Gibbs Energy Change Research Articles

Solubility, solvent effect, enthalpy–entropy compensation and solvation thermodynamics of 4-(bromomethyl)-2(1H)-quinolinone in several aqueous blends

The current study was mainly devoted to solubility for the systems formed by 4-(bromomethyl)-2(1H)-quinolinone (BMQ) and blended solvents of isopropanol, N-methyl-2-pyrrolidinone (NMP), ethanol and n-propanol with water. Experiments for solubility determination were conducted by employing the shake-flask equilibration method from 278.15 to 318.15 K under 101.2 kPa. For each aqueous cosolvent mixture, the minimum solubility was recorded in water at 278.15 K; and the maximum value, in neat organic solvents at 318.15 K. The solubility performance was illustrated by Hansen solubility parameters of water, BMQ and co-solvents. No occurrence of polymorphic transformation or solvation was observed after experiments based on the XRD spectra of raw BMQ and excess solids analyzed. The satisfactory correlation results for solubility data was obtained by modified Wilson model, mixture response surface model, modified van’t Hoff-Jouyban–Acree model and Jouyban–Acree model. The relative average deviations were calculated to be no more than 8.72 %. Investigation on the relative contributions from inter- and intra-molecular interactions to the solubility variation of BMQ at temperature of 298.15 K was quantitatively performed via the linear solvation energy relationships (LSER). The descriptors of solvent blends including solubility parameter, dipolarity-polarizability and hydrogen-bond basicity were primarily responsible for the solubility variation. As well, the preferential solvation of BMQ was researched quantitatively via the inverse Kirkwood–Buff integrals method on the basis of some obtainable properties of solvent blends. The positive preferential solvation parameters for BMQ in middle and cosolvent-rich blends strongly suggest that the crystalline solute of BMQ is preferentially solvated by cosolvents of isopropanol, NMP, ethanol and n-propanol. The transfer and apparent dissolution properties including apparent Gibbs energy change (298.15 K), dissolution enthalpy and dissolution entropy (298.15 K) were derived and discussed. Analysis of enthalpy–entropy compensation indicates the entropy-driven mechanism of BMQ dissolved in all blend solvents.

Solubility of N-(9-fluorenylmethoxycarbonyloxy)-succinimide in several aqueous co-solvent solutions revisited: Solvent effect, preferential solvation and dissolution and transfer properties

Preferential solvation of N-(9-fluorenylmethoxycarbonyloxy)-succinimide (Fmoc-OSu) in mixtures of DMF (1) + water (2), ethanol (1) + water (2), ethylene glycol (EG, 1) + water (2) and DMSO (1) + water (2) was investigated by inverse Kirkwood–Buff integrals method. In ethanol-rich and intermediate contents, ethanol preferentially solvated Fmoc-OSu; and for the four aqueous co-solvent blends in water-rich composition regions, Fmoc-OSu was preferentially solvated by water. The solvent effect was described through modeling the Gibbs energy change of Fmoc-OSu solubility by linear solvation energy relationships. The main contribution to solubility variation of Fmoc-OSu was the solvent dipolarity-polarizability and solubility parameter. The dissolution and transfer enthalpy, entropy and Gibbs free energy were discussed in detail. Analysis outcomes of thermodynamic dissolution and enthalpy–entropy compensation demonstrated that two different mechanisms, enthalpy-driven and entropy-driven controlled the solubility variation of Fmoc-OSu in the DMF/EG/DMSO + water mixtures; and enthalpy-driven, in the ethanol + water mixture.

DGPredictor: Automated fragmentation method for metabolic reaction free energy prediction and de novo pathway design.

Group contribution (GC) methods are conventionally used in thermodynamics analysis of metabolic pathways to estimate the standard Gibbs energy change (ΔrG'o) of enzymatic reactions from limited experimental measurements. However, these methods are limited by their dependence on manually curated groups and inability to capture stereochemical information, leading to low reaction coverage. Herein, we introduce an automated molecular fingerprint-based thermodynamic analysis tool called dGPredictor that enables the consideration of stereochemistry within metabolite structures and thus increases reaction coverage. dGPredictor has comparable prediction accuracy compared to existing GC methods and can capture Gibbs energy changes for isomerase and transferase reactions, which exhibit no overall group changes. We also demonstrate dGPredictor's ability to predict the Gibbs energy change for novel reactions and seamless integration within de novo metabolic pathway design tools such as novoStoic for safeguarding against the inclusion of reaction steps with infeasible directionalities. To facilitate easy access to dGPredictor, we developed a graphical user interface to predict the standard Gibbs energy change for reactions at various pH and ionic strengths. The tool allows customized user input of known metabolites as KEGG IDs and novel metabolites as InChI strings (https://github.com/maranasgroup/dGPredictor).

