Sizingand Discovery of Nanosized PolyoxometalateClusters by Mass Spectrometry

摘要

Ion mobility-mass spectrometry (IM-MS) is a powerful technique for structural characterization, e.g., sizing and conformation, particularly when combined with quantitative modeling and comparison to theoretical values. Traveling wave IM-MS (TW-IM-MS) has recently become commercially available to nonspecialist groups and has been exploited in the structural study of large biomolecules, however reliable calibrants for large anions have not been available. Polyoxometalate (POM) species—nanoscale inorganic anions—share many of the facets of large biomolecules, however, the full potential of IM-MS in their study has yet to be realized due to a lack of suitable calibration data or validated theoretical models. Herein we address these limitations by reporting DT-IM (drift tube) data for a set of POM clusters {M12} Keggin >1, {M18} Dawson >2, and two {M7} Anderson derivatives >3 and >4 which demonstrate their use as a TW-IM-MS calibrant set to facilitate characterization of very large (ca. 1–4 nm) anionic species. The data was also used to assess the validity of standard techniques to model the collision cross sections of large inorganic anions using the nanoscale familyof compounds based upon the {Se2W29} unit includingthe trimer, {Se8W86O299} >A, tetramer, {Se8W116O408} >B, and hexamer {Se12W174O612} >C, including their relative sizing in solution. Furthermore,using this data set, we demonstrated how IM-MS can be used to convenientlycharacterize and identify the synthesis of two new, i.e., previouslyunreported POM species, {P8W116}, unknown >D, and {Te₈W₁₁₆}, unknown >E, which are not amenable to analysis by other means with the approximateformulation of [H₃₄W₁₁₈X₈M₂O₄₁₆]^44–, where X = P and M = Co for >D and X = Te and M = Mn for >E. This work establishesa new type of inorganic calibrant for IM-MS allowing sizing, structuralanalysis, and discovery of molecular nanostructures directly fromsolution.