Martha J.M. Wells

Investigation of N-alkylbenzamides by reversed-phase liquid chromatography : I. Isocratic elution characteristics of the C1C5 N-alkylbenzamides

Abstract The reversed-phased liquid chromatographic retention of the C 1 C 5 N-alkylbenzamides was investigated in aqueous-organic solvent mixtures. The log k ′ values for the amides were found to increase dramaticaly in mobile phases of low organic content. This non-linear relationship of log k ′ and mobile phase composition was observed on C 18 bonded-phase columns from different manufacturers. Attempts to measure retention data in pure water were successful only for the smaller molecules of the series. In general, the order of elution appears to parallel the carbon content of the N-alkyl group while increased branching decreases retention among isomeric amides.

Investigation of N-alkylbenzamides by reversed-phase liquid chromatography : II. Application of the solvophobic theory to the prediction of retention data for the C1C5 N-alkylbenzamides

Abstract The relationship between capacity factor ( k ′) and eluent composition for the C 1 C 5 N-alkylbenzamides was not described adequately by either linear or quadratic equations. Using the chromatographic data determined in acetonitrile—water, the relationship between k ′ and eluent composition was described by the solvophobi theory. Regression coefficients obtained from the solvophobic equation were used to calculated the contact surface area of the solute-bonded ligand complex. The theory was used to calculate k ′ for each compound in a totally aqueous mobile phase. The results indicate that branched alkyl chains elute before their straight-chain analogues and among isomers the elution volume increases with the distance between the branching point and the amide nitrogen.

Investigation of N-alkylbenzamides by reversed-phased liquid chromatography : III. Correlation of chromatographic parameters with molecular connectivity indices for the C1C5 N-alkylbenzamides

Abstract Molecular connectivity indices were compared with measured and calculated reversed-phase liquid chromatographic retention data for the C 1 C 5 N-alkylbenzamides. Molecular connectivity is a topological index which encodes fundamental structural information about a molecule. The calculated indices are presented as bargraph spectra and in tabular form. The various parameters of the solvophobic theory used to calculate log k ′ w values for the amides were also compared to connectivity data. Highest correlations with k ′ were obtained for connectivity data which describes molecular bulk, branching, and site of branching in the hydrocarbon portion of the molecule.

Investigation of N-alkylbenzamides by reversed-phase liquid chromatography : IV. The study f a homologous series of N-alkylbenzamides using the solvophobic theory and molecular connectivity

Abstract The capacity factors for eighteen normal-chain N-alkylbenzamides in a reversed-phase chromatographic system are reported. Measured and calculated chromatographic parameters indicate that an adequate description of teh structure-retention process canbe achieved only if the amides are considered in groups of short, intermediate and long chain length. The inconsistent chromatographic behavior observed when all eighteen amides are considered may be due to conformational or critical chain-length effects.

Study of the relationship between dynamic and static equilibrium methods for the measurement of hydrophobicity : Comparison of capacity factors and partition coefficients for some 5,5-disubstituted barbituric acids

Abstract The capacity factors for twelve 5,5-disubstituted barbituric acid derivatives in a reversed-phase chromatographic system are reported. The solvophobic theory was used to described the relationship between the capacity factor and eluent composition in order to determine log k ′ w (the hypothetical capacity factor in totally aqueous eluent) for each solute. The dynamically derived descriptor of hydrophobicity, log k ′, was compared with log P , a static equilibrium descriptor. Comparisons were made between log k ′ values determined at various solvent compositions and log P values measured using solvents of differing polarities as the organic component of the binary mixture.

Investigation of N-alkylbenzamides by reversed-phase liquid chromatography : V. Charateristics of some tertiary alkylbenzamides

Abstract The capacity factors (k′) for sixteen tertiary N-alkylbenzamides in a reversed- phase chromatographic system are reported. Applying the solvophobic theory, the measured log k′ data from an acetonitrile—water eluent were used to calculate log k′w (the log k′ in 100% water). The values for the contact surface are, ΔA, between the benzamide-bonded ligand (stationary phase) complex were alos calculated. The measured and calculated capacity factor data and other chromatographic parameters calculated from the solvophobic equations were found to be highly correlated with those molecular connectivity indices which quantitatively describe molecular bulk.