Search Results

You are looking at 1 - 10 of 22 items for

  • Author or Editor: Alina Pyka x
  • All content x
Clear All Modify Search

Ergocalciferol, cholecalciferol, (±)-α-tocopherol, tocopherol acetate, retinol, retinol acetate, retinol palmitate, menadione, and phytonadione have been investigated on RP8F 254s and RP18F 254s TLC plates with methanol-water in different volume proportions as mobile phases. Linear relationships were obtained between the R M values of the fat-soluble vitamins and the volume fraction of methanol in the mobile phase. Retention values, R M , were extrapolated to zero methanol content and the lipophilicity values R MW(RP8) and R MW(RP18) obtained were compared with measured partition coefficients (log P exp ) and partition coefficients (AlogPs, AClogP, AB/logP, COSMOFFrag, milogP, Kowwin, xlogP) calculated using seven different software products. Cluster analysis was also used for comparison of the theoretical partition coefficients with the chromatographic lipophilicity ( R MW(RP8) and R MW(RP18) ) of the fat-soluble vitamins. It was found that lipophilicity values R MW(RP8) were most similar to AClogP whereas R MW(RP18) was most similar to the theoretical partition coefficient Kowwin. R MW(RP8) and R MW(RP8) values (i.e. values obtained on RP8F 254s and RP18F 254s plates) closely describe the lipophilic properties of fat-soluble vitamins.

Restricted access

Phenol and its methyl derivatives have been separated by RP-TLC on RP-2 plates with three mobile phases. R M values, toxicity (log 1/ C ), p K a values, and partition coefficients of the phenols were correlated with the numerical values of electrotopological states (SaasC, SaaCH, and SsOH). It was found that SaasC and SaaCH described R M , toxicity, and the experimental and theoretical partition coefficients better than SsOH, whereas SsOH best described the p K a values of the phenols. The equations introduced in this paper can be used to predict R M , toxicity, p K a , and partition coefficients for compounds omitted during derivation of the correlation equations.

Restricted access

Selected meta -and para -alkoxyphenols have been separated by RPTLC on cellulose impregnated with ethyl oleate, with ethanol-water, 40 + 60 (%, v/v ), as mobile phase. New methods of calculation of partition coefficients on the basis of the topological index ° B and experimental R F values have been proposed. These methods enable differentiation between the values of log P for the meta and para isomers of the alkoxyphenols.

Restricted access

Selected nicotinic acid derivatives have been chromatographed on RP-HPTLC plates with methanol-water in different volume proportions as mobile phases. Linear relationships were obtained between R M values of nicotinic acid derivatives and the volume fraction of methanol in the mobile phase. The retention values R M were extrapolated to zero methanol content and the lipophilicity values R M0 obtained were compared with measured (log P exp ) partition coefficients and values ( A log P s, IA log P , C log P , log P Kowin , and x log P ) calculated by use of five different software products. A linear relationship was obtained between R M0 and the slope, S , of the chromatography equation. The most significant correlation was found between the R M0 and A log P s values. For the nicotinic acid derivatives R M0 was a slightly better measure of lipophilicity than ϕ 0 . Chromatographic R M0 values can be use as a measure of the lipophilicity of the nicotinic acid derivatives investigated. Satisfactory linear correlation was obtained between R M0 and some topological indexes ( o χ v , 1 χ v , 1 B , 2 B , I SA , and Ī SA ).

Restricted access

Selected meta - and para -alkoxyphenols have been separated by RP TLC on cellulose impregnated with ethyl oleate, with ethanol-water, 25 + 75 and 40 + 60 (%, v/v ), as mobile phases. The R M values of the alkoxyphenols have been correlated with structural descriptors based on the adjacency matrix ( 2 χ v , 2 χ v , and χ 012 ), on the distance matrix ( W , A , 0 B , 1 B , D , C , 2 B , 3 B q , 3 B , 3 B q , I B ), and on electrotopological states (SssO, ScCH 3 , SaaCH, SaasC, SsOH). Most accurate prediction of the R M values of the all alkoxyphenols was achieved by use of second-or third-degree polynomial correlation equations with one structural descriptor from among the topological indexes W , A , 1 B , D , 3 χ v , and I B . The best correlation equations for prediction of R M values separately for meta - and para -alkoxyphenols were been obtained by use of the topological indexes 2 χ v , C and χ 012 .

Restricted access

The chromatographic behavior of the phenolic drugs niclosamide, hexachlorophene, ibuprofen, pentazocine, ethamivan, bithionol, salicylanilide, caffeic acid, p -coumaric acid, 4-aminosalicylic acid, ferulic acid, and methyldopa has been investigated on RP8F 254s and RP18F 254s TLC plates with methanol-water mixtures in different volume proportions as mobile phases. Linear relationships were obtained between the R M values of the drugs and the volume fraction of methanol in the mobile phase. Retention values, R M , were extrapolated to zero methanol content and the lipophilicity values R MW(RP8) and R MW(RP18) obtained were compared both with measured partition coefficients (log P exp ) and with partition coefficients (AlogPs, IAlogP, AB/logP, COSMOFFrag, miLogP, KOWWIN, and xlogP) calculated using seven different software products. Comparison of the calculated partition coefficients revealed IAlogP, KOWWIN, miLogP, and

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\overline {\log P}$$ \end{document}
(where is the average of all the theoretical partition coefficients) usually correlate best with chromatographic lipophilicity R MW . The results indicate that chromatographic lipophilicity R MW can be used as a measure of the lipophilicity of the phenolic drugs investigated.

