Linear Solvation Energy Relationship Model Research Articles

Liquid-liquid extraction equilibrium for pyruvic acid recovery: experimental data and modeling

ABSTRACT Physical extraction studies of pyruvic acid from dilute aqueous solutions (0.025 kmol·m-3 to 0.200 kmol·m-3) using several pure solvents (tri-n-butylphosphate (TBP), 1-decanol, 1-octanol, toluene, Methyl-isobutylketone (MIBK), and n-heptane) and their binary mixtures are reported in this work. All the batch extraction experiments were carried out at isothermal conditions (T=303±1K) and the results are reported in terms of distribution coefficient (K D). The results obtained by the equilibrium studies of the different extraction system were correlated with solvatochromic parameters of the solvents. A linear solvation energy relationship (LSER) model was applied to interpret the extraction equilibrium which specifically considers physical interactions. The values of the LSER model parameters for the extraction system were optimized by regression technique and the model equations have been proposed. Experimental and model values were in good agreement (RMSD < 0.1).Reported outcomes are useful in the selection of a suitable extraction system and understanding the extraction mechanism for the separation of pyruvic acid from dilute aqueous solutions.

Solubility characteristics of poly(3‐hexylthiophene)

ABSTRACTSolubility data for poly(3‐hexylthiophene) (P3HT) in 29 pure solvents are presented and discussed in detail. Functional solubility parameter (FSP) and convex solubility parameter (CSP) computations are performed and the CSP and FSP results are compared to previously reported Hansen solubility parameters (HSPs) and to the parameters calculated using additive functional group contribution methods. The empirical data reveals experimental solubility parameters with substantial polar (δP) and hydrogen‐bonding (δH) components, which are not intrinsic to the structure of the P3HT polymer. Despite these apparent irregularities, it is shown that the predictor method based on the solubility function, f, does provide a reliable way to quantitatively evaluate the solubility of P3HT in other solvents in terms of a given set of empirical solubility data. The solubility behavior is further investigated using linear solvation energy relationship (LSER) modeling and COSMO‐RS computations of the activity coefficients of P3HT. The LSER model reveals that (1) the cavity term, δT, is the dominant factor governing the solubility behavior of P3HT and (2) the solvent characteristics that dictate the structural order (crystallinity) of P3HT aggregates do not similarly influence the overall solubility behavior of the polymer. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1075–1087

Mechanistic Model for Enantioselective Intramolecular Alkene Cyanoamidation via Palladium-Catalyzed C-CN Bond Activation.

We studied key aspects of the mechanism of Pd-catalyzed C-CN bond activation and intramolecular enantioselective alkene cyanoamidation. An Abboud-Abraham-Kamlet-Taft (AAKT) linear solvation energy relationship (LSER) model for enantioselectivity was established. We investigated the impact of Lewis acid (BPh3), Lewis base (DMPU), and no additives. BPh3 additive led to diminished enantioselectivity and differing results in 13CN crossover experiments, initial rate kinetics, and natural abundance 12C/13C kinetic isotope effect measurements. We propose two catalytic mechanisms to account for our experimental results. We propose that the DMPU/nonadditive pathway passes through a κ2-phosphoramidite-stabilized Pd+ intermediate, resulting in high enantioselectivity. BPh3 prevents the dissociation of CN-, leading to a less rigid κ2-phosphoramidite-neutral Pd intermediate.

Effect of water on the retention on diol and amide columns in hydrophilic interaction liquid chromatography.

The amount of water adsorbed on polar columns plays important role in hydrophilic interaction liquid chromatography. It may strongly differ for the individual types of polar columns used in this separation mode. We measured adsorption isotherms of water on an amide and three diol-bonded stationary phases that differ in the chemistry of the bonded ligands and properties of the silica gel support. We studied the effects of the adsorbed water on the retention of aromatic carboxylic acids, flavonoids, benzoic acid derivatives, nucleic bases, and nucleosides in aqueous-acetonitrile mobile phases over the full composition range. The graphs of the retention factors versus the volume fraction of water in mobile phase show "U-profile" characteristic of a dual hydrophilic interaction-reversed phase retention mechanism. The minimum on the graph that marks the changing retention mechanism depends on the amount of adsorbed water. The linear solvation energy relationship model suggests that the retention in the hydrophilic interaction liquid chromatography mode is controlled mainly by proton-donor interactions in the stationary phase, depending on the column type. Finally, the accuracy of hydrophilic interaction liquid chromatography gradient prediction improves for columns that show a high water adsorption.

