Development of amphiphile 4-armed PEO-based Ti4+ complex for highly selective enrichment of phosphopeptides.

Protein phosphorylation is a reversible and important post-translational modification. Identification of phosphopeptides without enrichment is difficult for the low-abundance of phosphopeptides in real complex biological samples. Therefore, the effective and selective concentration of phosphopeptides prior to proteomic identification by mass spectrometer is necessary. In this study, we synthesized a novel titanium-based immobilized metal ion affinity chromatography material for highly selective enrichment of phosphopeptides. To improve material hydrophilia to the maximum extent, titanium ions were immobilized on the 4-armed Poly(ethylene oxide)(4µ-PEO-Ti4+), a totally soluble polymer with large molecular weight (20000 g/mol). The 4µ-PEO-Ti4+ was used to enrich phosphopeptides from tryptic digests of standard proteins and real complex biological samples, followed by MALDI-TOF MS analysis. In enrichment of phosphopeptides from 4 pmol ß-casein, the 4µ-PEO-Ti4+ performed the best property with starting material of 99-132 µg, loading buffer of 50% ACN/5% TFA (v/v), elution buffer of 10% NH3·H2O (v/v) and elution time of 30 min. The 4µ-PEO-Ti4+ has a superior detection sensitivity as low as 2 fmol for phosphopeptides. The high selectivity of 4µ-PEO-Ti4+ allows a deep enrichment of phosphopeptides of ß-casein from a mixture with BSA of 1000-fold abundant. The 4µ-PEO-Ti4+ shows great stability and endurability and can be recycled up to at least 5 times. In addition, 4µ-PEO-Ti4+ could detect 10 and 15 phosphopeptides from non-fat milk and nonenzymatic human saliva, respectively. In total, 4µ-PEO-Ti4+ is a novel excellent material which shows great sensitive and selective enrichment of low-abundance phosphopeptides in real complex biological samples.

[Direct determination of Nb in titanium oxide using slurry sample introduction by axial viewing inductively coupled plasma optical emission spectrometry].

By using dispersant polyacrylate amine (NH4PAA) to disperse TiO2, effects of different dispersants, pH value and the amount of dispersant on TiO2 slurry were investigated. The pH value of the medium and the dispersant amount were optimized, and a stable and homogeneous suspension was prepared. Nb in TiO2 was determined by an axial viewing ICP-OES spectrometer. At the same time, the performance of the axial viewing ICP-OES using solid powder analysis was discussed. Under the optimum experimental conditions, the detection limit of the present method is 3.0 microg x L(-1) and the RSD is 3.1% (n = 3, c = 0.3 mg x L(-1)).

SnO2@Poly(HEMA-co-St-co-VPBA) core-shell nanoparticles designed for selectively enriching glycopeptides followed by MALDI-MS analysis.

The core-shell boronic-acid functionalized nanoparticles SnO(2)@Poly(HEMA-co-St-co-VPBA) are designed for selectively enriching glycopeptides, followed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis. Such 60 nm sized core-shell nanoparticles are prepared by means of copolymerization between 2-hydroxyethyl methacrylate (HEMA) grafted on SnO(2) nanoparticles, styrene, and 4-vinylphenylboronic acid (VPBA). All of the synthesis procedures are completed within 3 h. Cyclic boronate esters form between boronic-acid groups on the polymer chains and cis-diol groups on glycopeptides, and thus almost all intact glycopeptides from low-abundant horseradish peroxidase (HRP) and bovine asialofetuin (ASF) are enriched with high selectivity and efficiency. After enrichment, both intact N- and O-glycopeptides are characterized by multistage MS. Furthermore, we successfully apply this method to the human serum sample for characterizing the target glycoproteins haptoglobin and alpha-1-acid-glycoprotein. The present selective enriching method followed by multistage-MS analysis is proven to be a good choice for routine glycopeptide characterization.