Showing papers on "Equilibrium constant published in 2022"

Improper Estimation of Thermodynamic Parameters in Adsorption Studies with Distribution Coefficient KD (qe/Ce) or Freundlich Constant (KF): Considerations from the Derivation of Dimensionless Thermodynamic Equilibrium Constant and Suggestions

Abstract: Adsorption processes often include three important components: kinetics, isotherm, and thermodynamics. In the study of solid–liquid adsorption, “standard” thermodynamic equilibrium constant K Eq o ; dimensionless) plays an essential role in accurately calculating three thermodynamic parameters: the standard Gibbs energy change (∆G°; kJ/mol), the standard change in enthalpy (∆H°; kJ/mol), and the standard change in entropy [∆S°; J/(mol × K)] of an adsorption process. Misconception of the derivation of the K Eq o constant that can cause calculative errors in values (magnitude and sign) of the thermodynamic parameters has been intensively reflected through certain kinds of papers (i.e., letters to editor, discussions, short communications, and correspondence like comment/rebuttal). The distribution coefficient (KD) and Freundlich constant (KF) have been intensively applied for calculating the thermodynamic parameters. However, a critical question is whether KD or KF is equal to K Eq o . This paper gives (1) thorough discussion on the derivation of thermodynamic equilibrium constant of solid–liquid adsorption process, (2) reasonable explanation on the inconsistency of (direct and indirect) application of KD or KF for calculating the thermodynamic parameters based on the derivation of K Eq o , and (3) helpful suggestions for improving the quality of papers published in this field.

Solvent and Counteranion Assisted Dynamic Self-Assembly of Molecular Triangles and Tetrahedral Cages.

Abstract: Self-assembly of naked PdII ions separately with newly designed bis(3-pyridyl)benzothiadiazole (L1) and bis(3-pyridyl)thiazolo[5,4-d]thiazole (L2) donors separately, under varying experimental conditions, yielded Pd4L8 (L= L1 or L2) tetrahedral cages and their homologous Pd3L6 (L= L1 or L2) double-walled triangular macrocycles. The resulting assemblies exhibited solvent, temperature, and counteranion induced dynamic equilibrium. Treatment of L1 with Pd(BF4)2 in acetonitrile (ACN) resulted in selective formation of a tetrahedral cage [Pd4(L1)8](BF4)8 (1a), which is in dynamic equilibrium with its homologue triangle [Pd3(L1)6](BF4)6 (2a) in dimethyl sulfoxide (DMSO). On the other hand, similar self-assembly using L2 instead of L1 yielded an equilibrium mixture of tetrahedral cage [Pd4(L2)8](BF4)8 (3a) and triangle [Pd3(L2)6](BF4)6 (4a) forms in both ACN and DMSO. The assembles were characterized by multinuclear NMR and ESI-MS while the structure of the tetrahedral cage (1a) was determined by single crystal X-ray diffraction. Existence of a dynamic equilibrium between the assemblies in solution has been investigated via variable temperature 1H NMR. The equilibrium constant K = ([Pd4L8]3/[Pd3L6]4) was calculated at each experimental temperature and fitted with the Van't Hoff equation to determine the standard enthalpy (ΔH°) and entropy (ΔS°) associated with the interconversion of the double-walled triangle to tetrahedral cage. The thermodynamic feasibility of structural interconversion was analyzed from the change in ΔG°, which suggests favorable conversion of Pd3L6 triangle to Pd4L8 cage at elevated temperature for L1 in DMSO and L2 in ACN. Interestingly, similar self-assembly reactions of L1 and L2 with Pd(NO3)2 instead of Pd(BF4)2 resulted in selective formation of a tetrahedral cage [Pd4(L1)8](NO3)8 (1b) and double-walled triangle [Pd3(L2)6](NO3)6 (4b), respectively.

