Equilibrium Constants Of Complexes Research Articles

Study on extraction kinetics of α -cyclopentylmandelic acid enantiomers with hydroxyethyl- β -cyclodextrin as chiral selector

Abstract In this work, the kinetic study on reactive extraction of α -cyclopentylmandelic acid ( α -CPMA) enantiomers was performed in a Lewis cell using hydroxyethyl- β -cyclodextrin (HE- β -CD) as chiral selector. The enantioselective complexation equilibrium between HE- β -CD and α -CPMA enantiomers was studied by phase solubility method. The important process parameters affecting the initial extraction rate were separately studied and the reaction rate equations were deduced. The optimal conditions for kinetic study were as follows: stirring speed of 75 r·min − 1 , interfacial area of 12.56 cm 2 , pH of 2.5, initial HE- β -CD concentration of 0.05 mol ·L − 1 , initial α -CPMA concentration of 5 mmol·L − 1 , and temperature of 278 K. The reaction has been found to be first order in α -CPMA and second order in HE- β -CD with the forward rate constants of 2.056 × 10 − 3 m 6 ·mol − 2 ·s − 1 and 1.459 × 10 − 3 m 6 ·mol − 2 ·s − 1 for ( S )- α -CPMA and ( R )- α -CPMA, respectively. The complexation equilibrium constants were evaluated as 61 L·mol − 1 and 117 L·mol − 1 for ( S )- α -CPMA and ( R )- α -CPMA, and the intrinsic enantioselectivity is estimated as 1.92.

Enantiomeric separation of the antiuremic drug colchicine by electrokinetic chromatography. Method development and quantitative analysis

Two analytical methodologies were developed by CE enabling the enantiomeric separation of colchicine, an antiuremic drug commercialized as pure enantiomer. Succinyl-γ-CD and Sulfated-γ-CD were selected as chiral selectors after a screening with different anionic CDs. Under the optimized conditions, chiral resolutions of 5.6 in 12min and 3.2 in 8min were obtained for colchicine with Succinyl-γ-CD and Sulfated-γ-CD, respectively. An opposite enantiomeric migration order was observed with these two CDs being S-colchicine the first-migrating enantiomer with Succinyl-γ-CD and the second-migrating enantiomer with Sulfated-γ-CD. H NMR experiments showed a 1:1 stoichiometry for the enantiomer-CD complexes in both cases. However, the apparent and averaged equilibrium constants for the enantiomer-CD complexes could be calculated only for Succinyl-γ-CD. The developed methods were applied to the analysis of pharmaceutical formulations but only the use of Succinyl-γ-CD enabled to detect a 0.1% of enantiomeric impurity in colchicine formulations.

Recovery of Glutaric Acid Using Tri-N-Butyl Phosphate: Effect of Diluents and Temperature

Reactive separation of glutaric acid with tri-n-butyl phosphate in ethyl acetate and hexanol was studied to explain the effect of temperature on the extraction. Extraction was carried out at different temperature range of 308-338 K. The reactive extraction results were discussed in terms of overall distribution coefficients (KD), degree of extraction (η%), loading ratio (φ), and equilibrium complexation constants (KE). The results showed that an increase in temperature reduced distribution coefficients and extraction efficiency for both diluent used in the organic phase. Moreover, thermodynamic function viz enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) were calculated. Reactive extraction of glutaric acid by tri-n-butyl phosphate resulted in negative values of enthalpy. Thus, the reactive extraction process is an exothermic reaction.

Determination of the equilibrium constant of C60 fullerene binding with drug molecules.