Recent advances in stationary phases and understanding of retention in hydrophilic interaction chromatography. A review

Hydrophilic interaction chromatography (HILIC) is a rapidly developing liquid chromatography mode suitable for separation of strongly or moderately polar samples on polar columns in highly organic mixed mobile phases. In the past five years many new types of columns appeared based on silica gel, organic polymers and other types of supports. The present work reviews the new additions to their family. Further, the progress in the understanding of theoretical principles of the HILIC mode, especially of the role of the mobile phase, and of the adsorbed water are addressed. The amount of adsorbed water strongly depends on the type of the polar column and may be used to distinguish between “conventional HILIC” and “aqueous normal phase chromatography (ANP)”. Further, sample structural effects on the retention are treated in terms of the Linear Solvation Energy Relationship model adopted for partially ionized polar compounds. The impact of dual HILIC-reversed phase (RP) mechanism on a possible increase of the applications of some polar columns is discussed. Attention is paid also to the increasing role of the HILIC mode in various two-dimensional LC techniques and the related mobile phase compatibility problems.

Investigation of the effective parameters on the gas-solvent partition coefficient of trans -stilbene using solvent-solubility approaches

Abstract Stilbenes and its various derivatives have been studied in different branches of science, because of their unique properties such as fluorescence, phosphorescence, photophysical, photochrome, photochemical and various biological properties. Despite of these potentials, one of the problems of stilbenes is their poor solubility which limits some of their applications. In the current study, quantitative structure property relationship (QSPR) and linear solvation energy relationship (LSER) were used to investigate the solubility of trans-stilbene as a sample solute in organic phase. LSER is an approach which deals with the effects of solvent–solute interactions on physicochemical properties and reactivity parameters. A five parametric QSPR and a LSER model contains five empirical scales was proposed to predict and descript Ostwald solubility coefficient of trans-stilbene in 44 organic solvents. The squared correlation coefficient of different training and test sets in the proposed model were above 0.84 and 0.87 respectively in the LSER model and above 0.90 and 0.86 in QSPR model. Description of scales involved in the proposed models obtained valuable information regarding the solubility of trans-stilbene in organic phase. Donor strength of solvents, solvent acidity, polarity of solvents, dipolarity and polarizability are some of important properties and thus it was concluded that polar interactions has a principal role in the solubility of trans-stilbene.

Graphene oxide/chitosan nanocomposite coated quartz crystal microbalance sensor for detection of amine vapors

Graphene oxide/chitosan (GO/CS) nanocomposite was synthesized using a facile method and employed as the sensing material of a quartz crystal microbalance (QCM) sensor to detect amine vapors. Scanning election microscopy (SEM), Fourier transform infrared spectrometer (FT-IR) and UV–visible spectra analysis were performed to characterize the morphology and physicochemical properties of the nanocomposite. The GO/CS obtained was in a porous mesh structure composed of interconnected nanofibers with diameters of approximately 50nm. A GO/CS functionalized QCM sensor was fabricated and its sensing properties were investigated. Being tested at room temperature, the sensor exhibited high sensitivity to aliphatic amines including methylamine (MA), dimethylamine (DMA) and trimethylamine (TMA), with the sensitivity values of 2.7, 2.3 and 4.8Hz/ppm, respectively. Their detection limits were all below 3ppm. The sensor maintained reasonable reversibility, repeatability as well as long-term stability. Combining the specific adsorption properties of chitosan (CS) with some inherent properties of graphene oxide (GO), the GO/CS coated sensor also performed favorable selectivity, especially for MA, DMA and TMA. The sensing mechanism might involve an adsorption–desorption process mainly caused by hydrogen bonding of the protonated amine and hydroxyl sites of the GO/CS film with the amine vapors. The underlying analyte sorption properties were further investigated based on the linear solvation energy relationship (LSER) model. This work might contribute to the future development of sensors for detection of amine vapors and broaden the application of GO and CS composite materials.

Solubility Characteristics of PCBM and C60.

Empirical data indicate that several good solvents for C60 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have substantial polar and hydrogen-bonding components, which are not intrinsic to the structure of the C60 and PCBM molecules themselves. Functional solubility parameter (FSP) and convex solubility parameter (CSP) computations are performed on C60 and PCBM using solubility data available in the literature. The CSP and FSP results are compared to previously reported Hansen solubility parameters (HSPs) and to the parameters calculated using additive functional group contribution methods. The CSP and FSP methods confirm the anomalously large polar and hydrogen-bonding parameters, δP and δH, obtained experimentally for C60 and PCBM. This behavior, which is quite irregular given the structure of the molecules, is due to the fact that several good solvents have high δP and δH values. Thus, these irregularities are highlighted by the CSP and FSP calculations. Additional contradictory solubility characteristics are disclosed by comparing the experimental solubility parameters to a linear solvation energy relationship (LSER) model, additive functional group calculations, and COSMO-RS computations. The FSP solubility function strongly suggests that the solubility parameters do not accurately represent the cohesive energy density properties of C60 and PCBM, as intended, but rather they manifest the properties of the solvents, e.g., high δP and δH values, that are necessary to accommodate these molecules in the liquid phase.