The Acid-Base/Deprotonation Equilibrium Can Be Studied with a MicroScale Thermophoresis (MST)

Abstract: MicroScale thermophoresis (MST) is a rapidly developing bioanalytical technique used routinely for the examination of ligand-target affinity. It has never been used so far for the analysis of acid-base dissociation and the determination of pKa constant. This work is the-proof-of-concept of this new idea. It demonstrates that the pKa values obtained from the thermophoretic data are consistent with the reference methods. As a result, the analytical potential and utility of the MST technology can become even greater, especially if the new detection system of thermophoretic movement will be developed in the future. Even now, taking into account the necessity to use fluorescence, the proposed method may be useful in many respects.

Exploiting the "Lego brick" approach to predict accurate molecular structures of PAHs and PANHs.

Abstract: Polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic nitrogen heterocycles (PANHs) are important and ubiquitous species in space. However, their accurate structural and spectroscopic characterization is often missing. To fill this gap, we exploit the so-called "Lego brick" approach [Melli et al., J. Phys. Chem. A, 2021, 125, 9904] to evaluate accurate rotational constants of some astrochemically relevant PAHs and PANHs. This model is based on the assumption that a molecular system can be seen as formed by smaller fragments for which a very accurate equilibrium structure is available. Within this model, the "template molecule" (TM) approach is employed to account for the modifications occurring when going from the isolated fragment to the molecular system under investigation, with the "linear regression" model being exploited to correct the linkage between different fragments. In the present work, semi-experimental equilibrium structures are used within the TM model. The performance of the "Lego brick" approach has been first tested for a set of small PA(N)Hs for which experimental data are available, thus leading to the conclusion that it is able to provide rotational constants with a relative accuracy well within 0.1%. Subsequently, it has been extended to the accurate prediction of the rotational constants for systems lacking any spectroscopic characterization.

Synthesis of Methylal and Poly(oxymethylene) Dimethyl Ethers from Dimethyl Ether and Trioxane

Abstract: Poly(oxymethylene) dimethyl ethers (OME) are interesting synthetic fuels that could replace fossil diesel fuel. Therefore, economic routes for OME production have to be developed. One particularly interesting route is the synthesis of OME from dimethyl ether (DME) and formaldehyde. The principal feasibility of this route is established, but the physico-chemical information on essential steps is still lacking. In particular, there is no data on the first step in this synthesis, which is the formation of methylal (MAL) from DME and formaldehyde. Kinetic batch experiments were carried out in a stirred batch autoclave with a commercially available acidic ion-exchange resin as a catalyst in the temperature range of 353–373 K for up to 200 h. Trioxane was used as a water-free source of formaldehyde. Due to the volatility of DME, the experiments were carried out under pressure; high-pressure magnetic resonance (NMR) spectroscopy was applied for the analysis. During the reaction, not only MAL but also OME are formed, as well as a side product, methyl formate (MeFo). Therefore, the equilibrium constant of the MAL formation had to be determined based on a reaction kinetic model of the entire reaction network. The formation of MAL was found to have a larger equilibrium constant than the subsequent oligomerization reactions leading to OME, but it is also much slower than these reactions.

Why Equilibrium Constants Are Unitless.

Abstract: The importance of the nonexistence of a unit for equilibrium constants is well-recognized by the chemistry community. However, it is still common to encounter the use of equilibrium constants with units in recent chemistry education papers, which may mislead students and even instructors. This is mainly due to the lack of studies on the representation of the derivations of equilibrium constants in a logical manner. We hope that the explanations provided in this Viewpoint will help to clarify this issue.

Temperature and Pressure-Dependent Rate Constants for the Reaction of the Propargyl Radical with Molecular Oxygen

