METAL COMPLEXATION REACTIONS OF QUINOLONE ANTIBIOTICS IN A QUADRUPOLEION-TRAP

We have undertaken a systematic study of the nature of quinolone metal complexes formed by electrospray ionization and laser desorption/ion- molecule reactions to evaluate the analytical utility of metal complex ation as an alternative to conventional ionization via protonation. Me tal ionization with laser-desorbed copper and nickel ions results in a ddition products of the form (L + Cu+) and (L + Ni+), respectively, wh ere L is the quinolone, whereas addition-elimination products of the f orm (L + Co+ - 28) are observed when cobalt is used. The elimination o f CO in order to form this unusual latter product seems to be favored by the formation of a cyclized structure that is stabilized by intramo lecular hydrogen bonding. The CAD patterns of the Ni+ complexes prove to be the most structurally informative, more so than the fragmentatio n patterns of the protonated quinolones. Quinolone-metal complexes of the type [M(II)(L - H+)(dipy)](+), where M is either Cu, Co, or Ni and dipy is 2,2'-dipyridine, are generated by electrospray ionization of a methanolic solution containing a quinolone antibiotic, a transition metal ion salt, and an auxiliary diimine ligand. Upon collisional acti vation, the ESI-generated complexes dissociate predominantly by loss o f CO2, which is also the most common fragmentation pathway for the met al complexes formed through laser desorption/ion-molecule reactions. H owever, there are fewer structurally diagnostic fragment ions in the C AD spectra of the ESI complexes relative to those of the LD complexes.