Development of immobilized Sn4+ affinity chromatography material for highly selective enrichment of phosphopeptides.

In this work, we first immobilized tin(IV) ion on polydopamine-coated magnetic graphene (magG@PDA) to synthesize Sn4+ -immobilized magG@PDA (magG@PDA-Sn4+ ) and successfully applied the material to highly selective enrichment of phosphopeptides. The material gathered the advantages of large surface area of graphene, superparamagnetism of Fe3 O4 , good hydrophilicity and biocompatibility of polydopamine, and strong interaction between Sn4+ and phosphopeptides. The enrichment performance of magG@PDA-Sn4+ toward phosphopeptides from digested β-casein at different concentrations, with and without added digested BSA was investigated and compared with magG@PDA-Ti4+ . The results showed high selectivity and sensitivity of the Sn4+ -IMAC material toward phosphopeptides, as good as the Ti4+ -IMAC material. Finally, magG@PDA-Sn4+ was applied to the analysis of endogenous phosphopeptides from a real sample, human saliva, with both MALDI-TOF MS and nano-LC-ESI-MS/MS. The results indicated that the as-synthesized Sn4+ -IMAC material not only has good enrichment performance, but also could serve as a supplement to the Ti4+ -IMAC material and expand the phosphopeptide coverage enriched by the single Ti4+ -IMAC material, demonstrating the broad application prospects of magG@PDA-Sn4+ in phosphoproteome research.