Letter:: Collision-induced dissociation of [Metal(L)2]2+ complexes (Metal = Cu, Ca and Mg) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine allows distinction of the acyl groups at the sn1 and sn2 positions

The collision-induced dissociation (CID) spectra of the divalent metal complexes of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, [Metal(II)(L)(2)](2+) (where Metal=Cu2+, Mg2+ and Ca2+, L= [16:0/18: 1GPCho]), formed by electrospray ionization, reveal interesting metal dependent fragmentation chemistry. Six main classes of reaction are observed corresponding to: two competing carboxylate abstraction pathways (from the sn1 and sn2 positions); phosphate abstraction; competing losses of the two different carboxylic acids from the sn1 and sn2 positions; loss of a protonated ligand, [L + H](+). The relative ratios of the competing carboxylate abstraction reactions are dependent on the metal, with the Cu and Ca complexes favoring the abstraction of the larger carboxylate (18: 1) and the Mg complex favoring the abstraction of the smaller carboxylate (16: 0).