Cofactor-specific covalent anchoring of cytochrome b 562 on a single-walled carbon nanotube by click chemistry †
Résumé
Redox-active cytochrome b 562 with a tethered azide group on the heme propionate side chain is covalently linked to an acetylene moiety introduced on the sidewall of a single-walled carbon nanotube (SWNT) by copper-catalyzed click chemistry forming a triazole ring with the heme active site directly linked to the SWNT. The cytochrome b 562 –SWNT hybrid is characterized by electrochemistry and atomic force microscopy. Interfacing redox-active enzymes with electrode materials is a key technology used in the development of high performance biosensors and biofuel cells. 1–3 Recent advances in carbon nanomaterials have enabled us to design hybrid systems with linked enzymes. Carbon nanotubes (CNTs), of the single-or multi-walled type, are promising building blocks for fabrication of hybrid materials. 4–8 CNTs have large surface areas, high strength, chemical stability, and attractive electronic properties. CNTs have also provided a wide variety of synthetic tools applicable for introduction of a range of substituents for linking the enzymes. A copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction is a widely utilized method used to form a covalent linkage which includes a triazole ring between building blocks containing azide and alkyne groups. 9,10 The CuAAC reaction has thus been used in organic synthesis, bio-conjugation chemistry, and surface chemistry. This powerful coupling reaction can be applied in efforts to efficiently tailor the chemical modication of single-walled CNTs (SWNTs) to construct hybrid materials 11–13 including enzymes. 14 Redox-active hemoproteins form a major class of enzymes that are useful for constructing enzyme-immobilized electrodes due to their diverse functions including electron transfer, catal-ysis, and sensing. 15–25 Many hemoproteins possess a replaceable heme b cofactor in the heme pocket, enabling immobilization on the electrode via the heme–heme pocket interaction. 26–45 In this paper, we demonstrate specically oriented covalent immobili-zation of azide-linked cytochrome b 562 (CYT) on the sidewall of SWNT using the CuAAC reaction (Fig. 1). The advantage of this method which uses a replaceable heme tethered to an azide moiety, lies in the wide range of applications for functionaliza-tion of wild-type hemoproteins. The characterization and elec-trochemical properties of the covalently-linked hybrid materials of SWNT and cytochrome b 562 are described. Fig. 1 (a) SWNT with covalently-linked cytochrome b 562 and (b) the preparation scheme using a copper-catalyzed azide–alkyne cyclo-addition (CuAAC) reaction.