Direct transesterification of gases by “dry” immobilized lipase

Abstract

Several different reactor configurations, including single pass, continuous recycle, and batch reactor modes, were used to investigate the effects of temperature and water activity, or relative humidity, on lipase-catalyzed, gas-phase transesterifications. Temperature and relative humidity were controlled both inside reactors and throughout the course of the reaction to account for and optimize their effects. Results indicated that, at low relative humidity, reaction rates increased with temperature up to 60 degrees C. However, when relative humidity was increased, a similar increase in temperature resulted in the loss of nearly all enzyme activity. These results are consistent with the idea that enzymes without free water are more thermally stable. Furthermore, at constant ambient temperatures, production increased dramatically with an increase in relative humidity, confirming the idea that an increase in water activity increases catalytic activity. A mass balance performed on reactors at higher relative humidity revealed that hydrolysis (rather than transesterification) of the ester substrate could significantly decrease product yields.

Structured fiber supports for gas phase biocatalysis

“…A mass balance performed on the reactants revealed that the molar yield of acetic acid accounted for about 6-13% of the initial propanol concentration depending on the temperature. Similar results were reported with vinyl acetate/isoamyl acetate transesterification [21]. Fig.…”

“…Therefore, initial substrate concentrations varied when changing the temperature or H R and comparison on the basis of initial rates was not possible [21]. As a result, all reaction rates were measured under steady-state conditions.…”

The use of gas–phase substrates to study enzyme catalysis at low hydration

“…As with the study by Cameron et al (2002), a significant amount of activity, determined from initial rate measurements, was seen at a RH equal to zero. The rate of reaction was then seen to decrease with increasing water activity, as shown in figure 14.…”

“…As noted by the authors, explaining this behaviour is difficult as the exact distribution of the water between the support and the enzyme is unknown. Cameron et al (2002) also studied the effect of water activity on the rate of transesterification by porcine pancreatic lipase. The enzyme was immobilized on glass wool that was then used in reactors of various configurations.…”

Electrospray ion mobility spectrometry of intact viruses

“…ESI has previously been demonstrated to generate intact non-covalent complexes in the gas phase [5,6] and empty virus particles have been successfully mass measured [7]. Specifically, hapten binding by an antibody [8], stability of protein conformers [9] and enzymatic activity [10] in the gas phase all suggest that the native fold of a protein can be retained. It should be noted that gas phase binding affinities [11] and the distribution of folding intermediates [12] can differ from the solution conformation.…”