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1

Qualitative evaluation of composition of the volatile fraction in commercial samples of Cistus incanus L.

Szeremeta D, Knaś M., Długosz E., Sajewicz M.

Acta Chromatographica

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2017

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Vol. 29, no. 3

427--442

EN

The present research is focused on identification of volatile components of different commercial products containing raw herbs of Cistus incanus L. The dried herbal material was hydrodistilled, and the obtained essential oils were analyzed by means of gas chromatography with mass spectrometric detection. Alternatively, the headspace analysis of the volatile sample components was also performed. It was found out that the investigated samples of the C. incanus L. species show a wide variation in terms of quality and quantity of the respective essential oils, which might result in their variable biological activity also. In conclusion, a postulate for standardization of chemical composition of the raw plant material used in therapeutic preparations is formulated.

2

Circadian rhythm of spontaneous non-linear peptidization with proteinogenic amino acids in abiotic solutions versus homochirality

Maciejowska A., Godziek A., Sajewicz M., Kowalska T.

Acta Chromatographica

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2017

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Vol. 29, no. 1

135--142

EN

In this short communication, we report on three striking phenomena of the circadian rhythm. One was observed with the non-linear concentration changes of the monomeric L-Cys and the non-linear yields of the L-Cys derived peptides, when undergoing spontaneous non-linear peptidization. The other one was observed with the binary L-Phe-L-Pro system, and the third one with L-Ser, D-Ser, and DL-Ser. So far, no analogous reports have been released on the circadian rhythm of the spontaneous non-linear peptidization of proteinogenic amino acids in a sterile abiotic environment (70% aqueous acetonitrile, or 70% aqueous methanol solutions). At the moment, we cannot find any rational explanation of this phenomenon, yet it seems highly probable that its origin is analogous to or even of a primordial nature for the circadian rhythm phenomena abundantly found in biological samples by other researchers. An experimentally established lack of the circadian rhythm with peptidization of the non-proteinogenic amino acid (D-Ser) can encourage us to revisit a still unsolved question of homochirality preconditions.

3

A Comparison of Antioxidant, Antibacterial, and Anticancer Activity of the Selected Thyme Species by Means of Hierarchical Clustering and Principal Component Analysis

Orłowska M., Pytlakowska K., Mrozek-Wilczkiewicz A., Musioł R., Waksmundzka-Hajnos M., Sajewicz M., Kowalska T.

Acta Chromatographica

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2016

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Vol. 28, no. 2

207--221

EN

In this study, six numerical data sets are presented valid for eighteen thyme (Thymus L.) species and characterizing three biological properties of these herbs, i.e., antioxidant, antibacterial, and anticancer activity. Four data sets characterize antioxidant properties, one data set characterizes antibacterial property, and one data set characterizes anticancer activity. Antioxidant properties were measured with two free radical standards (DPPH and ABTS), two free radical scavenger standards (trolox and gallic acid), and three analytical techniques (EPR spectroscopy, ultraviolet–visible [UV–vis] spectrophotometry, and the dot blot test with bioautographic detection). Antibacterial activity was tested upon the Gram-positive Bacillus subtilis (ATCC 6633) strain, and anticancer activity was evaluated upon the human colon adenocarcinoma cells (HCT116). It was found out that the thyme extracts characterize with all three biological activities (yet with anticancer activity not very strongly pronounced) and that in quantitative terms, each activity strongly depends on the thyme species considered. An ultimate goal of this study was to investigate if any quantitatively confirmed correlation exists among these three biological activities, which might point out to a common mechanism of their action. To this effect, six sets of numerical data underwent hierarchical clustering and Principal Component Analysis. Based on the results obtained, no quantitative correlation was established among antioxidant, antibacterial, and anticancer activity of the thyme species, which seems indicative of different molecular mechanisms of these three actions.

4

Chiral conversion and condensation of l-hydroxyproline in an abiotic liquid system

Maciejowska A., Godziek A., Sajewicz M., Kowalska T.