We report a new analytical method that allows the determination of the magnitude of the equilibrium constant of complexation, Kh, of small molecules to C60 fullerene in aqueous solution. The developed method is based on the up-scaled model of C60 fullerene-ligand complexation and contains the full set of equations needed to fit titration datasets arising from different experimental methods (UV-Vis spectroscopy, 1H NMR spectroscopy, diffusion ordered NMR spectroscopy, DLS). The up-scaled model takes into consideration the specificity of C60 fullerene aggregation in aqueous solution and allows the highly dispersed nature of C60 fullerene cluster distribution to be accounted for. It also takes into consideration the complexity of fullerene-ligand dynamic equilibrium in solution, formed by various types of self- and hetero-complexes. These features make the suggested method superior to standard Langmuir-type analysis, the approach used to date for obtaining quantitative information on ligand binding with different nanoparticles.

Effect of Temperature on Reactive Extraction of Gallic Acid Using Tri-n-butyl Phosphate, Tri-n-octylamine and Aliquat 336

The present work is focused on the effect of temperature on extraction of gallic acid using Aliquat 336, tri-n-butyl phosphate and tri-n-octylamine in hexanol and octanol. Distribution coefficient, loading ratio, percent extraction, equilibrium complexation constant, water coextraction, enthalpy, and entropy change were evaluated for various acid–extractant–diluent combinations with varying temperature. The extraction of GA was found to be highly exothermic at lower molality of TBP in octanol with evaluated enthalpy change as −28 743 J/mol. The extraction of gallic acid process was favored at low temperature as the process was evaluated as an exothermic in nature. Maximum extraction efficiency of 97.3% was observed at higher molality of Aliquat 336 in hexanol at lower temperature.

Elucidation of adsorption mechanisms of solvent molecules with distinct functional groups on amylose tris(3,5-dimethylphenylcarbamate)-based sorbent

Although polysaccharide derivative-based sorbents have been widely used for chiral separation, for a long time it remained unclear how these CSPs interact with the molecules associated with different functional groups. In this study, six molecules were chosen for retention behavior studies: acetone (AC), tetrahydrofuran (THF), methanol (MET), isopropanol (IPA), tert-butanol (TBA), and benzene (BZN). An immobilized amylose carbamate stationary phase, amylose tris(3,5-dimethylphenylcarbamate)-based sorbent, or Chiralpak IA, was used. Van’t Hoff plots of ln k versus 1/T showed that alcohol molecules may simultaneously form two H-bonds with the IA sorbent. The results of density functional theory simulations and IR spectra support this inference showing that alcohol may bind with amide groups in three possible configurations. Frontal tests of AC and IPA were performed to estimate adsorbed solute concentration. Langmuir isotherm for IPA adsorption and mass action model for IPA self-aggregation were used for analyzing the IPA frontal results. Average IPA aggregation numbers range from 1.4 to 2.3. More than fifty percent of IPA molecules were found to be in aggregate form. From the frontal test results, thermodynamic properties of the adsorptions were determined. Retention behaviors of the five solutes as a function of IPA concentration were investigated. The absolute values B of the slopes from plots of the logarithms of the retention factor versus the logarithms of the IPA concentration increase in the order THF<AC<TBA<MET. U-shaped retention curves were observed for BZN, indicating that π-interactions of BZN aromatic group with the IA sorbent may involve both electrostatic and hydrophobic interactions. For THF, the slightly concave upward retention curves also suggested potential hydrophobic interactions between THF and IA. A monovalent retention model was used to estimate equilibrium constants (KSL-A) of solute-IPA complexation. The retention factors of the solutes with larger KSL-A values increase more rapidly with a decrease in the IPA concentration. Hence, a combination of the thermodynamic analysis and retention model has been shown to be reliable approach for elucidating the adsorption mechanisms of monovalent molecule containing different functional groups.

