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

• Autorzy: Sajewicz M. , John E. , Kronenbach D. , Gontarska M. , Wróbel M. , Kowalska T.
• Języki publikacji: EN

Abstrakty

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.

Słowa kluczowe

EN

oscillatory chiral conversion; L-lactic acid; Cu(II)-lactic acid complexes; thin-layer chromatography; polarimetry; circular dichroism (CD) spectroscopy

• Wydawca: University of Silesia in Katowice ; Akademiai Kiado
• Czasopismo: Acta Chromatographica
• Rocznik: 2009
• Tom: Vol. 21, no. 1
• Strony: 39--55
• Opis fizyczny: Bibliogr. 16 poz., rys., tab.

Twórcy

autor

Sajewicz M.

autor

John E.

autor

Kronenbach D.

autor

Gontarska M.

autor

Wróbel M.

autor

Kowalska T.

• Silesian University Institute of Chemistry 9 Szkolna Street 40-006 Katowice Poland,

Bibliografia

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