| In recent years,the immbolization of protein onto solid surface has attracted many interests in biotechnology, materials and chemical field. Since protein are amphiphilic molecules which contain both positive and negative charges, it can adsorbed on any charged surface.Polyelectrolyte modified nanoparticles can interact with protein via electrostatic interaction,hydrophobic interaction,hydrogen bonding and other ligand interaction.Therefore,functionalized nanoparticles can be ideal candidate for protein separation,in vivo and in vitro biological monitoring and diagnostic field.Fe3O4 nanoparticles with a covalently bonded poly(methacryloyloxyethyl trimethyl ammonium chloride) (PMATAC) were prepared by surface initiated atom transfer radical polymerization(ATRP).Fe304 nano-clusters were embeded into polystyrene(PS) core by miniemulsion polymerization and then poly(2-aminoethyl ester hydrochloride)(PAEMH) chains grafted from the surface of PS particles under UV light.Interaction between proteins and the above nanaoparticles were studied under different pH and ionic strength. The main contents are as follows:(1) Fe3O4 nanoparticles were prepared by co-percipitation method using oleic acid (OA) as surfactant, then OA modified Fe3O4 nanoparticles were functionalized with ATRP initaitor via the combination of ligand exchange and condensation of 2-bromo-2-methyl-N-(3-trimethoxysiyl) propanamide(BMTP),poly(2-(methacryloxy) ethyltrimethyl ammonium chloride)were initiated on the surface of BMTP modified Fe3O4 nanoparticles by CuBr catalyzed atom transfer radical polymerization(ATRP).TEM image shows a narrow size distribution and no apparent aggregation. The length of the PMATAC chains are around 20 nm determined by DLS.The functionalized nanoparticles have great dispersibility and stability in water with a zata potential of 50 mV at pH 6.The copper catalyst can be removed under magnetic field, ICP showed the residual content of copper ion is 0.92 ppb,more than 99% copper complex are removed.(2) BLG is empolyed as model protein to investigate their interaction with PMATAC-Fe3O4 bruses.The pH and ionic strength dependence of phase state and binding affinity were examined by tubidimetric titration, dynamic light scattering(DLS),and isothermal titration calorimetry(ITC).Both turbidity and ITC show binding affinitites for BLG display a non-monotonic ionic strength dependence trend and a maxima appears at ionic strength of 50 mM.Such observation should arise from the protein charge anisotropy, visualized by DelPhi electrostatic modeling on proteins and the strong electrostatic replusion among NPs simultaneously during the interactions at a variety of ionic strengths.(3) The interaction between BSA and PMATAC-Fe3O4 were investigated following the characterization methods as above,the surface potential distributions of BSA and BLG are quite different, BSA lack dipole-like charge patch, so the pHc(onset of binding)shifts to large pH than BLG at the selected ionic strength.The sequence binding affinity and stoichometry of protein onto PMATAC-Fe3O4 was observed by ITC as BLG>BSA.Similar non-monotonic ionic strength dependence for the onset of binding was obseved for BSA and PMATAC-Fe3O4.(4) Magnetic spherical poly(2-aminoethyl methacrylate hydrochloride) brushes(MSPB-PAEMH) were prepared by a combination of miniemulsion polymerazation and photo-emulsion polymerazation.TGA shows the magnetic content are about 8% and the magnetic reponse are more quickly than a single magnetic nanoparticle. The MSPB-PAEMH consist of a polystyrene core embeded with magnetic nanoparticles with a diameter around 100 nm and a polyelectrolyte shell with a thickness about 30 nm.The effect of pH and ionic strength dependent interaction between BSA and MSPB-PAEMH were investigated by turbidimetric titration and dynamic light scaring(DLS), higher ionic strength could inhibit the BSA adsorption onto MSPB-PAEMH, SPBs with magnetic nanoparticles in the core become recyclable after the immobilization of proteins. |
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