Theoretical characterization of gas–liquid chromatographic stationary phases with quantum chemical descriptors (original) (raw)
Related papers
2009
Quantum chemical based investigation is presented on the Abraham solvation parameters for 23 molecular (non-polymeric) GLC stationary phases. PM6 semiempirical calculations combined with conductor-like screening model (COSMO) have been utilized. Comprehensive search for an optimal model was carried out, based on best subset selection from 86 variables considered. A unified quantitative structure-property relationship model has been developed for all five Abraham parameters reported. The selected set of five structure-driven descriptors was subjected to statistical analyses, and was shown to be useful for stationary phase classification.
Journal of Chromatography A, 2011
It has been demonstrated for a long time that in the particular case of gas-liquid chromatography (GLC), a linear free energy relationship (LFER) of five terms can be established, each term including a parameter of solute and a parameter of solvent. The nature of some of these parameters has been quite clearly identified, even if not always well predicted from the molecular structure. First of all, the five solute parameters: two involved in the hydrogen bonding and three in the Van der Waals forces; secondly, the two solvent parameters involved in hydrogen bonding. It was remaining an uncertainty concerning the nature of the solvent parameters named D, W and E, respectively associated with the solute parameters of dispersion, orientation and induction/polarizability. This uncertainty has been solved using experimental chromatographic data of McReynolds (56 phases) and of the Kováts group (11 phases). The parameter W appears as of polar nature strictly speaking. The parameters D and E can be expressed by two opposite bilinear functions of 1/V (inverse of molecular volume) and PSA/V (ratio of the polar surface area over the molecular volume). These results are in agreement with previous studies limited to alkanes by the Kováts group.
Development of Abraham model correlations for solvation characteristics of linear alcohols
Fluid Phase Equilibria, 2009
Data have been compiled from the published literature on the partition coefficients of solutes and vapors into the anhydrous linear alcohols (methanol through 1-heptanol, and 1decanol) from both water and from the gas phase. The logarithms of the water-to-alcohol partition coefficients (log P) and gas-to-alcohol partition coefficients (log K) were correlated with the Abraham solvation parameter model. The derived correlations described the observed log P and log K values to within average standard deviations of 0.14 and 0.12 log units, respectively. The predictive abilities of the each correlation were assessed by dividing databases into a separate training set and test set.
Journal of Chemical Information and Modeling, 2006
In a recent paper appearing in this Journal Laffort and Héricourt 1 presented a generalized method to establish the numerical values of the solvation parameters of solutes. The solvation parameters, when combined with the five solvent solvation parameters, describe the intermolecular forces present in fluid solutions. As part of their discussion the authors suggested two sets of optimized values of solute solvation parameters. The first set of parameters was based on the published Abraham solute descriptors (E, S, A, B, and L), modified by the authors to include scaling factors and greater independence (orthogonality). In eqs 1-5, δ 2 denotes the solute's Laffort et al. dispersion parameter, ω 2 is the solute's orientation factor, 2 refers to the polarizability-induction parameter of the solute, and R 2 and 2 represent the solute's acidity and basicity parameters, respectively. Laffort et al. 1,2 deduced their second set of solvation parameters from experimental gas-liquid chromatographic retention indices of the solute on five selected stationary phases. The selected stationary phases were prepared in limited quantity and are not commercially available. Numerical solvation parameters were reported for 133 substances for the second of the two
New J. Chem., 2004
Experimental partition coefficient data have been compiled from the published literature for the water/methyl acetate, water/ethyl acetate and water/butyl acetate partition systems, log P data, and for the gas/methyl acetate, gas/ethyl acetate and gas/butyl acetate partition systems, log K data. Application of the Abraham solvation parameter model to the sets of partition coefficients leads to equations that correlate the log P data and log K data to 0.18 log units for the three dry alkyl acetate solvents. Slightly larger deviations were noted for solute partition into both wet ethyl acetate and wet butyl acetate. The derived correlations were validated using training set and test set analyses.
Journal of chemical …, 2003
We present an extended QSPR modeling of solubilities of about 500 substances in series of up to 69 diverse solvents. The models are obtained with our new software package, CODESSA PRO, which is furnished with an advanced variable selection procedure and a large pool of theoretically derived molecular descriptors. The squared correlation coefficients and squared standard deviations (variances) range from 0.837 and 0.1 for 2-pyrrolidone to 0.998 and 0.02 for dipropyl ether, respectively. The predictive power of the models was verified by using the "leave-one-out" cross-validation procedure. The QSPR models presented are suitable for the rapid evaluation of solvation free energies of organic compounds.
