Yassin Darwish

Effect of support characteristics on the determination of the lipophilicity of some neutral, acidic and alkaline compounds by reversed-phase thin-layer chromatography

The lipophilicity of some neutral, acidic and alkaline compounds was determined by reversed-phase thin-layer chromatography applying silica, aluminium oxide and cellulose in different degrees impregnated with paraffin oil as support. The lipophilicity of all compounds increased on all supports at increasing extent of impregnation; paraffin oil gradually covered the active adsorption sites of supports. The lowest RM values were determined on cellulose support owing to its lower adsorptive capacity. The alkaline compounds showed higher RM values on silica and the acidic compounds on aluminium oxide, proving that also the surface pH value of the support influences the lipophilicity determination.

Anomalies in the reversed-phase thin-layer chromatographic behaviour of some heterocyclic quaternary ammonium salts

Abstract The determination of the lipophilicity of 3,3,5-trimethyl-1-azocycloheptane- and 1,3,3-trimethyl-6-azobicyclo[3.2.1]octane derivatives by reversed-phase thin-layer chromatography shows marked anomalies. In ion-free eluent systems the RM values show an extremely small dependence on the proportio of organic solvent solvent in the mobile phase. A logarithmic relationship was found between the RM value and the pH of the eluent system. The effect of ion concentration can be modelled by a polynomial function. These anomalies can be explained by the change in the ion-pair formation of the very hydrophilic quaternary ammonium group and by the change in the solvate shell around the very lipophilic organic part of the molecule caused by different pH values and by different ion concentrations.

Liquid chromatographic and electrophoretic characterisation of extracellular β-glucosidase of Pleurotus ostreatus grown in organic waste

The production of beta-glucosidase by the ligninolytic fungus Pleurotus ostreatus has been studied in different culture media containing agro-industrial wastes. The enzyme is purified by anion-exchange chromatography, the molecular mass and isoelectric point of purified beta-glucosidase are measured by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and isoelectric focusing and the stability and kinetic parameters of the enzyme assessed by spectrophotometry. It has been established that the retention time, molecular mass and isoelectric point of the enzyme depend on the composition of the culture media while the activity and stability of beta-glucosidases of different origin were very similar. The combined chromatographic and electrophoretic methods have proved to be suitable techniques for the purification and characterisation of the beta-glucosidases produced by the ligninolytic fungus Pleurotus ostreatus in different culture media.

Reversed-phase retention characteristics of some bioactive heterocyclic compounds

Abstract The lipophilicities and specific hydrophobic surface areas of sixteen bioactive heterocyclic compounds were determined by reversed-phase thin-layer chromatography using various eluent systems. The data were evaluated by principal component analysis (PCA), separately calculated from the correlation and covariance matrices, and by cluster analysis. The ratio of the variances explained by the first PC component was high and was very similar for both PCA methods, suggesting that the eluents have common elution characteristics. The lipophilicities and specific hydrophobic surface areas of the compounds are well separated on the two-dimensional non-linear maps of PC variables, indicating the different information contents of the two physico-chemical parameters. The information contents of cluster analysis and two-dimensional non-linear mapping techniques were found to be similar but not identical.

Use of principal component analysis and cluster analysis in quantitative structure-activity relationships: A comparative study

Abstract The inhibitory effect of some new benzothiazole derivatives on Bacillus subtilis, Aspergillus niger, Helminthosporium sativum and Fusarium graminearum was determined. Hydrophobicity and specific hydrophobic surface area of the pesticides were measured by reversed-phase thin-layer chromatography in neutral, acidic, alkaline and salt-containing environments. To find the relationship between the physicochemical parameters and biological activity, stepwise regression analysis, principal component analysis, nonlinear mapping technique and cluster analysis were applied. Good linear correlations were found between the biological activity, steric parameter and calculated hydrophobicity value of compounds proving the significant impact of the above physicochemical parameters on the inhibitory effect. Nonlinear mapping technique cannot be used on the original data matrix, but it can be successfully applied for the principal component loadings and variables. Cluster analysis requires the lowest computational time and the results are commensurable with those of principal component analysis. Both methods indicate that the pH and salt concentration have a negligible impact on the hydrophobicity and specific hydrophobic surface area of pesticides, whereas the biological activity and the measured physicochemical parameters form two different clusters suggesting the poor correlation between the two groups of variables.

Effect of reduced glutathione on the stability of pigments in paprika powders studied by multiwavelength spectrometry and high-performance liquid chromatography

Multiwavelength spectrometry and reversed-phase high-performance liquid chromatography have been employed for the study of the effect of reduced glutathione and storage time on the pigments of paprika powders. The evaluation of the data by principal component analysis and cluster analysis proved that the storage time exerts the highest effect of the decomposition rate of pigments. The stability of some pigment fractions was modified in the presence of reduced glutathione. However, the effect was of secondary importance. Multiwavelength spectrometry combined with HPLC can be successfully used for the study of the stability of pigments of paprika powder.

Interaction of Pesticides with a β-Cyclodextrin Derivative Studied by Reversed-phase Thin-layer Chromatography and Principal Component Analysis

The interaction of 18 pesticides with a water-soluble β-cyclodextrin polymer (BCDP) was studied by reversed-phase thin-layer chromatography and principal component analysis (PCA) was employed for the elucidation of the relationship between the relative strength of interaction and the calculated surface parameters of the guest molecules. Except for penconazole the lipophilicity of the pesticides decrease in the presence of BCDP. PCA indicated that apolar surface parameters are highly positively correlated with the strength of interaction. The data indicate that the agrochemical characteristics (adsorption, leakage, decomposition, etc) of complexed pesticide molecules can be different from those of uncomplexed onesresulting in modified efficacy.

Reversed-phase thin-layer chromatography of various pesticides in the presence of water-soluble beta-cyclodextrin polymer

SummaryThe modification of the hydrophobicity of 28 commercial pesticides with a water-soluble β-cyclodextrin polymer (SCDP) in the presence of aqueous NaCl has been studied by reversed-phase thin-layer chromatography. The pesticides formed inclusion complexes with SCDP and these complexes are less lipophilic than the parent pesticides. The sodium chloride exerted a typical saltingout effect, the retention of each pesticide increased with increasing concentration of the salt in the eluent. This effect can be tentatively explained by the suppression of the dissociation of the polar groups in the solute molecules resulting in increased apparent lipophilicity. The correlation between lipophilicity and salting-out effect was found to be significant, that is the salting-out effect increases with increasing polarity (lower lipophilicity) of the pesticides, whereas the lipophilicity has negligible influence on the inclusion-forming capacity of non-homologous series of pesticides.

Gas chromatographic determination of the energy of interaction between some commercial pesticides and a non-ionic surfactant.

Abstract Gas–liquid chromatography has been used for the determination of the energy of interaction between some commercial pesticides and the non-ionic surfactant tributylphenyl(ethyleneglycol) 30 . The energy of interaction was calculated from the temperature dependence of the retention time of pesticides. The similarities and dissimilarities between the retention behaviour of pesticides and gas chromatographic columns was evaluated by principal component analysis (PCA) followed by two-dimensional non-linear mapping and cluster analysis (CA). The energies of interaction of pesticides showed considerable differences. Significant linear correlation was found between the energies of interaction determined on Carbowax 20M and the surfactant column suggesting that their retention mechanism may be similar. This result makes probable that the pesticides bind to the polar ethyleneglycol moiety of the surfactant by hydrophilic (electrostatic) forces and the involvement of hydrophobic forces in the pesticide — surfactant interaction is negligible. The comparison of the results of PCA and CA indicate that both methods can be successfully used for the evaluation of the retention data matrix.