REGIOSELECTIVE OXIDATIVE POLYMERIZATION OF 1,5-DIHYDROXYNAPHTHALENE CATALYZED BY BILIRUBIN OXIDASE IN A WATER-ORGANIC SOLVENT MIXED-SOLUTION

Bilirubin oxidase (EC1.11.1.7) was used to catalyze the oxidative poly merization of 1,5-dihydroxynaphthalene to its polymer in a mixed solve nt composed of dioxane, ethyl acetate, and acetate buffer. In an aqueo us solution, the enzymatic oxidative polymerization hardly occurred an d resulted in negligible yield mainly due to the poor solubility of 1, 5-dihydroxynaphthalene. In the mixed solvent the conversion proceeded with a yield of ca. 70%. The polymer yield was studied with respect to reaction time and solvent components. Elemental analysis, UV-visible, fluorescent, and FT-IR spectroscopic analyses, proton NMR and electro chemical studies, and solubility in various organic solvents revealed that 1,5-dihydroxynaphthalene is polymerized by the C - C coupling. Th e molecular weight of the polymeric products solubilized with DMF vari ed from low molecular weight product to high molecular weight polymer. From the chromatographic studies, the organic solvent-insoluble resid ue was suggested to be highly polymerized material. Based on these fin dings a possible mechanism for enzymatic polymerization of 1,5-dihydro xynaphthalene is presented: less stable intermediates produced enzymat ically from 1,5-dihydroxynaphthalene undergo coupling and polymerizati on to ortho-1,5-dihydroxynaphthalene polymer, thereby resulting in a r egioselective polymerization of 1,5-dihydroxynaphthalene. (C) 1993 Joh n Wiley & Sons, Inc.