On-line Abstract Book

Counter-Ion Perturbation of the Fragmentation Pathways of Multiply Charged Anions: From Transition Metal Complexes to Biomolecular Ions

Ruth Mary Burke¹, William Edward Boxford¹, Caroline E. H. Dessent¹

Correspondence address: Ruth Mary Burke, University of York, Chemistry, Heslington, York, YO10 5DD United Kingdom.

Keywords: Collision Induced Dissociation (CID)/Collision Activated; Electrospray Ionization (ESI); Negative Ion; Salts.

Novel aspect: The first application of ESI-MS and resonance excitation within a quadrupole ion-trap to explore the ground-state potential energy surfaces of contact ion-pair complexes that contain multiply charged anions (MCAs).

 

We report the first application of ESI-MS and resonance excitation within a quadrupole ion-trap to explore the ground-state potential energy surfaces of contact ion-pair complexes that contain multiply charged anions (MCAs). Low energy excitation of model systems such as K⁺·Pt(CN)₄^2- and K⁺·Pt(CN)₆^2- results in fragmentation products associated with decay of the isolated constituent dianions, revealing that the ground state ion-pair surfaces are dominated by the intrinsic characteristics of the MCA. This observation is important since it indicates that counter-ion complexation only weakly perturbs the electronic structure of an MCA, and that the cation-dianion clusters can therefore accurately be described as isolated ion-pair complexes.

For K⁺·Pt(CN)₄^2-, where the Pt(CN)₄^2- dianion decays with production of two ionic fragments, we observe evidence for the existence of a novel exit-channel complex corresponding to a polar KCN salt unit bound to the Pt(CN)₃^- anion. Further results are presented for a series of gas-phase cation-dianion clusters, e.g. M⁺·Pt(CN)₆^2-, M⁺·Pd(CN)₄^2-, and M⁺·PtCl₆^2- (where M= Na, K, Rb), to illustrate their generality. Density functional theory calculations are also presented to support the experimental results.

The results described provide a basis for understanding the potential energy surfaces and fragmentation characteristics of other ion-pair complexes that involve MCAs. Such species represent important features of the ESI-MS of common biomolecular ions. Towards this goal, we present new results extending our work to larger, more flexible systems such as K⁺·H₃P₃O₁₀^2- and counter-ion complexes of Adensoine 3'-triphosphate.