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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.

2

Comparative study on starch modification with lactic acid and poly(lactic acid)

Tudorachi N., Lipsa R.

Polimery

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2006

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T. 51, nr 6

425-430

EN

In the present study, we report on starch modification with L-lactic acid or poly(L-lactic acid) (PLA) with low molecular weight (Mn ť 3000), with potential uses in biomedical area. Molecular weights of copolymers obtained from starch and lactic acid were higher than that of copolymer obtained from starch and PLA. Unmodified starch showed greater stability than the two copolymers. We can notice that starch modified with L-lactic acid shows higher solubility than starch modified with PLA, although the latter is soluble in most organic solvents used.

PL

Opisano metodę modyfikacji skrobi za pomocą kwasu mlekowego lub poli(kwasu mlekowego) (PLA) o stosunkowo małym ciężarze cząsteczkowym (Mn ť 3000). Otrzymane kopolimery scharakteryzowano metodą IR (rys. 1). Ciężary cząsteczkowe wyznaczone metodą chromatografii żelowej są większe w przypadku kopolimerów z kwasem mlekowym niż kopolimerów z PLA (rys. 2, tabela 1). Stwierdzono, że stabilność termiczna skrobi niemodyfikowanej jest lepsza niż zsyntetyzowanych kopolimerów (rys. 3 i 4, tabela 2). Oceniono wpływ modyfikacji na rozpuszczalność w wodzie i różnych rozpuszczalnikach organicznych (tabela 3) i wykazano, że skrobia modyfikowana za pomocą kwasu mlekowego jest lepiej rozpuszczalna w wodzie niż niemodyfikowana oraz modyfikowana PLA.

3

Synteza i właściwości fizykochemiczne biodegradowalnych kopolimerów PET i hydroksykwasów otrzymywanych w stopie

Czerwiński W., Olewnik E.

Chemik

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2004

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Vol. 57, nr 5

170-174

PL

Przedstawiono wyniki badań mających na celu otrzymanie nowych biodegradowalnych kopolimerów na bazie tereftalanu bis(2-hydroksyetylu) (BHET), uzyskanego w procesie glikolizy butelek PET oraz oligomerów kwasu mlekowego i glikolowego. Największym problemem okazało się określenie warunków reakcji polikondensacji prowadzących do uzyskania jak największej wydajności procesu.

EN

Presented are the results of investigations targeted at receiving a novel series of biodegradable copolymers based on the bis-2-hydroxyethyl terephthalate (BHET) with l-lactic or glycolic oligomers by melt polycondensation methods. The most important achievement was determination conditions leading to the formation of our copolymers with high yield of reaction.