Enantioselective separation of chiral aromatic amino acids with surface functionalized magnetic nanoparticles

Chiral resolution aromatic amino acids, dl-tryptophan (dl-Trp), dl-phenylalanine (dl-Phe), dl-tyrosine (dl-Tyr) from phosphate buffer solution was achieved in present study employing the concept of selective adsorption by surface functionalized magnetic nanoparticles (MNPs). Surfaces of magnetic nanoparticles were functionalized with silica and carboxymethyl-β-cyclodextrin (CMCD) to investigate their adsorption resolution characteristics. Resolution of enantiomers from racemic mixture was quantified in terms of enantiomeric excess using chromatographic method. The MNPs selectively adsorbed l-enantiomers of dl-Trp, dl-Phe, and dl-Tyr from racemic mixture and enantiomeric excesses (e.e.) were determined as 94%, 73% and 58%, respectively. FTIR studies demonstrated that hydrophobic portion of enantiomer penetrated into hydrophobic cavity of cyclodextrin molecules to form inclusion complex. Furthermore, adsorption site was explored using XPS and it was revealed that amino group at chiral center of the amino acid molecule formed hydrogen bond with secondary hydroxyl group of CMCD molecule and favorability of hydrogen bond formation resulted in selective adsorption of l-enantiomer. Finally, stability constant (K) and Gibbs free energy change (−ΔG°) for inclusion complexation of CMCD with l-/d-enantiomers of amino acids were determined using spectroflurometry in aqueous buffer solution. Higher binding constants were obtained for inclusion complexation of CMCD with l-enantiomers compared to d-enantiomers which stimulated enantioselective properties of CMCD functionalized magnetite silica nanoparticles.