBE)) were measured over the entire concentration range at temperatures of 293.15–353.15 K and atmospheric pressure. From the experimental results, the excess molar volume (VE), viscosity deviations (∆η) and excess Gibbs free energy of activation of viscous flow (∆G⁎E) were calculated and the excess/deviations properties for the studied binary systems were fitted with the Redlich-Kister equation to estimate the binary interaction parameters. The results were analyzed in terms of intermolecular interactions between unlike molecules and intramolecular interactions within like associated molecules. The densities and viscosities of CO2-loaded solutions were also measured and correlated with the proposed correlations. The calculated values of density and viscosity for the binary/ternary systems are in good agreement with the experimental values, with AADs within 0.2% for density and 3.2% for viscosity. The FTIR spectral analysis for the binary mixtures of MEA with 2-alkoxyethanols at various concentrations suggests the presence of weak interactions between component molecules in the systems, and also supports the findings of excess properties.

Thermokinetic Analysis of Protein Subunit Exchange by Variable-Temperature Native Mass Spectrometry.

Many protein complexes are assembled from a varying number of subunits, which are continuously exchanging with diverse time scales. This structural dynamics is considered to be important for many regulatory and sensory adaptation processes that occur in vivo. We have developed an accurate method for monitoring protein subunit exchange by using native electrospray ionization mass spectrometry (ESI-MS), exemplified here for an extremely stable Rad50 zinc hook (Hk) dimer assembly, Zn(Hk)2. The method has two steps: appropriate protein/peptide mutation and native ESI-MS analysis using a variable-temperature sample inlet. In this work, two Hk mutants were produced, mixed with wild-type Hk, and measured at three different temperatures. A thermokinetic analysis of heterodimer formation allowed us to determine the enthalpy, entropy, and Gibbs free energy of activation for subunit exchange, showing that the reaction is slow and associated with a high enthalpic barrier, consistent with the exceptionally high stability of the Zn(Hk)2 assembly.

SORPTION OF NICKEL (II) IONS BY CHELATING RESIN WITH IMINODIACETATE FUNCTIONALITY

The regularities of sorption of nickel (II) ions from a monocomponent system on macroporous weakly acidic cationite Lewatit MonoPlus TP 207 were studied. Sorption isotherms were obtained. It is shown that the extraction process can be fairly reliably described by Langmuir and Freundlich equations. The static exchange capacity (SEC) of the resin was determined. The SEC dependencies at temperatures of 305 and 328 K during the sorption process were revealed. Integral kinetic curves were obtained. It is defined that the equilibrium concentration of nickel (II) ions is reached about 13 times faster with temperature increase from 305 to 328 K. The experimental data were processed using equations that take into account the influence of external, internal diffusion, "sorbent-sorbate" and "sorbate-sorbate" chemical interactions. It was found that the main limiting stage of sorption of nickel (II) ions is the internal diffusion. The values of external and internal diffusion rate constants at the indicated temperatures were determined. The kinetic curves were processed by pseudo first and pseudo second order models, which satisfactorily describe the experimental data. According to transition-state theory the thermodynamic characteristics of the activation process (activation energy, entropy, enthalpy, and Gibbs free energy) were calculated. Relatively low activation energy indicates the decisive contribution of diffusion in the process of sorption of nickel (II) ions. Positive entropy is the evidence of nickel hydration shells destruction during the sorption process. Positive enthalpy proves an endothermic nature of interaction of nickel (II) ions and ionogenic groups. Negative Gibbs free energy witnesses to spontaneous course of the reaction in the forward direction. For known values of stability constants the contents of nickel ionic forms and SEC’s were calculated in terms of pH value. Nickel extraction from solution increases with the appearance of singly-charged NiOH+ ions in the pH range from 8 to 9.

