Unimolecular dissociation characteristics of cationic complexes between nicotinic acid and Cu(II) and Ni(II)

Cu2+ and Ni2+ form dimeric ML(L-H)(+) complexes with nicotinic acid (M = Cu, Ni; L= nicotinic acid) upon electrospray ionization. Quantum chemical calculations indicate thermochemical preference for coordination of the carboxylate groups rather than the ring nitrogens to the central metal ion in both cases. In analogy to the dimeric metal complexes of amino acids the primary dissociation reaction upon collisional activation of ML(L-H)(+) is the loss of CO2 in both cases. Further dissociation of the decarboxylated species show preference for loss of a 3-pyridinyl radical for M = Cu and NiCO2 for M = Ni. This can be understood in light of the redox properties of the two metals and from previous studies of similar complexes with amino acids. Loss of the pyridinyl radical bonded to the carboxylate group in these cationic entities does not lead to M(eta(2)-O2C) structures previously observed for similar anionic metal species. (C) 2013 Elsevier B.V. All rights reserved.