Apparent Equilibrium Constant Research Articles

Extraction Equilibria of Lithium with Tributyl Phosphate, Diisobutyl Ketone, Acetophenone, Methyl Isobutyl Ketone, and 2-Heptanone in Kerosene and FeCl3

The extraction equilibrium behavior of Li by tributyl phosphate (TBP), diisobutyl ketone, acetophenone, methyl isobutyl ketone, and 2-heptanone in kerosene were investigated. The partition coefficient of Li with TBP in kerosene decreased significantly when the volume concentration of TBP was greater than 60%. The values derived for the partition coefficients of four selected ketones in kerosene were smaller than that of TBP in kerosene. The stoichiometric coefficients between TBP and Li, the stoichiometric coefficients between the four selected ketones and Li, and the apparent equilibrium constant for the extraction reaction equation for TBP and the four ketones in kerosene were obtained. The tendency in extraction with the TBP and four selected ketones in kerosene can be predicted from these parameters. The polar solvents used as diluents for TBP can yield higher Li partition coefficients, strong dilution effects for TBP, and strong polarity and low density of the extracting solvents formed with both pol...

Sensorially important aldehyde production from amino acids in model wine systems: Impact of ascorbic acid, erythorbic acid, glutathione and sulphur dioxide

The efficiency of different white wine antioxidant systems in preventing aldehyde production from amino acids by oxidative processes is not well understood. The aim of this study was to assess the efficiency of sulphur dioxide alone and in combination with either glutathione, ascorbic acid or its stereoisomer erythorbic acid, in preventing formation of the sensorially important compounds methional and phenylacetaldehyde from methionine and phenylalanine in model white wine. UHPLC, GC–MS/MS, LC–MS/MS, flow injection analysis and luminescence sensors determined both compositional changes during storage, and sulphur dioxide–aldehyde apparent equilibrium constants. Depending on temperature (25 or 45°C) or extent of oxygen supply, sulphur dioxide was equally or more efficient in impeding the production of methional compared to the other antioxidant systems. For phenylacetaldehyde, erythorbic acid or glutathione with sulphur dioxide provided improved inhibition compared to sulphur dioxide alone, in conditions of limited oxygen consumption. The results also demonstrate the extent to which sulphur dioxide addition can lower the free aldehyde concentrations to below their aroma thresholds.

MATLAB simulation of preparation of Sm-loaded extractant directly from HEH(EHP)

Computer simulation of the preparation process loading rare earth (RE) directly from acidic extractant and RE chloride was established using MATLAB software. The mechanism of the extraction reaction was assumed, and then an experiment was conducted to confirm the mechanism and the apparent equilibrium constant of the reaction was determined as well. Owing to the involvement of H+ ion in the reaction between acidic extractant and RE chloride, the computer simulation of the process was more complicated than that of the extraction only between different rare earths. In the present work, MATLAB software was therefore introduced to handle the resolution of the complicated processing equation, and the simulation was performed by varying some key parameters including feed composition and phase ratio, etc. Consequently this work presented a simple method to simulate the H+ ion involved countercurrent extraction process of rare earths and also provided the practical references for the relative process designing.

Reactive Extraction of o-, m-, and p-Chlorophenol from Aqueous Solution Using Tri-n-butyl Phosphate in Kerosene

Reactive extractions of o-, m-, and p-chlorophenol (o-, m-, and p-CP) from aqueous solutions using tri-n-butyl phosphate (TBP) dissolved in kerosene were studied. The influences of equilibrium aqueous pH (pHeq) and initial TBP concentrations on distribution ratio (D) were discussed. Effective extractions of CP were observed only under pHeq lower than 7.0. D values increased with the increase of initial TBP concentration. TBP mainly reacted with the neutral form of CP by forming 1:1 (TBP:CP) complex through a hydrogen-bond between phosphoryl in TBP and hydroxyl in CP. The apparent reaction extraction equilibrium constant (K) for o-, m-, and p-CP was found in good linear relationship with the addition of dissociation constant (pKa) and the hydrophobic parameter (Log P) of CP, namely, log K = −0.1171 × pKa + 0.0680 × Log P + 2.5848, suggesting pKa plays a much more important role that affects K than Log P. Back-extraction experiments supported > 95 % CP could be recovered using 0.5 mol·L–1 NaOH as stripping ...

