Reaction kinetics for laccase-catalyzed polymerization of 1-naphthol NahitAktas ß a ,HasanC ß ic ßek b ,ArzuTas ßpõnar Unal b ,G unayKibarer c ,NazifKolankaya b , Abdurrahman Tanyolac ß a, * a Chemical Engineering Department, Faculty of Engineering, Hacettepe University, Beytepe 06532, Ankara, Turkey b Biology Department, Hacettepe University, Beytepe 06532, Ankara, Turkey c Chemistry Department, Hacettepe University, Beytepe 06532, Ankara, Turkey Received 28 December 2000; received in revised form 22 March 2001; accepted 2 April 2001 Abstract Laccase-catalyzed oxidative polymerization of 1-naphthol was carried out in a closed system containing acetone and sodium acetatebuer.Theeectsofinitial1-naphtholanddissolvedoxygenconcentrationsontheinitialreactionratewereinvestigated.A multiplicative mathematical model, using a function of 1-naphthol and dissolved oxygen concentrations, was developed for enzy- maticpolymerizationandthecorrespondingbiokineticparametershavebeenevaluatedforthe®rsttime.Theactivationenergyand reactionrateconstantofthelaccase-catalyzed1-naphtholpolymerizationwerecalculatedas57kJ/moland311l/s,respectively.The activationenergycalculatedwasinthetypicalrangeof30±60kJ/molandrateconstantwasoftheorderofmagnitudeofpreviously reported values for laccase-catalyzed reactions with dierent monomers. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Laccase; 1-Naphthol; Enzyme kinetics; Activation energy; Enzymatic polymerization; Reaction rate constant 1. Introduction Naphthols are intermediate chemicals for producing dyes, medicinals, plastics, rubbers and man-made ®bers Shreve, 1967). Speci®cally, 1-naphthol is a toxic hy- droxylatedmetaboliteofthepolycyclicaromatichydro- carbonPAH)naphthalene.Itisalsoamajorcomponent of the pesticide napropamide and a principal reaction product in hydrolysis of the pesticide carbaryl Consi- dine,1974;Karthikeyanetal.,1999).Likemanyphenols and phenol derivatives, 1-naphthol is a toxic and haz- ardous pollutant. However, inert phenolic polymers are widely used in wood composites, ®ber bonding, lami- nates, foundry resins, abrasives, friction and molding materials,coatingsandadhesivesDodricketal.,1987). Therefore,theremovalof1-naphtholviapolymerization maybebene®cialbothforwastewatertreatmentandalso forproducingpoly1-naphthol),ausefulsideproduct. Nevertheless, conventional polymerization methods mostly rely on inorganic catalysts made of toxic and precious materials. As an alternative catalyst, non-toxic oxidoreductive enzymes have been recently investigated to catalyse the oxidation of aqueous aromatic com- pounds, in the presence of a water-miscible organic solvent, to produce high molecular weight polymers of low solubility Kobayashi et al., 1996a). These enzymes are lipase Ajima et al., 1985; Okumura et al., 1984), soybean peroxidase Uyama et al., 1995), bilirubin oxi- dase Aizawa and Wang, 1996), horseradish peroxidase Kobayashi et al., 1995; Kobayashi et al., 1996a,b; Kuriokaetal.,1994),tyrosinaseAtlowetal.,1984)and laccaseMilsteinetal.,1994;Ikadaetal.,1996a,b).For the polymerization of phenolic monomers, horseradish peroxidasewaswidelyusedinthepresenceofH 2 O 2 and various reactor designs were suggested for wastewater treatment Wu et al., 1999; Buchanan et al., 1998). In contrast to horseradish peroxidase, the enzyme laccase uses only dissolved molecular oxygen for catalytic ac- tivity Yaropolov et al., 1994). Therefore, it is advan- tageous to replace horseradish peroxidase with laccase sinceitutilizesmolecularoxygeninsteadofH 2 O 2 ,which causes inhibition and deactivation of the enzyme as an oxidant Wu et al., 1999; Buchanan and Nicell, 1997). Therehavebeenfewstudiesdealingwiththelaccase- catalyzed polymerization of phenolic compounds and corresponding kinetic parameter estimation Xu et al., 1995; Tianzhi et al., 1996), though kinetics of horse- radishperoxidasehasbeeninvestigatedsucientlyWu Bioresource Technology 80 2001) 29±36 * Corresponding author. Tel.: +90-312-2977404; fax: +90-312- 2992124. E-mail address: tanyolac@hacettepe.edu.tr A. Tanyolac ß). 0960-8524/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0960-852401)00063-3