Retention data from reverse‐phase high‐performance thin‐layer chromatography in characterization of some bis‐salicylic acid derivatives

The chromatographic behaviour of salicylic acid derivatives was investigated using reversed‐phase high performance thin‐layer chromatography (RP HPTLC) with methanol–water and dioxane–water binary mixtures as mobile phase in order to establish relationships between chromatographic data and selected physico‐chemical parameters that are related to ADME (absorption, distribution, metabolism and elimination). Some of the investigated compounds were screened for antioxidant activity. Examination of chromatographic behaviour revealed a linear correlation between R_M values and the volume fraction of mobile phase modifier. Obtained R_M⁰ values were correlated with lipophilicity, solubility, human intestinal absorption, plasma‐protein binding, and blood–brain barrier data. The comparison among chromatographic data obtained by two mobile phase was performed with a statistical technique, principle component analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Theoretical calculation of the optimum separation in thin-layer chromatography

Summary Up to now the optimum composition of a binary mobile phase for separation in thin-layer chromatography has been determined mainly by the method of successive trials. In this paper a simple way is presented to determine the mobile phase composition and the maximum difference in the R_M values of two substances. The equation introduced has been illustrated with examples of adsorption thin-layer chromatography on magnesium silicate. Calculation of the largest difference in the R_M values of two substances in relation to the composition of the binary mobile phase has been compared with the corresponding values determined experimentally. A good agreement of the obtained theoretical data and experimental values has been found.     

Reversed-Phase Systems for the Separation of Coumarins and Furocoumarins by Thin-Layer and High-Performance Liquid Chromatography

Abstract

The retention behaviour of eleven derivatives of counarin was investigated by reversed-phase (RP) thin-layer and high performance liquid chromatography. The linear relationships between log k'or R_M values and the content of organic modifier in the aqueous mobile phase obtained for wide composition ranges indicate that the plots can be used to determine R_Mw and log k_w values by extrapolation to pure water. The effects of individual substituants on the retention and the correlation between TLC and HPLC data was analysed.     

The Role of the Specific Surface Area of an Adsorbent in the Optimization of Mixture Separation Conditions in Thin-Layer Chromatography

Abstract

The very important aspect of effect of the magnitude of specific surface area on R_M values obtained by using TLC method is presented. In experiments were performed on 4 adsorbents of different specific surface areas 50 – 500 m²/g and with mixed binary mobile phases.

It is shown that R_M values of chromatographed substances aromatic hydrocarbons are lineary dependente upon the specific surface area of adsorbents for each composition of mobile phase. This relationship can be described by a straight line, with the parameters a and b that can be tabularized. These lines can be used to calculate the R_M values of chromatographed substances for any adsorbent if is specific surface area is known. The illustrational comparison of experimentally obtained and theoretically predicted R_M values for different chromatographic system are presented.     

A simple molecular model for adsorption chromatography. VII. Relationship between the RM value and the composition for phenols in systems of the type (cyclohexane+polar solvent)/silica

Summary The effect of the composition of binary developing solvents on R_M values of phenols with one, two or three hydroxyl groups was investigated. In most cases linear R_M vs. (log X_S) relationship were obtained for wide composition ranges (X_S — mole fraction of polar solvent; diluting solvent: cyclohexane), the slope of the lines being related to the molecular mechanism of adsorption. The slopes of some derivatives of quinoline, aniline and phenols are compared and the effects of the molecular structure of the solute and the eluen strength of solvent are discussed. The experimental data for phenols are interpreted in terms of competitive solvation in the mobile phase by electron donor solvents; practical rules concerning optimization of TLC systems for the analysis of the compounds investigated are formulated.     

The Correlations between Capacity Factors k′ and RM Values in Liquid Column and Thin-Layer Chromatography

Abstract

The purpose of this studie being carried out is to define some regularities between Thin-layer and Liquid Column Chromatography; i.e. between experimental obtained and theotetical calculated R_M-values and experimental obtained logk-values for some non-active organic substances in mixed binary solvents systems. It was studied the kind these correlations change with changing mobile phase compositions. The present paper is a certain aspect of new studies on possibilities of the use Thin-layer Chromato-graphy as a pilot technique for Liquid Column Chromatography (1,2). In a study on the optimization of chromatographic process it is necessary to define the correlations between R_M-values which characterize the retention in TLC and k′-values which characterize the retention in in LCC.

In the paper the changes of these correlations with the changes of mobile phase compositions are studied. The conformity between theoretical calculated and experimental obtained R_M-values of chromatographed substances for differemt mobile phase compositions are investigated. A good agreement between theoretical and experimental data makes possible to foresee on the basis of the correlations between log k′- and R_M-values the retention in column chromatography.     

Thin-layer adsorption chromatography with mixed mobile phases. 1. Characterization of chromatographic systems showing energetic heterogeneity of adsorbent surfaces with regard to admolecules of solvents and solutes

Thin-layer adsorption chromatography with a multicomponent mobile phase is discussed. A new equation for predicting R_M-values in TLC with mixed mobile phases using the R_M-ValUeS obtained for pure solvents is proposed. This equation takes into account effects of energetic heterogeneity of the adsorbent surface with regard to adsorbed molecules of solvents and solutes. Experimental verification of this equation is presented for R_M-data obtained by TLC using a binary mobile phase.     

