title: Electrocatalytic features of a heme protein attached to polymer-functionalized magnetic nanoparticles.
abstract: Direct electron-transfer and electrocatalytic kinetics of covalently attached myoglobin (MB) films on magnetic nanoparticles (MB-MNP(covalent)), in comparison to the corresponding physisorbed films and individual components, are reported for the first time. MB-MNP(covalent) ("-" denotes a covalent linkage) was adsorbed onto a cationic poly(ethyleneimine) layer (PEI) coated high-purity graphite (HPG) electrode. Similarly, films of myoglobin physisorbed on magnetic nanoparticles (MB/MNP(adsorbed), "/" denotes a noncovalent nature), only MB, or only MNP were constructed on HPG/PEI electrodes for comparison. The observed electron-transfer rate constants (k(s), s(-1)) were in the following order: MB-MNP(covalent) (69 ± 6 s(-1)), MB/MNP(adsorbed) (37 ± 2 s(-1)), only MB (27 ± 2 s(-1)), and only MNP (16 ± 3 s(-1)). The electrocatalytic properties of these films were investigated with the aid of tert-butylhydroperoxide as a model reactant, and its reduction kinetics were examined. We observed the following order of catalytic current density: MB-MNP(covalent) > MB/MNP(adsorbed) > only MNP > only MB, in agreement with the electron-transfer (ET) rates of MB-MNP(covalent) and MB/MNP(adsorbed) films. The crucial function of MNP in favorably altering the direct ET and electrocatalytic properties of both covalently bound MB and physisorbed MB molecules are discussed. In addition, the occurrence of a highly enhanced electron-hopping mechanism in the designed covalent MB-MNP(covalent) films over the corresponding physisorbed MB/MNP(adsorbed) film is proposed. The enhanced electron-transfer rates and catalytic current density suggest the advantages of using metalloenzymes covalently attached to polymer-functionalized magnetic nanoparticles for the development of modern highly efficient miniature biosensors and bioreactors.
authors.affiliation: Department of Chemistry, Oklahoma State University , Stillwater, Oklahoma 74078, United States.
authors.forename: Sadagopan
authors.initials: S
authors.lastname: Krishnan
authors.forename: Charuksha
authors.initials: C
authors.lastname: Walgama
mesh_terms: D000818:Animals; D055664:Electrochemical Techniques / Q000379:methods*; D006420:Hemeproteins / Q000737:chemistry* / Q000378:metabolism; D006736:Horses; D008280:Magnetics / Q000379:methods*; D053758:Nanoparticles / Q000737:chemistry* / Q000378:metabolism; D011108:Polymers / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D006420:Hemeproteins; D011108:Polymers