Electrospray ionization (ESI) of uranyl nitrate solutions generates a wide variety of positively and negatively charged ions, including complex adducts of uranyl ions with methoxy, hydroxy, and nitrate ligands. In the positive ion mode, ions detected by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry are sensitive to instrumental tuning parameters such as quadrupole operating frequency and trapping time. Positive ions correspond to oligomeric uranyl nitrate species that can be characterized as having a general formula of [(UO2)n(A)m(CH3OH)s] + or [(UO2)n(O)(A)m(CH 3OH)s]+ with n = 1-4, m = 1-7, s = 0 or 1, and A = OH, NO3, CH3O or a combination of these, although the formation of NO3-containing species is preferred. In the negative ion mode, complexes of the form [(UO2)(NO3)m] - (m = 1-3) are detected, although the formation of the oxo-containing ions [(UO2)(O)n(NO3) m]- (n = 1-2, m = 1-2) and the hydroxy-containing ions [(UO2)(OH)n(NO3)m]- (n = 1-2, m = 0-1) are also observed. The extent of coordinative unsaturation of both positive and negative ions can be determined by ligand association/exchange and H/D exchange experiments using D2O and CD3OD as neutral reaction partners in the gas-phase. Positive ions are of varying stability and reactivity and may fragment extensively upon collision with D2O, CD3OD and N2 in sustained off-resonance irradiation/collision-induced dissociation (SORI-CID) experiments. Electron-transfer reactions, presumably occurring during electrospray ionization but also in SORI-CID, can result in reduction of U(VI) to U(V) and perhaps even U(IV).
|Original language||English (US)|
|Number of pages||11|
|Journal||Journal of the American Society for Mass Spectrometry|
|State||Published - Feb 2006|
ASJC Scopus subject areas
- Structural Biology