Extraction equilibria of 2,4,6-Trinitrophenol by (amberlite LA2 + ester) solvents

Extraction equilibria of 2,4,6-Trinitrophenol (picric acid (PAH)) between aqueous and organic phases was investigated at 298.15 K. All experiments was reported on the extraction of picric acid by amberlite LA2 which is secondary amine dissolved in different seven (7) esters such as diethyl malonate, dimethyl phthalate, diethyl glutarate, propyl acetate, diethyl succinate, diethyl sebacate, ethyl propionate, as well as single diluents. Experimental results obtained from batch extraction were evaluated in respect to distribution coefficients (KD), loading factors (TT), stoichiometric loading factor (TS), separation factor (Sf) and extraction efficiency (E). The dimethyl phthalate gave highest synergistic effect with LA2 as extraction efficiency value of 95%. The highest values of possible equilibrium complexation constants for (acid/amine) (1:1) K11 was determined as 10.969 for dimethyl phthalate at 1.762 mol kg−1 amine concentration.

Reactive Separation of Benzeneacetic Acid with Tri-n-caprylyl Amine: Equilibrium and Modeling

Benzeneacetic acid is an important carboxylic acid extensively used in pharmaceutical industries. Thus, interest has been growing in the scientific community toward its recovery from aqueous streams or fermentation broth. Extraction of carboxylic acids by reactive extraction using extractant-diluent is the emerging area of study. With this concept, the reactive extraction of benzeneacetic acid was carried out to study (i) effect of diluents, such as benzene, toluene, xylene, and hexanol; (ii) effect of concentration of extractant, tri-n-caprylyl amine; (iii) effect of pH; and (iv) equilibrium modeling, namely, relative basicity model and mass action law. The equilibrium results are discussed in terms of partition coefficient (P), dimerization constant (D), distribution coefficient (KD), extraction efficiency (η%), overall equilibrium complexation constant (Ke), and loading factor (ϕ). Distribution coefficient trend was observed as xylene > benzene > toluene > hexanol. The extraction efficiency of benzenea...

Enantioselective extraction of phenylsuccinic acid in aqueous two-phase systems based on acetone and β-cyclodextrin derivative: Modeling and optimization through response surface methodology

A novel aqueous two-phase system (ATPS) composed of β-cyclodextrin (β-CD) derivative and acetone was developed for enantioselective extraction of racemic phenylsuccinic acid (PSA). Binodal curves, tie-lines, and critical points for the investigated ATPS were determined and the experimental tie-lines data were successfully correlated by Othmer-Tobias, Bancroft, and Setschenow-type equations. ATPS containing sulfobutyl ether-β-CD (SBE-β-CD) exhibited better enantioselectivity than that using carboxymethyl-β-CD (CM-β-CD). To optimize enantioselective partitioning conditions of PSA in acetone/SBE-β-CD ATPS, three factors (PSA concentration, pH, and equilibrium temperature) were analyzed by using central composite design in response surface methodology. The calculated equilibrium constants of inclusion complexation are 1638.64M−1 for SBE-β-CD-(R)-PSA and 835.84M−1 for SBE-β-CD-(S)-PSA, respectively. Under the optimized conditions, the separation factor of 3.14 and high enrichment efficiency (ER=98.06%, ES=99.25%) were simultaneously achieved in a single step.

Reactive Extraction of Phenol from Aqueous Solution Using Trioctylmethylammoniumchloride and Trioctylamine in Nonane and Isoamyl alcohol

Reactive extraction of phenol (0.053 mol kg−1) from aqueous solution is carried out using two aminic extractants, trioctylmethylammoniumchloride (TOMAC) and trioctylamine (TOA) considering four concentrations (0.023 to 0.091 mol kg−1) and dissolving them in solvents like nonane and isoamyl alcohol (IAA) at 298 K. The effects of extract type (TOMAC and TOA), their concentrations, and type of diluent on the separation efficiency of extraction have been determined. Data show that the neutral phenol molecule is more effectively extracted by TOA than TOMAC into the organic phase. Increase in the extractant concentration from 0.023 to 0.091 mol kg−1 obviously enhances the recovery of phenol (2.3 times with nonane + TOMAC or TOA; 2.97 times with IAA + TOMAC; and 4.83 times with IAA + TOA). The equilibrium extraction results are presented in terms of distribution coefficient (D), degree of extraction (%E), and loading ratio (Z). Maximum value of D (=12.25) is obtained with TOA + IAA (0.091 mol kg−1) which could extract 92.45 % of phenol from the water phase. A suitable mathematical model for the determination of equilibrium D is expressed by employing the mass action law. The equilibrium constant (KE) and the stoichiometric coefficient (n) of extraction are determined graphically. Also, the individual equilibrium constants (K11, K21, and K12) for the phenol-extractant complexes formed are estimated from the regression of the experimental values. The better extraction power of the TOA + IAA extract system is also shown from the estimated value of complexation constant (KE = 164.44). Phenol molecules form 1:1 and 2:1 and 1:1 and 1:2 solvates with nonane and IAA, respectively, with both the extractants.