Abstract: Ab initio CCSD(T)/CBS(T,Q,5)//B3LYP/6-311++G(3df,2p) calculations have been conducted to map the C3H3O2 potential energy surface. The temperature- and pressure-dependent reaction rate constants have been calculated using the Rice–Ramsperger–Kassel–Marcus Master Equation model. The calculated results indicate that the prevailing reaction channels lead to CH3CO + CO and CH2CO + HCO products. The branching ratios of CH3CO + CO and CH2CO + HCO increase both from 18 to 29% with reducing temperatures in the range of 300–2000 K, whereas CCCHO + H2O (0–10%) and CHCCO + H2O (0–17%) are significant minor products. The desirable products OH and H2O have been found for the first time. The individual rate constant of the C3H3 + O2 → CH2CO + HCO channel, 4.8 × 10–14 exp[(−2.92 kcal·mol–1)/(RT)], is pressure independent; however, the total rate constant, 2.05 × 10–14 T0.33 exp[(−2.8 ± 0.03 kcal·mol–1)/(RT)], of the C3H3 + O2 reaction leading to the bimolecular products strongly depends on pressure. At P = 0.7–5.56 Torr, the calculated rate constants of the reaction agree closely with the laboratory values measured by Slagle and Gutman [Symp. (Int.) Combust.1988, 21, 875−883] with the uncertainty being less than 7.8%. At T < 500 K, the C3H3 + O2 reaction proceeds by simple addition, making an equilibrium of C3H3 + O2 ⇌ C3H3O2. The calculated equilibrium constants, 2.60 × 10–16–8.52 × 10–16 cm3·molecule–1, were found to be in good agreement with the experimental data, being 2.48 × 10–16–8.36 × 10–16 cm3·molecule–1. The title reaction is concluded to play a substantial role in the oxidation of the five-member radicals and the present results corroborate the assertion that molecular oxygen is an efficient oxidizer of the propargyl radical.

Calculation and Visualization of Binding Equilibria in Protein Studies

Abstract: A set of simulation applets has been developed for visualizing the behavior of the association and dissociation reactions in protein studies. These reactions are simple equilibrium reactions, and the equilibrium constants, most often dissociation constant KD, are useful measures of affinity. Equilibria, even in simple systems, may not behave intuitively, which can cause misconceptions and mistakes. These applets can be utilized for planning experiments, for verifying experimental results, and for visualization of the equilibria in education. The considered reactions include protein homodimerization, ligand binding to a receptor (or heterodimerization), and competitive ligand binding. The latter one can be considered as either a ligand binding to two receptors or a binding of two ligands to a single receptor. In general, the user is required to input the total concentrations of all proteins and ligands and the dissociation constants of all complexes, and the applets output the equilibrium concentrations of all protein species graphically as functions of concentration and as numerical values at a specified point. Also, a curve fitting tool is provided which roughly estimates the concentrations or the dissociation constants based on the experimental data. The applets are freely available online (URL: https://protsim.github.io/protsim) and readily hackable for custom purposes if necessary.

Equilibrium Composition of Products Formed by Non-catalytic Conversion of Hydrocarbons

Abstract: Abstract The kinetic patterns of the attainment of the equilibrium product composition in non-catalytic processes of partial oxidation and of steam and carbon dioxide reforming of hydrocarbons in the temperature range 1400–1800 K, characteristic of these processes, were analyzed. The need for such analysis is caused by the rapidly increasing consumption of natural gas as a chemical feedstock and by growing attention to environmental problems, in particular, to a decrease in СО 2 emissions or to partial CO 2 utilization. The forward and reverse water gas shift reactions (WGSRs) play an important role in approach to the equilibrium product composition in these processes. Analysis has shown that the elementary reactions characteristic of forward and reverse WGSRs start to play a significant role long before the equilibrium in the system is attained. Already in the intermediate steps of the process, the distribution of the major reaction products, Н 2 , СО, Н 2 О, and СО 2 , almost corresponds to the equilibrium value of K t = ([H 2 ][CO 2 ])/([CO][H 2 O]), close to the WGSR equilibrium constant K eq , and further conversion of the products occurs at K t values close to K eq .