Acta Chromatographica

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2014

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Vol. 26, no. 2

355--369

EN

This study is devoted to the thin-layer chromatographic demonstration of spontaneous chiral conversion of l-hydroxyproline (l-Hyp) to d-hydroxyproline (d-Hyp), and to its spontaneous peptidization, when dissolved in 70% aqueous methanol and stored at room temperature in a stoppered glass vessel. The adopted enantioseparation conditions were the same ones, as employed earlier for a successful enantioseparation of l- and d-proline. To this effect, we used microcrystalline cellulose as stationary phase and a quaternary mixture composed of 2-butanol:pyridine:glacial acetic acid:water (30:20:4:24, v/v) as mobile phase. Structural difference between proline and hydroxyproline consists in the presence of one hydroxyl group per molecule of the latter amino acid, which makes the respective enantioseparation a more difficult task. Consequently, the obtained separation effect was not a complete (i.e., a baseline) resolution of the two Hyp antimers yet a sufficient enough proof of the appearance of d-Hyp, apparently due to spontaneous chiral conversion taking place in the course of the l-Hyp solution storage and ageing period. The condensation products were discovered both in the fresh and the aged l-Hyp solution, yet in the aged sample, the condensation product yields were considerably higher than in the freshly prepared one (as convincingly demonstrated by mass spectrometry). Demonstration of the condensation products was performed with the aid of thin-layer chromatography (TLC), liquid chromatography-mass spectrometry (LC-MS), and thin-layer chromatography-mass spectrometry (TLC-MS).

5

Specific mobility of selected phytochemicals in thin-layer chromatographic systems and its possible relevance to pharmacokinetics

Knaś M., Szeremeta D., Polański J., Sajewicz M., Kowalska T.

Acta Chromatographica

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2013

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Vol. 25, no. 4

765--776

EN

In many publications on the thin-layer chromatographic analysis of the medicinal plant extracts, striking skewness of the separated chromatographic bands with many phytochemicals can be seen, although no attention has ever been paid to this odd mass transfer effect. In our earlier studies on the thin-layer chromatographic enantioseparation of certain low molecular weight carboxylic acids, lateral relocation thereof (i.e., the side-wise deviation of their migration route from linearity) was registered. Then we found out that lateral relocation was observed with these analytes only, which structurally resembled molecular rotors. In this study, we investigate the role played by the thin-layer chromatographic stationary phases in lateral relocation of botanically relevant molecular rotors. Thus, three carboxylic acids were selected as the test analytes, all of them resembling molecular rotors and abundantly present in the medicinal plant extracts. We selected two most popular thin-layer chromatographic stationary phases also, i.e., silica gel (characterizing with microcrystalline chirality) and alumina (achiral). Lateral relocation of the test analytes was observed on the silica gel stationary phase only. A conclusion was drawn that the chiral stationary phase makes a complementary contribution to lateral relocation (along with the propeller-like molecular structure of the analytes). In our view, specially devised thin-layer chromatographic systems can prove a convenient nano-platform for future investigation of the drug transport patterns, advantageous in the pharmacokinetic studies.

6

On ups and downs by analysis of profen drugs. A mini review

Sajewicz M., Kowalska T.

