Jacques R. Chrétien

New perspectives in the prediction of kováts indices

Abstract Sets of Kovats indices corresponding to different chromatographic conditions and/or to different chemical families can be rendered coherent by the use of topology-information correlations established according to the principles of the DARC (Description, Acquisition, Retrieval and Conception) topological system. These correlations are based on the Kovats indices or on data derived from these indices (Kovats index increment, δI, and isotopology factor, τI). They serve to demonstrate the prediction potential, the minimization of the number of parameters and of the number of data, and the precision of our approach. Chromatographic retention data banks can be envisaged on the basis of this approach.

Factor analysis and experiment design in high-performance liquid chromatography. II: Normal-phase high-performance liquid chromatography on columns of different polarities

Abstract The separation of 47 chalcones, giving two series of the E-s-cis- and Z-s-cis-isomers in normal-phase high-performance liquid chromatography (H

Topological analysis of the behaviour of linear alkenes up to tetradecenes in gas-liquid chromatography on squalane

Abstract DARC topological analysis (DTA) has been applied to Kovats retention indices for a series of 84 linear alkenes up to tetradecenes studied by gas-liquid chromatography on squalane at 100 °C. The topology-information diagram gives information at the skeletal carbon atom level of the alkene molecules. Very small structural effects are detected and discussed on a statistical basis. This set of n -alkenes constitutes a good model for testing the interpretative and physico-chemical potentialities of DTA in order to establish a set of precise reference data for higher n -olefins of petrochemical interest.

Gas-solid chromatography on cation-exchange resins: Darc topological analysis of the behavior of alkenes on nickel ions

Abstract Retention indices of 44 alkenes in gas-solid chromatography were determined on the Ni2+ form of a cation-exchange resin and on the corresponding unsulfonated copolymer matrix. The Ni2+ form was prepared from a sulfonated Porapak Q ethylvinylbenzene-divinylbenzene copolymer. DARC topological analysis (DTA) was applied to the Kovats retention indices determined at 175°C. DTA helps to delineate the evolution of specific π bond-Ni2+ ion interactions with progressive variations of the structural effects of the alkenes.

Gas—liquid chromatographic retention behaviour of hindered aliphatic esters

Abstract Relative retentions and Kovats retention indices of sixteen crowded aliphatic ethyl or methyl esters (R 1 R 2 CHCO 2 R or R 1 R 2 R 3 CCO 2 R; R = ethyl or methyl) have been systematically determined on nine stationary phases of increasing polar character from the non-polar branched-chain hydrocarbon C 87 H 176 to the highly polar cyanopropylsiloxane Silar–10C. A qualitative pattern showing the retention behaviour of the branched acyl group of the esters is developed. An unexpectedly strong contribution of polar effect occurs with highly congested acyl groups in α,α,α-trialkyl esters.

Chemometrics in chromatography

Abstract The impact of chemometrics in chromatography is presented. The development of systematic experiments is encouraged to exploit simultaneously the richness of teh chromatographic data and the possibilities of complementary data processing techniques.

Quantitative study of structural parameters of specific adsorption of alkenes on zinc ions using gas—solid chromatography and topological data-processing techniques

Abstract Gas—solid chromatography can provide information on the adsorption processes involved in heterogeneous catalysis. Retention indices of a set of 44 alkenes on the zinc form of a sulfonated porous polymer are analyzed to evaluate the polar and steric contributions to adsorption on this metal ion. DARC/PELCO topological analysis is used to evaluate the effect of each carbon atom in the environment of the double bond on the overall retention of a compound by adsorption.

Specific interactions of alkenes with different metal ion forms of ion exchangers in gas solid chromatography

SummaryThe gas chromatographic selectivity of K+, Zn2+, Ag+, Ni2+, and Cd2+ forms of a cation exchange packing have been determined for a set of 44 C2 to C8 alkenes. The retention characteristics of each ion are broken down into electronic (charge-transfer) and steric effects associated with the alkene sub-populations of each carbon number. Almost every pair of alkenes tested can be separated on at least one of these packings. Retention is much stronger on the ion exchangers than on metal-ion containing packings in gas-liquid chromatography, even with shorter columns and higher temperatures.

Factor analysis in ion chromatography of carboxylate ions

Abstract The retention times of five carboxylate ions (formate, acetate, propionate, n -butanoate and n -pentanoate) in ion chromatography were determined using 25 eluents prepared from NaHCO 3 and Na 2 CO 3 . Principal component analysis (PCA) and correspondence factor analysis (CFA) were applied to describe the behaviour of the carboxylate anions and the influence of the carbonate concentration of the eluents. With PCA, only one factor is necessary to model the retention times of each ion studied. CFA offers an analysis of second-order effects and shows how the selectivities of the chromatographic systems are modified with either the carbonate concentration or the concentration ratio of NaHCO 3 and Na 2 CO 3 .

A molecular electrostatic potential study of phenothiazine dopaminergic antagonists

Abstract The recognition of the dopaminergic receptor by antagonists has been studied for a set of phenothiazine compounds. This study was based on molecular electrostatic potential (MEP) calculations. The first step of the recognition involves the interaction of the nitrogen atom of the chain fragment of the series of phenothiazines: promazines, perazines and phenazines. The second step involves the adaptation of the aromatic fragment deduced from the examination of the molecular orientation vector. The simultaneous influences of the orientation vector and of a binding step parameter, the energy of the lower unoccupied molecular orbital (LUMO) , on the variation of activity of a series of promazines were studied. The variations of the structural parameters which induce a counterclockwise rotation of the orientation vector, in a range of about 70 degrees, are related to activity increases.