Experimental determination of activation rate constant and equilibrium constant for bromo substituted succinimide initiators for an atom transfer radical polymerization process

Abstract: Abstract Alkyl bromides are used as initiators in most of the atom transfer radical polymerization (ATRP) process and play an important role for controlling the ATRP equilibrium. In this work, the effect of solvent on equilibrium constant of ATRP (K ATRP) and rate constant of activation (k act) of three isomeric alkyl bromides [namely, N-phenyl(3-bromo-3-methyl)succinimide, N-phenyl(3-bromo-4-methyl)succinimide, and N-phenyl(3-bromomethyl)succinimide] is reported. The k act and K ATRP values of alkyl bromide are determined experimentally using UV–Vis-NIR spectrometry. The termination rate constant for model compound is calculated using DOSY NMR spectroscopy. The k act and K ATRP values for the mentioned alkyl bromides are determined in five different polar solvent and the effect of polarity is observed. The obtained values of k act and K ATRP of N-phenyl(3-bromo-3-methyl)succinimide in acetonitrile at 25 °C is 6.60 × 10−2 L mol−1 s−1 and 1.42 × 10−9, respectively. These values are quite comparable with the experimentally determined reported k act and K ATRP of values of acrylates and benzyls initiators. Alternatively, the investigation of possible chain initiation activity for the ATRP process for the mentioned alkyl bromides is carried out theoretically using density functional theory (DFT) method [B3LYP/6-31+G(d) level]. A good correlation is obtained between the experimentally determined and theoretically calculated K ATRP values of studied alkyl bromides in chosen solvents. Significantly, it is found that the values of k act and K ATRP of alkyl bromides is solvent dependent and the magnitude values of the k act and K ATRP increases with increasing the solvent polarity. The proposed bromo substituted succinimides can be used as the initiator for the polymerization of acrylates, benzyls, maleimides, and itaconimides monomer under the selected solvent system.

Synthesis of zeolitic imidazolate framework-8 and gold nanoparticles in a sustained out-of-equilibrium state

Abstract: The design and synthesis of crystalline materials are challenging due to the proper control over the size and polydispersity of the samples, which determine their physical and chemical properties and thus applicability. Metal - organic frameworks (MOFs) are promising materials in many applications due to their unique structure. MOFs have been predominantly synthesized by bulk methods, where the concentration of the reagents gradually decreased, which affected the further nucleation and crystal growth. Here we show an out-of-equilibrium method for the generation of zeolitic imidazolate framework-8 (ZIF-8) crystals, where the non-equilibrium crystal growth is maintained by a continuous two-side feed of the reagents in a hydrogel matrix. The size and the polydispersity of the crystals are controlled by the fixed and antagonistic constant mass fluxes of the reagents and by the reaction time. We also present that our approach can be extended to synthesize gold nanoparticles in a redox process.

Synthesis of zeolitic imidazolate framework-8 and gold nanoparticles in a sustained out-of-equilibrium state

Abstract: The design and synthesis of crystalline materials are challenging due to the proper control over the size and polydispersity of the samples, which determine their physical and chemical properties and thus applicability. Metal - organic frameworks (MOFs) are promising materials in many applications due to their unique structure. MOFs have been predominantly synthesized by bulk methods, where the concentration of the reagents gradually decreased, which affected the further nucleation and crystal growth. Here we show an out-of-equilibrium method for the generation of zeolitic imidazolate framework-8 (ZIF-8) crystals, where the non-equilibrium crystal growth is maintained by a continuous two-side feed of the reagents in a hydrogel matrix. The size and the polydispersity of the crystals are controlled by the fixed and antagonistic constant mass fluxes of the reagents and by the reaction time. We also present that our approach can be extended to synthesize gold nanoparticles in a redox process.

Determination of polyligand complexes of cobalt (ii) with citrate and pyrophosphate ions

Abstract: In the work it is shown by the spectrophotometry method that depending on the concentration ratio of ligands [PPi4–]/[Cit3–] in the pyrophosphate-citrate electrolyte, cobalt (II) ions form not only citrate [Co(Cit)2]4– and pyrophosphate [Co(PPi)2]6–, but also polyligand complexes [Co(PPi)m(Cit)n]+2–(4m+3n). The composition of polyligand complexes [Co(PPi)Cit]5– was determined, and the equilibrium constant of the reaction of their formation and the constant of their stability were calculated (pβ=8.47). The dependence of the degree of formation of citrate, polyligand, and pyrophosphate complexes of cobalt (II) in the pyrophosphate-citrate electrolyte on the logarithm of the ratio of equilibrium concentrations of ligands is calculated.

