An On‐Tissue Paternò–Büchi Reaction for Localization of Carbon–Carbon Double Bonds in Phospholipids and Glycolipids by Matrix‐Assisted Laser‐Desorption–Ionization Mass‐Spectrometry Imaging

Abstract

Matrix‐assisted laser desorption ionization mass spectrometry imaging (MALDI‐MSI) visualizes the distribution of phospho‐ and glycolipids in tissue sections. However, C=C double‐bond (db) positional isomers generally cannot be distinguished. Now an on‐tissue Paternò–Büchi (PB) derivatization procedure that exploits benzaldehyde as a MALDI‐MSI‐compatible reagent is introduced. Laser‐induced postionization (MALDI‐2) was used to boost the yields of protonated PB products. Collision‐induced dissociation of these species generated characteristic ion pairs, indicative of C=C position, for numerous singly and polyunsaturated phospholipids and glycosphingolipids in mouse brain tissue. Several db‐positional isomers of phosphatidylcholine and phosphatidylserine species were expressed with highly differential levels in the white and gray matter areas of cerebellum. Our PB‐MALDI‐MS/MS procedure could help to better understand the physiological role of these db‐positional isomers.

Imaging and Analysis of Isomeric Unsaturated Lipids through Online Photochemical Derivatization of Carbon–Carbon Double Bonds**

“…A complementary distribution of the 9Δ isomer is shown in Figure 4 d. These results are consistent with previous studies [5, 22–24] . MS 2 I of the characteristic fragments of the isobaric PE 40:6 at m / z 771.5 and PE 42:9 at m / z 673.5 present in the same isolation window are shown in Figures 4 f,g, respectively.…”

“…Alternatively, derivatization methods including Paternò‐Büchi, [15, 16] ozonolysis, [17, 18] epoxidation, [4, 19, 20] and thiol‐ene [21] reactions have been used for the untargeted analysis of the double bond in unsaturated lipids thereby dramatically expanding the depth of molecular coverage obtained in lipidomics experiments. When coupled with mass spectrometry imaging (MSI), these approaches reveal the spatial localization of isomeric lipids in biological systems otherwise invisible with traditional MSI techniques [5, 22–24] …”

Identification of Double Bond Position Isomers in Unsaturated Lipids by m-CPBA Epoxidation and Mass Spectrometry Fragmentation

“…The oxetane ring could be cleaved upon MS fragmentation to yield diagnostic ion pair for carbon–carbon double bond localization. P–B strategy has been rapidly applied into multiple types of lipid analysis on both electrospray ionization (ESI) − and matrix-assisted laser desorption/ionization (MALDI) instrument platforms. However, the conversion of P–B reactions is limited.…”

Imaging mass spectrometry reveals complex lipid distributions across Staphylococcus aureus biofilm layers

“…These approaches provide quantitation of the overall lipid content, but come at the expense of spatial information that is especially important in biofilm formation. Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) [22] is a technology that is effective for mapping hundreds-to-thousands of molecules, including small metabolites [23] , [24] , glycans [25] , [26] , [27] , lipids [28] , [29] , peptides [30] , [31] and intact proteins [32] , [33] in tissue at biologically-relevant spatial resolutions [22] , [34] . The ability to interrogate molecular distributions within bacterial communities by MALDI IMS has been previously demonstrated for a wide range of microbial molecules including phenol-soluble modulins [35] , [36] , [37] , metabolites [35] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] , oligosaccharides [46] and some lipids [40] , [41] , [46] , [47] , [48] .…”