Solubility factors for 240 solutes and 207 stationary phases in gas-liquid chromatography
Analytical Chemistry, 1982
A method for calculating "solubility factors" in gas-liquld chromatography was developed by Laffort and Patte by using the retention indexes of a given solute on five stationary phases. This method Is reflned and applied to 240 different compounds covering a large scatter of functlonal groups and structures. I n additlon, by using McReynolds' data, solubility factors of 207 stationary phases are proposed. Predlctablllty of retention Indexes on the basis of these solubility factors can be compared to the experlmental data. Propertles llke octanol-water partition coefficient (Hansch p factor), air-water partition coefflclent, and saturated vapor pressure at glven temperature are predlcted. In 1976, Laffort and Patte (1) made an experimental comparison between two attempts a t characterizing all the solubility factors involved in gas-liquid chromatography. The first approach, semitheoretical, was developed by Karger et al. (2, 3), through an expanded version of the Hilclebrand solubility parameter. The second one, purely empirical, was due to Dravnieks and Laffort (4) and Laffort et al. (5), who applied to unpublished Kovats' retention indexes, measured by McReynolds (6), an original computer program related to factor analysis. This comparison gave a mutual improvement of both approaches (approximately 80% of mutual agreement). It also provided a simple way to derive the factors of a given solute from its retention indexes on five standard stationary phases. Similarly the five factors of a given stationary phase could be obtained from its retention indexes of five standard solutes. In the second approach, the solute factors, represented by Greek letters, and the stationary phases factors, represented by Latin letters, are involved in a linear equation of predictability of retention indexes (I) as follows: I = aA-Iw 0-I-tE + TP-t-@I3 f 100 (1) Meaning of t h e Solute Factors. In the above equation, similar to that proposed by Rohrschneider in 1966 (7), physicochemical meanings can be given to the solute factors: CY, or apolar factor, is proportional to mole volume at boiling point, Le., to the actual molecular volume. w, or orientation Ifactor, is proportional to the square of the dipole moment for simple molecules. The values are high for ketones, aldehydes, carboxylic acids, esters, nitro, and nitrile compounds. e, or electron factor, is proportional, for molecules with electrons regularly distributed like benzene, to the ratio between molecular refraction and mole volume at boiling point. The values are high for sulfur, iodide, bromide, polychlorid and ring compounds. The values are negative for carboxylic acids and branched substances. A, or proton donor factor, could also be called acidity factor. The values are high for carboxylic acids and alcohols. p, or basicity factor, is proportional to the ability to receive protons. The values are high for carboxylic acids, amines, nitro, and nitrile compounds. Notice that, except for a, the solute factors very partially depend on the size of the molecule. They essentially reflect the influences of functional groups and the shape of molecules. All solute factors are referred to methane (values equal to zero for this substance). This explains the constant 100 used in eq 1. Meaning of the Stationary Phase Factors. The stationary phase factors A , 0, E, P, and B must be previously multiplied by the slopes b for n-paraffins according to eq 2 where V, is the specific retention volume. Vgid log-=-(a A + w 0 + EE + TP + OB) (2) Vg(CH.J 100 Among these factors the first one, A , is a constant. Only one term of eq 2 was clearly identified by Claverie (8). The product Eb reflects the "compactability" of the solvent, Le., the relative absence of "holes". For stationary phases with the same kind of atoms, it is proportional to the density at
Modeling liquid properties, solvation, and hydrophobicity: A molecular size-based perspective
2000
A recently introduced molecular size-based model that allows a unified description of enthalpies of vaporization, boiling points, gas-liquid solubilities, and vapor pressures for simple organic liquids using a free energy expression obtained from molecular-level assumptions is summarized. By changing the interaction-related constant ω used by the model when water is the solvent, the model can be extended to describe alkane-water partition, octanolwater partition, and water solubility of solutes that have no hydrogen-bonding or strongly polar substituents. Here, it is shown that this ω change, which is most likely related to the changes that the solute produces in the hydrogen-bonded structure of water, agrees very well with the value that can be derived from the modified hydration-shell hydrogen-bond model of Muller. By combining the present molecular size-based model with this hydrogenbonding model, a simplified but consistent description is obtained for the properties of water and for the hydrophobic effect. This indicates that many unusual properties of water may be accounted for by a proper combination of the nonspecific interactions as extrapolated from other liquids, the unusually small size of its molecules, and an adequate model of hydrogenbonding. A fully computerized method (QLogP) that can estimate octanol-water log P for a large variety of organic solutes also fits within this unified approach. Despite using only two parameters (molecular volume and a novel, quantified parameter that is probably hydrogenbonding-related), the predictive power of this method is similar to that of the considerably more complex fragment-contribution methods often used by medicinal chemists (ACD/LogP, AFC, CLOGP, KLogP, MLogP, Rekker), as illustrated by a comparison based on various structures.