Biomedical subjects

E Forgács

Publications and source records attributed to E Forgács.

At least 55 records · Page 3Linked to original sources

PubMed1998

Phenoxyacetic acids: separation and quantitative determination.

The various chromatographic methods suitable for the separation and quantitative determination of phenoxyalkyl acid herbicides in environmental samples are reviewed, with special emphasis being placed on sample preparation methods such as liquid-liquid, solid-phase and supercritical fluid extractions. Techniques are classified (high-performance liquid chromatography, gas-liquid chromatography, capillary zone electrophoresis, micellar electrokinetic chromatography) and discussed separately. The advantages and disadvantages of the various preparation and separation methods and their combinations are evaluated.

Chromatography, Gas↗

PubMed1998

Separation of steroidal drugs on porous graphitized carbon column.

The retention time of 11 steroidal drugs was determined on a porous graphitized carbon (PGC) column using water tetrahydrofuran mixtures as eluents. Linear correlations were calculated between the logarithm of the capacity factor (k') and the tetrahydrofuran concentration in the eluent. To find the molecular parameters significantly influencing the retention the intercept and slope values of the above relationship were correlated with the physicochemical characteristics of steroidal drugs using principal component analysis (PCA). Both the slope and intercept values show high differences proving that steroidal drugs can be successfully separated on a PGC column. Five principal components explained > 90% of the total variance. Calculations indicated that both electrostatic interactions and sterical conditions can influence the retention of steroidal drugs on PGC column.

Chemistry Techniques, Analytical↗

PubMed1998

Inclusion complex formation of steroidal drugs with hydroxypropyl-beta-cyclodextrin studied by charge-transfer chromatography.

The interaction between 17 steroidal drugs and hyroxypropyl-beta-cyclodextrin (HPbetaBCD) was determined by charge-transfer chromatography and the relative strength of interaction was calculated. HPbetaCD interacted with each steroidal drugs decreasing the hydrophobicity of the guest molecules. The relative strength of interaction considerably depended on the structure of the drug molecule. Hydrophobicity parameters of drugs significantly influenced the strength of interaction indicating the involvement of hydrophobic forces in the binding of drugs to HPbetaCD. The marked influence of HPbetaCD on the hydrophobicity of drugs suggests that this interaction may modify the biological properties (adsorption, uptake, half-life etc.) of drug-HPbetaCD complexes drug resulting in modified efficacy.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed1998

Effect of molecular parameters on the retention of steroid drugs on alumina support.

The retention of 18 steroids was determined on an alumina HPLC column and in TLC carried out on alumina layers using dichloroethane-dioxane mixtures as eluents. R(M0)-values of steroids decreased linearly with increasing concentration of dioxane in the eluent. The adsorption capacity and specific hydrophilic surface area of steroids were not correlated indicating the inhomogenous character of steroids as solutes. The prediction power of TLC for HPLC was low probably due to the different pH of alumina surface. The hydrogen donor and hydrogen acceptor capacities of steroids have the highest impact on the retention. Steroids with free -OH group differ in their retention behavior from the other derivatives.

Aluminum Oxide↗

PubMed1998

Relationship between retention characteristics and physicochemical parameters of solutes on porous graphitized carbon column.

The retention of 44 barbituric acid derivatives was determined on porous graphitized carbon (PGC) column using dioxane water mixtures as eluents. Linear correlations were calculated between the logarithm of the capacity factor and the dioxane concentration in the eluent. Free Wilson analysis combined with stepwise regression analysis was used to elucidate the role of individual substituents in the retention behaviour. Calculations indicated that the apolar substituents lie parallel to the surface of PGC surface increasing in this manner the retention and--as opposed to the retention characteristics of traditional reversed-phase supports--the position of substituents also exerts a marked influence on the retention.

Barbiturates↗

PubMed1998

Modification of the apparent lipophilicity of steroidal drugs with gamma-cyclodextrin.

The interaction between 17 steroidal drugs and gamma-cyclo-dextrin (gamma-CD) was determined by charge-transfer chromatography and the relative strength of interaction was calculated. The relationship between the strength of interaction and the physico-chemical parameters of steroidal drugs was elucidated with principal component analysis. Gamma-CD interacted with each steroidal drug decreasing the apparent hydrophobicity of the guest molecules. Calculations indicated that the interaction between the drugs and gamma-CD is of mixed character: steric, hydrophobic and electronic forces are involved in the complex formation. The marked influence of gamma-CD on the apparent hydrophobicity of drugs suggests that this interaction may modify the biological properties (absorption, uptake, half-life etc.) of drug-gamma-CD complexes resulting in modified efficacy.

Cyclodextrins↗

PubMed1998

[Investigation of molecular interactions by chromatographic methods].