Acta Chromatographica

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2012

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Vol. 24, no. 2

145--161

EN

Drug analysis is among the most sensitive areas of chemical analysis, simply because of its relevance to human health. Profens make the most important group of nonsteroidal anti-inflammatory drugs (NSAIDs), and in many countries some of them are freely sold over the counter. The in vitro liquid chromatographic analysis of profen drugs faces certain not commonly recognized yet acute and often impassable problems, due to the specific physicochemical properties of these compounds. In this mini review, we share our experience on the practical failures with the enantioseparation of profen drugs both by means of chiral planar and column chromatography. By use of such analytical techniques as polarimetry, 1H and 13C NMR spectroscopy, and mass spectrometry, we point out objectively the reasons that make liquid chromatographic enantioseparation of profens an almost impossible task. These compounds have an inherent ability (both in aqueous and nonaqueous solutions) to undergo oscillatory chiral conversion and oscillatory condensation, combined with a highly pronounced gelating ability. In our view, the oscillatory chiral conversion of profens questions the credibility of widespread claims on the superiority of the curative potential with the (+)-profens over that of the respective (−)-antimers (although the rightfulness of such claims cannot be dismissed, as the in vivo and in vitro behavior of many drugs are known to sometimes fundamentally differ). Moreover, it seems highly probable that, due to their highly pronounced gelating property, profen drugs can easily clog the blood vessels and thereby jeopardize living organisms.

7

On simple experimental evidence confirmed by HPLC data of supramolecular aggregation and aggregate mobility with S(+)-naproxen in aqueous ethanol solution

Sajewicz M., Gontarska M., Kowalska T.

Acta Chromatographica

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2012

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Vol. 24, no. 1

131--141

EN

In our earlier studies performed with the use of thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), polarimetry, and several other instrumental techniques, we have provided abundant experimental evidence for the oscillatory chiral conversion and the oscillatory condensation of the low-molecular-weight carboxylic acids from the groups of profen drugs, amino acids, and hydroxy acids. We have also proposed several kinetic-diffusive models aimed at elucidation of these striking phenomena, which in the diffusive term assumed contribution from the density inhomogeneity of the investigated liquid systems. Moreover, each model laid special emphasis on the importance of cyclic H-bonded carboxylic acid homodimers of the SS and RR type. In this paper, we introduce a simple experimental approach enabling convenient registration of the density inhomogeneity in the S(+)-naproxen solution prepared in 70% aqueous ethanol. To this effect, we use a zooming scanner that is able to scan this solution in a Petri dish placed in UV light (λ = 254 nm). Scanning in the selected time intervals allows tracing the dynamics of supramolecular aggregation of the investigated profen drugs. The mobility of these aggregates can probably result from the energy released in the process of chemical polycondensation. The obtained results seem to correlate well with those originating from HPLC, and the relevant conclusions are drawn. It seems possible that the zooming scanner can prove helpful in monitoring some other interesting chemical processes as well, thus contributing to the studies on the mechanism and kinetics of the nonlinear organic reactions.

8

Condensation oscillations in the condensation of mandelic acid

Sajewicz M., Gontarska M., Kronenbach D., Berry E, Kowalska T.

Acta Chromatographica

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2012

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Vol. 24, no. 1

1--13

EN

In our earlier studies, we were the first to discover a spontaneous chiral conversion of the low-molecular-weight carboxylic acids dissolved in aqueous media, running in vitro. The investigated chiral carboxylic acids belong to the classes of profen drugs, amino acids, and hydroxy acids. Then, the spontaneous chiral conversion running in vitro and accompanied by the spontaneous condensation of the discussed compounds was discovered. From the literature, we learnt that spontaneous condensation of certain chiral compounds sometimes can be oscillatory in nature. Thus, we considered it noteworthy to check if spontaneous condensation of the chiral low-molecular-weight carboxylic acids follows a linear or a nonlinear dynamic pattern. In this paper, we present the results of our studies on the dynamics of condensation of S-, R-, and rac-mandelic acid, carried out with the aid of the high-performance liquid chromatography with the diode-array detection (HPLC-DAD), and with the aid of mass spectrometry (MS). The obtained data furnish reliable evidence that condensation of mandelic acid is oscillatory in nature. Finally, a theoretical model is recalled, which jointly describes the oscillatory chiral conversion and the oscillatory condensation with S-, R-, and rac-mandelic acid.

9

Exploration of the possibility of combined HS-GC-MS and 13C NMR spectroscopic investigation of the composition of the essential oils of selected sage (Salvia) species

Sajewicz M., Matlengiewicz M., Rzepa J., Wojtal Ł., Hajnos M., Waksmundzka-Hajnos M., Kowalska T.

