Chromatographic study of electron acceptor-donor properties of of 4-(trans-4'-n-alkylcyclohexyl) benzoates.

A new approach of characterizing the specific properties of 4-(trans-4'-n-alkylcyclohexyl) benzoates, based on the interaction of the acidic and basic testing substances, for their form Crystalline, Smectic B and Nematic have been proposed. The testing substances selected for our study have been considered in the light of the results obtained in the previous research and the data available in the literature for other liquid crystals with different structures. The DN values denoting the electron donor number in the Gutmann scale and the AN* values indicating the acceptor number in the Riddle-Fowkes scale have been chosen in the estimation of the electron acceptor parameter KA and electron donor parameter KD values. The temperature-dependent quotients of KA to KD are employed for the assessment of the electron donor-acceptor properties of 4-(trans-4'-n-alkylcyclohexyl) benzoates. The 4-(trans-4'-n-alkyl cyclohexyl) benzoates tested have the affinity to act as a donor of electrons concerning electron acceptor of the testing substance. The sizes and shapes effects of the testing substances (or penetrants) and the LCs tested (or solvents while in mesophases) are taken into account. The inverse gas chromatography tests were supported by the Quantitative Structure-Activity Relationship modelling technique to determine which part (or group) of liquid crystals tested was dominant in the interaction with the testing substances.

Chromatographic determination of the free energy of adsorption and absorption characteristic of 4-(trans-4'-n-alkylcyclohexyl) benzoates.

The characterisation of the energetic properties of liquid crystals, i.e., esters with elongated molecules has been performed. The changes of the free energies of adsorption and absorption (dissolutions), ΔG, for liquid crystals have been estimated, based on the retention times of the centre of gravity of the elution peaks determined for the substances with defined physicochemical properties. The temperature-dependent van der Waals component of the free energy, [Formula: see text] , for a crystalline form of liquid crystal has been estimated by employing the Dorris-Gray approach. These approaches have been widened to mesophases, namely, the absorption(dissolution) of n-alkanes in the smectic B and nematic phases.

Rediscovering the problem of interpretation of chromatographically determined enthalpy and entropy of adsorption of different adsorbates on carbon materials. Critical appraisal of literature data.

Adsorbate-adsorbent and adsorbate-adsorbate interactions having decisive influence on the distribution of adsorbate between gas-solid phases in inverse gas chromatography (IGC) have been thermodynamically explained. Specific retention volumes, second adsorption virial coefficients and Kováts retention indices, likewise their dependencies on column temperature, T, number of carbon atoms, n(C) (or methylene groups CH(2)) and mutual ones have been briefly presented. The results of the molar differential enthalpy and entropy of adsorption obtained for different carbon materials employing inverse gas chromatography have been collected and interpreted. An attempt has been made to elucidate abnormal behaviour of the specific and net retention volumes, the second adsorption virial coefficients and the Kováts retention indices, e.g., the magnitudes on which the values of the afore-mentioned thermodynamic values have been determined and compared. The detailed analysis of the errors associated with the experimental parameters necessary for calculating retention volumes, second adsorption virial coefficients and Kováts retention indices has been presented.

Comparison of the differential isosteric adsorption enthalpies and entropies calculated from chromatographic data.

The differential isosteric enthalpies, -deltaH(ads), and entropies, -deltaS(ads), of adsorption were calculated taking the retention times of the peak maxima and the centres of gravity of peaks into account and compared with the results obtained from the adsorption second virial coefficients. A mathematical link between the -deltaH(ads) and -deltaS(ads) magnitudes and experimental data was derived through the Antoine-type equation which enables the -deltaH(ads) and -deltaS(ads) magnitudes to be found from adsorption second virial coefficients, B2S, calculated on the basis of chromatographically determined adsorption isotherm data. The virial coefficients were calculated employing the values of the Tóth and Unilan equation parameters. There are no significant differences to be found between the isosteric enthalpies obtained, whereas the values of the adsorption entropies were the highest for the centre of peak gravity data.

Determination of dependencies between the specific retention volumes and the parameters characterising adsorbent properties.

Propane adsorption isotherms have been chromatographically determined on active carbon for different amounts of the injected adsorbate on column. The dependencies between the specific retention volume corrected to the standard temperature (273.15 K), Vg(273), and the molar differential work of adsorption, A, have been calculated on the basis of the propane isotherms and using the retention times of the peak maxima. The obtained equations: ln Vg(273) = f1(A) and (dW/dA)T.F(C) = f2(ln Vg(273)) have been used to explain the dependency between the chromatographic peak profile and the distribution function of pore volumes filled with propane with respect to the molar differential work of adsorption at different column temperatures (303-318 K).