Hydrodynamic Properties of Tris(2-methylbutyl) Phosphate and Tri-n-alkyl Phosphates in n-Dodecane – A Comparative Investigation between Unirradiated and Gamma Irradiated Solvent Systems

ABSTRACT The physicochemical parameters of tris(2-methylbutyl) phosphate (T2MBP), a molecule possessing the essential characteristics required to be considered as a promising extractant in the solvent extraction stage of fast reactor fuel reprocessing, have been evaluated in the present study. In this context, the density, viscosity and interfacial tension (IFT), which are considered to be few among the important solvent selection criteria prior to its deployment in the plant scale have been measured for T2MBP in n-dodecane (n-DD) based systems. Similar studies have been performed with its straight chain isomer, tri-n-amyl phosphate (TAP) as well as the widely utilized commercial extractant, tri-n-butyl phosphate (TBP) so as to emphasize on the structural effects. Though the trends on the physicochemical behaviour of TBP based systems (temperature and ligand concentration effects) are well known in the literature, the data on TBP have been generated in the present work for comparison with the T2MBP results under similar experimental conditions. Solutions of trialkyl phosphates (TalP) in n-DD of different concentrations have been used to generate the data on the variation of density, IFT and viscosity with the change in the ligand concentration. In addition, the transformation in their properties has been assessed after subjecting the solvents to various levels of gamma absorbed doses. Overall, it has been observed that there was no significant variation in the density of the irradiated TalPs; however, there was a significant rise in the viscosity and reduction in the IFT of the TalP samples upon irradiation. The data on the Gibbs energy change of activation of various 1.1 M TalP/n-DD solutions have been generated by fitting their respective dynamic viscosity value as a function of temperature using Andrade’s equation. Moreover, from the IFT value, the parameters relating to the interfacial activity of TalP/n-DD solutions have been determined using the Szyszkowski adsorption isotherm.

Spent kaolin filter cake as an effective adsorbent for the removal of Hexavalent Chromium [Cr (VI)] from aqueous solution: Comparative study of wastewater treatment methods

In this research three types of filter cake kaolin adsorbents were prepared using different method to remove hexavalent chromium Cr (VI) from aqueous solution. The surface functional groups, surface morphology and crystallinity of adsorbents were characterized using FTIR, SEM and XRD, respectively. The major and minor oxide compositional analysis confirmed a high SiO2 / Al2O3 for Beneficiated sample. The effects of operating factors like pH, initial concentration, adsorbent dosage, contact time and temperature have been investigated on batch adsorption experiment. The maximum removal efficiencies were 84.39, 77.32 and 71. 44 onto Beneficiated, Raw and calcined filter cake adsorbents, respectively. The adsorption process was further investigated using Langmuir and Freundlich isotherm models in which the equilibrium data obeyed Langmuir isotherm model. Thermodynamic parameters such as standard free Gibbs energy change (ΔGo), standard enthalpy changes (ΔHo) and standard entropy change (ΔSo) were calculated. Adsorption kinetics models resulted data fitted to the pseudo-first order model.

Computational studies of protein–drug binding affinity changes upon mutations in the drug target

AbstractMutations that lead to drug resistance limit the efficacy of antibiotics, antiviral drugs, targeted cancer therapies, and other treatments. Accurately calculating protein–drug binding affinity changes upon mutations in the drug target is of high interest as this can yield a better understanding into how such mutations drive drug‐resistance, especially when the mutation in question does not directly interfere with binding of the drug. The main aim of this article is to provide an up‐to‐date reference on the computational tools that are available for the calculation of Gibbs energy (free energy) changes upon mutation, their strengths, and limitations. The methods that are discussed include free energy calculations (free energy perturbation, thermodynamic integration, multistate Bennett acceptance ratio), analysis of molecular dynamics simulations (linear interaction energy, molecular mechanics [MM]/Poisson–Boltzmann solvated area, and MM/generalized Born solvated area), and methods that involve quantum mechanical calculations (including QM/MM). The possibility to use machine learning is also introduced. Given that the benefit of accurately calculating binding affinity changes upon mutation depends on comparing calculated values with experimental measurements, a brief survey on experimental methods and observables is provided. Examples of computational studies that go beyond calculating the Gibbs energy changes are given. Factors that need to be addressed by the computational chemist and potential pitfalls are discussed at length.This article is categorized under: Structure and Mechanism > Computational Biochemistry and Biophysics Molecular and Statistical Mechanics > Free Energy Methods Molecular and Statistical Mechanics > Molecular Interactions