Molecular interactions can be easily determined both by thin-layer and high performance liquid chromatography. The theory and practice of the determination of molecular interactions and the various methods for the calculation of the complex stability is presented. Examples for the application of liquid chromatographic methods for the measurements of molecular interactions are presented.

Chemistry, Organic↗

PubMed1997

Study of the binding of antibiotics to human serum albumin by charge-transfer chromatography.

The interaction of 13 antibiotics with human serum albumin was studied by charge-transfer reversed-phase thin-layer chromatography in neutral, acidic, basic and ionic environments (NaCl and MgCl2) and the relative strength of interaction was calculated. The pH and the presence of mono- and divalent cations markedly influenced the strength of interaction. The capacity of antibiotics to interact with HSA also considerably depended on their chemical structure.

Anti-Bacterial Agents↗

PubMed1997

Charge-transfer chromatographic study of the complex formation of some steroidal drugs with carboxymethyl-gamma-cyclodextrin.

The interaction between 15 steroidal drugs and carboxymethyl-gamma-cyclodextrin (CM-gamma-CD) was studied by reversed-phase charge-transfer thin-layer chromatography and the relative strength of interaction was calculated. CM-gamma-CD formed inclusion complexes with each compound, the complex always being less hydrophobic than the uncomplexed drug. The inclusion-forming capacity of drugs differed considerably depending on their chemical structures. The linear correlation between the hydrophobicity and specific hydrophobic surface area of anticancer drugs indicated that they can be considered as a homologous series of compounds, although their chemical structures are different. Hydrophobicity of drugs significantly influenced the strength of interaction, indicating the involvement of hydrophobic forces in the binding of drugs to CM-gamma-CD. The marked influence of CM-gamma-CD on the hydrophobicity of drugs suggests that this interaction may modify the biological properties (adsorption, uptake, half-life, etc.) of drug-CM-gamma-CD complexes drug, resulting in modified efficacy.

Chromatography, Thin Layer↗

PubMed1997

Inclusion of the standard deviation of data in principal component analysis. A graphical approximation.

The adsorption capacity and specific adsorption surface area of 13 anti-hypoxia drugs were determined in three chromatographic systems using methanol-carbon tetrachloride, chloroform-carbon tetrachloride and acetonitrile-carbon tetrachloride mixtures as eluents. The retention behaviours of the anti-hypoxia drugs were compared using principal component analysis (PCA). A graphical approximation was used for the inclusion of the standard deviations of both the variables and observations in PCA and the results were visualized by two-dimensional nonlinear mapping and cluster analysis. The results indicated that the graphical approximation can be successfully used for the inclusion of the standard deviation of data in PCA calculations. Nonlinear mapping and cluster analysis resulted in similar, but not identical, classification of drugs and chromatographic systems, indicating that each multivariate method can be successfully used for the comparison of solutes and chromatographic systems.

Chromatography↗

PubMed1997

Separation of oligomers of nonylphenyl ethylene oxide [correction of nonlphenylethylene oxide] on a porous graphitized carbon column.

The retention of nonylphenyl ethylene oxide oligomer surfactants was determined on a porous graphitized carbon (PGC) column using water--methanol mixtures as eluents. Linear correlations were calculated between the logarithm of the capacity factor (k') and the methanol concentration in the eluent. To test the validity of the hypothesis that in the case of homologous series of solutes the intercept and slope values are intercorrelated linear correlation was calculated between the two chromatographic parameters. To elucidate the role of the length of the polar ethylene oxide chain in the retention linear correlations were calculated between the chromatographic parameters and the number of ethylene oxide groups per molecule. Nonylphenyl ethylene oxide oligomers were well separated on the PGC column. Significant linear relationships were found between the corresponding chromatographic parameters indicating that the solutes behave as a homologous series of compounds. The retention of surfactants increased linearly with increasing number of ethylene oxide groups per molecule indicating hydrophilic interactions between the solutes and the surface of PGC support.

Chromatography, High Pressure Liquid↗

PubMed1997

Charge-transfer chromatographic study of the interaction of antibiotics with sodium dodecylsulfate.

The interaction of 29 antibiotics with the anionic surfactant sodium dodecylsulfate (SDS) was studied by charge-transfer reversed-phase chromatography carried out on impregnated silica layers using water-methanol mixtures as eluents. The hydrophobicity of antibiotics and the relative strength of SDS-antibiotic interaction was calculated separately for each antibiotic-SDS pair. SDS interacted with 17 antibiotics where the antibiotic-SDS complex was either more hydrophilic or more hydrophobic than the uncomplexed molecule. The relative strength of interaction depended considerably on the molecular structure of the antibiotics. No significant linear correlation was found between the hydrophobicity parameters of antibiotics and their capacity to interact with SDS. Stepwise regression analysis proved that the inductive effect of substituents, their electron-withdrawing power and proton-acceptor capacity exert a significance influence on the strength of interaction.

