No abstract

carbonate were studied at high concentrations in the temperature range from +25°C to -45°C Data are fitted by a least-squares method to a four-parametric empirical equation, yielding the maximum specific conductance KMAX and the corresponding concentration fi. Within the frame-work of a hydrodynamic model the Stokes-radii of the ions and the solvent viscosity are found to be the most important conductance-determining parameters, affecting both K MM and fi. Ionic association in solutions with propylene carbonate as the solvent is not of significant importance. Kinetic treatment of conductance yields temperature-dependent activation energies, but at any one temperature equal for all salts at concentration ^.

No abstract

The Monte Carlo technique is used to study the vapor-liquid interface of cyclopentane, cyclohexane, and benzene. The OPLS and TraPPE potential fields are compared in the temperature range from 298.15 to 348.15 K (273.15-298.15 K for C5H10). A new method for the treatment of the long-range interactions in inhomogeneous simulations is used. When this new method is employed, the obtained values of saturated liquid density and of enthalpy of vaporization are equal to those obtained using the bulk isothermal-isobaric Monte Carlo technique. The values of surface tension become independent of the cutoff distance and they are significantly larger than those when only simple spherical truncation of intermolecular interactions is used.

No abstract

No abstract

No abstract

Lipases from Candida antarctica and Mucor miehei were encapsulated in lecithin water-in-oil (w/o) microemulsion-based organogels (MBG). These gels were formulated with either hydroxypropylmethyl cellulose (HPMC) or gelatin. The esterification of lauric acid and 1-propanol catalyzed by these MBGs was examined in supercritical carbon dioxide (scCO 2 ; 35• C, 110 bar) as solvent for the substrates. The results were compared to those obtained with the reference substrate solvent isooctane. It turned out that the initial rates of this model reaction in scCO 2 were higher than those observed in the reference system. Various parameters affecting the biocatalysis such as pressure, alcohol and acid chain length, and gel composition were investigated. Kinetic studies showed that the ester synthesis catalyzed by the immobilized C. antarctica lipase occurs via a Ping Pong Bi Bi mechanism in which only inhibition by excess of alcohol was identified. Values of all kinetic parameters were determined. In addition, experiments on the reusability of these gels in scCO 2 were carried out and the state of water within the organogel was examined with the help of differential scanning calorimetry. The present study shows that biocatalysis using MBGs in scCO 2 is a promising alternative to other bioconversion processes.