Restricted access

Methyl laurate, methyl myristate, methyl palmitate, methyl isostearate, methyl stearate, and methyl arachidate have been separated by RPTLC on kieselguhr F 254 impregnated with different amounts of paraffin oil, using two different mobile phases. The R M values of these compounds for all the stationary phases and mobile phases investigated could be correlated with the dipole moments of the mobile phases, with the percentage impregnation of the stationary phase, and with numerical values of one topological index from among those based on the distance matrix ( W , A , ° B , 1 B ) or on the adjacency matrix ( 1 X , 1 X v ). The theoretical partition coefficient (log P ) for methyl isostearate was calculated from R M values or from one of the topological indexes mentioned above.

Restricted access

Nicotinic acid (NAC) and its derivatives methyl nicotinate (MN), ethyl nicotinate (EN), isopropyl nicotinate (IPN), butyl nicotinate (BN), hexyl nicotinate (HN), benzyl nicotinate (BNN), nicotinamide (NAM), and N -methylnicotinamide (MNAM) have been investigated on RP18WF 254 HPTLC plates with methanol-water in different volume proportions as mobile phases. Linear relationships were obtained between R M values of the compounds and the volume fraction of methanol in the mobile phase. Retention values R M were extrapolated to zero methanol content and the lipophilicity values R M0(RP18WF254) obtained were compared with measured partition coefficients (log P exp ) and with partition coefficients ( A log P s, IA log P , C log P , log P Kowin , and x log P ) calculated using five different software products. The most significant correlation was found between R M0(RP18WF254) and A log P s values. The values of chromatographic lipophilicities R M0(RP18WF254) and ϕ 0(RP18WF254) indicate that lipophilicity of the nicotinic acid derivatives should decrease in the order HN > BN ≈ BNN > IPN > EN > MN > MNAM > NAM > NAC. Chromatographic R M0 values can be used as a measure of the lipophilicity of the nicotinic acid derivatives investigated. Satisfactory linear regression equations were obtained between lipophilicity R M0(RP18WF254) or partition coefficients (log P exp , A log P s, IA log P , C log P , log P Kowin , x log P ) and some topological indexes ( 0 χ v , 1 χ v , 2 χ v , A , 1 B , 2 B , I SA , and Ī SA ) and between lipophilicity ϕ 0(RP18WF254) and electrotopological states SaaN and SdO.

Restricted access

Fifteen urea pesticides have been separated on RP-18WF 254 plates with methanol-water and mixed organic (acetonitrile-methanol, 1:1 v/v )-0.1% aqueous orthophosphoric acid (H 3 PO 4 ) mobile phases (RP-HPTLC), and on silica gel 60F 254 plates with benzene-methanol and benzene-ethanol mobile phases (NP-TLC). The pesticides could be classified into three groups:

  1. monolinuron (1), chlorotoluron (2), diuron (3), isoproturon (4), and linuron (5) dimefuron (6), diflubenzuron (7), teflubenzuron (8), and lufenuron (9); and thifensulfuron methyl (10), triasulfuron (11), chlorsulfuron (12), rimsulfuron (13), amidosulfuron (14), and tribenuron methyl (15).
Relationships between R F values and mobile phase composition were determined for the pesticides. Δ R F values, separation factors ( α ), and constants for separation of pairs of compounds ( R F α ) were used to determine optimum chromatographic conditions for the separations. Comparison of results from normal and reversed-phase TLC revealed the pesticides in the first group (except for isoproturon and chlorotoluron) were best separated by RP-TLC. Those in the second group could be separated by NP or RP-TLC. The sulfonylurea herbicides in the third group were best separated by NP-TLC, although chlorsulfuron could not be completely separated from thifensulfuron methyl by use of this technique. Separation of chlorsulfuron from thifensulfuron methyl could be achieved by RP-TLC with a mobile phase in which the volume fraction of organic modifier was 0.70.

Restricted access

Fatty acids from ethanoic to octanoic have been chromatographed on silica gel with n -hexane-acetone, 4 + 1 ( v/v ), and acetone-water-chloroform-ethanol-aqueous ammonia, 30 + 1 + 3 + 5 + 1 ( v/v ), as mobile phases. New visualizing agents and selected visualizing agents described in the scientific literature have been used for detection. The results obtained for the free fatty acids and their ammonium salts by use of the individual visualizing agents depend on method of application — spraying or dipping. Dipping of chromatographic plates into solutions of the visualizing agents leads to chromatographic spots of the fatty acids with better contrast than the spots obtained by direct spraying of the plates. In general better visualization was achieved with ammonium salts of the fatty acids than with the free acids. Of the agents described in the scientific literature free fatty acids from ethanoic to octanoic can be detected only by use of bromocresol green, bromophenol blue, potassium permanganate, and methyl red. Among the new visualizing agents investigated, dipping of chromatographic plates into an aqueous solution of alkaline blue enables detection of the free acids from propanoic to octanoic. The ammonium salts of fatty acids from ethanoic to octanoic can be detected by spraying or dipping using all the visualizing agents investigated except bromophenol blue.

Restricted access