Revisiting the calculation of thermodynamic parameters of adsorption processes from the modified equilibrium constant of the Redlich–Peterson model

Abstract: BACKGROUND The adsorption equilibrium constant of the Langmuir model (KL; L/mol) has been applied as the so-called standard thermodynamic equilibrium constant K Eq o for calculating the thermodynamic parameters (∆G°, ∆S°, and ∆H°) of adsorption process by using the van't Hoff equation. Some authors have (directly and indirectly) applied the constant KRP (L/kg) of the Redlich–Peterson model for such calculating. However, this is an incorrect application because the unit of KRP is not suitable (it is not equilibrium constant). Its new adsorption equilibrium constant Ke(RP) (L/mol) was revisited based on aRP (L/mol)g. In the literature, there is still uncertainty regarding the application of aRP as K Eq o for calculating the thermodynamic parameters. Therefore, the present study aimed to evaluate the feasibility of applying Ke(RP) to calculate thermodynamic parameters using available literature data. The thermodynamic parameters obtained from Ke(RP) were compared to those from KL. A case study on using a biosorbent for adsorbing methylene blue dye at different temperatures was carried out to re-verify the feasibility. RESULTS The Redlich–Peterson model is only valid when its exponent is in a strict range (0 ≤ g ≤1). The Redlich–Peterson model (68%; 227 observations collected from 52 published papers) describe adsorption equilibrium datasets better than the Langmuir model. The negative values ΔG° obtained based on Ke(RP) (11.7–47.6 kJ/mol) were significantly different (p = 2.98×10–12) from those on KL (12.2–40.8 kJ/mol). The magnitudes of ΔH° obtained based on Ke(RP) were significant different (p< 0.05) those on KL; however, such difference did not affect conclusions on dominant mechanism adsorption (physical or chemical). The magnitude of ΔH° for chemisorption (involved in covalent bonds) is higher than 200 kJ/mol. For the case study, the ∆H° (kJ/mol) and ∆S° [J/(mol×K)] values calculated based on Ke(RP) (11.65 and 111.5) were similar to those on KL (11.34 and 110.4, respectively). CONCLUSIONS New equilibrium constant Ke(RP) (L/mol) of the Redlich–Peterson model can be applied as K Eq o for calculating the thermodynamic parameters (∆G°, ∆S°, and ∆H°) of adsorption process under some specific cases (i.e., F, H, and L-shaped adsorption isotherms). The majority of the adsorption processes (98%) involve physical adsorption. This article is protected by copyright. All rights reserved.

Equilibration processes in alkaline Cu | Cu(II), glycine system

Abstract: The nature and kinetics of the equilibrium processes at the interface between the copper electrode and the alkaline solution containing glycine complexes of Cu(II) have been studied. The material balance equations that consider the formation of Сu(I) complexes were used to calculate the composition of the equilibrium system. It was found that the amount of Сu(I) compounds increases with increasing the pH and ligand concentration. Using the EQCM method it was found that the electrochemical dissolution of Cu electrode proceeds under open circuit conditions at potentials 60–70 mV higher than their equilibrium values. The generation of Cu+ ions obeys the laws of pseudo-first order processes at a rate constant of ~2 × 10–4 s–1. It is assumed that the final product of the equilibration is a monoligand complex of CuL (L– is a glycinate anion). Besides, there is a thermodynamic probability of the formation of cuprous oxide in the system.

DFT investigation on the carbonate radical formation in the system containing carbon dioxide and hydroxyl free radical.

