Tyrosinase reaction/chitosan adsorption for selectively removing phenols from aqueous mixtures

The goal of this work was to explore the technical feasibility of an enzymatic approach as an alternative to traditional approaches for phenol separations. Specifically, we examined a two-step approach to selectively remove phenols from mixtures containing nonphenolic isomers. Our model solutes, of molecular formula C7H8O, were the phenol, cresol; the alkyl aryl ether, anisole; and the alcohol, benzyl alcohol. The first step in this two-step approach employed the enzyme mushroom tyrosinase to selectively convert the phenolic, presumably to an o-quinone product. The tyrosinase was specific for the phenol and was not observed to react with either the ether or the alcohol. The second step of this two-step approach employed a sorbent of an appropriate surface chemistry to bind the products of the tyrosinase-catalyzed reaction of phenols. The sorbent used for this study was chitosan. Chitosan was observed to be unable to adsorb either nonphenol and was unable to adsorb unreacted cresol. However, chitosan effectively adsorbs UV-absorbing reaction products of the tyrosinase-catalyzed reaction of phenols. When mixtures of cresol and either anisole or benzyl alcohol were studied, the two-step approach was effective for completely removing the phenolic without loss of either the ether or alcohol (i.e., phenols were removed with high separation factors).