Acta Chromatographica

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2011

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Vol. 23, no. 1

181--190

EN

The objective of this study was to explore the possibility of combining headspace gas chromatography with mass spectrometric detection (HS-GC-MS) and 13C NMR spectroscopy to enhance the detectability of components of the essential oils of medicinal plants of the Salvia genus. Preliminary investigations were performed with two sage species, Salvia lavandulifolia and Salvia triloba, known for particularly abundant yields of their respective essential oils. By use of HS-GC-MS, characteristic fingerprints of the volatile fractions were obtained for plant species from two different vegetation seasons (2007 and 2008). Partial identification of the components of these volatile fractions was performed, and comparison of the chromatographic fingerprints confirmed seasonal fingerprint similarity within the same species. Preliminary 13C NMR measurements resulted in well shaped spectra with an abundance of regularly distributed signals. This suggested the possibility of using 13C NMR spectroscopy in phytochemical research, in parallel with HS-GC-MS, to enhance the detectability of volatile components of plant species belonging to this genus.

10

On the spontaneous condensation of profens, with ketoprofen as an example

Matlengiewicz M, Sajewicz M., Gontarska M., Kronenbach D., Kowalska T.

Acta Chromatographica

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2010

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Vol. 22, no. 1

81--90

EN

In a series of recently published full-length papers and short communications we attempted to gain deeper insight into elementary reactions which might contribute to the non-linear nature of the spontaneous chiral conversion of low-molecular-weight carboxylic acids. Earlier, we succeeded in demonstrating that amino acids and hydroxy acids can undergo spontaneous peptidization and spontaneous esterification (both regarded as condensation), respectively, when dissolved in 70% aqueous ethanol. In this study we provide experimental proof from thin-layer chromatography and 13 C NMR spectroscopy of spontaneous condensation of profens, with ketoprofen as an example. It can be expected that other profen drugs undergo an analogous condensation. In the future, an analogy between the ability of amino acids, hydroxy acids, and profens to undergo spontaneous peptidization or condensation (as reported in our papers), and the ability of selected organosilanols to undergo the spontaneous oscillatory condensation (as reported elsewhere), might prove essential for better understanding of detailed mechanism of the spontaneous oscillatory in-vitro chiral conversion of the selected low-molecular-weight carboxylic acids.

11

On the mechanisms of enantiomer separations by chiral thin-layer chromatography on silica gel, and implications when densitometric detection is used. A mini review

Sajewicz M., Kowalska T.

Acta Chromatographica

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2010

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Vol. 22, no. 4

499--513

EN

Enantiomer separations have been one of the most important and, simultaneously, one of the most difficult to accomplish analytical (and technological) tasks, present at the top of separation scientists’ agenda since the early sixties of the last century. Awareness of their importance has been awakened by an infamous case of the racemic drug thalidomide, a widely advertised sedative drug which had unexpected teratogenic activity in pregnant women that resulted in thousands of ‘flipper babies’ born in the late fifties and the early sixties in many countries around the world. Since that time, separation scientists have developed numerous methods for enantiomer separation, basically by use of gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE). In this respect, planar chromatography has remained to a large extent an undervalued enantiomer separation technique, despite separation performance sufficient to separate a pair of enantiomers. The large number of GC, HPLC, and CE enantiomer separation strategies and methods developed are evidence that — once confronted with this particular and no doubt very important challenge — instrumental chromatographic techniques have lost if not face, then, to a large extent, their reputation as robust, universal, and efficient separation tools. In these circumstances, planar chromatography on silica gel seems a very promising and tempting alternative, basically because of the advantageous properties of microcrystalline silica gel and the 2D effective diffusion available only in planar chromatographic mode. Enhancement of the enantiomer separating power of the silica gel by simple mechanical impregnation with a properly chosen chiral selector, and additional coupling of this with efficient instrumental detection (e.g. densitometric, DAD, or mass spectrometric) can yield in a simple, robust, and universal tool for separation of enantiomers comparable with the long-established chromatographic enantiomer-separation techniques. In this mini review, favourable preconditions for silica-gel-based planar chromatographic separation of enantiomers which can elevate planar chromatography to the status of leading tool for separation of enantiomers are discussed. Further improvements which can enhance the enantiomer separation performance of chiral planar chromatography are also indicated.

