Multivalency in the Gas Phase: H/D-Exchange Reactions Unravel the Dynamic 'Rock 'n Roll' Motion in Dendrimer-Dendrimer Complexes
Z. Qi, C. Schlaich, C. A. Schalley – 2013
Non-covalent dendrimer-dendrimer complexes were successfully ionized by electrospray ionization (ESI) of partly protonated amino-terminated polypropylene amin (POPAM) and POPAM dendrimers fully functionalized with benzocrown-7 on all branches. Hydrogen/deuterium exchange (HDX) experiments conducted on dendrimer-dendrimer complexes in the high vacuum of a mass spectrometer give rise to a complete exchange of all labile N-H hydrogen atoms. As crown ethers represent non-covalent protective groups against HDX reactions on the ammonium group they coordinate to, this result provides evidence for a very dynamic binding situation: Each crown is mobile enough to move from one ammonium binding site to another one. Schematically, one might compare this motion with two rock ‘n roll dancers that swirl around each other without completely losing all contact at any time. Although the multivalent attachment certainly increases the overall affinity, the “microdynamics” of individual site binding and dissociation remains fast.