Metal-ligand coordination interactions are widely employed for the self-assembly of supramolecular architectures. Depending on the building block(s) and metal ion(s) used, this process is kinetically controlled, leading irreversibly to several strongly bound products; or it proceeds through thermodynamically controlled equilibria favoring a specific, albeit more weakly bound product that may be difficult to purify. In both cases, electrospray ionization mass spectrometry (ESI-MS) offers an effective method for the determination of the compositional heterogeneity and structure(s) of the resulting assemblies. As a soft ionization method, ESI minimizes fragmentation; meanwhile, as a dispersive method, MS permits direct analysis of the stoichiometries of individual product components without prior separation. With complex product mixtures, further resolution is achieved by combining MS with ion mobility (IM) separation of the ions formed by ESI. In the IM dimension, assemblies are dispersed by charge and size/shape, which enables the deconvolution of overlapping charge states and the separation of isomeric complexes with distinct architectures (figure). Additional analytical information can be obtained by interfacing IM-MS with gradient tandem mass spectrometry (gMS2), in which the separated species are energetically excited to dissociate; the energies causing complete fragmentation reflect relative complex stabilities and help to distinguish isomers and to assess the assemblies' applicability as thermal sensors. These analytical capabilities will be demonstrated with applications to a variety of metallo-supramolecular polymers.

Top-Down multidimensional mass spectrometry methods for the characterization of metallo-supramolecular polymers

248th National Meeting (2014)

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