The role of activity coefficients in bioreaction equilibria: Thermodynamics of methyl ferulate hydrolysis

The Gibbs energy of reaction (ΔRg) is the key quantity in the thermodynamic characterization of biological reactions. Its calculation requires precise standard Gibbs energy of reaction (ΔRg+) values. The value of ΔRg+ is usually determined by measuring the apparent (concentration-dependent) equilibrium constants K, e.g., the molality-based Km. However, the thermodynamically consistent determination of ΔRg+ requires the thermodynamic (activity-based) equilibrium constant Ka. These values (Km and Ka) are equal only if the ratio of the activity coefficients of the reactants to the activity coefficients of the products (Kγ) is equal to unity.In this work, the impact of Kγ on the estimation of Ka for biological reactions was investigated using methyl ferulate (MF) hydrolysis as a model reaction. The value of Kγ was experimentally determined from Km values that were measured at different reactant concentrations. Moreover, Kγ was independently predicted using the thermodynamic model ePC-SAFT. Both the experimentally determined and the predicted Kγ values indicate that this value cannot be assumed to be unity in the considered reaction. In fact, in the reaction conditions considered in this work, Kγ was shown to be in the range of 3<Kγ<6 for different reactant molalities (2<mmol MF kg−1<10). The inclusion of Kγ and thus the use of the thermodynamically correct Ka value instead of Km lead to remarkable differences (almost 40%) in the determination of ΔRg+. Moreover, the new value for ΔRg+ increases the concentration window at which the reaction can thermodynamically occur.The influence of additives was also investigated both experimentally and theoretically. Both procedures consistently indicated that the addition of NaCl (0 to 1molkg−1 water) moderately decreased the value of Kγ, which means that the values of Km increase and that a higher amount of products is obtained as a result of the addition of salt. Additionally, Km was found to strongly depend on pH. A ten-fold increase in the Km values was observed in the pH range of 6 to 7; this increase corresponds to a change of more than 100% in the value of ΔRg+.

Separating ultra-high molecular weight polymers on monolithic capillary columns

The chromatographic behavior of a polystyrene sample with a molecular weight of 20 × 106 Da and narrow molecular weight distribution is studied on a monolithic capillary column based on polydivinylbenzene. It is found that either one symmetrical peak or two peaks that cannot be completely separated over the range of flow rates for the mobile phase can be observed in the chromatogram, depending on the flow rate of the mobile phase. The observed changes in the elution profile of polystyrene standards are attributed to the presence of dynamic equilibrium in the system (reaction chromatography), for which the apparent constants of forward and reverse reactions and the apparent equilibrium constant are obtained. It is noted that the apparent constant of direct reaction increases linearly with a rising eluent flow rate, while saturation and even a drop in the apparent rate constant of the reverse reaction is observed when the flow rate of the eluent rises. It is suggested that the observed changes are related to conformational transitions in the macromolecules of polystyrene, but a detailed explanation of the observed effect requires further investigation.

Nicotinic Receptor Transduction Zone: Invariant Arginine Couples to Multiple Electron-Rich Residues

Gating of the muscle-type acetylcholine receptor (AChR) channel depends on communication between the ACh-binding site and the remote ion channel. A key region for this communication is located within the structural transition zone between the ligand-binding and pore domains. Here, stemming from β-strand 10 of the binding domain, the invariant αArg209 lodges within the hydrophobic interior of the subunit and is essential for rapid and efficient channel gating. Previous charge-reversal experiments showed that the contribution of αArg209 to channel gating depends strongly on αGlu45, also within this region. Here we determine whether the contribution of αArg209 to channel gating depends on additional anionic or electron-rich residues in this region. Also, to reconcile diverging findings in the literature, we compare the dependence of αArg209 on αGlu45 in AChRs from different species, and compare the full agonist ACh with the weak agonist choline. Our findings reveal that the contribution of αArg209 to channel gating depends on additional nearby electron-rich residues, consistent with both electrostatic and steric contributions. Furthermore, αArg209 and αGlu45 show a strong interdependence in both human and mouse AChRs, whereas the functional consequences of the mutation αE45R depend on the agonist. The emerging picture shows a multifaceted network of interdependent residues that are required for communication between the ligand-binding and pore domains.

