Effects of Organic Solvents on the E-value

When the catalyst (enzyme) acts on a racemic mixture, Equation 4 also applies in the limit of low conversion (with the extent of conversion) (Equation 4a)  

However, in more general cases, the extent of conversion needs to be taken into account explicitly (Equation 5 and Equation 6)  

Although Equation 4, Equation 5, Equation 6, and Equation 7 may be used to establish the E-value of a catalyst in many cases of interest, they certainly do not cover the full range of possible situations. This holds in particular for the commonly employed hydrolases that show bi bi ping pong kinetics. For enzymes that follow this kinetic scheme, the ratio of reaction rates in the case of a so-called A-P resolution, Ars + = PR-S + Q (see [31]) takes the following form (Equation 7)  

From the point of view of organic synthetic applications, stereoselectivity is the most valuable property of enzymes [32]. However, whereas enzymes commonly show high (prochiral- and enantio-) selectivity when processing their natural 

Early reports on the effects of the choice of solvent on enzymatic enantioselectivity showed that substantial changes may be observed. For the transesterification reaction of sec-phenethyl alcohol with vinyl butyrate catalyzed by subtilisin Carlsberg, a 20-fold increase in the E-value was reported when the medium was changed from acetonitrile to dioxane [59]. Similar changes were recorded for the prochiral selectivity of Pseudomonas sp. lipase in the hydrolysis of 2-substituted 

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