Barna Bordás

Effect of water-soluble β-cyclodextrin polymer on the lipophilicity of polymyxine examined by reversed-phase thin-layer chromatography

Abstract Thin-layer chromatography has shown that the water-soluble β-cyclodextrin polymer forms inclusion complexes with the antibiotic polymyxine, reducing its lipophilicity and its adsorption energy on silica gel. A lower dielectric constant and increasing salt concentration of the solution as well as greater cation radii counteract the complex formation.

Comparison of the retention behaviour of phenol derivatives on porous graphitized and octadecylsilica columns

SummaryThe retention of 22 ring-substituted phenol derivatives on porous graphitized carbon (PGC) (eluents: acetonitrile — water and methanol — water mixtures) and on octadecylsilica (ODS) (eluents: methanol — 0.025 M KH2PO4 mixtures) was determined, and the relationship between retention and physicochemical parameters were evaluated by principal component analysis followed by two-dimensional nonlinear mapping and by cluster analysis as well as by canonical correlation analysis. Calculations proved that marked differences can be detected between the retention characteristics of PGC and ODS columns, and the electronic parameters of phenol derivatives have the highest impact on their retention. The comparison of various multivariate mathematical-statistical methods indicated that principal component analysis followed by two dimensional non-linear mapping is the most appropriate method for the evaluation of large data matrices in RP-HPLC.

Application of multivariate mathematical-statistical methods for the comparison of the retention behaviour of porous graphitized carbon and octadecylsilica columns

Abstract The retention of sixteen ring-substituted aniline derivatives on porous graphitized carbon (PGC) column (eluents: acetonitrilewater and methanolwater mixtures) and on octadecylsilica (ODS) column (eluents: methanol-0.025 M K 2 HPO 4 mixtures) was determined, and the relationship between retention characteristics and physico-chemical parameters were evaluated by principal component analysis followed by two-dimensional non-linear mapping and by cluster analysis and also by canonical correlation analysis. Calculations proved that marked differences can be detected between the retention characteristics of PGC and ODS columns, and the electronic and steric parameters of aniline derivatives have a great impact on their retention. The comparison of various multivariate mathematical-statistical methods indicated that principal component analysis followed by two-dimensional non-linear mapping is the most appropriate method for evaluation of large data matrices in reversed-phase liquid chromatography.

Lipophilicity determination of some fully protected peptides and amino acids

SummaryThe lipophilicity of 21 fully protected peptides and amino acids was determined by reversed-phase thin-layer chromatography. The RM values decreased linearly with growing methanol concentration of the eluent. The sequence and conformation of molecular substructures did not significantly influence the lipophilicity. The presence of salt and ammonia in the eluent had a negligible impact on retention; the effect of the pH value was also low. In the presence of 1M and 2M acetic acid the retention of each compound considerably decreased. Acetic acid also changed markedly the selectivity. Our data suggest that the acetic acid has a preponderant role in changing the retention and selectivity of fully protected peptides and amino acids in reversedphase thin-layer chromatography.

Classifying eluents in reversed-phase thin-layer chromatography by spectral mapping

The retentions of 17 substituted symmetrical triazine derivatives were determined in reversed-phase thin-layer chromatography using 27 organic solvents miscible with water. The data matrix was evaluated by multivariate techniques. It was established that a higher solvent lipophilicity means a higher solvent strength, but the lipophilicity explains only about 67% of total variance. The influence of lipophilicity was the lowest with acetonitrile, tetrahydrofuran, methyl ethyl ketone, di-methylformamide and ethylene glycol. Ch3 and CH2 groups increased significantly and primary OH, COC and groups decreased the solvent strength. The presence and position of nitrogen and oxygen atoms and free hydroxyl groups govern the solvent selectivity in reversed-phase thin-layer chromatography.

Theoretical molecular descriptors relevant to the uptake of persistent organic pollutants from soil by zucchini. A QSAR study.

