Grant Johnson - Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

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  Publication Details (including relevant citation   information):


  Volume:   24

    Issue: 9

    Pages: 1385-1395


Published: SEP 2013


    Electrospray ionization mass spectrometry (ESI-MS) combined with   in-source fragmentation and tandem mass spectrometry (MS/MS)   experiments were used to generate a wide range of singly and   multiply charged vanadium oxide cluster anions including VxOy   (n-) and VxOyCln- ions (x = 1-14, y = 2-36, n = 1-3), protonated   clusters, and ligand-bound polyoxovanadate anions. The cluster   anions were produced by electrospraying a solution of   tetradecavanadate, V14O36Cl(L)(5) (L = Et4N+,   tetraethylammonium), in acetonitrile. Under mild source   conditions, ESI-MS generates a distribution of doubly and triply   charged VxOyCln- and VxOyCl(L)((n-1)-) clusters predominantly   containing 14 vanadium atoms as well as their protonated analogs.   Accurate mass measurement using a high-resolution LTQ/Orbitrap   mass spectrometer (m/Delta m = 60,000 at m/z 410) enabled   unambiguous assignment of the elemental composition of the   majority of peaks in the ESI-MS spectrum. In addition,   high-sensitivity mass spectrometry allowed the charge state of   the cluster ions to be assigned based on the separation of the   major from the much less abundant minor isotope of vanadium.   In-source fragmentation resulted in facile formation of smaller   VxOyCl(1-2)- and VxOy ((1-2)-) anions. Collision-induced   dissociation (CID) experiments enabled systematic study of the   gas-phase fragmentation pathways of the cluster anions   originating from solution and from in-source CID. Surprisingly   simple fragmentation patterns were obtained for all singly and   doubly charged VxOyCl and VxOy species generated through multiple   MS/MS experiments. In contrast, cluster anions originating   directly from solution produced comparatively complex CID   spectra. These results are consistent with the formation of more   stable structures of VxOyCl and VxOy anions through low-energy   CID. Furthermore, our results demonstrate that solution-phase   synthesis of one precursor cluster anion combined with gas-phase   CID is an efficient approach for the top-down synthesis of a wide   range of singly and multiply charged gas-phase metal oxide   cluster anions for subsequent investigations of structure and   reactivity using mass spectrometry and ion spectroscopy   techniques.

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