ELECTRONIC SUBSTITUENT EFFECTS IN THE NITRILASE-CATALYZED HYDROLYSIS OF PARASUBSTITUTED BENZYL CYANIDES

The initial rates of the nitrilase (Novo)-catalyzed hydrolysis of a series of para-substituted benzyl cyanides (R = NO2, Cl, OCH3, OH NH2) were found to be susceptible to the nature of the para-substituent of the substrate and a Hammett-type linear free energy correlation was observed with rho = 0.96. In a separate study, effective solubilization of substituted benzyl cyanide substrates having electron-donating groups (OH, NH2, OCH3) was achieved upon mixing with beta-cyclodextrin to form 1:1 mol ratio inclusion complexes, but para-substituted benzyl cyanides with electron-withdrawing groups (Cl, NO2) were not fully solubilized under the same conditions. In addition, it was shown that the presence of beta-cyclodextrin not only had no inhibitory effect on the enzyme activity, but it actually increased the initial rate of hydrolysis of the unsubstituted benzyl cyanide: beta-cyclodextrin inclusion complex. However, the initial rates of hydrolysis were observed to be smaller when beta-cyclodextrin was added to the para-substituted benzyl cyanides.