title: Immobilization of lipases on alkyl silane modified magnetic nanoparticles: effect of alkyl chain length on enzyme activity.
abstract: BACKGROUND
  Biocatalytic processes often require a full recycling of biocatalysts to optimize economic benefits and minimize waste disposal. Immobilization of biocatalysts onto particulate carriers has been widely explored as an option to meet these requirements. However, surface properties often affect the amount of biocatalysts immobilized, their bioactivity and stability, hampering their wide applications. The aim of this work is to explore how immobilization of lipases onto magnetite nanoparticles affects their biocatalytic performance under carefully controlled surface modification.
  
  
  RESULTS
  Magnetite nanoparticles, prepared through a co-precipitation method, were coated with alkyl silanes of different alkyl chain lengths to modulate their surface hydrophobicity. Candida rugosa lipase was then directly immobilized onto the modified nanoparticles through hydrophobic interaction. Enzyme activity was assessed by catalytic hydrolysis of p-nitrophenyl acetate. The activity of immobilized lipases was found to increase with increasing chain length of the alkyl silane. Furthermore, the catalytic activities of lipases immobilized on trimethoxyl octadecyl silane (C18) modified Fe(3)O(4) were a factor of 2 or more than the values reported from other surface immobilized systems. After 7 recycles, the activities of the lipases immobilized on C18 modified nanoparticles retained 65%, indicating significant enhancement of stability as well through hydrophobic interaction. Lipase immobilized magnetic nanoparticles facilitated easy separation and recycling with high activity retaining.
  
  
  CONCLUSIONS
  The activity of immobilized lipases increased with increasing alkyl chain length of the alkyl trimethoxy silanes used in the surface modification of magnetite nanoparticles. Lipase stability was also improved through hydrophobic interaction. Alkyl silane modified magnetite nanoparticles are thus highly attractive carriers for enzyme immobilization enabling efficient enzyme recovery and recycling.
authors.affiliation: State Key Laboratory of Heavy Oil Processing and Centre for Bioengineering and Biotechnology, China University of Petroleum (East China), Qingdao, China.
authors.forename: Jiqian
authors.initials: J
authors.lastname: Wang
authors.forename: Gang
authors.initials: G
authors.lastname: Meng
authors.forename: Kai
authors.initials: K
authors.lastname: Tao
authors.forename: Min
authors.initials: M
authors.lastname: Feng
authors.forename: Xiubo
authors.initials: X
authors.lastname: Zhao
authors.forename: Zhen
authors.initials: Z
authors.lastname: Li
authors.forename: Hai
authors.initials: H
authors.lastname: Xu
authors.forename: Daohong
authors.initials: D
authors.lastname: Xia
authors.forename: Jian R
authors.initials: JR
authors.lastname: Lu
mesh_terms: D002384:Catalysis; D004800:Enzymes, Immobilized / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry; D052203:Ferrosoferric Oxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008049:Lipase / Q000737:chemistry* / Q000378:metabolism; D008280:Magnetics; D053768:Metal Nanoparticles / Q000737:chemistry; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry*; D011485:Protein Binding; D012821:Silanes / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D004800:Enzymes, Immobilized; D005290:Ferric Compounds; D012821:Silanes; C000499:ferric oxide; D008049:Lipase; D052203:Ferrosoferric Oxide