Thermodynamic analysis of ferulate complexation with α-, β- and γ-cyclodextrins

Isothermal titration calorimetry (ITC) was used to characterize the thermodynamics of the complexation processes of α-, β- and γ-cyclodextrin (CD) with ferulate (FER) in aqueous solutions. The equilibrium constants of ferulate complexation with CDs (Kc, in dm3mol−1) at pH 9.0 and 25.0°C were: 176.5±5.0 (β-CD), 53.2±3.4 (α-CD) and 19.4±0.4 (γ-CD). Although FER–β-CD is the tightest complex of the three studied, its binding reaction is also the least exothermic and the only one that is entropically favored. Calculated binding enthalpies, based on the buried surface area upon complexation, are close to those determined by ITC except for the FER–β-CD complex which is more than two times more exothermic. According to these results and those obtained by molecular docking simulations, it is proposed that ferulate binds to the hydrophobic cavity of β-CD, displacing more water molecules than in the other two CD complexes.

Recovery of Methacrylic Acid from the Aqueous Phase Using Trioctylmethylammonium Chloride (TOMAC) in Different Diluents

Methacrylic acid and its derivatives are used in the manufacture of important industrial polymeric products. They have a variety of industrial applications including plastics, thickening agents, surfactants, and chelating agents, etc. In the present work, equilibrium extraction of methacrylic acid is carried out to recover it from aqueous solution. A quaternary ammonium salt, trioctylmethylammonium chloride (TOMAC), is used along with different diluents which belong to different categories. These include isoamyl alcohol, n-butyl acetate, methyl isobutyl ketone (MIBK), toluene, carbon tetrachloride, rice bran oil, and kerosene. Parameters such as distribution coefficients, extraction efficiency, loading ratio, stoichiometric loading ratios, and the equilibrium complexation constants are reported. In both physical and chemical extraction processes, MIBK, being proton–accepting, provides maximum extraction efficiency. The values of equilibrium complexation constant of the TOMAC–diluent systems studied decrea...

Calibration free concentration analysis by surface plasmon resonance in a capture mode

Surface plasmon resonance (SPR) is the gold standard for determining rate and equilibrium constants of bimolecular complexes. Accuracy of these parameters depends on the correct determination of the concentration of the injected analyte. Calibration free concentration analysis (CFCA) has been developed to overcome the limitation of measuring protein concentrations spectroscopically, which may overestimate the fraction of the protein that really binds to the immobilized ligand, i.e. the active concentration. In this work, we demonstrate that CFCA can also be implemented in a capture format for measuring active concentrations. Capture CFCA (CCFCA) was first validated by measuring the concentration of a HLA-B*44:02 antigen solution. The active concentration of this molecule determined by CCFCA was similar to that obtained by covalent CFCA. CCFCA was then used to determine the concentration of the W6/32 pan class I HLA monoclonal antibody over three different HLA molecules captured by another specific antibody. This could not have been performed by covalent CFCA because immobilized HLA molecules cannot withstand regeneration. By exploring different capture levels we also show that CCFCA gives consistent results even at low capture levels. Knowing the active concentration of W6/32, we then determined the rate and equilibrium constants of W6/32-HLA complexes on the same flow cell. CCFCA is of general use for measuring active concentrations and of great interest for analytes recognizing ligands that cannot be covalently immobilized on sensor chips. The capture mode also allows determining the kinetic constants of multiple analyte-ligand complexes on the same flow cell. This increases experiments throughput and reduces sensor chip consumption.