12

On the spontaneous condensation of selected hydroxy acids

Sajewicz M., Matlengiewicz M., Kronenbach D., Gontarska M., Kowalska T.

Acta Chromatographica

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2009

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Vol. 21, no. 2

259--271

EN

In a previous study we provided thin-layer chromatographic, polarimetric, and other experimental evidence that phenylglycine can undergo easy spontaneous peptidization in abiotic aqueous media. From our unpublished results it is apparent that this behaviour is also characteristic of some other amino acids (e.g., alanine and phenylalanine). It seems highly probable that this abiotic peptidization of amino acids dissolved in aqueous media is directly linked to their ability to undergo spontaneous oscillatory chiral conversion. In our earlier research it was also shown that spontaneous oscillatory chiral conversion was characteristic not only of amino acids but also of several other classes of carboxylic acid, including profen drugs and hydroxy acids. We therefore decided to check whether selected chiral hydroxy acids — lactic acid and mandelic acid — previously recognized for their ability to undergo spontaneous oscillatory chiral conversion, could also furnish the respective polyacids. Condensation of hydroxy acids can be viewed as a reaction fully analogous with peptidization of amino acids and, hence, it seemed to us highly probable that it also can be triggered by oscillatory chiral conversion. In our study, we used thin-layer chromatography and 13 C NMR spectroscopy to check whether formation of polylactic acid and polymandelic acid occurred in stored solutions of lactic and mandelic acids. By means of polarimetry with continuous recording we provided experimental evidence that all three hydroxy acids investigated (i.e. L -(+)-lactic acid, S -(+)-mandelic acid, and R -(−)-mandelic acid) undergo continuous chiral conversion. From the thin-layer chromatographic results obtained it was apparent that — similar to the spontaneous and instantaneous peptidization of amino acids — the hydroxy acids investigated also undergo easy condensation to form the respective polyacids. 13 C NMR spectroscopy provided additional experimental confirmation of this.

13

On the spontaneous abiotic peptization of phenylglycine in an aqueous medium

Sajewicz M., Gontarska M., Kronenbach D., Kowalska T.

Acta Chromatographica

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2009

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Vol. 21, no. 1

151-160

EN

In this report we provide thin-layer chromatographic evidence that phenylglycine dissolved in 70% aqueous ethanol and kept at ambient temperature (22°C) undergoes spontaneous peptization, as additionally confirmed by use of the biuret test. It was also shown that an important precondition for instantaneous peptization of phenylglycine is the simultaneous presence of the R and S antimers in solution, and the most spectacular peptization effect is obtained with racemic R,S -phenylglycine. An assumption is made that polycondensation of phenylglycine results from its ability to undergo spontaneous oscillatory chiral conversion and can be regarded as a step following enolization, and competitive with chiral conversion.

14

How to suppress the spontaneous oscillatory in-vitro chiral conversion of α-substituted propionic acids? A thin-layer chromatographic, polarimetric, and circular dichroism study of complexation of the Cu(II) cation with L -lactic acid

Sajewicz M., John E., Kronenbach D., Gontarska M., Wróbel M., Kowalska T.

