title: Fatty acid neutral losses observed in tandem mass spectrometry with collision-induced dissociation allows regiochemical assignment of sulfoquinovosyl-diacylglycerols.
abstract: A full characterization of sulfoquinovosyldiacylglycerols (SQDGs) in the lipid extract of spinach leaves has been achieved using liquid chromatography/electrospray ionization-linear quadrupole ion trap mass spectrometry (MS). Low-energy collision-induced dissociation tandem MS (MS/MS) of the deprotonated species [M - H](-) was exploited for a detailed study of sulfolipid fragmentation. Losses of neutral fatty acids from the acyl side chains (i.e. [M - H - RCOOH](-)) were found to prevail over ketene losses ([M - H - R'CHCO](-)) or carboxylates of long-chain fatty acids ([RCOO](-)), as expected for gas-phase acidity of SQDG ions. A new concerted mechanism for RCOOH elimination, based on a charge-remote fragmentation, is proposed. The preferential loss of a fatty acids molecule from the sn-1 position (i.e. [M - H - R(1)COOH](-)) of the glycerol backbone, most likely due to kinetic control of the gas-phase fragmentation process, was exploited for the regiochemical assignment of the investigated sulfolipids. As a result, 24 SQDGs were detected and identified in the lipid extract of spinach leaves, their number and variety being unprecedented in the field of plant sulfolipids. Moreover, the prevailing presence of a palmitic acyl chain (16:0) on the glycerol sn-2 position of spinach SQDGs suggests a prokaryotic or chloroplastic path as the main route for their biosynthesis.
authors: Dipartimento di Chimica, Università degli Studi di Bari Aldo Moro, Campus Universitario, Via E. Orabona, 4-70126, Bari, Italy.
authors: Rosalia
authors: R
authors: Zianni
authors: Giuliana
authors: G
authors: Bianco
authors: Filomena
authors: F
authors: Lelario
authors: Ilario
authors: I
authors: Losito
authors: Francesco
authors: F
authors: Palmisano
authors: Tommaso R I
authors: TR
authors: Cataldi
mesh_terms: D005227:Fatty Acids / Q000737:chemistry*; D006017:Glycolipids / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D018515:Plant Leaves / Q000737:chemistry; D018724:Spinacia oleracea / Q000737:chemistry; D013237:Stereoisomerism; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D005227:Fatty Acids; D006017:Glycolipids; D008055:Lipids; C015518:sulfolipids; C013694:sulfoquinovosyl diglyceride