Drug Solubility and Dissolution Thermodynamic Approach in Various Solvents at Different Temperatures: A Review

In chemical science, pharmaceutical, food science, petrochemicals, and material science, the solubility parameter is one of the most important factors. The studies of solubility and thermodynamics properties are directly used in crystallization-recrystallization, purification of yields, low toxicity of solvent or green solvent, modification, and many more. The experimental mole fraction solubility of compounds may be determined by various methods such as static gravity, laser dynamic, isothermal equilibrium, shake flask, and a number of other ways. The present review is focusing on the shake flask method. Further, the experimental mole fraction solubility was correlated with a theoretical model such as the Appellate and Buchowski equations. With the help of model correlation such as the Relative Average Deviation (RAD), Absolute Relative Deviation (ARD), and Root Mean Square Deviation (RMSD) for prediction of the best model fitting in theoretical approach. The Van't Hoff equation is most effective in the prediction of the dissolution thermodynamic factors such as ∆H°(mixing enthalpy change), ∆G°(mixing Gibbs energy change), and ∆S°(mixing entropy change). It had been given consequence details about endothermic or exothermic and entropy drive, which was directly applied in industrial production and purification of the drug.

Methylene blue adsorption on thermo plasma expanded graphite in a multilayer column system

The removal of dyes from wastewater is an important topic in environmental applications. Methylene blue (MB) is one of the most worrisome compounds, as it is widespread and used in many industrial activities. Adsorption represents an effective technique for the removal of this contaminant. Thermo plasma expanded graphite (TPEG) is an industrial material characterized by a fibrous morphology, a very low density and overlapped graphene layers. TPEG has a higher specific surface compared to conventional thermo-expanded graphite and it can establish effective attractive forces with charged pollutants. These properties make TPEG a very promising adsorbent material.In the present work, TPEG was tested in an innovative multilayer column system to treat MB contaminated solutions. Several batch experiments were carried out by varying pH, initial MB concentration and temperature.The optimal adsorption performance was assessed at pH 11, around which the TPEG assumed the maximum negative charge. Based on these results, the adsorption mechanism appeared to be related mainly to electrostatic interactions. At room temperature, the greatest amount of MB adsorbed on TPEG was detected by treating solutions with an initial concentration of 30 mgMB/L. The temperature increase from 20 to 40 °C caused an enhanced adsorption capacity when concentrations higher than 10 mgMB/L were treated. The adsorption trends were accurately described by a pseudo-second order kinetic law and the adsorption isotherms at 20 and 40 °C were found to follow both the features of Freundlich and Langmuir models. The adsorption capacity was estimated to reach threshold values around 95 mgMB/gTPEG and 265 mgMB/gTPEG at 20 and 40°C, respectively. The Gibbs energy change (ΔG°) was calculated to about −7.80 kJ/mol, which proved that the process is spontaneous from a thermodynamic point of view. Finally, it was verified that TPEG can be efficiently reused 5 times after a simple chemical regeneration phase with HCl.

Complexation of Cyclodextrins with Benzoic Acid in Water-Organic Solvents: A Solvation-Thermodynamic Approach.

The aim of this research is to obtain new data about the complexation between β-cyclodextrin (β-CD) and benzoic acid (BA) as a model reaction of the complex formation of hydrophobic molecules with cyclodextrins (CDs) in various media. This research may help developing cyclodextrin-based pharmaceutical formulations through the choice of the appropriate solvent mixture that may be employed in the industrial application aiming to control the reactions/processes in liquid phase. In this paper, NMR results for the molecular complex formation between BA and β-CD ([BA⊂β-CD]) in D2O-DMSO-d6 and in D2O-EtOH have shown that the stability of the complex in the H2O-DMSO-d6 varies within the experimental error, while decreases in H2O-EtOH. Changes in the Gibbs energy of BA resolvation in water and water–dimethylsulfoxide mixtures have been obtained and have been used in the analysis of the reagent solvation contributions into the Gibbs energy changes of the [BA⊂β-CD] molecular complex formation. Quantum chemical calculations of the interaction energy between β-CD and BA as well as the structure of the [BA⊂β-CD] complex and the energy of β-CD and BA interaction in vacuum and in the medium of water, methanol and dimethylsulfoxide solvents are carried out. The stability of [BA⊂β-CD] complex in H2O-EtOH and H2O-DMSO solvents, obtained by different methods, are compared. The thermodynamic parameters of the [BA⊂β-CD] molecular complexation as well as the reagent solvation contributions in H2O-EtOH and H2O-DMSO mixtures were analyzed by the solvation-thermodynamic approach.