Adsorption of Cr (VI) From Polluted Water using Activated Carbon Prepared from Vincarosea Apocynaceae

The performance removal of chromium (VI) from polluted water is discussed in this paper. The sorption characteristic of Nitric Acid activated carbon derived from Vincarosea Apocynaceae plants through oxidation process and was proposed for the removal of Cr (VI) from polluted solutions. The surface chemistry characteristics of the prepared adsorbent were analysis by XRD, FTIR and SEM-EDAX. The effects are determined for removal of chromium they are initial concentration, PH level and adsorbent dose. The metal ion removal was pH dependent and, to a lesser extent, ionic strength. Kinetics data were found to follow the pseudo-second order kinetic model. Activation thermodynamic parameters, such as activation enthalpy (ΔH*), activation entropy (ΔS*), activation Gibbs free energy (ΔG*) and activation energy(E), have been evaluated and the possible adsorption mechanism also was suggested.

The Use of papaver somniferum L. Plant Extract as Corrosion Inhibitor

The corrosion inhibition and adsorption characteristics of the extract obtained from the plant Papaver somniferum L. (PSL) by electrochemical methods at different temperatures (25, 35 and 45°C) were investigated in 0.2 M HCl and 0.2 M HCl + x ppm PSL solutions on AISI 304 stainles steel (AISI 304 SS), ETIAL 150 aluminum alloy (ETIAL 150 Al) and copper. The best inhibition was obtained containing 0.2 M HCl + 500 ppm PSL inhibitor concentration solutions. Surface observations of metals after standing experiments were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy scattering X-ray method EDX). The inhibition effect was increased with an increase in inhibitor concentration. Extract adsorbed on the surface of metals obeyed the Langmuir adsorption isotherm. The Langmuir adsorption isotherms confirm the physical adsorption mechanism and the inhibitor is a mixed type inhibitor. SEM images show cracks and pits on the surfaces in extract free solutions. AFM and SEM were showed thick dense film on metal surfaces in containing extract solutions. The occuring film closed all the active corrosion sites on metals and inhibited corrosion mechanism. Some thermodynamic and kinetic parameters for the adsorption process, that were adsorption equilibrium constant (Kads), Gibbs adsorption free energy (Gads), and activation energy of corrosion reaction (Ea), were calculated and discussed by using Tafel results. Arrhenius energies increased with an increase in inhibitor concentration. Activation energies and Gibbs free energies for the inhibition reactions were supported the physical adsorption mechanism.

Prediction of viscosity for high-concentrated ternary solution (CH3SO3H + VOSO4 + H2O) in vanadium flow battery

In this paper, a model for viscosity of high-concentrated additive (methanesulfonic acid) in vanadium electrolyte is reported. Methanesulfonic acid was evaluated as a possible stabilizing agent for the thermal precipitation of supersaturated V(V) solutions at elevated temperatures. Viscosity (η) of the ternary solution CH3SO3H + VOSO4 + H2O was measured between the temperatures 283.15 K and 318.15 K under atmospheric pressure. Based on the viscosity, viscosity B-coefficient, activation energy (Δμ0≠0) and Gibbs free energy of activation (ΔG≠) were further calculated. With the help of these paraments, a semi-empirical predicting function is established to estimate the viscosity of high-concentrated additive, i.e. methanesulfonic acid in vanadium electrolyte. AARD of this semi-empirical method is 0.22%, which demonstrates that viscosity estimation for high-concentrated ternary solution CH3SO3H + VOSO4 + H2O can be achieved.

An electron localization function analysis of the molecular mechanism and the C–O bond formation in the [3+2] cycloaddition reaction involving zwitterionic type between a nitrone and an electron deficient ethyne

The mechanistic nature of a [3+2] cycloaddition reaction involving zwitterionic species has been investigated, and the changes of electron density related to the O–C and C–C bond formation along the intrinsic reaction coordinate have been characterized. This polar [3+2] cycloaddition reaction, which takes place through a non-concerted two-stage one-step mechanism, proceeds with a moderate Gibbs free activation energy of 21 kcal mol−1. The reaction begins by the creation of a pseudoradical centre at the central carbon, first on the dimethyl acetylenedicarboxylate, and second on the nitrone framework. This immediately favours the formation of the first O–C single bond by donation of some electron density of the oxygen atom lone pairs, which represents the most attractive centre in this cycloaddition reaction.