Solvent Extraction Equilibrium of Zinc from Nitrate Solutions with 2-Ethylhexylphosphonic Acid Mono-2-ethylhexyl Ester

The solvent extraction equilibrium of zinc with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) in an alkane diluent, Shellsol D70, was studied at a constant ionic strength of 1 mol/L from nitrate solutions considering the correction of the extractant nonideality in the organic phase by Alstad’s method. On the basis of the slope analysis of the obtained data, a molar ratio of 1:2 for the zinc to the EHPNA dimer in the extracted complex was indicated. Apparent extraction equilibrium constants obtained at each temperature from 283 to 323 K showed the endothermic nature of the extraction reaction and gave the apparent standard enthalpy and entropy changes. These two constants enable the calculation of the zinc distribution ratio at each temperature which correlates the experimental data with good accuracy.

Reactive Extraction of Nicotinic Acid with Trialkylamine in n-Octanol

The distributions of nicotinic acid (NA) between water and trialkylamine (N235) dissolved in n-octanol was studied. The complexes of N235 and NA were investigated by Fourier transformation infrared spectrometry to deduce the reaction mechanism. It was found that N235/n-octanol was an efficient extractant for extracting nicotinic acid. The favorable operation conditions were equilibrium aqueous pH 4.2 to 5.5 and initial N235 concentration<0.42 mol·L−1. The reaction processes included the reaction between neutral N235 and neutral NA and the reaction between protonated N235 and anionic NA. Based on the mass action law and some assumptions, an expression for distribution coefficient D was proposed. The apparent extraction equilibrium constants were calculated by fitting the experimental data and the results were satisfactory.

Extraction of 8-Hydroxyquinoline by Tributylphosphate in Kerosene

Extractions of 8-hydroxyquinoline (8-HQ) by tributylphosphate (TBP) in kerosene, as well as pure TBP and kerosene, were carried out. The investigations involved the equilibrium pH (pHeq) of 3.0 to 11.5, initial 8-HQ concentrations of (0.5 to 5.0) mmol·L–1, and initial TBP concentrations of (0.05 to 1.0) mol·L–1. The distribution ratio (D) was found to be highly dependent on pHeq, and larger D values appeared at pHeq range of 6.3 to 8.4. The distribution constants (KD) for pure TBP and kerosene were calculated to be 236.6 and 26.98, respectively. The experimental KD for TBP/kerosene was expressed by KD,TBP, KD,kerosene, and the volume fractions of TBP or kerosene. The mix of TBP and kerosene was found to be a nonideal process. The deviation of KD from the ideal is proportional to the product of volume fractions of TBP and kerosene. The (1:1) TBP:8-HQ complex was verified by fitting experimental data, and the apparent extraction reaction equilibrium constant was calculated to be 64.58 L·mol–1. The results are of significant importance for the practical separation of 8-HQ from diluents.

Solvent extraction of uranyl by N,N,N′,N′-tetraoctylsuccinylamide from nitric acid solution

Synthesis and characterization of N,N,N′,N′-tetraoctylsuccinylamide (TOSA) was carried out and used for extraction of U(VI) from nitric acid solutions. The effect of different factors affecting the extraction distribution ratio (TOSA concentration, concentrations of nitric acid, salting-out agent LiNO3 concentration, equilibration time, temperature and effect of diluents) have been investigated. The results obtained indicated that TOSA have a great capability to extract uranyl with kerosene-1,3,5-trimethylbenzene than other diluents, it have a high extraction distribution ratios when the concentration of TOSA is lower and not found the third matter. It was found that the main extracted species is UO2(NO3)2·TOSA. The apparent equilibrium constant of extraction determined is (2.32 ± 0.31) L3/mol3 at (298 ± 1) K. The enthalpy of extraction is −35.20 ± 0.352 kJ/mol.

