Molecular dynamics simulation of fluorination effect for solvation of trifluoromethylbenzoic acid isomers in supercritical carbon dioxide

A molecular dynamics (MD) simulation was applied to carbon dioxide+trifluoromethylbenzoic acid isomer and carbon dioxide+methylbenzoic acid isomer systems to investigate the interactions between carbon dioxide and the solutes. The pair correlation functions between the carbon dioxide and trifluoromethyl group or methyl group in the solutes were calculated to study the fluorination effect of solvation. As a result, it was found that the interactions between carbon dioxide and trifluoromethyl group in trifluoromethylbenzoic acid isomers were stronger than those between carbon dioxide and the methyl group in methylbenzoic acid isomers. The simulation results had the same tendency as the experimental solubility enhancements and coincided with the trend of the interaction parameters of the Peng-Robinson equation of state that were determined from the solubility data.     

Comparison of lipase-catalysed esterification in supercritical carbon dioxide and in n-hexane

Summary Oleic acid esterification by ethanol has been performed by an immobilized lipase fromMucor miehei in supercritical carbon dioxide and in n-hexane as solvents. In both media, determination of apparent kinetic constants has been achieved and influence of water content has been shown to be different due to various rates of water solubilities. Stability of the lipase has been proved to be correct and similar in both solvents. Inhibition by ethanol excess has been found but is greater in n-hexane. That can explain the higher initial velocities obtained in supercritical carbon dioxide for the highest ethanol concentrations.     

Subtilisin-catalyzed transesterification in supercritical carbon dioxide

Summary Subtilisin Carlsberg was found to catalyze transesterification between N-acetyl-L-phenylalanine chloroethyl ester and ethanol in supercritical carbon dioxide. The effects of different temperatures and carbon dioxide/ethanol ratios on the reaction rate were investigated. A comparative study showed that enzymatic transesterification is faster in supercritical carbon dioxide than in anhydrous organic solvents.     

Enantioselective esterification of ibuprofen in supercritical carbon dioxide by immobilized lipase

The enantioselective esterification of racemic ibuprofen with n-propanol by immobilized Mucor miehel lipase in supercritical carbon dioxide was studied. The enantiomeric excess of the product (ee_p) was 70 % at 15...20 % conversion. The enantioselectivity was faintly affected by temperature and the concentration of ibuprofen and lipase. The optimum temperature was 45 °C. The initial reaction rate increased with pressure, but enantioselectivity was not affected by pressure changes. The reaction rates in supercritical carbon dioxide at optimized conditions and in n-hexane were similar.     

On the solubility of disodium p-nitrophenyl phosphate in supercritical carbon dioxide

Summary The title compound is shown to be insoluble in supercritical carbon dioxide, and an earlier report of its enzymatic hydrolysis in supercritical carbon dioxide is shown to be erroneous.     

Oxygen monitoring in supercritical carbon dioxide using a fibre optic sensor

Investigations of enzymatic reactions in supercritical CO(2) are often hindered by the high pressure involved in these processes, making reaction monitoring extremely difficult. This paper describes the implementation of a fiber optic based oxygen sensor into a high pressure reactor for supercritical carbon dioxide. The sensor is pressure resistant, working in supercritical carbon dioxide and reusable after depressurisation. The sensor signal is found to be affected by pressure changes, but stable at constant pressure. Oxygen concentration in supercritical CO(2) is monitored using the disproportionation of hydrogen peroxide as a simple oxygen producing reaction.     

Effects of pressure and temperature of supercritical carbon dioxide on the extraction of triacylglycerols from plant tissue

The rate of extraction of triacylglycerols with supercritical carbon dioxide can be greatly enhanced by raising the pressure of the fluid to 600 bar, or higher, and its temperature to 60°C, or higher. Both the amount of carbon dioxide and the time required for complete extraction are reduced at such high pressures and temperatures.     

Characterisation of a novel support for biocatalysis in supercritical carbon dioxide

The work presents a characterisation study of Accurel EP100 (polypropylene based hydrophobic granules) as support material for lipase (Lypozyme 10,000 l, from native Rhizomucor miehei) operating as biocatalyst in supercritical CO₂ as solvent. The study involved assay of biocatalytic activity and operational stability as functions of system pressure and temperature. Furthermore, the presence of diffusion limitations was tested, by varying the bed diameter and support particle size. In addition, SEM and Gas Absorption were employed to test the mechanical stability. Results were compared with the commercially available biocatalyst Lipozyme™ IM60.

Pressure did not have a significant effect on the activity or the stability, while temperature had a positive effect on the activity and negative effect on the stability. As expected, an ‘optimum’ value of system water content gave maximum catalytic activity for each biocatalyst. External- and internal-diffusion limitations were both found negligible. The mechanical stability analysis demonstrated little (if any) effect of supercritical carbon dioxide (scCO₂) on the structural integrity of Accurel EP100, although subtle increases in pore volume and surface area were observed.     

