title: Effect of N-doping of single-walled carbon nanotubes on bioelectrocatalysis of laccase.
abstract: Nondoped and N-doped SWCNTs (N-SWCNTs) were used to clarify the effect of N-doping on a direct electron transfer (DET) reaction of laccase (Lac, from Trametes sp.). The level of N-doping in the carbon phase of the N-SWCNTs, which were synthesized by a CVD method, was determined to be 0.1, 2.4, and 4.1% from X-ray photoelectron spectroscopy measurements. The N-SWCNTs were also carefully characterized using electron microscopy, Brunauer-Emmett-Teller (BET) specific surface area measurements, Raman spectroscopy, and electrochemistry. The bioelectrocatalytic current for the DET reaction of Lac immobilized onto the N-SWCNTs tended to decrease with increasing N dopant ratio, whereas the amount of Lac adsorbed per BET surface area of the N-SWCNTs did not depend on the N dopant ratio. There were two main explanations for this behavior. First, an electrostatic interaction between the positively charged interface of the N-SWCNTs due to nitrogen species surface functional groups and the negative charges of carboxylate residues surrounding the T1 site. Second, the surface potential of the N-SWCNTs during Lac modification, because the slope value of the surface potential versus N dopant ratio of the N-SWCNTs was about 53 mV/N%. From additional investigations into the surface potential effect and thermodynamic investigations, we carefully concluded that the above behaviors may be due to denaturation and/or decreasing of the DET reaction rate caused by the strong electrostatic interaction between Lac and the N-SWCNTs surface.
authors.affiliation: Graduate School of Science and Technology, Kumamoto University , 2-39-1 Kurokami Chuo-ku, Kumamoto 860-8555, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Tominaga
authors.forename: Makoto
authors.initials: M
authors.lastname: Togami
authors.forename: Masayuki
authors.initials: M
authors.lastname: Tsushida
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kawai
mesh_terms: D002384:Catalysis; D004800:Enzymes, Immobilized; D042845:Laccase / Q000737:chemistry*; D008958:Models, Molecular; D037742:Nanotubes, Carbon / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D004800:Enzymes, Immobilized; D037742:Nanotubes, Carbon; D042845:Laccase