Determination of kinetic triplet, thermal degradation behaviour and thermodynamic properties for pyrolysis of a lignocellulosic biomass

Kinetic triplet, thermal degradation behaviour and thermodynamic properties of peanut shells were determined on the basis of non-isothermal thermogravimetric experiments conducted at three different heating rates under N2 atmosphere. A single differential peak was observed for the devolatilization stage. The kinetic triplet of devolatilization stage was determined using Coats-Redfern and a combined method consisting the utilization of isoconversional and Criado methods. Kinetic validation revealed that the kinetic triplet determined using the combined method described the experimental values more precisely. The reaction mechanism ascertained by the combined method was D5-D3 combination. The Ea value was strong function of conversion, and computed using isoconversional methods (Boswell, Flynn-Wall-Ozawa, Starink, Tang) between 169 and 268 kJ/mol. Entalphy, entrophy and Gibbs energy changes were computed in 164–259 kJ/mol, −37–141 J/(mol.K) and 173–187 kJ/mol ranges, respectively. The comprehensive pyrolysis index values were also calculated, and shown to increase with increasing heating rate.

Kavun çekirdeği pirolizine ait kinetik parametrelerin ve termodinamik özelliklerin belirlenmesi

The aim of this study is to examine the behaviour of melon seed pyrolysis and to calculate its kinetic parameters along with thermodynamic properties. The thermogravimetric analysis experiments were conducted from ambient temperature to 800°C under nitrogen atmosphere at the heating rates of 5, 10, 20 and 40°C/min. It was determined that the pyrolysis process underwent through four stages where the second and third stages were the active pyrolysis stages. Kinetic calculations were carried out using model-free Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink and model-based Coats-Redfern methods. The apparent activation energy values of the second and third stages were calculated to be in the ranges of 123.9–215.5 and 141.9– 234.2 kJ/mol, respectively. The Coats-Redfern method demonstrated that the second and third stages fit the reaction mechanisms of F1.65 and D5, respectively. Moreover, the enthalpy, entropy and Gibbs energy changes of the active pyrolysis stages performed at 10°C/min heating rate were determined using the results calculated from the model-free kinetic methods. The results obtained in the present study will be useful to provide necessary information needed for the design of melon seed pyrolysis processes.

Improved water solubility of quercetin by preparing complexation with cyclodextrins in binary solvent

The antioxidant capacity of polyphenols have been widely used in food and pharmaceutical industries. Quercetin (Quer) is a polyphenolic flavonoid that shows several biological effects such as antioxidant, antitumor, antibacterial and antiproliferative effects both in-vitro and in-vivo. However, the solubility of quercetin in water is poor. Thus, it is essential to improve solubility of quercetin in pharmaceuticals by making its complexation with other compounds. In this study, the synthesis of the 2-hydroxypropyl-β-cyclodextrin complex with quercetin (Quer-HPβCD) in the form of nanoparticles in water-ethanol solvents has been carried out. The results showed that the obtained yield of (Quer-HPβCD) complexation in binary solvent was greater than that in pure water. The highest Y value was 80% in a binary solvent with 20% v/v of ethanol. The composition, morphology, structural and thermodynamic properties of the nanoparticles Quer-HPβCD have been determined. This study demonstrated that using mixed water- ethanol solvent and lyophilization technique was able to produce quercetin nanoparticles with significantly smaller particle size. The nanoparticles have a spherical shape with an average size of about 40-60 nm. The results of the phase solubility diagram showed that in water the solubility of quercetin increased and linearly depended on the concentration of host’s molecule while Quer and HP-βCD obtained a 1:1 stoichiometric complex. The stability constant of (Quer-HPβCD) complex was found to be logK = 2.56. The Gibbs energy change of the complexation reaction was found to be -14.60 kJ/mol.

