Biotransformations in near-critical carbon dioxide

Performance in synthetic applications of a yeast surface display-based biocatalyst

Organic synthesis with surface-displayed lipase: alkyl esters of fatty acids. Compared performance to commercial preparations. Catalyst is reusable and stable up to 50–60 °C. Kinetics of surface-displayed synthesis of butyl decanoate.

Immobilized Candida antarctica lipase B: Hydration, stripping off and application in ring opening polyester synthesis

This work reviews the stripping off, role of water molecules in activity, and flexibility of immobilized Candida antarctica lipase B (CALB). Employment of CALB in ring opening polyester synthesis emphasizing on a polylactide is discussed in detail. Execution of enzymes in place of inorganic catalysts is the most green alternative for sustainable and environment friendly synthesis of products on an industrial scale. Robust immobilization and consequently performance of enzyme is the essential objective of enzyme application in industry. Water bound to the surface of an enzyme (contact class of water molecules) is inevitable for enzyme performance; it controls enzyme dynamics via flexibility changes and has intensive influence on enzyme activity. The value of pH during immobilization of CALB plays a critical role in fixing the active conformation of an enzyme. Comprehensive selection of support and protocol can develop a robust immobilized enzyme thus enhancing its performance. Organic solvents with a log P value higher than four are more suitable for enzymatic catalysis as these solvents tend to strip away very little of the enzyme surface bound water molecules. Alternatively ionic liquid can work as a more promising reaction media. Covalent immobilization is an exclusively reliable technique to circumvent the leaching of enzymes and to enhance stability. Activated polystyrene nanoparticles can prove to be a practical and economical support for chemical immobilization of CALB. In order to reduce the E-factor for the synthesis of biodegradable polymers; enzymatic ring opening polyester synthesis (eROPS) of cyclic monomers is a more sensible route for polyester synthesis. Synergies obtained from ionic liquids and immobilized enzyme can be much effective eROPS.

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.

Escherichia coli inactivation mechanism by pressurized CO2

The effects of pressurized CO2 on the survival of Escherichia coli and the mechanism of cell inactivation were studied. Bacterial cultures were inoculated in nutrient broth and incubated at 30 °C for 18 h. Exposure of the cells to CO2 under pressures ranging from 2.5 to 25 MPa and at temperatures between 8 and 40 °C was performed in a double-walled reactor with a 1 L capacity. The effect of the treatment on the cells was evaluated by plating and by transmission and scanning electron microscopy observation. Vapour CO2 generated a bacteriostatic effect. In liquid or supercritical state, CO2 provided a bactericidal effect. The bactericidal effect increased with pressure and temperature. The mechanism of cell inactivation by liquid CO2 involved two stages. First, cell stress caused by the CO2 penetration provoked cell wall collapse and cellular content precipitation. Second, the cell death caused by supercritical extraction of intracellular substances and cell envelope perforation resulted in leaking of intracellular constituents. In supercritical conditions, the cell inactivation process had one single phase: cellular death.Key words: Escherichia coli, CO2 under pressure, inactivation mechanism, bactericidal effect.

Determination of log P for pressurized carbon dioxide and its characterization as a medium for enzyme reaction

The log P value of pressurized CO(2) at 50 degrees C was determined from the solubility of 1-octanol in CO(2) and compared with other solvent parameters such as permittivity, epsilon, and polarity parameter, E(T)(30). The log P indicated that pressurized CO(2) is rather hydrophilic although it seems hydrophobic being judged from epsilon(r) and E(T)(30). With a change in pressure from 3 to 11.8 MPa, the log P changed from 0.9 to 2.0 while epsilon(r) and E(T)(30) changed only slightly. The log P was linearly correlated to the logarithm of the solubility of water among organic solvents. Pressurized CO(2) was located close to the linear correlation line among the solvents at high pressure (>11 MPa) but its location deviated to the hydrophilic side with a decrease in pressure. Lipase-catalyzed esterification of stearic acid with ethanol and hydrolysis of ethyl stearate were carried out in pressurized CO(2), benzene (log P = 2.0), and n-hexane (log P = 3.5). In spite of the lowest log P value for CO(2), the reaction rate in CO(2) was the highest among solvents tested in pressure range over 10 MPa. The reaction rate was strongly dependent on pressure of CO(2).