Development of new lanthanide(iii) ion-based magnetic affinity materials for phosphopeptide enrichment

Abstract

Lanthanide(III) ion-based magnetic IMAC materials consisting of core–shell-like silica-coated magnetic nanoparticles as supporting materials, chelidamic acid as a chelating agent, and Ln³⁺ ions as metal ions were developed in this study. Magnetic nanoparticles in the core were prepared using the co-precipitation method and their surface was covered with a silica shell. The size, morphology as well as structural and magnetic properties of the synthesized nanoparticles were characterized by TEM, XRD, and VSM measurements, respectively. The spherical particles with a core–shell structure constitute a cubic magnetic Fe₃O₄ core with 8 ± 2 nm and an amorphous shell around it and their size was estimated as 120 ± 10 nm. The silica coating reduces the magnetization of the magnetic Fe₃O₄ nanoparticles in the core; however, it has been determined that this situation has little effect on the response time of the nanoparticles to the magnet in practical use. The spherical and core–shell-like silica-coated magnetic nanoparticles were modified with tridentate chelidamic acid, which is used as a chelating agent in such an IMAC material for the first time. The chelidamic acid modification was characterized by FTIR and TGA measurements and found to bind 5% (w/w) of chelidamic acid on the surface of silica-coated magnetic nanoparticles. To form Ln³⁺-Mag-IMAC materials, Er³⁺ and Dy³⁺ ions were coordinated on the surface in the final step, and their concentrations on the surface were determined as 2.99 ± 0.12 × 10⁻⁴ mol g⁻¹ and 2.80 ± 0.30 × 10⁻⁴ mol g⁻¹, respectively. The potential of the developed Ln³⁺-Mag-IMAC materials in the enrichment of phosphopeptides was modelled by phosphate adsorption studies in aqueous solution at 25 °C. It was found to have good phosphate adsorption capacity with a stoichiometry of ∼1.2 phosphate ions per Ln³⁺ ion present. The developed Ln³⁺-Mag-IMAC materials were applied on trypsin-digested β-casein solutions, and their phosphopeptide enrichment potential was determined by LC-MS/MS analysis.