The uptake of persistent organic pollutants (POPs) from soil by plants allows the development of phytoremediation protocols to rehabilitate contaminated areas. The use of diverse theoretical descriptors has been reported in the literature for developing quantitative structure-activity relationship (QSAR) models for predicting the bioconcentration factors (BCFs) of POPs in different plants. In this paper an evaluation is given on the molecular properties of POPs in terms of theoretical molecular descriptors that are relevant to the uptake and accumulation of these persistent pollutants from soil by two zucchini varieties. Statistically significant and predictive linear regression models have been developed for the BCF values of 20 polychlorinated dibenzo-p-dioxins/dibenzofurans and 14 polyhalogenated biphenyls in two zucchini varieties based on retrospective data. The relevant parameters have been selected from a set of 1660 DRAGON, 150 VolSurf, and 11 quantum chemical descriptors. The two most significant regression models, containing VolSurf, DRAGON GETAWAY, and quantum chemical descriptors, displayed the following statistical parameters: (eq 3) n = 27, R(2) = 0.940, q(2) = 0.922, SE = 0.155, F = 392.1; (eq 4) n = 27, R(2) = 0.921, q(2) = 0.898, SE = 0.161, F = 140.4. Predictive capabilities of the equations have been validated by using external validation sets. The QSAR models proposed might contribute to the development of viable soil remediation strategies.

Gas chromatographic behaviour of carboxamide derivatives

Abstract Gas—liquid chromatographic retention indices of 28 substituted carboxamide derivatives were measured on apolar (Apolan 87) and polar (Carbowax 20M) stationary phases. Relationships were sought between these retention indices and the lipophilicities of the compounds. The influence of the structural elements on retention indices and lipophilicity was studied.

Interpretation of Scoring Functions Using 3D Molecular Fields. Mapping the Diacyl-Hydrazine-Binding Pocket of an Insect Ecdysone Receptor

A method is presented for the interpretation of receptor docking score values (rough measures of binding affinities) of ligands in terms of 3D molecular field interaction contributions. The FlexX and FlexX-Pharm methods were used to dock the structures of designed sets of ligands into the ligand-binding pocket of a selected receptor. In the next step the relationship was investigated between the FlexX and CScore scores and 3D molecular fields obtained for the docked conformations of the ligands, using the CoMFA (Comparative Molecular Field Analysis) and CoMSIA (Comparative Molecular Similarity Indices Analysis) methods. The approach yielded highly significant CoMFA and CoMSIA models demonstrating that a high portion of the variance in the docking score values of the ligands can be explained by steric, electrostatic, hydrophobic, and hydrogen bond donor and acceptor molecular field interaction contributions. The approach was exemplified by using the crystal structure of the ligand-binding domain of the ecdysone receptor (EcR) of the moth Heliotis virescens as well as virtual molecule libraries of analogues of known diacyl-hydrazine (DAH) type ecdysteroid agonists. By docking appropriately designed virtual compound libraries into the DAH binding pocket of EcR followed by CoMFA and CoMSIA of the docked conformations, hitherto unexplored regions of the receptor cavity could be mapped. By mapping the significant molecular field interaction contributions onto the model of the receptor-ligand complex, important receptor-ligand interactions could be highlighted that may help the design of novel highly scored receptor ligands. An advantage of the method is that no experimental biological activity data are required to exhaustively map the receptor-binding site.

Phospholipid - Amino Acid Interactions

Abstract Interaction of 17 amino acids with dipalmitoyl phosphatidylethanolamine and with dipalmitoyl phosphatidylcholine was studied by differential scanning calorimetry. Amino acids influenced the main transition temperature, the enthalpy of main transition and the half width of main transition suggesting the existence of amino acid-phospholipid interactions. Stepwise regression analysis proved that the effect of amino acids depended equally on their lipophilicity and on the pK values of α amino and α carboxyle groups that is the effect observed is the results of the interplay of hydrophobic and hydrophilic interactions. Principal component analysis proved that tryptophan exerted the highest impact on the thermal behaviour of phospholipids.

Thin-layer chromatography of some methylated amino acids with aqueous salt solutions used as eluents.

The retention order of methylated lysine and arginine derivatives followed a reversed-phase separation pattern on various silicas with aqueous salt solutions used as eluents. Principal component analysis established that the origin of the silica exerts a dominant influence on their chromatographic performance, and the effect of impregnation and salt quality are of secondary importance. Good linear correlations were found between the lipophilicity-decreasing effect of monovalent cations and their ionic radii.