Enhanced Efficiency of Inorganic CsPbI3−xBrx Perovskite Solar Cell via Self‐Regulation of Antisite Defects

AbstractDeep defects often act as Shockley–Read–Hall recombination centers in semiconductor materials, degrading the photoelectric performance and long‐term stability of assembled photovoltaic devices. In this report, deep level transient spectroscopy is probed to determine defect concentrations and defect energy levels in all‐inorganic CsPbI3−xBrx perovskite solar cells. Combining that data with the density functional theory calculation, the dominant deep defect states are assigned to antisite defect pairs (PbI and IPb) and interstitial defects (Pbi) in freshly prepared CsPbI3−xBrx films. Astonishingly, all these defects are reduced by approximately one or two orders of magnitude after resting the films overnight, in excellent agreement with the defect‐reduced trends from the fluorescence spectra, transient photovoltage, and space‐charge‐limited current measurements. The reduced defect concentrations are proposed to be connected with their self‐regulation during the storage. To assess the thermodynamics possibilities, two reaction procedures are designed to calculate their formation enthalpies and negative Gibbs energy change revealed their spontaneous processes. Then, strain relief is the direct driving force for ion migration, thus defect‐regulation by tracing the X‐ray diffraction patterns. Furthermore, the power conversion efficiency is improved and the J–V hysteresis is suppressed due to reduced ion migration via relaxed strain.

Computational Estimation of the Aqueous Acidities of Alcohols, Hydrates, and Enols.

Alcohols are ubiquitous chemical species, and their acid dissociation constants are critical properties in many applications. It is useful to have a reliable and convenient computational procedure for estimating these acidities. Here we describe a quantitative structure-activity relationship (QSAR) for the pKas of alcohols in aqueous solution employing density functional theory computations at the B3LYP/6-31+G(d,p) level with the CPCM implicit solvent model for the aqueous solutions. For the pKas, the energy difference in solution between the parent compound and the anion, ΔE(H2O), was used as a single descriptor. High quality QSAR equations are obtained both for the gas-phase Gibbs energy changes (ΔGr0s, R2 = 0.9764) and the aqueous pKas (R2 = 0.9594). It is shown that the aqueous equation can also be used to estimate the pKas of fluorinated alcohols, hydrates formed by carbonyl compounds in aqueous solution, and enols that appear as minor components in keto-enol equilibria.

Solubility profile of phenytoin in the mixture of 1-propanol and water at different temperatures

The aims of the current study are solubility behavior investigation of phenytoin in the mixtures of 1-propanol and water at different temperatures and correlation of the generated data to some linear and non-linear cosolvency models. As another physico-chemical property, the density of phenytoin saturated solutions is also measured and the results are mathematically represented using the Jouyban-Acree model. The accuracy of applied models is checked by the computation of the mean relative deviations (MRD %). Moreover, the apparent thermodynamic properties of the phenytoin dissolution process are also calculated according to van't Hoff and Gibbs equations. It is observed that all the thermodynamic quantities, namely Gibbs energy, enthalpy and entropy changes, are positive in every solvent system. Furthermore, by means of the inverse Kirkwood-Buff integrals it is shown that phenytoin is preferentially solvated by water molecules in water-rich mixtures and preferentially solvated by 1-propanol molecules in the composition interval 0.19 <x1 < 1.0.

Phase separation phenomena and thermodynamics of octylphenol polyoxyethylene ether in micellar solutions: Effect of high concentration of inorganic salts and linear correlation

The phase separation phenomena or cloud points (CP) behavior of nonionic octylphenol polyoxyethylene ether with oxyethylene glycol ether unit of 15 (OP-15) were investigated in aqueous micellar solutions containing high concentrations of inorganic salts including NaCl, KCl, MgCl2, CaCl2, BaCl2, AlCl3, FeCl3, Na2SO4 and Na2SiO3. The change in CP induced by salts and its mechanism are discussed theoretically. In aqueous solutions containing high concentration of salt, for the first time the linear relationship between CP and salt concentration is well established to characterize the depression of CP. Based on pseudo phase separation model, thermodynamic parameters are estimated and adopted to further describe the phase separation process and the interactions between OP-15 molecules or the OP-15/water interactions. Thermodynamic parameters including standard Gibbs energy change (ΔGCP0), enthalpy change (ΔHCP0) and entropy change (ΔSCP0) indicate that the additions of different salts result in the change in entropy-driven nonspontaneous process of phase separation. These data, which are from the compensation temperatures and the change of molar heat capacity, also prove that different ions induce the change in the interactions between surfactant molecules or the surfactant–water interaction and thus affect the depression of CP. These findings help with understanding the effect of inorganic salts, especially the high concentration of salt, on CP of nonionic surfactant and then broadening the application of nonionic surfactant based on CP such as the extraction of biomaterials in biological samples derived from animals or plants, etc.

