title: Manganese peroxidase degrades pristine but not surface-oxidized (carboxylated) single-walled carbon nanotubes.
abstract: The transformation of engineered nanomaterials in the environment can significantly affect their transport, fate, bioavailability, and toxicity. Little is known about the biotransformation potential of single-walled carbon nanotubes (SWNTs). In this study, we compared the enzymatic transformation of SWNTs and oxidized (carboxylated) SWNTs (O-SWNTs) using three ligninolytic enzymes: lignin peroxidase, manganese peroxidase (MnP), and laccase. Only MnP was capable of transforming SWNTs, as determined by Raman spectroscopy, near-infrared spectroscopy, and transmission electron microscopy. Interestingly, MnP degraded SWNTs but not O-SWNTs. The recalcitrance of O-SWNTs to enzymatic transformation is likely attributable to the binding of Mn2+ by their surface carboxyl groups at the enzyme binding site, which inhibits critical steps in the MnP catalytic cycle (i.e., Mn2+ oxidation and Mn3+ dissociation from the enzyme). Our results suggest that oxygen-containing surface functionalities do not necessarily facilitate the biodegradation of carbonaceous nanomaterials, as is commonly assumed.
authors.affiliation: College of Environmental Science and Engineering/Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria/Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University , Tianjin 300071, People's Republic of China.
authors.forename: Chengdong
authors.initials: C
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Pedro J J
authors.initials: PJ
authors.lastname: Alvarez
mesh_terms: D001665:Binding Sites; D055162:Biocatalysis; D002264:Carboxylic Acids / Q000737:chemistry*; D006418:Heme / Q000378:metabolism; D042845:Laccase / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared; D013059:Spectrum Analysis, Raman; D013379:Substrate Specificity; D013499:Surface Properties
chemical_list: D002264:Carboxylic Acids; D037742:Nanotubes, Carbon; D006418:Heme; D008345:Manganese; D042845:Laccase; D010544:Peroxidases; C042858:lignin peroxidase; C051129:manganese peroxidase