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 complexation as an alternative to conventional ionization via protonation. Metal ionization with laser-desorbed copper and nickel ions results in addition products of the form (L + Cu+) and (L + Ni+), respectively, where L is the quinolone, whereas addition-elimination products of the form (L + Co(+)-28) are observed when cobalt is used. The elimination of CO in order to form this unusual latter product seems to be favored by the formation of a cyclized structure that is stabilized by intramolecular hydrogen bonding. The CAD patterns of the Ni+ complexes prove to be the most structurally informative, more so than the fragmentation patterns of the protonated quinolones. Quinolone-metal complexes of the type [MII(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 activation, the ESI-generated complexes dissociate predominantly by loss of CO2, which is also the most common fragmentation pathway for the metal complexes formed through laser desorption/ion-molecule reactions. However, there are fewer structurally diagnostic fragment ions in the CAD spectra of the ESI complexes relative to those of the LD complexes.

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For a series of polyether/transition metal ion complexes, collisionally activated dissociation reactions that are mediated by the flexibility of the polyether and the number of coordination sites are reported. The metal ions are generated by a pulsed laser desorption technique, and collision-activated dissociation methods are used to characterize the structures of the resulting metal/polyether complexes. The CAD patterns for the different polyether/metal ion complexes show striking variations depending on the flexibility of the ether, its number of coordination sites, and the type of metal ion. For example, (18-crown-6 + Co+) dissociates by loss of CHCH• or C2H3O• radicals, each pathway in conjunction with multiple losses of C2H4O, and resulting in products incorporating one covalent or ionic bond between the Co+ ion and the crown ether. In contrast, (12-crown-4 + Co+) dissociates by loss of CH2CH2 or C2H4O closed shell neutrals, each pathway in conjunction with additional losses of C2H4O and resulting in products that incorporate no covalent bonds to Co+. The polyether/Ni+ complexes show dissociation behavior that is similar to that observed for the Co+ complexes, but the polyether/Cu+ complexes show uniform dissociation trends that seem to be independent of the flexibility and number of coordination sites of the ether. These differences are rationalized based on the nature of the metal ion, and both the flexibility of the crown ether and its number of coordinating sites, factors which affect the geometry during coordination of the metal ion. This idea is supported by comparative dissociation reactions of metal complexes containing acyclic polyethers (glymes) which have more flexible structures. MS/MS/MS experiments and CAD of complexes formed by model compounds offer support for the dissociation mechanisms.

The analysis of a targeted group of nucleoside antibiotics has been accomplished through the use of selective ion-molecule reactions and collision-activated dissociation (CAD) techniques in a quadrupole ion trap. A series of homologous ether reagent ions generated from dimethyl ether, di-n-butyl ether and 2-methoxyethanol were used as chemical ionization reagents. Because chemical ionization with dimethyl ether and di-n-butyl ether reagent ions did not provide selectivity and signal enhancement for the analysis of these biopharmaceuticals, a chemical ionization reagent with special hydrogen-bonding capabilities was used. The reagent ion that showed the greatest promise is a product of 2-methoxyethanol, CH,OCH,CH,OCH, +. This highly reactive species, which reacts selectively with nitrogen-containing compounds, can undergo both nucleophilic attack and anchoring via hydrogen bond formation between the methoxy oxygen and an acidic hydrogen of the nucleoside substrate. The reaction of the CH30CH,CH20CH,+ ion with each of the nucleoside antibiotics resulted in formation of ( M + 131' and [ M + 891 + products. The CAD spectra indicated that the adducts are covalently bound species and that the nucleotide moiety dominates both the reactive and dissociative behavior of the nucleoside antibiotics.

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