Evaluation of an amide‐based stationary phase for supercritical fluid chromatography

J. Sep. Sci. 2016, 39, 3469-3476 A stationary phase containing an amide group embedded in a hydrophobic backbone (i.e., C18-amide) attached to silica particles was characterized by means of the linear solvation energy relationship model, which relates the chromatographic retention factor to specific solute interactions. The evaluationwas conducted under supercritical fluid chromatographic conditions using a mobile phase composition of carbon dioxide and methanol as co-solvent. The stationary phase showed to provide an alternate separation selectivity that is attractive to separate drug-like polar compounds in a relatively fast analysis time.

Evaluation of an amide-based stationary phase for supercritical fluid chromatography.

A relatively new stationary phase containing a polar group embedded in a hydrophobic backbone (i.e., ACE®C18-amide) was evaluated for use in supercritical fluid chromatography. The amide-based column was compared with columns packed with bare silica, C18 silica, and a terminal-amide silica phase. The system was held at supercritical pressure and temperature with a mobile phase composition of CO2 and methanol as cosolvent. The linear solvation energy relationship model was used to evaluate the behavior of these stationary phases, relating the retention factor of selected probes to specific chromatographic interactions. A five-component test mixture, consisting of a group of drug-like molecules was separated isocratically. The results show that the C18 -amide stationary phase provided a combination of interactions contributing to the retention of the probe compounds. The hydrophobic interactions are favorable; however, the electron donating ability of the embedded amide group shows a large positive interaction. Under the chromatographic conditions used, the C18 -amide column was able to provide baseline resolution of all the drug-like probe compounds in a text mixture, while the other columns tested did not.

Development of TLSER model and QSAR model for predicting partition coefficients of hydrophobic organic chemicals between low density polyethylene film and water

Partition coefficients are vital parameters for measuring accurately the chemicals concentrations by passive sampling devices. Given the wide use of low density polyethylene (LDPE) film in passive sampling, we developed a theoretical linear solvation energy relationship (TLSER) model and a quantitative structure-activity relationship (QSAR) model for the prediction of the partition coefficient of chemicals between LDPE and water (Kpew). For chemicals with the octanol–water partition coefficient (log Kow) <8, a TLSER model with Vx (McGowan volume) and qA− (the most negative charge on O, N, S, X atoms) as descriptors was developed, but the model had relatively low determination coefficient (R2) and cross-validated coefficient (Q2). In order to further explore the theoretical mechanisms involved in the partition process, a QSAR model with four descriptors (MLOGP (Moriguchi octanol-water partition coeff.), P_VSA_s_3 (P_VSA-like on I-state, bin 3), Hy (hydrophilic factor) and NssO (number of atoms of type ssO)) was established, and statistical analysis indicated that the model had satisfactory goodness-of-fit, robustness and predictive ability. For chemicals with log KOW>8, a TLSER model with Vx and a QSAR model with MLOGP as descriptor were developed. This is the first paper to explore the models for highly hydrophobic chemicals. The applicability domain of the models, characterized by the Euclidean distance-based method and Williams plot, covered a large number of structurally diverse chemicals, which included nearly all the common hydrophobic organic compounds. Additionally, through mechanism interpretation, we explored the structural features those governing the partition behavior of chemicals between LDPE and water.

Modeling and Optimization of Reactive Extraction of Citric Acid

Reactive extraction of citric acid from dilute aqueous solutions was studied using three different extractants, namely tri-n-butylphosphate (TBP), tri-n-octylamine (TOA), and Aliquat 336 (A336), dissolved in three different diluents: butyl acetate, decanol, and benzene. The isothermal batch equilibrium experiments were carried out at T = 300.15 ± 1 K. The extraction was interpreted in terms of the distribution coefficient (KD). Maximum extraction efficiency (E = 95.5%) was obtained at 20% (v/v) TOA in butyl acetate with complexation constant KE2 = 1039.7 (kg mol–1)2 for the (2:1) complex. In addition to having a higher loading ratio (Z > 0.5), the overloading of amine(TOA) in the case of the citric acid + TOA + decanol system was also confirmed by spectroscopic (FTIR) analysis. The linear solvation energy relationship model was successfully applied to predict the distribution coefficient. The complex stoichiometry was also optimized using differential evolution. A close resemblance was observed between ex...