Abstract: A density functional theory (DFT) study was performed to explore the reaction mechanisms of CO2-containing systems(CO2,HCO3-,H2CO3) with hydroxyl radical using UM06-2X/aug-cc-pVTZ for geometry optimization and UCCSD(T)-F12/cc-pVDZ-F12 for electronic energies, the effect of solvation is considered using the implicit solvent model with two explicit water molecule. The final transformation of hydroxyl radical into carbonate anion radical by reaction with CO2-containing system was studied. The energy barriers, Gibbs free energy, reaction enthalpy changes and reaction rate constants for reaction of CO2-containing systems by hydroxyl radical are calculated. The results show that the reaction of hydroxyl with HCO3- has the lowest energy barrier (5.6 kcal/mol) and maximum reaction rate constant (7.60 × 107dm3mol-1s-1). However, the reaction of hydroxyl radical with CO2 has the highest energy barrier (20.3 kcal/mol) and the minimum reaction rate constant (8.88 × 10-10 dm3mol-1s-1) respectively. The equilibrium constant and rate ratio were calculated by the concentration ratio and free energy of the two conformations of H2CO3 in aqueous solution. The results show that the cc conformation of carbonate has a little higher reaction energy barrier and a higher reaction rate than ct conformation. ∙HCO3 generated by the reaction of CO2 and H2CO3 with hydroxyl radical is further dissociated in aqueous solution to form carbonate radical anion. The calculated free energy of the dissociation process is -2.5 kcal/mol and pKa is -1.9, indicating that HCO3- is a strong acid. Therefore, hydroxyl radicals are spontaneously converted to carbonate radical anions in CO2-containing systems.

Adsorption of Methylene Blue on Chestnut Shell-Based Activated Carbon: Calculation of Thermodynamic Parameters for Solid–Liquid Interface Adsorption

Abstract: Chestnut shell-based activated carbon was prepared with chestnut shell as the raw material and ZnCl2 as the activating agent. Based on thermodynamic parameters, the adsorption behavior of methylene blue (MB) on chestnut shell-based activated carbon was studied, and the effect of temperature on the thermodynamic parameters and adsorption behavior was investigated. The Langmuir equilibrium constant (KL) and the standard equilibrium constant (K0) were used to calculate the thermodynamic parameters, respectively. Comparative analysis showed that spontaneous adsorption (ΔG0 < 0) was more compatible with the standard equilibrium constant (K0). Furthermore, the thermodynamic parameters at 30, 40 and 50 °C were measured, and the adsorption potential was investigated and calculated. Eventually, the mechanism of the adsorption process was determined. It was concluded that the adsorption process mainly involved chemical adsorption, which indicated that MB adsorption was caused by the force of the chemical bond.

Application of pervaporation membranes to the direct carboxylation of ethene glycol using CeO2-based catalysts—Comparison of the batch reaction to a flow reaction in SC-CO2

Abstract: The reaction between ethene glycol-EG and CO2 to afford the cyclic ethene carbonate-EC has been studied in solvent-less conditions and in absence of water traps but using pervaporation membranes to eliminate water. The parameter space of the reaction (temperature, pressure, catalyst loading, time of reaction) has been investigated, filling a gap existing in the scientific literature, and the optimal reaction conditions set as: 408 K, 2 h, 10% w/w cat, 5.0 MPa of CO2. Under such conditions an equilibrium constant equal to 8.3 × 10−4 has been calculated based on the equilibrium composition of the reaction mixture that contains 0.33% mol of EC. Such value is higher than that calculated from available thermodynamic data in the scientific literature (3 ×10−26) showing that they need a correction to be adapted to a condensed phase. Using a SC-mixture of EG and CO2 (with a molar ratio CO2/EG equal to 60), 0.25 ± 0.01% EC is formed in a contact-time of the order of 4–6 min with respect to 120 min in a batch reaction, justified by the higher CO2/EG molar ratio. Water is formed in excess with respect to the reaction stoichiometry, due to parasite reactions that bear to the formation of di- and tri-ethers and linear carbonate. Such excess water (up to ten times the expected value) strongly influences the equilibrium composition and disfavour the formation of EC. The application of a NaA-type pervaporation membrane can increase the EC-equilibrium concentration of 3–4 times. EG is shown to be less performant than ethanol due to the easier etherification that causes extra-formation of water, that pushes the equilibrium to the left, and to its viscosity that affects the performance of the membrane. The reaction time must be kept under control as a long reaction time favours the formation of ethers, more than EC. A DFT study aimed to explore suitable intermediate species in the catalysed reaction explains that etherification and carbonation are competitive reactions.