Anti-Bacterial Agents↗

PubMed1996

Use of thin-layer and high-performance liquid chromatography for the study of the adsorption of surfactants on a river sediment.

The adsorption of tributylphenol ethylene oxide isomers containing various lengths of ethylene oxide chain and positional isomers of tributylphenol on a riverine sediment was studied by thin-layer chromatography combined with high-performance liquid chromatography. The adsorption capacity of the sediment was compared with that of silica, alumina and diatomaceous earth. It was established that the adsorption capacity of the riverine sediment is similar to that of silica. The adsorption of surfactants on the sediment surface is not selective. Neither the length of the ethylene oxide chain nor the position of the butyl substituents on the phenol ring influence significantly the adsorption.

Adsorption↗

PubMed1996

Effect of beta-cyclodextrin derivatives on the retention of steroidal drugs.

The retention of eighteen steroid drugs was determined on a beta-cyclodextrin polymer (beta CDP)-coated silica column using methanol-water mixtures as eluents. The relative strength of inclusion formation between the drugs and hydroxypropyl-beta CD (HP beta CD) and dimethyl-beta CD was determined by charge transfer chromatography carried out on reversed-phase thin-layer chromatography plates. The retention characteristics of drugs were correlated with their physicochemical parameters and with their inclusion complex-forming capacity. Calculations indicated that the inclusion complex-forming capacity of the drugs has little impact on the retention that is due to the HP beta CD and water-insoluble beta CD polymers exposed to different retention characteristics. The hydrophilic molecular parameters of drugs significantly influenced their retention. This result suggests that the selectivity of the beta CDP-coated column may be different from that of the traditional reversed-phase columns.

Chromatography, High Pressure Liquid↗

PubMed1996

Effect of physicochemical parameters on the retention of some monoamine oxidase inhibitory drugs on a porous graphitized carbon column.

The retention of sixteen monoamine oxidase inhibitory drugs (proparlgylamine derivatives) was determined on a porous graphitized carbon (PGC) column using ethanol-water mixtures as eluents. The HPLC retention characteristics of drugs were correlated with their physicochemical properties using stepwise regression analysis and principal component (PC) analysis. The dimensions of the matrices for PC loadings and variables was reduced using a non-linear mapping technique, varimax rotation and cluster analysis. It has been established that the drugs can be well separated on the PGC column in ethanol-water eluents. Calculations proved that the retention behavior of monoamine oxidase drugs on PGC column is of mixed character: both steric and electronic parameters influence the retention.

Chromatography, High Pressure Liquid↗

PubMed1996

Use of principal component analysis for the study of the retention behaviour of anticancer drugs on a beta-cyclodextrin polymer-coated silica column.

The retention parameters of eighteen commercial anticancer drugs were determined on a beta-cyclodextrin polymer-coated silica support (beta CDP) using methanol-water mixtures as eluent and the relationship between the retention behaviour and physico-chemical parameters was elucidated by principal component analysis (PCA) followed by two-dimensional non-linear mapping. No significant linear correlation was found between the retention behaviour of drugs on octadecylsilica and beta CDP silica columns, indicating that the retention capacity and selectivity of the columns are considerably different. The results of PCA indicated that hydrophobic and electronic interactions and steric conditions govern the retention of anticancer drugs on beta CDP column, suggesting a mixed retention mechanism.

Antineoplastic Agents↗

PubMed1996

Taxol content of various Taxus species in Hungary.

The anticancer drug taxol was separated and quantitatively determined in bark and foliage of different Taxus species by high-performance liquid chromatography to prove the presence of taxol in Hungarian Taxus species. The measurements were carried out with photodiode array detection using a porous graphitized carbon column, and a water:dioxan 54:46 v/v eluent. Taxol was established as being present in measurable amounts in each Hungarian Taxus species. According to the results bark was richer in taxol than foliage. It could also be observed that the older the bark or foliage, the more taxol it contained. The validation process proved that the method is reliable and can be used for the separation and quantitative determination of taxol in both the bark and foliage of Taxus species grown in Hungary.

Antineoplastic Agents, Phytogenic↗

PubMed1996

Binding of non-homologous series of anticancer drugs to cytosine.

The interaction of 20 anticancer drugs with cytosine was studied by charge-transfer reversed-phase thin-layer chromatography. The hydrophobicity, the specific hydrophobic surface area and the relative strength of interaction was calculated. Significant linear correlation was found between the hydrophobicity and specific hydrophobic surface area of drugs; this means that, from the chromatographic point of view, they form a homologous series of solutes. Only eight anticancer drugs showed significant interaction with cytosine. The binding of these drugs to cytosine (and possibly to other nucleotides) might be an important interaction which plays a role in the biological activity of drugs.

Antineoplastic Agents↗