title: Speciation of uranium-mandelic acid complexes using electrospray ionization mass spectrometry and density functional theory.
abstract: BACKGROUND
  Mandelic acid is a complexing agent employed for the liquid chromatographic separation of actinides. However, the types of species and the structural details of the uranyl-mandelate complexes are still unknown. Understanding the nature of these complex species would provide better insight into the mechanism of their separation in liquid chromatography.
  
  
  METHODS
  Formation of different species of the uranyl ion (UO2) with mandelic acid was studied using electrospray ionization mass spectrometry (ESI-MS) with a quadrupole time-of-flight analyzer. The different species of uranyl nitrate with mandelic acid (MA) at ligand (L) to metal ratios in the range 1-10 were examined in both positive and negative ion modes. The stability of different species with the possible pathways of formation was scrutinized using density functional theory (DFT) calculations.
  
  
  RESULTS
  In negative ion mode, nitrate-containing UO2(MA)1, UO2(MA)2and UO2(MA)3species were found in good abundance. In positive ion mode, under-coordinated uranyl-mandelate species, and solvated (S) species of types UO2(MA)1(S), UO2(MA)1(S)2and UO2(MA)2(S), were observed whereas nitrate-containing species were absent. Interestingly, doubly and singly charged dimeric species were also identified in positive ion mode. The theoretically computed energetics of the various species are in close agreement with their experimentally observed intensities in ESI-MS.
  
  
  CONCLUSIONS
  The most intense peak observed in ESI-MS, UO2(MA)3, was found to be the energetically most favorable amongst different UO2(MA)ntype species. Metal-ligand equilibria studied in the two modes yielded similar results. The combined experimental and quantum chemical investigations predict that T-shape complexes may be formed even in the gas phase. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Fuel Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: Pranaw
authors.identifier: http://orcid.org/0000-0003-3220-545X
authors.initials: P
authors.lastname: Kumar
authors.affiliation: Fuel Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: P G
authors.initials: PG
authors.lastname: Jaison
authors.affiliation: Fuel Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: V M
authors.initials: VM
authors.lastname: Telmore
authors.affiliation: Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: Biswajit
authors.initials: B
authors.lastname: Sadhu
authors.affiliation: Theoretical Chemistry Section, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: Mahesh
authors.identifier: http://orcid.org/0000-0002-1522-124X
authors.initials: M
authors.lastname: Sundararajan