An Approximate Linear Solvation Energy Relationships Model Based on Snyder’s Selectivity Parameters. Chromatographic Behavior of Some 1-Aralkyl-4-Arylpiperazines

In order to elucidate the influence of the mobile phase composition on the retention of some 1-aralkyl-4-arylpiperazines, Snyder’s selectivity and polarity concept for building a simple linear solvation energy relationships model of chromatographic behavior was used. Maximum variability of mobile phase selectivity was achieved by using ternary mixtures of solvents from three different corners of the Snyder selectivity triangle: methanol as a strong proton donor, acetone as a strong proton acceptor and dimethyl formamide as a dipole interactor. Water was added to keep elution strength constant. Mobile phase composition was varied using Simplex–lattice mixture design. Selectivity parameters were calculated on the basis of linear relationships between volume fractions of pure solvents and their χ _e , χ _d , χ _n values. For seven-substituted 1-aralkyl-4-arylpiperazines R _M values were measured and correlated with previously calculated selectivity parameters. Mathematical models obtained are discussed according to the structural properties of the studied compounds.     

Chromatographic properties ofs-triazines in the presence of soluble β-cyclodextrin polymer

The effect of a water-soluble β-cyclodextrin polymer on the lipophilicity and adsorption strength of 17 substituteds-triazine derivatives was studied by thin-layer chromatography. Beta-cyclodextrin polymer dissolved in the mobile phase modifies the chromatographic behaviour ofs-triazine derivatives and, consequently, higherR _f and lowerR _M values were observed. LiCl exerts an opposite influence, it decreases theR _f and increases theR _M values. The β-cyclodextrin polymer enhances the mobility of thes-triazine derivatives on silica gel and reduces their lipophilicity, thus promoting their penetration through the hydrophilic membranes of the target organism. The presence of LiCl decreases the stability of inclusion complexes. The first and second substituents on thes-triazine ring result in an increase of the inclusion complex stability but — due to steric hindrances — the third substituent decreases it.     

The Influence of the Specific Surface Area of Adsorbent upon the Optimization of the Process of Adsorption Thin-Layer Chromatography

Abstract

An important aspect of the influence of specific surface area of adsorbent on R_M values of substances obtained in the process of adsorption thin-layer chromatography has been presented in the paper. The experiments have been conducted with four adsorbents, each having different specific surface area, that is, from 50 to 500 m²/g and with the use of mixed binary solvent mobile phases of benzene-aliphatic alcohol type. It has been proved that R_M values of investigated substances of group B change regulary according to the specific surface area of adsorbent for individual concentrations of mobile phase. The relationship may be described by means of square trinominal. The parameters of trinominal may be tabulated and the differentiation of the parameters for particular substances is observable at the same time. The relationship in question may be utilized to calculate R_M, values of studied substances on any adsorbent with known specific surface area.     

Lipophilicity of Some Preservatives Estimated by RP-TLC Using Stationary Phases with Different Polarity

Lipophilcity of some preservatives was determined by reversed phase high performance thin layer chromatography (RP-HPTLC) using methanol–water mixtures in different volume proportions as mobile phase on three stationary phases of different polarity: RP-18F_254s, RP-18WF_254s and CNF_254s plates. The R _M values decreased linearly with increasing methanol concentration in the mobile phase in all cases. The regression determination coefficients obtained for all stationary phases were excellent (higher than 0.98 in most cases). The chromatographic behavior of the preservatives on the RP-HPTLC plates used in this study is similar and in a very good agreement with their polarity. Good chromatographic regularities found for retention factors and by applying principal component analysis for all three types of stationary phases indicate that the same lipophilic interactions are dominants in all cases. The relationships between different RP-HPTLC retention parameters (R _M0 , b, scores of R _F -PC1/R _F and scores of R _M -PC1/R _M ) and various calculated log P values of the same preservatives show highly significant correlations for all types of stationary phases.     

Optimized Method for the Determination of Flavonoid Glycosides and Aglycones

The relationship R_M=f (log % S; S- modifier) of several flavonoids and their sugar derivatives was examined by using chromatographic systems chosen by preliminary experiments. The dependence for flavonoid aglycones was flat in the whole mobile phase concentration. Two types of the R_M=f (log % S) plots, related to the size of sugar molecule, were found. For glycosides with smaller sugar moiety (arabinose or glucose) the plot was almost parallel, while plots of derivatives with larger sugar moiety (rutose) were convergent. After plotting the relationship R_M=f (log % S), even if standards are not available, it is possible to qualify the examined compound as containing single or complex sugar moiety. For all mentioned above compounds the R_M=f (log %S) values were given. Silica gel Si60 was used as polar adsorbent. Mobile phase composition was determined in preliminary experiments; it was composed of two solvents: methanol in ethyl acetate in increasing concentration of methanol: 5 – 20%.     

