Evidence for gas-phase redox chemistry inducing novel fragmentation in a complex natural product.

The fragmentation of monensin A, in the presence of calcium, barium, silver and copper salts was studied by electrospray ionisation tandem accurate-mass mass spectrometry. The results showed that the calcium, barium and silver complexes of monensin A showed no significant alteration in their fragmentation to that previously observed for the sodium salts. However, the fragmentation of the copper(ii) salt resulted in new fragmentation routes. We propose that the copper might be initiating a novel gas-phase redox reaction resulting in a series of highly diagnostic ions. This methodology is demonstrated by locating the change in structure between the naturally occurring analogues monensin A and B.