Polymer topology revealed by ion mobility coupled with mass spectrometry

Hyperbranched and star shaped polymers have raised tremendous interests
because of their unusual structural and photochemical properties which provide them potent
applications in various domains, namely in the biomedical field. In this context, the
development of adequate tools aiming to probe particular three-dimensional features of such
polymers is of crucial importance. In this present work, ion mobility coupled with mass
spectrometry was used to experimentally derive structural information related to cationized
linear and star-shaped poly-ε-caprolactones as a function of their charge state and chain
length. Two major conformations were observed and identified using theoretical modeling:
(1) near spherical conformations whose size is invariant with the polymer topology for long
and lightly charged chains and (2) elongated conformations whose size varies with the
polymer topology for short and highly charged chains. These conformations were further
confirmed by collisional activation experiments based on the ejection thresholds of the coordinated cations that vary according to the elongation amplitude of the polymer chains.
Finally, a comparison between solution and gas-phase conformations highlights a compaction
of the structure with a loss of specific chain arrangements during the ionization and
desolvation steps of the electrospray process, fueling the long-time debated question related to
the preservation of the analyte structure during the transfer into the mass spectrometer.