Ternary complexes of the type AH???M
2+???L
– (AH = diol, including diethylene and triethylene glycol, M = Ca, Mn, Fe, Co, Ni, Cu and Zn and auxiliary anion ligand L
– = CH
3COO
–, HCOO
– and Cl
–) have been generated in the gas phase by MALDI and ESI, and their dissociation characteristics have been obtained. Use of the auxiliary ligands enables the complexation of AH with the divalent metal ion without AH becoming deprotonated, although A
–???M
2+ is often also generated in the ion source or after MS/MS. For M = Ca, dissociation occurs to AH + M
2+???L
– and/or to A
–???M
2+ + LH, the latter being produced from the H‐shifted isomer A
–???M
2+???LH. For a given ligand L
–, the intensity ratio of these processes can be interpreted (barring reverse energy barriers) in terms of the quantity
PA(A
–) –
Caaff(A
–), where
PA is the proton affinity and
Caaff is the calcium ion affinity. Deuterium labeling shows that the complex ion HOCH
2CH
2OH???Zn
2+???
–OOCCH
3, in addition to losing acetic acid (60 Da), also eliminates glycolaldehyde (HOCH
2CH=O, also 60 Da); it is proposed that these reactions commence with a hydride ion shift to produce the ion–dipole complex HOCH
2CHOH
+??? HZnOOCCH
3, which then undergoes proton transfer and dissociation to HOCH
2CH=O + HZn
+???O = C(OH)CH
3. In this reaction, ethylene glycol is oxidized by consecutive hydride ion and proton shifts. A minor process leads to loss of the isomeric species HOCH=CHOH. Copyright © 2012 John Wiley & Sons, Ltd.
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