Linear Solvation Energy Relationship Parameters Research Articles

Design, synthesis and evaluation of a series of alkylsiloxane-bonded stationary phases for expanded supercritical fluid chromatography separations

Supercritical fluid chromatography (SFC) today represents an alternative technique in analytical chemistry due to its obvious benefits in kinetic performance and its complementarity to liquid chromatography. In this paper, a series of alkylsiloxane-bonded stationary phases were synthesized and evaluated to expand their SFC applications. Five kinds of non-endcapped C8 stationary phases (C8-1 to C8-5) with increasing bonding density were synthesized, and the carbon content was 3.91%, 6.07%, 7.97%, 8.65% and 9.10% respectively. Retention mechanism of the C8 phases in SFC in SFC was investigated by the use of a linear solvation energy relationship (LSER) model. Results underlined a close relationship between the bonding density of alkyl chain and the dispersion and polar interactions of the stationary phase. Complementary evaluation was studied based on the calculation of vector angle (θ), and the widest θ of 123° was found between silica and C8 with the highest bonding density. Selective diversity also existed between the two C8 phases with the highest and lowest bonding densities. In addition, the effect of modifier on the SFC mechanism was investigated. Modifiers (methanol, ethanol, isopropanol and acetonitrile) had insignificant influence on the dispersion interaction but they mainly affected the hydrogen bonding interaction by changing the LSER parameters a and b. Finally, C8 and silica columns were applied for separation of eight amide alkaloids of Piper kadsura. Silica provided better retention but limited selectivity while C8 can distinguish alkaloids different in alkyl chain, double bond and cis-trans structure. This research further contributed to demonstrate the potential of alkylsiloxane-bonded stationary phase in improving selectivity of SFC.

Partial Solvation Parameters of Drugs as a New Thermodynamic Tool for Pharmaceutics.

Partial solvation parameters (PSP) have much in common with the Hansen solubility parameter or with a linear solvation energy relationship (LSER), but there are advantages based on the sound thermodynamic basis. It is, therefore, surprising that PSP has so far not been harnessed in pharmaceutics for the selection of excipients or property estimation of formulations and their components. This work introduces PSP calculation for drugs, where the raw data were obtained from inverse gas chromatography. It was shown that only a few probe gases were needed to get reasonable estimates of the drug PSPs. Interestingly, an alternative calculation of LSER parameters in silico did not reflect the experimentally obtained activity coefficients for all probe gases as well, which was attributed to the complexity of the drug structures. The experimental PSPs were proven to be helpful in predicting drug solubility in various solvents and the PSP framework allowed calculation of the different surface energy contributions. A specific benefit of PSP is that parameters can be readily converted to either classical solubility or LSER parameters. Therefore, PSP is not just about a new definition of solvatochromic parameters, but the underlying thermodynamics provides a unified approach, which holds much promise for broad applications in pharmaceutics.

Variation in predicted internal concentrations in relation to PBPK model complexity for rainbow trout

The present study is motivated by the increasing demand to consider internal partitioning into tissues instead of exposure concentrations for the environmental toxicity assessment. To this end, physiologically based pharmacokinetic (PBPK) models can be applied. We evaluated the variation in accuracy of PBPK model outcomes depending on tissue constituents modeled as sorptive phases and chemical distribution tendencies addressed by molecular descriptors. The model performance was examined using data from 150 experiments for 28 chemicals collected from US EPA databases. The simplest PBPK model is based on the “Kow-lipid content” approach as being traditional for environmental toxicology. The most elaborated one considers five biological sorptive phases (polar and non-polar lipids, water, albumin and the remaining proteins) and makes use of LSER (linear solvation energy relationship) parameters to describe the compound partitioning behavior. The “Kow-lipid content”-based PBPK model shows more than one order of magnitude difference in predicted and measured values for 37% of the studied exposure experiments while for the most elaborated model this happens only for 7%. It is shown that further improvements could be achieved by introducing corrections for metabolic biotransformation and compound transmission hindrance through a cellular membrane. The analysis of the interface distribution tendencies shows that polar tissue constituents, namely water, polar lipids and proteins, play an important role in the accumulation behavior of polar compounds with H-bond donating functional groups. For compounds without H-bond donating fragments preferable accumulation phases are storage lipids and water depending on compound polarity.

