Browsing by Author "Aktas, N"

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Effects of Reaction Conditions on Laccase-Catalyzed Α-Naphthol Polymerization
(John Wiley & Sons Ltd, 2000) Aktas, N; Kibarer, G; Tanyolaç, A
Enzymatic oxidative polymerization of alpha-naphthol was carried out batch-wise with the laccase enzyme, produced by Trametes versicolor (ATCC 200801). The polymerization reaction was conducted in a closed, temperature controlled system containing acetone (solvent) and sodium acetate buffer for pH control. The effects of the organic solvent (acetone) composition, monomer (alpha-naphthol) and enzyme concentrations, buffer pH and temperature on the polymerization rate were investigated with respect to initial reaction conditions and depletion rate of dissolved oxygen. The optimum acetone composition, pH, monomer, dissolved oxygen and enzyme concentrations were determined as 50% (v/v), 5, 3409 gm(-3), 20.3 gm(-3) and 0.173 U cm(-3), respectively; these values provided the most desirable conditions for initial reaction rate. Temperature rise supported the rate increase up to 37 degrees C, after which the rate tended to be stable due to a drop in dissolved oxygen concentration. The product polymer, poly(alpha-naphthol), with an average molecular weight of 4920 Da was soluble in common organic solvents. (C) 2000 Society of Chemical Industry.
Influence of Reaction Conditions on the Rate of Enzymic Polymerization of Pyrogallol Using Laccase
(Elsevier Sci Ltd, 2005) Güresir, M; Aktas, N; Tanyolaç, A
Laccase produced from Trametes versicolor (ATCC 200801) was utilized to synthesize poly (pyrogallol) in aqueous solution. The polymerization reaction was conducted batchwise in a closed, temperature controlled system containing sodium acetate buffer for pH stability. The effects of monomer (pyrogallol), enzyme and dissolved oxygen concentrations, reaction mixture pH and temperature on the polymerization rate were investigated with respect to initial reaction conditions and depletion rate of dissolved oxygen in the reaction mixture. Maximum initial oxygen consumption rates. defined as initial polymerization reaction rate, were achieved with sodium acetate buffer of pH 4.5, temperature at 45 degreesC and 18 mg/L of dissolved oxygen concentration. Typical saturation enzyme kinetics were observed for enzymic polymerization using 1000 mg/L initial pyrogallol and 216 U/L enzyme. The initial dissolved oxygen consumption rate increased with temperature up to 45 degreesC, after which the rate decreased due to apparent enzyme denaturation. (C) 2004 Elsevier Ltd. All rights reserved.
Optimization of Biopolymerization Rate by Response Surface Methodology (Rsm)
(Elsevier Science inc, 2005) Aktas, N
Response surface methodology was successfully applied to enzymatic biopolymerization of catechol, which was conducted in a closed system containing acetone and sodium-acetate buffer, with laccase enzyme to produce poly(catechol). Laccase enzyme used as catalyst was derived from Trametes versicolor (ATCC 200801). The enzymatic biopolymerization rate of catechol, based on measurements of initial dissolved oxygen (DO) consumption rate in the closed system, was optimized by the application of response surface methodology (RSM). The independent variables, which had been found the most effective variables on the initial DO consumption rate by screening experiments, were determined as medium temperature, pH and acetone content. A quadratic model was developed through RSM in terms of related independent variables to describe the DO consumption rate as the response. Based on contour plots and variance analysis, optimum operational conditions for maximizing initial DO consumption rate, while keeping acetone content at its minimum value, were 31 degrees C. of temperature, pH 4.87 and acetone content of 13.5% to obtain 0.128 mg DO/min L for initial oxidation rate. The FT-IR spectrum of the poly(catechol) produced revealed that catechol units in the enzymaticaly produced polymer were combined with each other via ether linkage. (c) 2005 Elsevier Inc. All rights reserved.