Extractive Separation of Pentanedioic Acid by Amberlite LA-2 in Various Solvents

Reactive extraction of pentanedioic acid using Amberlite LA-2 in different diluents, such as hexane, methylbenzene, kerosene, 4-methyl-2-pentanone, 2,6-dimethyl-4-heptanone, n-hexanone, 3-methyl-1-butanol, n-octanol, n-nonanol, and n-decanol, respectively, was studied. At lower amine concentrations, KD values of less than 1 were obtained but it improves as amine concentration was raised. Increase in amine concentration was found to increase the KD by 80–85% in inert diluents (hexane, methylbenzene and kerosene). In the chosen ketones, the extraction percentage follows the following trend 4-methyl-2-pentanone > DIBK > n-hexanone. Among the various diluents used, higher KD was obtained when alcohols were used as diluents. Mass action equilibria, linear solvation energy relationship modeling, and differential evolution (DE) was applied for estimating the model parameter and compare the model values with the experimental results of extraction equilibria.

Is the solvation parameter model or its adaptations adequate to account for ionic interactions when characterizing stationary phases for drug impurity profiling with supercritical fluid chromatography?

Nine commercially available polar and aromatic stationary phases were characterized under supercritical fluid chromatographic (SFC) conditions. Retention data of 64 pharmaceutical compounds was acquired to generate models based on the linear solvation energy relationship (LSER) approach. Previously, adaptation of the LSER model was done in liquid chromatography by the addition of two solute descriptors to describe the influence of positive (D+) and negative (D−) charges on the retention of ionized compounds. In this study, the LSER models, with and without the ionization terms for acidic and basic solutes, were compared. The improved fits obtained for the modified models support inclusion of the D+ and D− terms for pharmaceutical compounds. Moreover, the statistical significance of the new terms in the models indicates the importance of ionic interactions in the retention of pharmaceutical compounds in SFC. However, unlike characterization through the retention profiles, characterization of the stationary phases by modelling never explains the retention variance completely and thus seems less appropriate.

Linear solvation energy relationships (LSER) for adsorption of organic compounds by carbon nanotubes

The objective of this paper was to create a comprehensive database for the adsorption of organic compounds by carbon nanotubes (CNTs) and to use the Linear Solvation Energy Relationship (LSER) technique for developing predictive adsorption models of organic compounds (OCs) by multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs). Adsorption data for 123 OCs by MWCNTs and 48 OCs by SWCNTs were compiled from the literature, including some experimental results obtained in our laboratory. The roles of selected OCs properties and CNT types were examined with LSER models. The results showed that the r2 values of the LSER models displayed small variability for aromatic compounds smaller than 220 g/mol, after which a decreasing trend was observed. The data available for aliphatics was mainly for molecular weights smaller than 250 g/mol, which showed a similar trend to that of aromatics. The r2 values for the LSER model on the adsorption of aromatic and aliphatic OCs by SWCNTs and MWCNTs were relatively similar indicating the linearity of LSER models did not depend on the CNT types. Among all LSER model descriptors, V term (molecular volume) for aromatic OCs and B term (basicity) for aliphatic OCs were the most predominant descriptors on both type of CNTs. The presence of R term (excess molar refractivity) in LSER model equations resulted in decreases for both V and P (polarizability) parameters without affecting the r2 values. Overall, the results demonstrate that successful predictive models can be developed for the adsorption of OCs by MWCNTs and SWCNTs with LSER techniques.

Effect of Solvent and pH on the Extraction of Carbolic Acid from Aqueous Solution by TOMAC

Studies on the extraction of carbolic acid (phenol) at different pHs by trioctyl methylammonium chloride (TOMAC) diluted in octane, decan, octan-1-ol, and decan-1-ol are reported. Experimental results of batch extraction experiments are calculated and reported for distribution coefficients (KD), loading factors (Z), and extraction efficiency (E). All measurements were carried out at 298.15 K. The maximum removal of phenol was observed to be 88.679% at pH = 5 for octan-1-ol. The results of the liquid–liquid equilibrium measurements were correlated with a linear solvation energy relationship (LSER) model, which takes into account physical interactions. The remaining parameters were fitted to the experimental results. Experimental results for the liquid–liquid equilibrium were compared to the model. The LSER model was applied to correlate experimental values.

