Role of Aqueous Phase Volume

The volume ratio of organic to aqueous phases can greatly affect the reaction. The majority of reported studies recommend using only enough water to dissolve 

Once the organic solvent has been selected and the optimum volume ratio of organic to aqueous phases is determined, the water content of the solvent must be considered. There are several different reasons for this. First, using the same solvent from different suppliers leads to different results due to dissimilar water contents of the solvents (Yokozeki et al., 1982). To remedy the situation, water-saturated solvent can be used. It has also been found that when solvents are poorly hydrated, the solutes may drag water molecules into the organic phase (Tsai et al., 1993 Fan et al., 1994). A theoretical analysis of this water-dragging effect in biphasic systems has also been attempted. 

When the products in the organic phase are susceptible to hydrolysis, the activity of the water content must be reduced while maintaining the activity of the catalyst. This can be accomplished either by immersing a desiccant in the organic solvent to lower the water activity of the liquid phase or by placing it in the headspace of the reactor to reduce the activity of the water vapor. 

MATCHING THE pH OPTIMA FOR REACTION EQUILIBRIUM AND CATALYST ACTIVITY 

We have seen how the pH of the medium can influence the activity of an enzyme, as well as the thermodynamic conversion of a reaction. Usually, the pH optima for the two are far removed from each other. Thus optimization with respect to one can be done only at the expense of the other. For instance, for jd-lactam antibiotics, the optimum pH is in the range of 3-5 (Margolin et al., 1980), for / -nitroanilides the optimum pH is 2-3, and for N-substituted amino acid esters the optimum pH is 3 (Kozlov and Ginodman, 1965 D Yachenko et al., 1971). But most of the enzymes that catalyze these reactions, for example, penicillin amydase and tripsin, are active and stable only at neutral and near neutral pH. 

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