Prediction of Partition Coefficients of Organic Compounds in Ionic Liquids Using a Temperature-Dependent Linear Solvation Energy Relationship with Parameters Calculated through a Group Contribution Method

A temperature-dependent linear solvation energy relationship (LSER) is proposed for estimating the gas-to-ionic liquid partition coefficients. The model calculates the LSER parameters using a group contribution method. Large sets of partition coefficients were analyzed using the Abraham solvation parameter model to determine the contributions of 21 groups: 12 groups characterizing the cations and 9 groups for the anions. The derived equations correlate the experimental gas-to-ionic liquid coefficient data to within 0.13 log units. The 21 group parameters are used to predict the partition coefficients of solutes in alkyl or functionalized ionic liquids with good accuracy.

Prediction of Partition Coefficients of Organic Compounds in Ionic Liquids: Use of a Linear Solvation Energy Relationship with Parameters Calculated through a Group Contribution Method

A group contribution method is proposed to determine linear solvation energy relationship parameters (GC-LSER) in view of estimating the gas-to-ionic liquid partition coefficients and water-to-ionic liquid partition coefficients. Large sets of partition coefficients were analyzed using the Abraham solvation model to determine the contributions of 21 groups: 12 groups characterizing the cations and 9 groups for the anions. The derived equations correlate the experimental gas-to-ionic liquid and water-to-ionic liquid partition coefficient data to within 0.15 and 0.17 log units, respectively. The 21 group-parameters can be used to predict the partition coefficients of solutes in alkyl or functionalized ionic liquids with a good accuracy.

Investigation of solvent effects on UV–vis absorption spectra of dihydroxybenzene derivatives by solvatochromic parameters

The solvatochromism of dihydroxybenzene derivatives as probes in 18 solvents were investigated in the UV–vis spectra. The position, intensity and shape of absorption bands change with various solvent nature. These changes were rationalized by solvatochromic parameters such as α, β, E T(30), DN and AN using multiple linear regression (MLR) method. The studied dihydroxibenzene derivatives show negative solvatochromism and the correlation coefficients of derived equations by MLR method were obtained in the range 0.974–0.996. The linear solvation energy relationship parameters of the backward regression were applied to the Kamlet and Taft equation for the interaction of these three probes and solvents. The best LSER equation for these three probes, and the LSER parameters of backward regression with their mean effects and the regression coefficient have been calculated.

Cationic surfactants for micellar electrokinetic chromatography: 1. Characterization of selectivity using the linear solvation energy relationships model

MEKC and the linear solvation energy relationship (LSER) model have been applied to two series of cationic surfactants. The synthetic flexibility of the quaternary ammonium group is exploited to generate the two series, one consisting of linear substitutions and the other incorporating the ammonium into ring structures of varying size. The effects of the head group structure on the CMC, aggregation number, and electrophoretic properties of the surfactants were determined. These surfactants were also characterized with the LSER model, which allowed the contributions of five chemical factors to the interactions between solutes and the micelles to be evaluated. Trends were observed in the cohesivity and polarity of the linear surfactant series, with both increasing with the size of the head group. No trends in the LSER parameters were observed in the cyclic series, but the LSER results do show that the surfactants with cyclic head groups provide a significantly different solvation environment from the linear series. Additional trends were observed in the aggregation behavior and chromatographic properties of the surfactants. These included changes in the CMCs, aggregation numbers, EOF, and electrophoretic mobility of the micelles that correlate to changes in head group size.

Using temperature gradient gas chromatography to determine or predict vapor pressures and linear solvation energy relationship parameters of highly boiling organic compounds

An isothermal chromatographic method allowing determination of ∑ β 2 H and ∑ α 2 H descriptors of the linear solvation energy relationship (LSER) was tested and results obtained are presented. This method is based on the use of four stationary phases of various polarity. On the other hand, it was demonstrated that the temperature gradient chromatography may be successfully used to determine LSER descriptors. Results of π 2 H, ∑ β 2 H and log L 16 determination are reported. This approach opens new possibilities of precise and rapid determination of LSER descriptors of high boiling compounds using a small number of phases. It was demonstrated that the log L 16 descriptor may be used to estimate vapor pressures of high boiling organic compounds with a better accuracy than those usually obtained with chromatographic methods.