Acta Chromatographica

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2009

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Vol. 21, no. 1

39-55

EN

In our earlier investigations we showed, for the first time, with numerous practical examples that α-substituted propionic acids dissolved in the low-molecular-weight solvents are able to undergo spontaneous oscillatory in-vitro chiral conversion. In this study, we focused on attempting to suppress the spontaneous oscillatory in-vitro chiral conversion of α-substituted propionic acids using, as example, L -lactic acid dissolved in water in the presence of copper(II) cations. Our intention was to check whether the coordinate covalent bonds between copper(II) and L -lactic acid ligands prevented the latter species from oscillatory chiral conversion. To do this we stored aqueous solutions of copper(II) acetate and lactic acid in the molar ratios 1:1, 1:2, and 1:3 for a long period of time. Scrutiny of possible chiral conversion of L -lactic acid was carried out by thin-layer chromatography (TLC), polarimetry, and circular dichroism (CD) spectroscopy. Seemingly contradictory results were obtained from our investigations. From the TLC data it was apparent that chelating of copper(II) cations with L -lactic acid molecules did not result in suppression of the spontaneous oscillatory in-vitro chiral conversion of the acid. It was also established that different molar proportions of copper(II) cation and L -lactic acid molecules had somewhat different effects on the dynamics of conversion. In contrast, from polarimetric and circular dichroism studies it was apparent that when L -lactic acid is dissolved in water in the presence of copper(II) cations almost no chiral conversion is observed. Hence a final conclusion was drawn that chelating of copper(II) cations with L -lactic acid stabilizes the chiral structure of the acid in solution. Intermolecular interactions between the copper(II)-L -lactic acid complex and the silica gel stationary phase evidently affects the structure of the complex, however, most probably resulting in partial "liberation" of L -lactic acid ligands. Thus the chiral structure-stabilizing effect of copper(II) cations is apparently weakened by the TLC system and the freed L -lactic acid molecules can undergo chiral conversion.

15

GC-MS study of the performance of different techniques for isolating the volatile fraction from sage ( Salvia L.) species, and comparison of seasonal differences in the composition of this fraction

Sajewicz M., Rzepa J., Hajnos M., Wojtal Ł., Staszek D, Kowalska T., Waksmundzka-Hajnos M.

Acta Chromatographica

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2009

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Vol. 21, no. 3

453--471

EN

Application of chemotaxonomy to the plant kingdom can be regarded as a future challenge to the traditional binomial classification system. Construction of a classification system based on the chemical composition of plants has only recently become possible with the development of sophisticated chromatographic and hyphenated techniques. Successful chemotaxonomy can, however, be achieved only if sufficient experimental evidence is collected confirming the reproducibility of the chemical composition of plant species (irrespective of the specimen, its growing season, location of the collection site, etc.). The objective of this study was to compare, by use of gas chromatography with mass spectrometric detection (GC-MS) the efficiency of isolation of volatile compounds from five different Salvia L. (sage) species ( S. lavandulifolia, S. staminea, S. hians, S. triloba , and S. nemorosa ) by use of four different techniques [head-space extraction at 70 and 80°C, vapour distillation in a Deryng apparatus, and accelerated solvent extraction (ASE)]. We also compared the composition of the volatile fractions of these species collected during two different seasons (2007 and 2008). It was established that the composition of the volatile fractions is very dependent on the species considered and, in a much less pronounced way, on the growing season. This statement is valid irrespective of the technique used to isolate the volatile compounds from the plant matrix. The seasonal reproducibility of the compounds regarded as chemotaxonomic markers and chemotaxonomic advice compounds (and the repeated absence of such compounds from a species) makes the volatile fraction suitable for chemotaxonomic evaluation of sage. Finally, it was shown that head-space extraction of the volatile fraction at 70°C was the best extraction technique for the purpose of this study.

16

Comparative analysis of the chromatographic fingerprints of twenty different sage ( Salvia L.) species

Daszykowski M., Sajewicz M., Rzepa J., Hajnos M., Staszek D, Wojtal Ł., Kowalska T., Waksmundzka-Hajnos M., Walczak B.

