Pyrene-based covalent organic framework for selective enrichment of hydrophobic peptides with simultaneous proteins exclusion.

Owing to the desirable structures, covalent organic frameworks (COFs) have emerged as promising porous crystalline materials in bioanalytical and biomedical science. However, the application of their merits for analysis of hydrophobic peptides in complicated bio-samples has not been well investigated, possibly due to challenges in developing materials with high-specific binding effect of target peptides and accurate controllable pore-size for high selectivity. In this study, we proposed the size-exclusive peptide enrichment with Azo-COF constructed from 1,3,6,8-tetrabromopyrene (TBPy) building block and p-azoaniline linking units. The as-synthesized sieve-like COFs show high surface area together with accessible nanometer pore size (∼2.5 nm). With these advantages, specific enrichment of hydrophobic peptides using Azo-COF can be achieved by simply packing them in a 100 µL Axygen pipette tip. A maximum capacity of 36 mg g-1 for FGFGF was obtained, which is more than a magnitude order larger than those of hydrophilic peptides. Furthermore, this method was successfully applied in analysis of hydrophobic peptides in tryptic digest of proteins and real human serum samples, indicating that the proposed method is promising for high-selective peptides enrichment from complex biological samples, and is of great value for further application of the functional materials in bioanalysis.

TiO2-modified fibrous core-shell mesoporous material to selectively enrich endogenous phosphopeptides with proteins exclusion prior to CE-MS analysis.

As an important post-translational modification of proteins, phosphorylation plays a key role in regulating a variety of complicated biological reactions. Owing to the fact that phosphopeptides are low abundant and the ionization efficiency could be suppressed in mass spectroscopic detection, highly efficient and selective enrichment methods are essential to identify protein phosphorylation by mass spectrometry. Here, we develop novel titanium oxide coated core shell mesoporous silica (CSMS@TiO2) nanocomposites for enrichment of phosphopeptides with simultaneous exclusion of massive proteins. The CSMS@TiO2 nanocomposites have essential features, including uniform 1.0 µm diameter, 120 nm thick shell, 7.0 nm mesopores perpendicular to the surface, large surface area of 77 m2/g and pore volume of 0.15 cm3/g, therefore can greatly improve the sensitivity for identifying phosphopeptides by capillary electrophoresis-mass spectrometry. The proposed CSMS@TiO2 nanocomposites are applied for analysis of ß-casein tryptic digest and bovine serum albumin (BSA) protein mixture, respectively. The results show that the number of phosphopeptides detected is tremendously increased by using CSMS@TiO2 nanocomposite, proving selectively enriching phosphopeptides due to the size-exclusive and specific interaction of the TiO2-modified mesopores. The enrichment of the phosphopeptides is achieved even for the digests at very low concentration of ß-casein (1 fmol/µL). This research would open up a promising idea to utilize mesoporous materials in peptidomics analysis.