Extraction of squalene from yeast by supercritical carbon dioxide

Squalene produced under anaerobic conditions, by a strain of Torulaspora delbrueckii was extracted from the biomass using supercritical carbon dioxide. Minimum use of solvent, lower time of isolation and a higher selectivity of extraction merit use of supercritical fluid extraction (SFE) technique over solvent extraction of squalene, as optimized and reported previously. A maximum squalene yield of 11.12 g g^–1 (dry weight) of yeast cells was obtained at a temperature of 60 °C and pressure of 250–255 bar at a constant flow rate of 0.2l min^–1 of carbon dioxide. Lyophilization prior to SFE increased the squalene yield to 430.52 g g^–1 dry weight of yeast cells, an amount that is far greater than that obtained by (2:1) chloroform–methanol solvent extraction.     

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.Author for correspondence     

The effect of carbon dioxide on egg production inMyrmica rubra

Summary An earlier study suggested that anaesthetization with heavy doses of carbon dioxide can be harmful to ants. It is shown that a light dose of carbon dioxide can be a safe and convenient anaesthetic for laboratory studies of ants of the genusMyrmica.     

Preparation of peptide-loaded polymer microparticles using supercritical carbon dioxide

In this study, peptide-loaded microparticles were prepared using an aerosol solvent extraction system (ASES) by employing supercritical carbon dioxide as an antisolvent. The effects of the molecular weight of poly(Llactide) (PLLA), poly(ethylene glycol) (PEG), the block length of methoxy poly(ethylene glycol)-b-poly(L-lactide) (mPEG-PLLA), the blending of PLLA and PEG, and the drug-to-polymer feed ratio on the formation of leuprolide acetate (LA)-loaded microparticles and their release characteristics were investigated. Scanning electron microscope observations showed that the LA-loaded polymer particles had a spherical morphology with a smooth surface. The entrapment efficiency of LA in the ASES-processed microparticles was found to be extremely high (about 99%), whereas the initial release rate of the LA-loaded microparticles was very low for PLLA. The release rate of LA was observed to increase as the PEG block length of mPEG-PLLA and/or the drug content in the microparticles increased. When PLLA was blended with PEG, the release rate of LA from the PLLA/PEG microparticles was significantly faster compared with the corresponding mPEG-PLLA copolymer.     

Effect of moisture on enzymatic reaction in supercritical carbon dioxide

The continuous acidolysis of triolein and stearic acid was carried out by an immobilized lipase to elucidate the characteristics of supercritical carbon dioxide (SC-CO₂) as a reaction medium. At first, an effect of temperature and pressure on the water adsorption to the immobilized lipase in the SC-CO₂ was examined. Then, the continuous interesterification of triolein and stearic acid by the moist immobilized lipase was examined. The amount of water adsorption to the immobilized lipase in the supercritical carbon dioxide measured under the condition of a different temperature and pressure has been expressed by a correlation equation of Freundlich type by using relative water standardized with the solubility of water in each condition. Optimum operating conditions of the interesterification by immobilized lipase in the SC-CO₂ was 323 K, 16.9 MPa and adsorbed-water concentration of 2 wt%. The production rate obtained by enzymatic acidolysis in the SC-CO₂ was found to be about 0.03 mmol/h2g-immobilized enzyme, leaving 74% residual triglyceride at the optimum operating conditions.     

Production of micronic particles of biocompatible polymer using supercritical carbon dioxide

Three micronization techniques, based on the use of supercritical carbon dioxide, were investigated to produce microspheres of a natural biocompatible polysaccharide. Particles smaller than 20 mum were obtained by means of the rapid expansion of a supercritical solution method (RESS), both with and without cosolvents. The mean diameter of the particles was reduced to about 0.5 mum when a solution of the polymer in an organic solvent was expanded by using carbon dioxide as a supercritical antisolvent (SAS). The SAS process was operated both in a continuous and in a batch mode. The former leads to aggregated structures and fibers, and the latter to the formation of micronic spherical particles. It was found that the experimental temperature did not substantially affect the shape and dimension of the particles. A stronger dependence is shown with respect to the solute concentration in the starting solution. The proposed method is attractive as the basis of a new process for the preparation of drug delivery systems. (c) 1997 John Wiley & Sons, Inc.     

Plant cell growth under different levels of oxygen and carbon dioxide

Summary An experimental system, in which gases of known composition were passed through flasks, was used to systematically study the effects of oxygen and carbon dioxide on plant cell growth. As expected, oxygen limiting conditions resulted in suppressed growth of Catharanthus roseus cultures. Oxygen limitations did not alter the amount of cell mass produced per gram of sugar consumed which suggests that the production of fermentative metabolites was limited. Varying levels of carbon dioxide were observed to have no effect on the growth rates of either C. roseus or Daucus carota cultures. The amount of C. roseus cell mass generated per gram of sugar consumed appeared to be slightly increased at higher carbon dioxide levels.     