Thermodynamics of Copper Arsenious Raw Materials Dissolution in Nitric Acid

This article describes thermodynamic study of hydrometallurgical method for processing of copper arsenious gold-containing raw material. Chemical and phase composition of the material were researched. Calculations of the Gibbs energy change were conducted for possible reactions of the main minerals, present in the raw material, with nitric acid. Eh-pH diagrams and solid/liquid equilibrium distribution diagrams, which were constructed in order to confirm the possibility of obtaining the required reaction products through nitric acid leaching of the studied raw material.

Physicochemical Parameters of the Methylparaben Adsorption from Aqueous Solution Onto Activated Carbon and Their Relationship with the Surface Chemistry.

The methylparaben adsorption from aqueous solution onto activated carbon is a relevant topic because of the toxicity of this compound for human and environmental health. The physicochemical parameters allow us to evaluate the performance of the adsorption and the relationship between the surface chemistry and the adsorbed amount of methylparaben. The effect of the solution chemistry on the adsorption was also evaluated. In this work, the methylparaben adsorption on three activated carbons with different physicochemical properties, specifically different contents of oxygenated groups and total basicity, is presented. Kinetic, equilibrium, and calorimetry tests were conducted. The maximum adsorbed amount of methylparaben was achieved on an activated carbon with basic characteristics, Qmax = 1.64 mmol g–1; in the same activated carbon, the initial rate was 0.20 mmol g–1 h–1, and the value determined for the interaction enthalpy was −12.6 × 10–20 J molecules–1, and the Gibbs energy change was close to −14.96 kJ mol–1.

Thermodynamic analysis of the solubility of clozapine in organic solvents

The solid-liquid equilibrium solubility of clozapine in eighteen organic solvents (i.e., methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, n-pentanol, i-pentanol, acetone, 2-butanone, acetonitrile, N, N-dimethylformamide, tetrahydrofuran, chloroform, ethyl formate, methyl acetate, and ethyl acetate) was determined using a gravimetric method over a temperature ranging from 278.15 K to 323.15 K at atmospheric pressure. The modified Apelblat equation, λh equation, NRTL equation, and Wilson equation were selected to correlate the solubility data. The fitting degree of thermodynamic models was evaluated by the relative average deviation, and root mean root mean square deviation. Dissolution properties, including enthalpy, entropy, and Gibbs energy changes of clozapine were evaluated by the Wilson model. The solubility data, thermodynamic parameters and dissolution properties for clozapine will be of crucial guiding value for the optimization of the industrial crystallization process.

SO2 absorption in highly efficient chemical solvent AChBr + Gly compared with physical solvent ChBr + Gly

Deep eutectic solvents (DESs) have been identified as optimal gas absorbents. A tertiary amine-containing task-specific DES AChBr+Gly and a conventional DES ChBr+Gly have been designed, prepared and used to capture SO2. It is found that absorption capacity of 3.74 and 2.97 mol of SO2 per mole of DES can be obtained by AChBr+Gly and ChBr+Gly, respectively, at 293.2 K and 1 bar. When SO2 partial pressure was decreased to 0.01 bar, the capacity decreased to 0.93 and 0.13 mol SO2 of per mole of AChBr+Gly and ChBr+Gly, respectively. Mechanism and thermodynamic studies show that absorption by former absorbent includes physisorption, quasi-chemisorption (a strong physisorption) and chemisorption, while absorption by later absorbent only includes physisorption and quasi-chemisorption. Two equations were first proposed for the description of SO2 absorption. In these equations, the physisorption capacity is correlated with Henry's law, and the quasi-chemisorption and chemisorption are correlated with the quasi-chemical equilibrium constant of halogen···SO2 interaction and the chemical equilibrium constant of tertiary amine···SO2 interaction, respectively. In addition, the corresponding enthalpy change, entropy change, and Gibbs energy change have been calculated and discussed.