Human serum albumin-resveratrol complex formation: Effect of the phenolic chemical structure on the kinetic and thermodynamic parameters of the interactions

The thermodynamics and kinetics of binding between human serum albumin (HSA) and resveratrol (RES) or its analog (RESAn1) were investigated by surface plasmon resonance (SPR). The binding constant and the kinetic constants of association and dissociation indicated that RESAn1 has higher affinity toward HSA than does RES. The formation of these complexes was entropically driven (TΔS0HSA-RES≅33.8, TΔS0HSA-RESAn1≅56.4 KJ mol−1). However, for both polyphenols, the activation energy (Eact) of association (a) of free molecules was higher than that for dissociation (d) of the stable complex (EactaHSA-RES=11.37,EactdHSA-RES=-3.06,EactaHSA-RESAn1=30.76,EactdHSA-RESAn1=-5.24 KJ mol−1), and the rate of association was faster than that of dissociation since the activation Gibbs free energy (ΔG‡) was lower for the former (ΔGaHSA-RES‡≅54.73,ΔGdHSA-RES‡≅73.83,ΔGaHSA-RESAn1‡≅54.14,ΔGdHSA-RESAn1‡≅73.97 KJ mol−1). This study showed that small differences in the structure of polyphenols such as RES and RESAn1 influenced the thermodynamics and kinetics of the complex formation with HSA.

Investigation on the kinetics and thermodynamics of polyacrylonitrile-b-poly(hydroxyethyl acrylate) via organotellurium-mediated living radical polymerization by micro-calorimeter

The polyacrylonitrile-b-poly(hydroxyethyl acrylate) (PAN-b-PHEA) was synthesized of polyacrylonitrile-TeMe (PAN-TeMe) and 2-Hydroxyethyl acrylate (HEA) via organotellurium-mediated living radical polymerization (TERP), and the PAN-TeMe and PAN-b-PHEA were characterized by several methods. A Calvet micro-calorimeter was used to investigate the polymerization of PAN-TeMe and HEA at different temperatures (358.15 K, 363.15 K, 368.15 K, 373.15 K, 378.15 K and 383.15 K). The kinetic equations of polymerization at different temperatures were obtained, and the apparent activation energy (E) of polymerization is 16.43±0.17 kJ∙mol−1 and the pre-exponential factor (A) is 0.6845±0.0366 s−1. Furthermore, the thermodynamic parameters including the standard molar Gibbs free energy of activation (ΔG≠θ), the standard molar enthalpy of activation (ΔH≠θ) and the standard molar entropy of activation (ΔS≠θ) are acquired.

Novel Tautomerisation Mechanisms of the Biologically Important Conformers of the Reverse Löwdin, Hoogsteen, and Reverse Hoogsteen G*·C* DNA Base Pairs via Proton Transfer: A Quantum-Mechanical Survey.

For the first time, in this study with the use of QM/QTAIM methods we have exhaustively investigated the tautomerization of the biologically-important conformers of the G*·C* DNA base pair—reverse Löwdin G*·C*(rWC), Hoogsteen G*′·C*(H), and reverse Hoogsteen G*′·C*(rH) DNA base pairs—via the single (SPT) or double (DPT) proton transfer along the neighboring intermolecular H-bonds. These tautomeric reactions finally lead to the formation of the novel G·(rWC), C(rWC), G*′N2·C(rWC), C(H), and G*′N7·C(rH) DNA base mispairs. Gibbs free energies of activation for these reactions are within the range 3.64–31.65 kcal·mol−1 in vacuum under normal conditions. All TSs are planar structures (Cs symmetry) with a single exception—the essentially non-planar transition state TSG*·C*(rWC)↔G+·C−(rWC) (C1 symmetry). Analysis of the kinetic parameters of the considered tautomerization reactions indicates that in reality only the reverse Hoogsteen G*′·C*(rH) base pair undergoes tautomerization. However, the population of its tautomerised state G*′N7·C(rH) amounts to an insignificant value−2.3·10−17. So, the G*·C*(rWC), G*′·C*(H), and G*′·C*(rH) base pairs possess a permanent tautomeric status, which does not depend on proton mobility along the neighboring H-bonds. The investigated tautomerization processes were analyzed in details by applying the author's unique methodology—sweeps of the main physical and chemical parameters along the intrinsic reaction coordinate (IRC). In general, the obtained data demonstrate the tautomeric mobility and diversity of the G*·C* DNA base pair.