Supercritical carbon dioxide extraction of colchicine and related alkaloids from seeds of Colchicum autumnale L

A method for the extraction of the alkaloids colchicine, 3-demethylcolchicine and colchicoside from seeds of Colchicum autumnale by supercritical carbon dioxide has been established. Several parameters such as pressure, temperature, percentage of modifier and extraction time have been examined. Two extraction steps with constant carbon dioxide density (0.90 g/mL) and flux (1.5 mL/min) were required to extract the alkaloids in 110 min using 3% methanol as modifier. The quantitative determination of the alkaloids was performed by HPLC; the percentages of recovery were higher than 98% for the three alkaloids. This extraction procedure was compared with a conventional method involving maceration and sonication, and the same levels of alkaloids were obtained in each case. The supercritical carbon dioxide method is, however, very efficient, more rapid and more environmentally friendly than conventional methods.     

Over-expression of carbon monoxide dehydrogenase-I with an accessory protein co-expression: a key enzyme for carbon dioxide reduction

Carbon monoxide dehydrogenase-I (CODH-I) from the CO-utilizing bacterium Carboxydothermus hydrogenoformans are expected to be utilized as a part of reproducible carbon dioxide photoreduction system. However, the over-expression system for CODH-I remains to be constructed. CODH-I constitutes a hydrogenase/CODH gene cluster including a gene encoding a Ni-insertion accessory protein, CooC (cooC3). Through co-expression of CooC3, we found an over-expression system with higher activity. The Rec-CODH-I with the co-expression exhibits 8060?U/mg which was approximately threefold than that without co-expression (2270?U/mg). In addition, co-expression resulted in Ni²⁺ content increase; the amount of Ni atoms of Rec-CODH-I was approximately thrice than that without co-expression.     

Distribution of aflatoxins between extract and extraction residue of paprika using supercritical carbon dioxide

Paprika powder, naturally contaminated with aflatoxins, was extracted by supercritical carbon dioxide at standard conditions (300 bar and 50 degrees C). A lipophilic top phase and an aqueous base phase were obtained. These and the extraction residue were analysed by HPLC for aflatoxins. The main quantity of aflatoxins, about 60% of aflatoxin B1 and about 70% of aflatoxin B2 related to the original paprika powder, was found to be located in the extraction residue. This confirms the results of previous studies with other spices and demonstrates that the use for flavouring purposes of supercritical carbon dioxide extracts, rather than natural spice, offers potential application in reducing aflatoxin levels in spiced foods.     

Supercritical carbon dioxide extraction of griseofulvin from the solid matrix obtained after solid-state fermentation

Globally there is an increasing concern to minimize the use of organic solvents, particularly the chlorinated ones because of their suspected human carcinogenicity. The use of ecofriendly carbon dioxide as an alternative to organic solvents would be appropriate in the perspective of green technology. Supercritical carbon dioxide (SC-CO(2)) extraction is suitable for extraction of nonpolar compound with molecular weights less than 400. Griseofulvin is an antifungal antibiotic having a molecular weight of 353, making it amenable to SC-CO(2) extraction. This work brings out the potential of supercritical carbon dioxide extraction (SCFE) for downstream processing of griseofulvin from the solid matrix obtained after solid-state fermentation (SSF). The optimized conditions for SCFE of griseofulvin from dried media after SSF were a flow rate of 0.4 L/min, temperature of 60 degrees C, and contact time of 90 min (30 min static + 60 min dynamic) at a pressure of 450-455 bar.     

High anti-inflammatory activity of harpagoside-enriched extracts obtained from solvent-modified super- and subcritical carbon dioxide extractions of the roots of Harpagophytum procumbens

Solvent-modified carbon dioxide extractions of the roots of Harpagophytum procumbens have been investigated with respect to extraction efficiency and content of harpagoside, and compared with a conventional extract. The effects of pressure, temperature, type and concentration of the modifier have been examined. Two extraction steps were necessary in order to achievehigh anti-inflammatory harpagoside-enriched extracts. The first extraction step was carried out in the supercritical state using carbon dioxide modified with n-propanol to remove undesired lipophilic substances. The main extraction was performed either in the supercritical or in the subcritical state with carbon dioxide modified with ethanol. The supercritical fluid extraction resulted in extracts containing up to 30% harpagoside. The subcritical extracts showed a harpagoside content of ca. 20%, but the extraction yield was nearly three times greater compared with supercritical conditions. The total harpagoside recovery resulting from the sum of the extract and the crude drug residue was greater than 99% in all experiments. The conventional extract and two carbon dioxide extracts were tested for in-vitro inhibition of 5-lipoxygenase or cyclooxygenase-2 biosynthesis. Both carbon dioxide extracts showed total inhibition on 5-lipoxygenase biosynthesis at a concentration of 51.8 mg/L. In contrast, the conventional extract failed to show any inhibition of 5-lipoxygenase biosynthesis.