Marie Zarevúcka

Solubility of two vegetable oils in supercritical CO2

Abstract Dynamic method was applied to measure the solubility of oils from seed of Ribes nigrum (blackcurrant) and Vitis vinifera (grape-vine) in supercritical CO 2 at pressures up to 29 MPa. The solubility of blackcurrant seed oil, which had been refined prior to the measurement and therefore it contained only triglycerides, was measured at 40–60°C. It was correlated with CO 2 density and temperature by adjusting the constants of Adachi–Lu equation. The obtained equation is suitable for predicting the solubility of triglycerides of most vegetable oils. The solubility of grape seed oil, containing large percentage of free fatty acids, mono- and diglycerides, was measured at 40°C. It was twice as large as the solubility of refined blackcurrant seed oil, and it decreased after most of the free fatty acids had been extracted. A simplified stepwise model describing fractionation of the mixture during the solubility measurement was derived and applied to estimate the grape seed oil solubility and its changes.

A review on the effects of supercritical carbon dioxide on enzyme activity.

Different types of enzymes such as lipases, several phosphatases, dehydrogenases, oxidases, amylases and others are well suited for the reactions in SC-CO2. The stability and the activity of enzymes exposed to carbon dioxide under high pressure depend on enzyme species, water content in the solution and on the pressure and temperature of the reaction system. The three-dimensional structure of enzymes may be significantly altered under extreme conditions, causing their denaturation and consequent loss of activity. If the conditions are less adverse, the protein structure may be largely retained. Minor structural changes may induce an alternative active protein state with altered enzyme activity, specificity and stability.

A Series of Bicyclic Insect Juvenile Hormone Analogs of Czech Origin: Twenty Years of Development

Research results are summarized from a series of insect juvenile hormone analogs derived from 2-(4-hydroxybenzyl)-1-cycloalkanones, which have been investigated at the Institute of Organic Chemistry and Biochemistry in Prague during the past 20 years. At present, practical application of several prospective structures for insect control is under investigation. Biological activity values were determined to delineate the most important subseries of compounds and the most promising insect juvenile hormone analogs selected from the subseries. Carbamates, and in particular compound 47 proved to be highly active against aphids, cockroaches, flies, and many other insect species.

Selective enzymic esterification of free fatty acids with n-butanol under microwave irradiation and under classical heating

Selective enzymic esterification of free fatty acids, obtained from blackcurrant oil by chemical saponification, with n-butanol using four immobilized lipases under microwave irradiation and under classical heating was studied. A positive effect of microwave irradiation on chemical yields of the products of the enzymic reactions and specificity of lipases were observed in comparison with a controlled heating in an incubator equipped with shaking (classical heating) applied during the identical enzyme-mediated processes. The maximum quantity of γ-linolenic acid (30%) was obtained with Lipozyme used as biocatalyst of the reaction under microwave irradiation. The maximum quantity of butyl γ-linolenate (20%) was obtained by a Pseudomonas cepacia lipase catalyzed esterification under classical heating.

Lipase-catalysed hydrolysis of blackcurrant oil in supercritical carbon dioxide

Abstract The effect of reaction conditions on the extent of conversion in hydrolysis of blackcurrant oil was investigated. The enzyme used was Lipozyme, a lipase from Mucor miehei immobilised on macroporous anionic resin. The reaction was carried out in a continuous flow reactor at 10– 28 MPa and 30–50°C with carbon dioxide saturated with oil and water (55–100%) flowing up through the enzyme bed. Analysis of product composition indicated unfavourable hydrodynamics with significant mixing in the reactor when solvent interstitial velocity was lower than 4 cm min −1 , while above this velocity value the flow pattern was near to plug flow. Lipase stability was very good with no activity reduction observed during a long-term experiment. The reaction rate was a function of the ratio of enzyme load to solvent volumetric flow rate. A complete hydrolysis of oil was achieved in the experiments carried out with the enzyme load of 0.8 g and CO 2 flow rate of 0.4– 0.9 g min −1 . The effects of pressure (10– 25 MPa ) and temperature (30–40°C) on the reaction rate were small, and the effects of CO 2 saturation with water and of enzyme distribution in the reactor were negligible. Lipozyme displayed specificity towards linolenic acids; the release of α -linolenic acid was faster and that of γ -linolenic acid slower than the release of other constituent acids present in blackcurrant oil.

Plant Products for Pharmacology: Application of Enzymes in Their Transformations

Different plant products have been subjected to detailed investigations due to their increasing importance for improving human health. Plants are sources of many groups of natural products, of which large number of new compounds has already displayed their high impact in human medicine. This review deals with the natural products which may be found dissolved in lipid phase (phytosterols, vitamins etc.). Often subsequent convenient transformation of natural products may further improve the pharmacological properties of new potential medicaments based on natural products. To respect basic principles of sustainable and green procedures, enzymes are often employed as efficient natural catalysts in such plant product transformations. Transformations of lipids and other natural products under the conditions of enzyme catalysis show increasing importance in environmentally safe and sustainable production of pharmacologically important compounds. In this review, attention is focused on lipases, efficient and convenient biocatalysts for the enantio- and regioselective formation / hydrolysis of ester bond in a wide variety of both natural and unnatural substrates, including plant products, eg. plant oils and other natural lipid phase compounds. The application of enzymes for preparation of acylglycerols and transformation of other natural products provides big advantage in comparison with employing of conventional chemical methods: Increased selectivity, higher product purity and quality, energy conservation, elimination of heavy metal catalysts, and sustainability of the employed processes, which are catalyzed by enzymes. Two general procedures are used in the transformation of lipid-like natural products: (a) Hydrolysis/alcoholysis of triacylglycerols and (b) esterification of glycerol. The reactions can be performed under conventional conditions or in supercritical fluids/ionic liquids. Enzyme-catalyzed reactions in supercritical fluids combine the advantages of biocatalysts (substrate specificity under mild reaction conditions) and supercritical fluids (high mass-transfer rate, easy separation of reaction products from the solvent, environmental benefits based on excluding organic solvents from the production process).

