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Mass Spectrometry and Gas-Phase Chemistry of Dendrimers and their Complexes

Mass spectrometry is an excellent tool not only to characterize dendrimers with respect to molecular mass and the presence of defects, but also offers experiments to examine dendrimers and their non-covalent complexes with respect to their reactivity under environment-free conditions as isolated ions. One highlight of our work is the detailed analysis of fragmentation mechanisms of Frechet dendrons which exhibit "self-immolative" fragmentation cascades that commence at the focal point, but then quickly proceed into the periphery.

Another example is the detailed analysis of the host-guest complexes of Frechet dendrimers with a dicationic viologen core. From the fragmentation reactions - and in particular their sequence - evidence for backfolding was obtained. The larger and more electron-rich the branches are, the better the dications are stabilized.

Finally, H/D exchange experiments provide evidence that crown ethers are capable of migrating from one side chain to another in POPAM complexes. This behavior was coined the "spacewalk" of the crown ethers.

Forth generation POPAM dendrimer/crown ether complex. H/D-exchange experiments unravel the crowns to migrate between different branches on the dendrimer surface.


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