On the thermodynamics and kinetics of scorodite dissolution

Scorodite (FeAsO4·2H2O)–water interaction is critical to As distribution and storage in surface environment but is inadequately understood due to ambiguities in the mineral’s stability and weathering rate at atmospheric conditions. In the present study we attempted to experimentally determine the thermodynamic and kinetic parameters needed to compute solubility and dissolution rate of scorodite at 25 °C. Experiments were carried out in low pH (1.15) solutions using specially synthesized large scorodite crystals (with Mean Diameter of 27.9 μm). Such experimental conditions ensured the results were not subject to the influence of secondary Fe-bearing phase precipitation and grain size effect. Measured equilibrium concentrations of Fe and As, along with newly published Fe-As complexes association constants, were first used to determine the solubility products Ksp and dissolution rates rn at 50–90 °C. The obtained Ksp ∼ T and rn ∼ T dependence was then used to derive the Gibbs free energy, enthalpy, entropy, heat capacity, and activation energy for the dissolution reaction. Finally, we extrapolated the measurements to 25 °C and obtained room temperature solubility and dissolution rate, scrutinized the pH effect on dissolution, and analyzed the ΔG ∼ rn relation of the dissolution reaction. Our results show that literature data are likely overestimated scorodite solubility at pH > 4 ∼ 4.5 due to neglecting the effect of ferric iron hydrolysis. Estimated ambient condition dissolution rate is an order magnitude lower than the earlier report, implicating the importance of size effect, but is one to two orders of magnitude higher than that of common rock-forming minerals, cautioning the proposed use of scorodite for As fixation and storage. The determined rn ∼ ΔG relation cannot be fully fitted by the transition state model, particularly at near equilibrium, suggesting dissolution in this study may be controlled by defect-assisted surface reactions.

Effect of multi-frequency counter-current S type ultrasound pretreatment on the enzymatic hydrolysis of defatted corn germ protein: Kinetics and thermodynamics

Abstract In this paper, the impact of ultrasound pretreatment on the kinetics and thermodynamics of defatted corn germ protein (DCGP) enzymatic hydrolysis was evaluated. The enzymatic hydrolysis kinetics and thermodynamics were studied for traditional method and ultrasonic pretreatments with a single-frequency counter-current S type (20 KHz) (SFU) and a multi-frequency counter-current S type (20, 28, 35 and 40 KHz) (MFU). The results showed that the traditional, SFU and MFU pretreated enzymatic hydrolysis of DCGP followed the First-order kinetic model. Again, the SFU and MFU pretreatments enhanced the enzymatic hydrolysis of DCGP. Compared to traditional enzymatic hydrolysis, the reaction rate constant values were increased by 50.0%, 54.7%, 47.8% and 52.3% for SFU pretreated enzymatic hydrolysis, and 58.0%, 58.5, 53.6% and 54.7% for MFU pretreated enzymatic hydrolysis at 20, 30, 40 and 50 oC respectively. Also, the results showed that the SFU and MFU ultrasound pretreatments of DCGP reduced the thermodynamic parameters which included the activation energy (Ea), enthalpy (ΔH), entropies (ΔS) and Gibbs free energy (ΔG) in enzymatic hydrolysis reaction.