Differences in hydrolytic abilities of two crude lipases from Geotrichum candidum 4013

The fungus Geotrichum candidum 4013 produces two types of lipases (extracellular and cell‐bound). Both enzymes were tested for their hydrolytic ability to p‐nitrophenyl esters and compounds having a structure similar to the original substrate (triacylglycerols). Higher lipolytic activity of extracellular lipase was observed when triacylglycerols of medium‐ (C12) and long‐ (C18) chain fatty acids were used as substrates. Cell‐bound lipase preferentially hydrolysed trimyristate (C14). The differences in the abilities of these two enzymes to hydrolyse p‐nitrophenyl esters were observed as well. The order of extracellular lipase hydrolysis relation velocity was as follows: p‐nitrophenyl decanoate > p‐nitrophenyl caprylate > p‐nitrophenyl laurate > p‐nitrophenyl palmitate > p‐nitrophenyl stearate. The cell‐bound lipase indicates preference for p‐nitrophenyl palmitate. The most striking differences in the ratios between the activity of both lipases (extracellular : cell‐bound) towards different fatty acid methyl esters were 2.2 towards methyl hexanoate and 0.46 towards methyl stearate (C18). The Michaelis constant (Km) and maximum reaction rate (Vmax) for p‐nitrophenyl palmitate hydrolysis of cell‐bound lipase were significantly higher (Km 2.462 mM and Vmax 0.210 U/g/min) than those of extracellular lipase (Km 0.406 mM and Vmax 0.006 U/g/min). Copyright

Lipase-mediated hydrolysis of blackcurrant oil

Four commercially available lipases, both free and immobilized, were tested for their ability to catalyze hydrolysis of blackcurrant (Ribes nigrum) oil using two different approaches. The lipase from Mucor miehei was studied free and immobilized in two different ways. The former series of enzymic reactions were performed in tap water at 40 degrees C, but the latter series of enzymic processes were carried out in mixtures of isooctane and phosphate buffer (in a typical 2/1 ratio of the components) at 30 degrees C. These conditions were optimized to increase and/or to maximize the yields of the products, which were priority targets in this study. A rate of hydrolysis and a selective preference of the hydrolytic enzymes towards fatty acids, with a special focus on enrichment of alpha-linolenic acid and/or gamma-linolenic acid, were studied. Higher rates of hydrolysis of the blackcurrant oil in the former series of reactions were observed with the immobilized lipase from Pseudomonas cepacia used as biocatalyst. In the latter approach, the most favorable results of the rate of hydrolysis of the target blackcurrant oil were achieved with the immobilized lipase from Mucor miehei employed as biocatalyst. Only three lipases, selected from a series of lipases tested during this investigation, displayed specificity towards alpha-linolenic acid and gamma-linolenic acid, i.e. the immobilized lipase from P. cepacia, lipase from M. miehei and lipase from P. fluorescens.

Chiral precursors of optically active juvenoids

Abstract For preparation of all four enantiomers of 2-(4-hydroxybenzyl)-1-cyclohexanol ( 1a–4a ) by biotransformation reactions, Saccharomyces cerevisiae (SC) and pig pancreatic lipase (PPL) were used in aqueous media. The THP-protected substrates ( 5b, 6b and 7b ) gave products with a good enantiomeric excess comparable with that of the CH 3 -protected substrates ( 5c, 6c and 7c ), whereas the deprotection was much easier in case of the THP-protected compounds.

A comparison of the enantioselective reduction potential of five strains of Saccharomyces cerevisiae towards a selected ketone

The enantioselectivity potential of five strains of Saccharomyces cerevisiae was studied for the reduction of ethyl N-{2-{4-[(2-oxocyclohexyl)methyl]phenoxy}ethyl} carbamate (1), an insect juvenile hormone bioanalog. The products of the reaction, the cis and trans isomers of ethyl N-{2-{4-[(2-hydroxycyclohexyl)methyl]phenoxy}ethyl} carbamate (2 and 3), were obtained in 45–49% (w/w) chemical yields and with 79 to > 99% enantiomeric purity values. The absolute configurations of the major products were assigned as ethyl (1S,2S)-N-{2-{4-[(2-hydroxycyclohexyl)methyl]phenoxy}ethyl} carbamate (2) and ethyl (1S,2R)-N-{2-{4-[(2-hydroxycyclohexyl)methyl]phenoxy}ethyl} carbamate (3). The products 2 and 3 belong to the series of the chiral insect juvenile hormone analogs.