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

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Sajewicz M. , Gontarska M. , Kowalska T.

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tom 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.

2

On the spontaneous abiotic peptization of phenylglycine in an aqueous medium

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

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tom 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.

3

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

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

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tom 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.

4

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

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

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2007

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tom 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.