Reactive Extraction of o-, m-, and p-Aminophenol Using Trialkylphosphine Oxide/Kerosene

Reactive extractions of o-, m-, and p-aminophenol (OAP, MAP, and PAP) using trialkylphosphine oxide/kerosene (TRPO/kerosene) have been studied. The equilibrium aqueous pH (pHeq) and the concentrations of TRPO in organic phases were found to be of important effects on the distribution coefficient (D) of OAP, MAP, and PAP between TRPO/kerosene and water. Infrared spectra results suggested pHeq had no influence on the complexes' structures, and TRPO mainly reacted with neutral aminophenol through forming a hydrogen bond between its P═O and aminophenol OH. An expression of D was proposed, and the apparent reactive extraction equilibrium constants (K) were calculated by fitting the experimental data. The dissociation constant of the OH group of aminophenol (namely, pKa2) played a vital role that affected K, while the hydrophobic parameter (log P) of aminophenol had little effect. K was statistically calculated to be in accordance with the equation of log K + pKa2 = 10.94 under all experimental test conditions. D values calculated from the model were in good agreement with experimental ones.

Extraction Equilibria of 4-Hydroxypyridine using Di (2-ethylhexyl) Phosphoric Acid

Extractions of 4-Hydroxpyridine (4HP) from aqueous solutions using Di(2-ethylhexyl)phosphoric acid (D2EHPA) as extractant in 1-octanol and kerosene were studied. The factors that affected the distribution coefficient (D), such as equilibrium pH, the concentration of D2EHPA, and the type of diluents were discussed. The interaction mechanism between 4HP and D2EHPA was validated by infrared spectroscopic analysis. D increased with the increase of the concentration of D2EHPA and peak values appeared at equilibrium pH = 3.6–5.0. D in the polar diluent (1-octanol) was much higher than those in the non-polar diluent (kerosene). The extraction reaction was found to be a proton-transfer process and D2EHPA mainly reacted through its –OH with –N– of 4HP. The apparent reactive extraction equilibrium constants K 11 and K 12 were obtained by fitting the experimental data of extraction equilibrium. By comparing calculated D values from the proposed model with the experimental ones, the accuracy of the proposed model was examined.

Equilibrium of the Extraction of V(IV) in the V(IV)-SO&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;2-&amp;lt;/sup&amp;gt;(H&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt;, Na&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt;)—Cyanex 302-Kerosene System

The title system has been investigated from the equilibrium point of view. Significant extraction occurs above pH 2. Equilibration time is 20 min. The extraction ratio (D) remains constant with increasing [V(IV)] of at least 0.50 g/L. It is inversely proportional to [H+]2, [H+] and [H+]0.3 in the lower pH (2; and [SO42-]0 and [SO42-]-1 in the lower [SO42-] (42-] (>1 mol/L) regions, respectively. The apparent extraction equilibrium constant (Kex) in 0.02 mol/L SO42- medium and at 303 K is found to vary from 10-3.447 to 101.508 with increasing equilibrium pH from 2.25 to 4.00. Various sulphated, hydrolyzed, hydrated and mixed sulphated hydrolyzed species of V(IV) have been considered at different extraction conditions to propose the extraction equilibrium reactions to form always [VO(HA2)2] as the extractable species. The system is highly temperature dependent with ?H value of ~90 kJ/mol and ~25 kJ/mol in lower and higher temperature regions, respectively. The calculated loading capacity is low (4.05 g V(IV)/100 g Cyanex 302). Kerosene is a better diluent over CHCl3, Cyclo-C6H12 and CCl4; but much better solvents are C6H6, C6H5CH3, n-C7H16,C6H4(CH3)2, petroleum benzin, 1,2-C2H4Cl2, C6H5Cl. Mineral acids (1 mol/L) are able to strip off V(IV) from the organic phase in a single-stage. Using Cyanex 302, almost complete separations of V(IV) from Cu(II) at pH 1.0 and from Ni(II) at pH(eq) 4.5 are possible in a single-stage of extraction; whereas, its separation from Zn(II) at pH(eq) 2.5, Co(II) at pH(eq) 3.5, Fe(III) at pH(eq) 2.0 and Ti(IV) at pH(eq) 2.5 will require counter-current multi-stage extractions.