Experimental Determination of Solubility Constants of Saponite at Elevated Temperatures in High Ionic Strength Solutions

Abstract: Abstract Saponite occurs in a wide range of environments from hydrothermal systems on the Earth to surface deposits on Mars. Of practical importance is that Mg-saponite forms when glasses for nuclear waste are altered in Mg-bearing aqueous solutions. In addition, saponite is favorably considered as candidate buffer material for the disposal of high-level nuclear waste and spent nuclear fuel in harsh environments. However, the thermodynamic properties, especially for Mg-saponites, are not well known. Here the author synthesized Mg-saponite (with nitrate cancrinite) following a previously reported procedure and performed solubility experiments at 80 °C to quantify the thermodynamic stability of this tri-octahedral smectite in the presence of nitrate cancrinite. Then, in combination with the equilibrium constant at 80 °C for the dissolution reaction of nitrate cancrinite from the literature, the author determined the solubility constant of saponite at 80 °C based on the solution chemistry for the equilibrium between saponite and nitrate cancrinite, approaching equilibrium from the direction of supersaturation, with an equilibrium constant of –69.24 ± 2.08 (2σ) for dissolution of saponite at 80 °C. Furthermore, the author extrapolated the equilibrium constant at 80 °C to other temperatures (i.e., 50, 60, 70, 90, and 100 °C) using the one-term isocoulombic method. These equilibrium constants are expected to have applications in numerous fields. For instance, according to the extrapolated solubility constant of saponite at 50 and 90 °C, the author calculated the saturation indexes with regard to saponite for the solution chemistry from glass corrosion experiments at 50 and 90 °C from the literature. The results are in close agreement with the experimental data. This example demonstrates that the equilibrium constants determined in this study can be used for reliable modeling of the solution chemistry of glass corrosion experiments.

Development of Novel Analysis and Characterization Methods Utilizing Reaction Dynamics in a Separation Capillary

Abstract: Electrophoretic migration of an analyte in capillary electrophoresis (CE) reflects reaction dynamics of the analyte in solution. In affinity CE, an analyte of interest interacts with a modifier added in the separation buffer in fast equilibrium, and effective electrophoretic mobility of the analyte is contributed from its equilibrium species. Precise measurement of effective electrophoretic mobility allows analyzing the equilibrium. Analysis of equilibria under CE separation possesses several advantages against traditional analyses in homogeneous solution; coexisting substances including impurities and kinetically generated substances are resolved by CE from the equilibrium species of interest. Characteristics of the CE analysis have been applied to analyses of acid-base equilibria of degradable substances and ion-association equilibria in an aqueous solution. Since CE is operated in an open-tubular capillary, it is also suitable for the characterization of carbon nanoclusters such as graphene and carbon nanotube, and measurement of effective electrophoretic mobility helps characterization of nanoclusters. A novel analysis technique of capillary electrophoresis/dynamic frontal analysis (CE/DFA) has also been proposed for the analysis of such reactions as involving equilibria and kinetic reactions. In CE/DFA, kinetically generated product is continuously resolved from the equilibrium species, and a plateau signal would be detected when the reaction rate is constant. Michaelis-Menten constants have successfully been determined through the plateau height by CE/DFA. In this review, analysis and characterization methods utilizing reaction dynamics in a separation capillary are summarized.

A strategy for determining the equilibrium constants for heteromeric ion channels in a complex model

Abstract: Benndorf et al. present a strategy to analyze the functionality of heteromeric ligand-gated ion channels by combining subunit concatenation, mutagenesis, and extensive global fit strategies with intimately coupled Markov models.