Electron capture dissociation of multiply-charged oxygenated cations. A nonergodic process

Several mechanistic aspects have been proposed as important in causing the unusual ion chemistry induced in multiply-charged protein cations by electr on capture. The 5-7 eV energy released by neutralization appears to induce cleavage before energy randomization (nonergodic), and the electron forms r adical species whose activation energies for dissociation should be much lo wer. In contrast, electron capture by [HO(C2H4O)(24)H + 2H](2+) ions from p olyethylene glycol yields no radical ions losing H-. consistent with the lo wer H-. affinity of the hydroxyl and ether groups vs the amide and S-S func tionalities of proteins. However, the dominant product ions, [HO(C2H4O)(24- n)H + H](+) (n = 2 to 8), do appear to be formed by nonergodic dissociation of the hypervalent (M + 2H)(1+.) intermediate. The expected complementary alkoxy radical ion product is not found, possibly due to an energetic Franc k-Condon relaxation, Precursors ionized with (NH4)(2)(2+) and Na-2(2+) yiel d ECD products that are analogous but of different size (n values). Those f or Na-2(2+) can be rationalized with structures proposed by Bowers and cowo rkers, ECD spectra of polyethers should be useful for sequencing.