Stimuli-responsive polymers grafted to nanopores and other nano-curved surfaces: structure, chemical equilibrium and transport

This review discusses the properties of macromolecular layers on nano-curved surfaces, with special emphasis on the fast-growing field of polymer- and polyelectrolyte-modified nanopores and nanochannels. Organization in soft materials emerges from the competition between physical and chemical interactions acting on different length scales; the geometry of the system modulates this competition and, hence, dictates its structure and function. Theoretical studies of molecular organization in planar and curved geometries require the treatment of the coupling between interactions, chemical equilibrium and geometrical constraints. We analyse here how curvature affects the morphology of polymers on nano-curved surfaces and determines the apparent equilibrium constants of surface-confined chemical reactions, such as acid–base chemistry. We also review the practical implications of introducing soft materials into nanofluidic devices. In particular, we present and discuss recent theoretical studies and simulations of the transport of ions, solvent and large cargoes through polyelectrolyte-brush-modified pores. We believe that this basic understanding will guide experimental efforts towards the design of stimuli-responsive nanopore gates.

Mathematic modeling and experimental validation of macrostate quality expression for multicomponent in Chinese materia medica

To establish the unitive multicomponent quality system bridged macrostate mathematic model parameters of material quality and microstate component concentration for Chinese materia medica (CMM). According to law of biologic laws of thermodynamics, the state functions of macrostate qulity of the CMM were established. The validation test was carried out as modeling drug as alcohol extract of Radix Rhozome (AERR), their enthalpy of combustion was determined, and entropy and the capability of information by chromatographic fingerprint were assayed, and then the biologic apparent macrostate parameters were calculated. The biologic macrostate mathematic models, for the CMM quality controll, were established as parameters as the apparent equilibrium constant, biologic enthalpy, Gibbs free energy and biologic entropy etc. The total molarity for the 10 batchs of AERR were 0.153 4 mmol x g(-1) with 28.26% of RSD, with the average of apparent equilibrium constants, biologic enthalpy, Gibbs free energy and biologic entropy were 0.039 65, 8 005 J x mol(-1), -2.408 x 10(7) J x mol(-1) and - 8.078 x 10(4) J x K(-1) with RSD as 6.020%, 1.860%, 42.32% and 42.31%, respectively. The macrostate quality models for CMM can represent their intrinsic quality for multicomponent dynamic system such as the CMM, to manifest out as if the forest away from or tree near from to see it.

Hidden in plain sight: subtle effects of the 8-oxoguanine lesion on the structure, dynamics, and thermodynamics of a 15-base pair oligodeoxynucleotide duplex.

The base lesion 8-oxoguanine is formed readily by oxidation of DNA, potentially leading to G → T transversion mutations. Despite the apparent similarity of 8-oxoguanine-cytosine base pairs to normal guanine-cytosine base pairs, cellular base excision repair systems effectively recognize the lesion base. Here we apply several techniques to examine a single 8-oxoguanine lesion at the center of a nonpalindromic 15-mer duplex oligonucleotide in an effort to determine what, if anything, distinguishes an 8-oxoguanine-cytosine (8oxoG-C) base pair from a normal base pair. The lesion duplex is globally almost indistinguishable from the unmodified parent duplex using circular dichroism spectroscopy and ultraviolet melting thermodynamics. The DNA mismatch-detecting photocleavage agent Rh(bpy)(2)chrysi(3+) cleaves only weakly and nonspecifically, revealing that the 8oxoG-C pair is locally stable at the level of the individual base pairs. Nuclear magnetic resonance spectra are also consistent with a well-conserved B-form duplex structure. In the two-dimensional nuclear Overhauser effect spectra, base-sugar and imino-imino cross-peaks are strikingly similar between parent and lesion duplexes. Changes in chemical shift due to the 8oxoG lesion are localized to its complementary cytosine and to the 2-3 bp immediately flanking the lesion on the lesion strand. Residues further removed from the lesion are shown to be unperturbed by its presence. Notably, imino exchange experiments indicate that the 8-oxoguanine-cytosine pair is strong and stable, with an apparent equilibrium constant for opening equal to that of other internal guanine-cytosine base pairs, on the order of 10(-6). This collection of experiments shows that the 8-oxoguanine-cytosine base pair is incredibly stable and similar to the native pair.

