The Application Of Metal-Organic Frameworks In The Detection Of Quercetin And Phosphopeptides By MALDI-MS

Over the last several decades,matrix-assisted laser desorption/ionization mass spectrometry?MALDI-MS?has become a powerful analytical technique for the analysis of high molecular weight biomolecules,with its many advantages including easy sample preparation,high sensitivity,intact molecular ion peaks and wide detection range.Metal-organic frameworks?MOFs?are a novel class of crystalline porous materials consisting of metal ions as connectors and organic ligands as linkers,which possess high porosity and large surface area.In addition,the alterable functional groups and the coordinately unsaturated sites of MOFs have also attracted much attention.In this paper,MIL-101?Cr?and MIL-101?Fe?were used as matrix and enrichment material for detection of quercetin and phosphopeptides analysis in MALDI-MS.The detailed results are summarized as follow:MIL-101?Cr?as matrix for sensitive detection of quercetin by matrix-assisted laser desorption/ionization mass spectrometry.Matrix-assisted laser desorption/ionization mass spectrometry?MALDI-MS?has been proven as a useful and advanced technique in the identification of polymers and proteins.However,MALDI-MS still has the unavoidable drawback of self-signal interference with traditional organic matrices,which could suppress and overlap with the analyte signals in the low-mass region.In this work,MIL-101?Cr?,a kind of metal-organic frameworks which possess high molecular weight,?-conjugated 3-D structure,coordinately unsaturated chromium sites?CUS?and strong absorption in the UV range,was employed to replace traditional organic matrices,and it was found that MIL-101?Cr?can dramatically eliminate the background peaks,showing high signal-to-noise level in the analysis of small molecules.As proof-of-concept,quercetin,daidzein,genistein and naringenin,members of flavonol family which widely exists in food and natural products,were successfully determined by utilizing MIL-101?Cr?as the surface-assisted matrix,and the detection of quercetin was sensitive with good salt tolerance and reproducibility.Under optimal conditions,the mass peak intensity exhibited good linear relationships in the range from 0.25 ?g/mL-7.00 ?g/mL for quercetin?R2=0.996?with detection li mit 2.11 ng/mL?3?/k?,making the identification of quercetin in sophora japonica successfully.With this strategy we have demonstrated the potentiality of MIL-101?Cr?nanomaterials as MALDI-MS matrix for the detection of small molecules.Fe₃O₄/MIL-101?Fe?composites for phosphopeptides enrichment and MALDI-MS analysis.Phosphospecific enrichment techniques and mass spectrometry?MS?are primary tools for comprehending the cellular phosphoproteome.In this work,a rational and extremely facile route to synthesize the magnetic metal-organic frameworks?mMOFs?was employed and the prepared composite was first utilized as a "bait" for selective enrichment of phosphopeptides.Typically,the mMOFs was synthesized via electrostatic self-assembly between the negatively charged Fe₃O₄ magnetic nanoparticles?MNPs?and positively charged MIL-101?Fe?.The obtained Fe₃O₄/MIL-101?Fe?composite possessed well-defined structures,rough surface,highly specific surface area and excellent magnetic property.To demonstrate the ir ability for enrichment of phosphopeptides,we applied Fe₃O₄/MIL-101?Fe?as a "bait" to capture the phosphopeptides from standard protein digestion and practical samples.The enriched phosphopeptides were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry?MALDI-TOF MS?.The MS results show that the Fe₃O₄/MIL-101?Fe?exhibits superior enrichment performance for phosphopeptides with low detectable concentration assessed to be 8 fmol,selectivity investigated to be 1:1000 using ?-casein/bovine serum albumin mixture and enrichment recovery evaluated to be 89.8%.Based on these excellent properties,the prepared composite was used to enrich the phosphopeptides from tilapia eggs biological samples for the first time.A tota l number of 51 phosphorylation sites were identified from the digest of tilapia eggs proteins,suggesting the excellent potential of Fe₃O₄/MIL-101?Fe?composite in the practical application.