Linear solvation energy relationship parameters of some pure liquid organic compounds from solvatochromic investigations

The partitioning of an organic solute between an aqueous and an organic phase is governed by the properties of the phase forming aqueous/organic system as well as by the properties of the solute. As organic solutes are often highly diluted in such systems the infinite dilution partition coefficient is of particular interest. Partition coefficients at infinite dilution are often described using quantitative structure–activity relationships (QSAR), e.g. the linear solvation energy relationship (LSER) method of Kamlet and coworkers. The LSER method requires five parameters for the characterization of a solute j: a volume parameter v j , a polarity parameter π j , a parameter for the polarizability δ j , and two parameters describing the capability of the solute to undergo hydrogen bonding as a proton acceptor β j (basicity parameter) and as a proton donor α j (acidity parameter). This contribution reports new experimental data for the polarity parameter π j and the basicity parameter β j of about 90 liquid organic compounds. Such parameters can be used to predict thermodynamic properties such as the octanol–water partition coefficient or to develop methods for estimating such parameters.

PREDICTION OF LOG KW USING MCIS AND LSER METHODS FOR HETEROCYCLIC NITROGEN COMPOUNDS

The HPLC capacity factors(k') measured on a C18 column, using methanol-water mobile phase of different compositions, were determined for 15 heterocyclic nitrogen compounds. The linear relationship between the log k' values and the percentage of the methanol in the eluent was studied for each compound. The log kW′ values of these compounds were obtained by extrapolating the retention data in binary solvent system to pure water eluent. Various MCI's (molecular connectivity indices) were calculated and LSER(linear solvation energy relationship) parameters were observed for these compounds. Good correlations were established between MCI's and log kw', and between LSER parameters and log kw′. The present correlation can be used to predict log kw' values for other derivatives.

Surface Hydrogen-Bond Components and Linear Solvation Energy Relationship Parameters

In 1987, van Oss, Chaudhury and Good introduced the Lewis acid (or hydrogen-bond acidic) component, γ+, and Lewis base (or hydrogen-bond basic) component, γ−, and assumed the ratio of γ+ and γ− for water at 20°C to be 1.0. With that ratio, the base components, γ−, for other liquids and polymers appeared to be overestimated. Recently, we unexpectedly found a correlation between γ+ and γ− and the linear solvation energy relationship (LSER) parameters α (hydrogen-bond-donating ability, HBD) and β (hydrogen-bond-accepting ability, HBA), introduced by Taft and Kamlet in 1976. Interestingly, we found the ratio for the normalized α and β for water at ambient temperature to be 1.8 instead of 1.0. Based on this new ratio for the corresponding γ+ and γ−, the calculated total surface tensions for other liquids and polymers at 20°C are generally unchanged, as expected, despite the favorable changes in the γ+ and γ− ratio to make them less basic. In addition, the implications of other LSER parameters, e.g. ∏* and δ2 H on surface properties will be briefly mentioned.

Correlation between Lewis Acid−Base Surface Interaction Components and Linear Solvation Energy Relationship Solvatochromic α and β Parameters

In this paper, we report our unexpected finding about the correlation between Lewis acid−base surface interaction components and linear solvation energy relationship (LSER) solvatochromic parameters α and β. In 1987, van Oss, Chaudhury, and Good proposed to split the asymmetric acid−base parts of a bipolar system into separate surface tension components: Lewis acid (electron acceptor) γ+ and Lewis base (electron donor) γ-. It was assumed that the ratio of γ+ and γ- for water at 20 °C was to be 1.0. With that ratio as a reference, the base components, γ- for other liquids, biopolymers, polymers, and solids appeared to be overestimated. Recently, we unexpectedly found a correlation for liquids between γ+ and γ-, and α (solvent hydrogen-bond-donating ability) and β (solvent hydrogen-bond-accepting ability) introduced since 1976 by Taft and Kamlet. From that correlation, we obtained a more realistic ratio for the normalized α and β values for water at ambient temperature to be 1.8 instead of 1.0. Based on this new ratio, we calculated total surface tensions for related materials at 20 °C. They are generally unchanged as expected, despite the considerable, favorable change in the γ+ and γ- values in the direction of lowering the Lewis basicity. The predicability of solubility with interfacial tension is also unaffected. For example, the sign of those negative interfacial tensions that favor solubility remains the same. In addition, the implications of other LSER parameters, e.g. Π* and δH2, on surface properties will be briefly mentioned.