Acta Chromatographica

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2009

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Vol. 21, no. 4

513--530

EN

Comparative analysis of twenty different sage ( Salvia L.) species grown in Poland has been performed on the basis of two types of chromatographic fingerprints. For efficient preprocessing and comparison of these fingerprints, chemometric methods were used. The main emphasis was on preprocessing of herbal fingerprints and selecting a suitable preprocessing strategy for exploring differences among them. After successful preprocessing of the fingerprints, principal component analysis was used to reveal chemical differences among the samples. An outcome of the comparative analysis was to pinpoint specific regions of the fingerprints indicative of differences among the samples. In fingerprints of the volatile fraction from the sage ( Salvia L.) species, obtained from head-space gas chromatography coupled with mass spectrometry, important regions were identified and associated with the presence of camphene, limonene, and eucalyptol in these samples.

17

TLC study of the separation of the enantiomers of lactic acid

Sajewicz M., John E., Kronenbach D., Gontarska M., Kowalska T.

Acta Chromatographica

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2008

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Vol. 20, no. 3

367-382

EN

Enantiomer separation by TLC is still much less frequent than with other, mostly instrumental, chromatographic techniques. From a literature survey it is apparent that separation of the enantiomers of D,L -lactic acid is primarily of interest to the diary industry and that this particular separation is less frequently performed by chromatographic than by membrane techniques. As far as we are aware, before our studies only one report of TLC separation of the enantiomers of D,L -lactic acid was available in the literature; this is dated 1991 and describes the use of non-instrumental TLC only. In this study, we started by reproducing the TLC procedure originating from 1991, for this purpose using TLC with automatic sample application and densitometric detection. We managed to repeat the earlier procedure and to achieve full, i.e. baseline, separation of the enantiomers, with a remarkable distance between the two antimers. However, we revealed a significant drawback of this separation procedure - D -(-)-lactic acid was transported almost with the mobile-phase front and its densitometric quantification was barely possible because of the relatively high UV absorption of the mobile-phase front line. The reference method for separation of the enantiomers of D,L -lactic acid consisted in preliminary impregnation of commercial silica gel TLC plates with copper(II) acetate. In-situ formation of bidentate complexes of the D,L -lactic acid antimers with the Cu 2+ cation resulted in different mobilities of these complex cations in the planar chromatographic system. The objectives of this study were twofold - to investigate separation of the enantiomers of D,L -lactic acid with other transition metal cations (i.e., Co 2+, Ni 2+, and Mn 2+) used to impregnate the silica gel (to achieve resolution that might enable quantification of the two lactic acid antimers and not only the L -(+) enantiomer) and to gain deeper insight into the mechanism of separation with these metal cations. For purposes of comparison, we chromatographed D,L -lactic acid on non-impregnated silica gel layers. As a result, we managed to establish efficient separation conditions with the Ni 2+ and Co 2+ cations that outperformed the earlier established procedure involving the Cu 2+ cation, and - partially at least - to elucidate the mechanism of separation of the enantiomers of D,L -lactic acid by these TLC systems. The Mn 2+ cation proved unsuitable for the purpose. Finally, we managed to separate the enantiomers of D, L -lactic acid on non-impregnated silica gel layer also, which seems yet more proof of the microcrystalline chirality of silica gel used as stationary phase and of its substantial contribution to the enantiomer separation investigated.

18

Investigation of the spontaneous oscillatory in-vitro chiral conversion of L -(+)-lactic acid

Sajewicz M., Gontarska M., Kronenbach D., Kowalska T.