Surface complexation modeling calculation of Pb(II) adsorption onto the calcined diatomite

Removal of noxious heavy metal ions (e.g. Pb(II)) by surface adsorption of minerals (e.g. diatomite) is an important means in the environmental aqueous pollution control. Thus, it is very essential to understand the surface adsorptive behavior and mechanism. In this work, the Pb(II) apparent surface complexation reaction equilibrium constants on the calcined diatomite and distributions of Pb(II) surface species were investigated through modeling calculations of Pb(II) based on diffuse double layer model (DLM) with three amphoteric sites. Batch experiments were used to study the adsorption of Pb(II) onto the calcined diatomite as a function of pH (3.0–7.0) and different ionic strengths (0.05 and 0.1molL−1 NaCl) under ambient atmosphere. Adsorption of Pb(II) can be well described by Freundlich isotherm models. The apparent surface complexation equilibrium constants (logK) were obtained by fitting the batch experimental data using the PEST 13.0 together with PHREEQC 3.1.2 codes and there is good agreement between measured and predicted data. Distribution of Pb(II) surface species on the diatomite calculated by PHREEQC 3.1.2 program indicates that the impurity cations (e.g. Al3+, Fe3+, etc.) in the diatomite play a leading role in the Pb(II) adsorption and dominant formation of complexes and additional electrostatic interaction are the main adsorption mechanism of Pb(II) on the diatomite under weak acidic conditions.

Recovery of Pyruvic Acid using Tri-n-butylamine Dissolved in Non-Toxic Diluent (Rice Bran Oil)

An attempt has been made to investigate the effectiveness of the vegetable oil based biocompatible solvent for the separation of pyruvic acid from fermentation broth, by using rice bran oil as natural, non-toxic diluent. Reactive extraction of pyruvic acid (0.1–0.5 k mol/m3) from aqueous solutions has been studied using tri-n-butylamine (TBA; 10–70 %) as an extractant dissolved in non toxic rice bran oil at T = 30 ± 1 °C. Results were presented in terms of distribution coefficient (Kd), extraction efficiency (E %), loading ratio (Z), and complexation constant ( $$\varphi_{\alpha \beta }$$ ). Extraction equilibrium was interpreted using mass action modeling approach. Based on the extent of loading (Z < 0.5) only (1:1), pyruvic acid: TBA complex was proposed. Equilibrium complexation constant was evaluated to 1.22 m3/k mol. Results obtained are useful in understanding the extraction mechanism.

Complexation of ethyl 2-aryl(alkyl)sulfonylamino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylates with nonferrous metal ions

Complexation of sulfonyl derivatives of the Gewald thiophenes (SGT) with Cu(II), Co(II), Ni(II), Zn(II), and Cd(II) ions in ammonia solutions was studied. The molar ratio method, the Job’s method of continuous variation, and coductometric titration revealed ratios [M(II)]: [SGT] = 1: 2. The composition of preparatively isolated complexes was confirmed by IR spectroscopy and elemental analysis data. Solubility product constants for precipitates of the complexes and complexation equilibrium constants were calculated. Solubility product constants for M(II) complexes was shown to be dependent on the nature of sulfonyl substituent in SGT series.

