Ethylene glycol assisted preparation of Ti4+-modified polydopamine coated magnetic particles with rough surface for capture of phosphorylated proteins

• Ti4+-rPDA@Fe3O4 with rough surface was synthesized by introduction of EG.
• The particles demonstrated good selectivity for phosphoproteins based on IMAC.
• The adsorption capacity of Ti4+-rPDA@Fe3O4 for κ-Cas was 1105.6 mg g−1.
• The particles were successfully applied for isolation of phosphoproteins in milk.

The reversible protein phosphorylation is very important in regulating almost all aspects of cell life, while the enrichment of phosphorylated proteins still remains a technical challenge. In this work, polydopamine (PDA) modified magnetic particles with rough surface (rPDA@Fe3O4) were synthesized by introduction of ethylene glycol in aqueous solution. The PDA coating possessing a wealth of catechol hydroxyl groups could serve as an active medium to immobilize titanium ions through the metal-catechol chelation, which makes the fabrication of titanium ions modified rPDA@Fe3O4 particles (Ti4+-rPDA@Fe3O4) simple and very convenient. The spherical Ti4+-rPDA@Fe3O4 particles have a surface area of 37.7 m2 g−1 and superparamagnetism with a saturation magnetization value of 38.4 emu g−1. The amount of Ti element in the particle was measured to be 3.93%. And the particles demonstrated good water dispersibility. The particles were used as adsorbents for capture of phosphorylated proteins and they demonstrated affinity and specificity for phosphorylated proteins due to the specific binding sites (Ti4+). Factors affecting the adsorption of phosphorylated proteins on Ti4+-rPDA@Fe3O4 particles were investigated. The adsorption capacity of Ti4+-rPDA@Fe3O4 particles for κ-casein was 1105.6 mg g−1. Furthermore, the particles were successfully applied to isolate phosphorylated proteins in milk samples, which demonstrated that Ti4+-rPDA@Fe3O4 particles had potential application in selective separation of phosphorylated proteins.

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