Development of dual-ligand titanium (IV) hydrophilic network sorbent for highly selective enrichment of...

A hydrophilic metal-organic network based on Ti⁴⁺ and dual natural ligand, tannic acid (TA) and phytic acid (PA), has been developed to enrich phosphopeptides from complex bio-samples prior to liquid chromatography-mass spectrometric analysis. Due to the strong chelation ability of TA and PA, abundant Ti⁴⁺ can be immobilized in the material, forming hydrophilic network by one-step coordination-driven self-assembly approach. The sorbent, TA-Ti-PA@Fe₃O₄, exhibited satisfactory selectivity for the phosphopeptides in the tryptic digest of β-casein, and can eliminate the interference components in 1000-fold excess of bovine serum albumin. The adsorption capacity of the sorbents for phosphopeptides was up to 35.2 mg g^-1 and the adsorbing equilibrium can be reached in 5 min. The adsorbing mechanism has been investigated and the results indicated that the Ti⁴⁺ in forms of [Ti(f-TA)(H₂O)₄]²⁺, [Ti(f-PA)(H₂O)₄]²⁺ and Ti(f-PA)₂(H₂O)₂ may play an important role in the adsorption process. The sorbent of the TA-Ti-PA@Fe₃O₄ has been applied to enrichment of the phosphopeptides in tryptic digest of rat liver lysate, and 3408 phosphopeptides have been identified, while the numbers of the identified phosphopeptides were 2730 and 1217 when the sample was enriched by the commercial TiO₂ and Fe³⁺-IMAC kit, respectively. This work provides a strategy to enrich phosphopeptides from complex samples and shows great potential application in phosphoproteome research.