Extractive Separation of Benzylformic Acid with Phosphoric Acid Tributyl Ester in CCl4, Decanol, Kerosene, Toluene, and Xylene at 298 K

An equilibrium isotherm of benzylformic acid with phosphoric acid tributyl ester in carbon tetrachloride, decanol, kerosene, toluene, and xylene at 298 K has been studied. The equilibrium data are discussed in terms of partition coefficient (P), dimerization constant (D), overall equilibrium complexation constant (E), and loading factor (ϕ). Moreover, the distribution coefficient (KD) and extraction efficiency (η%) with phosphoric acid tributyl ester in CCl4 is 0.199 to 52.1 and 16.6 to 98.1; in decanol, 5.66 to 45.9 and 85 to 97.9; in kerosene, 0.03 to 73.2 and 2.9 to 98.7; in toluene, 0.381 to 70.3 and 27.6 to 98.6; and in xylene, 0.322 to 57.7 and 24.3 to 98.3, respectively. The extraction efficiency of benzylformic acid was found to be more than 95 % with all these diluents. Loading factor ϕ < 0.5 was observed and it indicates that only 1:1 benzylformic acid–phosphoric acid tributyl ester complex in above said diluents were formed. Furthermore, the values of overall equilibrium complexation are determ...

Ligand(s)-to-metal charge transfer as a factor controlling the equilibrium constants of late first-row transition metal complexes: revealing the Irving–Williams thermodynamical series

A unified relationship between the experimental formation constants and the ligand(s)-to-metal charge transfer values of versatile ligand complexes of late transition series first-row bivalent metal ions is uncovered. The latter property not only explicates the Irving-Williams series but also rationalizes quantitatively Pearson's concept of hard and soft acids and bases by correlating the gas-phase to aqueous solution-phase chemistry in a broad sense.

Extraction Equilibria of Gibberellic Acid by Tridodecylamine Dissolved in Alcohols

Gibberellic acid (1.877·10–3 mol·kg–1) extraction from aqueous solution using tridodecylamine (TDA, 0.1 mol·kg–1 to 0.8 mol·kg–1) as extractant dissolved in three solvents (isoamyl alcohol, octane-1-ol, and decane-1-ol) at 298 K has been studied. Extraction parameters such as loading factor Z, extraction efficiency E, and distribution coefficient D, have been found using experimental data. The highest removal of gibberellic acid is found to be 96.37 % (D = 26.602, TDA = 0.5 mol·kg–1) with isoamylalcohol, 87.74 % (D = 7.160, TDA = 0.4 mol·kg–1) with octane-1-ol, and 71.87 % (D = 2.554, TDA = 0.4 mol·kg–1) with decane-1-ol. As per the experimental values of Z (1.19 to 6.52 with isoamyl alcohol, 0.85 to 5.26 with octane-1-ol, and 0.71 to 4.18 with decane-1-ol) and Bizek’ approach, the equilibrium complexation constants for 1:1 and 1:2 acid–TDA complexes have been determined. The linear solvation energy relationship (LSER) model is used to represent the extraction equilibrium of acid by TDA. D values are predicted using the LSER model parameters which fit the experimental results.

Extraction Equilibria of Pyruvic Acid Using Tri-n-butyl Phosphate: Influence of Diluents

Pyruvic acid is extensively utilized in the chemical, pharmaceutical, and agrochemical industries. Novel biotechnological routes to pyruvic acid production receiving great attention and recent focus of research are toward its separation from fermentation broth or recovery from waste streams. Based on reversible complexation, extraction equilibria of the system (water + pyruvic acid + extractant/diluents) were measured at T = 308.2 K using various concentrations of pyruvic acid (0.1 kmol·m–3 to 0.5 kmol·m–3) and extractant (tri-n-butyl phosphate, TBP) (0.36 kmol·m–3 to 2.56 kmol·m–3) in different diluents (n-heptane, toluene, and methyl-iso-butyl ketone, MIBK). Different physiochemical properties such as dipole moment and ET parameter have been used for comparison. Results are given in terms of various parameters such as distribution coefficient, equilibrium complexation constant, loading ratio and extraction efficiency. Using expressions derived for extraction equilibria, equilibrium complexation constant...