Synthesis of betulin derivatives and the determination of their relative lipophilicities using reversed‐phase thin‐layer chromatography

A series of superlipophilic or highly lipophilic semisynthetic betulin derivatives was prepared and their relative lipophilicity was measured by reversed‐phase thin‐layer chromatography (RP‐TLC) at different pH values using 1,4‐dioxane–acetate buffer mixtures as mobile phases. Cholesterol, 17β‐estradiol and pure betulin were used as the reference compounds. Linear relationships were found between R_M values and 1,4‐dioxane concentrations in the mobile phases. LogP values were also calculated with computer programs ACD/LogP (ChemSketch 11.0, Advanced Chemistry Development Inc.) and ClogP (Daylight Chemical Information Systems Inc.). The empirical and theoretical data were compared, and the R_M0 values correlated well with logP. Two of the synthesized betulin derivatives are reported for the first time. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of Intramolecular Interactions on Some Parameters in Adsorption Thin-Layer Chromatography

Abstract

Using the equation connecting the R_M values with the appropriate data of the adsorption process from solutions the values of the parameters characterizing substance ? mobile phase interactions have been calculated for the systems: silica gel-benzene+acetone and silica gel-acetone+methanol.Quinoline, aniline, nitrobenzene, phenol and their derivatives were the chromatographed substances. An influence of the structure of the substance on the parameter values has been examined, special attention being paid to intramolecular effects, mainly those of hydrogen bonds.     

Quasi-column chromatography of barbituric acid derivatives II. Separation on Non-polar adsorbents using binary water-organic solvent mixtures as the mobile phase

Summary Twenty barbituric acid derivatives having four different types of substitution were separated in TLC-S chambers. Using non-polar adsorbents (silanized silica gel or silica gel coated with paraffin oil) and binary water-organic solvent mixtures as the mobile phase. Linear relationships between R_M and the concentration of the organic solvent were observed for the majority of the investigated compounds. The non-polar absorbents ensure a better separation than untreated silica gel especially for the therapeutically useful C₅ disubstituted barbiturates. The results can be used for the optimization of the systems for the chromatography of barbiturates. The R_f values were correlated with the number of carbon atoms of the substitutions, molecular connectivity and a parameter associated with the molecular volume. The best correlations were obtained for this last parameter.     

Lipophilicity study of eight cephalosporins by reversed‐phase thin‐layer chromatographic method

The lipophilicity (R_M0) and specific hydrophobic surface area for the representatives of four generation cephalosporins have been determined by reversed‐phase thin‐layer chromatography, and the effect of different mobile‐phase modifiers (such as methanol, acetonitrile, acetone, 1,4‐dioxane and 2‐propanol) on the retention has been studied. The compounds studied showed typical retention behavior; their R_M values decreased linearly with increasing concentration of the organic modifier in the eluent. The linear correlations between the volume fraction of the organic solvent and the R_M values over a limited range were established for each solute, resulting in high values of correlation coefficients (>0.95 in most cases). R_M values were determined by various concentrations of organic modifier, and the correlation obtained was extrapolated to 0% of organic modifier. Chromatographically established logP (R_M0) parameters were compared with computationally calculated partition coefficients values (AClogP, ALOGP, KOWWIN, ALOGPs, XLOGP2, MLOGP and XLOGP3) and experimental octanol–water logP values (measured by the shake flask method). The received results demonstrate that RP‐TLC may be a good alternative technique for analytics in describing the lipophilic nature of investigated cephalosporins as well as the activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of Methods for Determination of the RM Values of Substances in Thin - Layer Chromatography by Using Binary Mobile Phase

Abstract

Methods of calculating the function R_M= f(?₁) of some aromatic substances from the data of experimental and theoretically calculated parameters have been compared. It has been shown that there is a possibility to calculate this function with high accuracy on the basis of the measured partition coefficients of the substances chromatographed in partition systems consisting of components of the mobile phase as well as parameters obtained theoretically. Thus obtained results were also compared with the functions R_{M 1.2} = f (?₁) obtained experimentally and a high agreement was reached. This in turn contributes to optimization of systems of thin-layer chromatography.     

Determination of the lipophilicity of some aniline derivatives by reversed-phase thin-layer chromatography. The effect of the organic phase in the eluent

Summary The lipophilicity of aniline and 36 ring-substituted aniline derivatives was determined by reversed-phase thin-layer chromatography using methanol, acetone and acetonitrile as the organic phase. The R_M value of each compound linearly decreased with increasing concentration of the organic solvent, Acetonitrile showed the highest and methanol the lowest solvent strength, however, the difference between the solvent strength of methanol and acetone was negligible. The site of the substitution considerably influenced the lipophilicity particularly in the case of –NO₂ groups. Good correlation was found between the R_M value extrapolated to zero organic phase concentration and the partition coefficient between n-octanol:water. The change in the R_M value caused by a 1% increase of the organic phase concentration also correlated with the partition coefficient, however, it was of secondary importance. The lipophilicity parameters determined by reversed-phase thin-layer chromatography correlated to a lesser extent with the calculated lipophilicity values of aniline derivatives.