An improved classification of stationary phases for ultra-high performance supercritical fluid chromatography

Supercritical fluid chromatography (SFC) has recently benefited of new instrumentation, together with the availability of many ultra-high performance columns (sub −2μm fully porous particles or sub −3μm superficially porous particles), rendering it more attractive than ever. Most of these columns commonly used in SFC were initially developed for HPLC use, with an increasing number of stationary phases specifically designed for SFC. While the availability of different stationary phase chemistries is an advantage to achieve successful SFC separations, selecting a column for method development remains difficult. For this reason, we have previously developed a classification of stationary phases dedicated to SFC use. It is based on linear solvation energy relationships (LSER) with Abraham descriptors (for neutral species). While current interest in SFC is strong in the pharmaceutical industry, the need to take account of interactions occurring with ionisable species is pressing. We have previously shown how a modified version of the solvation parameter model, adapted to take account of ionic and ionizable species, could be applied to the characterization of SFC systems. In the present paper, based on this modified LSER model, and on the analysis of 109 neutral and ionisable species, we propose an improved classification of 31 ultra-high performance stationary phases to facilitate method development with SFC.

Linear solvation energy relationship for the adsorption of synthetic organic compounds on single-walled carbon nanotubes in water

The linear solvation energy relationship (LSER) was applied to predict the adsorption coefficient (K) of synthetic organic compounds (SOCs) on single-walled carbon nanotubes (SWCNTs). A total of 40 log K values were used to develop and validate the LSER model. The adsorption data for 34 SOCs were collected from 13 published articles and the other six were obtained in our experiment. The optimal model composed of four descriptors was developed by a stepwise multiple linear regression (MLR) method. The adjusted r2 (r2adj) and root mean square error (RMSE) were 0.84 and 0.49, respectively, indicating good fitness. The leave-one-out cross-validation Q2 () was 0.79, suggesting the robustness of the model was satisfactory. The external Q2 () and RMSE (RMSEext) were 0.72 and 0.50, respectively, showing the model’s strong predictive ability. Hydrogen bond donating interaction (bB) and cavity formation and dispersion interactions (vV) stood out as the two most influential factors controlling the adsorption of SOCs onto SWCNTs. The equilibrium concentration would affect the fitness and predictive ability of the model, while the coefficients varied slightly.

On the Solubility of Ferrocene in Nonaqueous Solvents

The solubility of ferrocene in various organic solvents is important because of its application in chemical process and its role as a standard electrochemical probe in nonaqueous systems. A multilinear quantitative structure property relationship (QSPR) model based on theoretical descriptors and a new linear solvation energy relationship (LSER) model based on empirical scales of solvents are suggested for Ostwald solubility coefficient of ferrocene in 35 organic solvents. The constructed models were validated using different statistical approaches such as internal validation and external test set. In addition to excellent external prediction ability, QSPR and LSER models covered 94 and 92% of cross-validated variance, respectively. The proposed models confirmed the role of polar interactions and basicity of solvents during the solvation of ferrocene in organic phase.

Tadpole toxicity prediction using chromatographic systems

Toxicity has been emulated in tadpole species through chromatographic systems. The parameter studied to evaluate the non-specific toxicity of a compound is the narcosis concentration (Cnar), which is defined as the concentration needed for the immobilization of the organism. Because experimental investigation with animals is lengthy, costly, technically difficult, and ethically questionable, there is a great interest in developing surrogate physicochemical systems able to emulate biological systems to obtain the same information in a faster, more economic, and easier manner.In order to see which chromatographic systems would be able to emulate tadpole narcosis, both, tadpole narcosis data and data in several chromatographic and electrophoretic systems, were fitted to a linear solvation energy relationship (LSER) model. Thus, by comparison of the models it was possible to see which of the chromatographic systems were more similar to the biological one. The physicochemical systems that best emulate tadpole narcosis were an HPLC system based on an immobilized artificial membrane (IAM) column, and two micellar electrokinetic chromatography (MEKC) systems based on sodium taurocholate (STC) and a mixture of sodium dodecylsulphate (SDS) and Brij 35 as surfactants. A system based on a RP18 HPLC column also was selected for comparison because it is a common column in most analytical laboratories.To establish the models, a set of compounds with known Cnar values were analyzed in the chromatographic, and electrophoretic selected systems and, then, the retention factor (k) was correlated to the concentration of narcosis. Statistics showed that the system based on STC micelles was the best to emulate toxicity in tadpoles. The robustness and predictive ability of the developed models were validated.