Adsorption of chiral aromatic amino acids onto carboxymethyl-β-cyclodextrin bonded Fe3O4/SiO2 core-shell nanoparticles

Abstract

Surface of magnetic silica nanoparticles is modified by grafting with carboxymethyl-β-cyclodextrin (CM-β-CD) via carbodiimide activation. The functionalized magnetic core-shell nanoparticles (MNPs) are characterized by Transmission Electron Microscopy (TEM), Fourier Transform Infra Red (FTIR) spectroscopy, X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Vibrating Sample Magnetometer (VSM). These nano-sized particles are scrutinized for adsorption of certain chiral aromatic amino acid enantiomers namely, d- and l-tryptophan (Trp), d- and l-phenylalanine (Phe) and d- and l-tyrosine (Tyr) from phosphate buffer solutions. Adsorption capacities of the coated magnetic nanoparticles toward amino acid enantiomers are in the order: l-Trp > l-Phe > l-Tyr and under the same condition, adsorption capacities are higher for l-enantiomers than the corresponding d-enantiomers. All the equilibrium adsorption isotherms are fitted well to Freundlich model. FTIR studies depict significant changes after adsorption of amino acids onto nanoparticles. The stretching vibration frequencies of N. H bonds of the amino acid molecules are changed with complex formation through host-guest interaction. The structure and hydrophobicity of amino acid molecules emphasize the interactions between amino acid molecules and the nano-adsorbents bearing cyclodextrin, thus play important roles in the difference of their adsorption behaviors. © 2010 Elsevier Inc.