Acta Chromatographica

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2008

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Vol. 20, no. 2

209-225

EN

In previous studies we focused our attention on the in-vitro oscillatory chiral conversion of selected profens and amino acids when dissolved in low-molecular-weight solvents. The results obtained encouraged us to check other propionic acid derivatives of biological importance and we therefore decided to investigate the tendency of L -(+)-lactic acid to undergo an analogous process of spontaneous oscillatory in-vitro chiral conversion. As far as we are aware, this type of investigation on lactic acid has not previously been conducted. In our studies, we used solutions of L -(+)-lactic acid in three different mixed solvents, ethanol-water, ethanol-glacial acetic acid, and ethanol-basic buffer (pH 9), in the volume proportion 7:3. The investigations were conducted by thinlayer chromatography (TLC) and polarimetry. The results obtained by TLC gave evidence of the spontaneous oscillatory chiral conversion of L -(+)-lactic acid solution. From TLC results alone it is hardly possible to judge whether this process commences in solution before chromatography, catalyzed by the solid-liquid interface of the TLC plate, or commences immediately on dissolution of the acid and occurs continuously without interruption, both outside and inside the chromatographic system. It is easy to believe that the highly active surface of the silica gel adsorbent acts as a catalyst of chiral conversion. From long-term polarimetric studies it was concluded that L -(+)-lactic acid also undergoes oscillatory chiral conversion in the bulk liquid phase at ambient temperature, i.e. outside the TLC system, although the rate is much lower than in TLC and the racemic mixture is obtained after approximately one month only. In TLC racemization is practically complete within one chromatographic run.

19

Analysis of selected phenolic acids and flavonoids in Amaranthus cruentus and Chenopodium quinoa seeds and sprouts by HPLC

Paśko P., Sajewicz M., Gorinstein S., Zachwieja Z.

Acta Chromatographica

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2008

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Vol. 20, no. 4

661-672

EN

Red amaranth (Amaranthus cruentus) and quinoa (Chenopodium quinoa ) are pseudocereals with particularly highly regarded nutritional value. Because of the high biological significance of the flavonoids and phenolic acids in these plants, qualitative and quantitative analysis has been performed by HPLC. Extracts from the seeds of two amaranth varieties (A. cruentus v. Rawa and v. Aztek) and quinoa seeds, and their sprouts grown in natural conditions and in the dark were analyzed. The main phenolic acid found both in seeds and sprouts was gallic acid. p -Hydroxybenzoic acid, vanillic acid, p -coumaric acid, caffeic acid, and cinnamic acid were also found in the seeds and p -coumaric acid, syringic acid, and ferulic acid in the sprouts. The main flavonoid found in the sprouts was rutin. Vitexin, isovitexin, and morin were also detected in the sprouts, and orientin, vitexin, isovitexin, morin, and traces of hesperidin and neohesperidin in the seeds. Although sprouting conditions (daylight or darkness) had no effect on gallic acid content, light caused an increase in the amount of rutin and darkness resulted in increased amounts of isovitexin and vitexin.

20

Study of the oscillatory in-vitro transenantiomerization of the antimers of flurbiprofen and their enantioseparation by thin-layer chromatography (TLC)

Sajewicz M., Gontarska M., Kronenbach D., Wojtal Ł., Grygierczyk G., Kowalska T.

Acta Chromatographica

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2007

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No. 18

226-237

EN

In our earlier studies on the spontaneous in-vitro oscillatory transenantiomerization of profens we investigated optically pure S-(+)-ibuprofen and S-(+)-naproxen and the racemic mixtures S,R-(š)-2-phenylpropionic acid and S,R-(š)-ketoprofen, which remained in a state of dynamic equilibrium between the two antimers yet also had the ability to transenantiomerize. In this study we have demonstrated, for the first time, the spontaneous oscillatory in-vitro transenantiomerization of S-(+)-flurbiprofen (an important non-steroidal anti-inflammatory drug, NSAID) and R-(-)-flurbiprofen, as monitored by polarimetry. It is also noteworthy that – as far as we are aware – this is the first report of separation of the enantiomers of flurbiprofen by TLC. This separation was achieved by two-dimensional development using a simple chromatographic system comprising a commercial silica gel layer impregnated with L-arginine as stationary phase and ethanol containing a few drops of glacial acetic acid as mobile phase. Unfortunately, this chromatographic system resulted in catalysis of structural conversion of the optically pure flurbiprofen enantiomer, either S-(+), or R-(-), to the scalemic or racemic mixture of the two antimers. This is an interesting contribution to general knowledge about the reactivity of this particular profen, although the spontaneous and rapid conversion observed prevents use of this TLC system for identification and quantification of individual flurbiprofen enantiomers.