Recommendations for terminology and databases for biochemical thermodynamics

Chemical equations are normally written in terms of specific ionic and elemental species and balance atoms of elements and electric charge. However, in a biochemical context it is usually better to write them with ionic reactants expressed as totals of species in equilibrium with each other. This implies that atoms of elements assumed to be at fixed concentrations, such as hydrogen at a specified pH, should not be balanced in a biochemical equation used for thermodynamic analysis. However, both kinds of equations are needed in biochemistry. The apparent equilibrium constant K′ for a biochemical reaction is written in terms of such sums of species and can be used to calculate standard transformed Gibbs energies of reaction Δ r G′°. This property for a biochemical reaction can be calculated from the standard transformed Gibbs energies of formation Δ f G i ′° of reactants, which can be calculated from the standard Gibbs energies of formation of species Δ f G j ° and measured apparent equilibrium constants of enzyme-catalyzed reactions. Tables of Δ r G′° of reactions and Δ f G i ′° of reactants as functions of pH and temperature are available on the web, as are functions for calculating these properties. Biochemical thermodynamics is also important in enzyme kinetics because apparent equilibrium constant K′ can be calculated from experimentally determined kinetic parameters when initial velocities have been determined for both forward and reverse reactions. Specific recommendations are made for reporting experimental results in the literature.

Extraction properties of phthalic acid and aromatic polycarboxylic acids using various solvents

BACKGROUND: To explore the extraction properties of aromatic acids produced in the oxidation of coal, the extraction equilibrium of phthalic acid (as a typical product) was studied using three solvents, 1-octanol, 50% tributylphosphate (TBP)/kerosene, and 10% trialkylphosphine oxide (TRPO)/kerosene, and the feasibility of separating phthalic, [1,1′-biphenyl]-2,2′-dicarboxylic and trimellitic acids is discussed. RESULTS: Phthalic acid extraction followed the sequence: 10% TRPO > 50% TBP > 1-octanol, with recoveries from the TRPO and TBP systems being much larger than that for 1-octanol. The stoichiometry of formation of the complexes of TBP and TRPO with phthalic acid was 1:1. The apparent extraction equilibrium constant for TRPO is much larger than that for TBP. The distribution coefficient of [1,1′-biphenyl]-2,2′-dicarboxylic acid is much larger than that of the other two acids using 1-octanol as the extractant and this acid could be removed by 1-octanol from a mixture of the three acids. The extraction equilibrium correlations obtained for the individual acid component systems can be used to predict that of the acid mixture. CONCLUSION: The extent of phthalic acid extraction by the three solvents investigated is as follows: 10% TRPO > 50% TBP > 1-octanol. The stoichiometry of the complex formation of TBP or TRPO and phthalic acid is 1:1, and the apparent extraction equilibrium constant for TRPO is much larger than that for TBP. 1-octanol shows a good extractive selectivity for [1,1′-biphenyl]-2,2′-dicarboxylic acid as compared with phthalic and trimellitic acids. Copyright © 2011 Society of Chemical Industry

Kinetic and thermodynamic study of the reaction catalyzed by glucose-6-phosphate dehydrogenase with nicotinamide adenine dinucleotide

The enzyme glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49) from Leuconostoc mesenteroides has a dual coenzyme specificity with oxidized nicotinamide adenine dinucleotide (NAD ox) and oxidized nicotinamide adenine dinucleotide phosphate as electron acceptors. The G6PD coenzyme selection is determined by the metabolic cellular prevailing conditions. In this study a kinetic and thermodynamic analysis is presented for the reaction catalyzed by G6PD from L. mesenteroides with NAD ox as coenzyme in phosphate buffer. For this work, an in situ spectrophotometric technique was employed based on the detection of one product of the reaction. Substrate and coenzyme concentrations as well as temperature and pH effects were evaluated. The apparent equilibrium constant, the Michaelis constant, and the turnover number were determined as a function of each experimental condition. The standard transformed Gibbs energy of reaction was determined from equilibrium constants at different initial conditions. For the product 6-phospho- d-glucono-1,5-lactone, a value of the standard Gibbs energy of formation is proposed, Δ f G° = −1784 ± 5 kJ mol −1.