Collision‐induced dissociation of [UO₂(NO₃)(O₂)]⁻ and reactions of product ions with H₂O and O₂

Abstract

We recently reported a detailed investigation of the collision‐induced dissociation (CID) of [UO2(NO3)3]− and [UO2(NO3)2(O2)]− in a linear ion trap mass spectrometer (J. Mass Spectrom. DOI:10.1002/jms.4705). Here, we describe the CID of [UO2(NO3)(O2)]− which is created directly by ESI, or indirectly by simple elimination of O2 from [UO2(NO3)(O2)2]−. CID of [UO2(NO3)(O2)]− creates product ions as at m/z 332 and m/z 318. The former may be formed directly by elimination of O2, while the latter required decomposition of a nitrate ligand and elimination of NO2. DFT calculations identify a pathway by which both product ions can be generated, which involves initial isomerization of [UO2(NO3)(O2)]− to create [UO2(O)(NO2)(O2)]−, from which elimination of NO2 or O2 will leave [UO2(O)(O2)]− or [UO2(O)(NO2)]−, respectively. For the latter product ion, the composition assignment of [UO2(O)(NO2)]− rather than [UO2(NO3)]− is supported by ion‐molecule reaction behavior, and in particular, the fact that spontaneous addition of O2, which is predicted to be the dominant reaction pathway for [UO2(NO3)]− is not observed. Instead, the species reacts with H2O, which is predicted to be the favored pathway for [UO2(O)(NO2)]−. This result in particular demonstrates the utility of ion‐molecule reactions to assist the determination of ion composition. As in our earlier study, we find that ions such as [UO2(O)(NO2)]− and [UO2(O)(O2)]− form H2O adducts, and calculations suggest these species spontaneously rearrange to create dihydroxides.

Ion‐molecule reactions of mass‐selected ions

“…Other uranyl nitrate complexes have been studied including the [UO 2 (NO 3 ) 3 ] − and the [UO 2 (NO 3 ) 2 (O 2 )] − ions. Numerous CID reactions were performed on the complexes resulting in the elimination of O 2 , NO 2 , or NO 3 with the elimination of NO 2 being the most energetically favorable (Bubas et al, 2021). The [UO 2 (O)(NO 3 )] − ion performed an addition reaction with water to form [UO 2 (O)(NO 3 )(H 2 O)] − and spontaneously rearranged to form the dihydroxide [UO 2 (OH) 2 (NO 3 )] − ion (Scheme 4).…”

“…Reactions of the [UO 2 (NO 3 ) 3 ] − and the [UO 2 (NO 3 ) 2 (O)] − ions with the CID fragmentation products shown in blue and IMR products in red (from reference: Bubas et al, 2021). CID, collision‐induced dissociation; IMR, ion‐molecule reactions.…”

“…The [U VI O 2 (ClO 4 )] + ion was studied previously in a 3D ion trap and was found to react immediately with water after collisional activation to either form the hydrated [U VI O 2 (OH)] + ion or perform a charge reduction reaction resulting in the [U V O 2 ] + ion (Van Stipdonk et al, 2004, 2005 most energetically favorable (Bubas et al, 2021). The [UO 2 (O)(NO 3 )] − ion performed an addition reaction with water to form [UO 2 (O)(NO 3 )(H 2 O)] − and spontaneously rearranged to form the dihydroxide [UO 2 (OH) 2 (NO 3 )] − ion (Scheme 4).…”