dc.description.abstract
Synthetic supramolecular systems share many similarities with
natural biological assemblies,
especially when considering that the structure and guest binding are typically governed by
non-covalent interactions.
As such, the defining characteristic is that only comparably weak forces define the shape
of a synthetic supramolecule or the tertiary structure of a protein, so that the resulting
dynamic binding mode makes structure elucidation challenging.
One of the major advances in recent analytical chemistry has been the development of ion mobility-mass
spectrometry (IM-MS) to tackle the challenging problems
faced in proteomics, glycomics, metabolomics, and lipidomics.
By analogy, the prospects of applying IM-MS to supramolecules are bright and it is
to be expected that unprecedented analytical insights into diverse
systems such as host-guest
complexes, molecular devices, self-assemblies and metallosupramolecular complexes
will be obtained.
The recurrent theme throughout this dissertation is that both structure (differentiation of
diastereomers, photoisomers, mechanoisomers) and
non-covalent interactions (hydrogen bonding, $TTF^{n+}/TTF^{n+}$-charge repulsion, dispersive
interactions) can be investigated by a combination of the three methods of ion-mobility mass
spectrometry (IM-MS), collision-induced dissociation (CID) and gas-phase H/D-exchange (GP-HDX).
In the study of the gas-phase chiral recognition of crown-ether ammonium complexes,
the importance of a single hydrogen bond for the enantiodifferentiation was revealed.
Similarly, in an azobenzene model a hydrogen bonding interaction led to an increased
stability of the (Z)-photoisomer.
This surprising observation illustrates an important aspect, namely that there can be significant
differences between the gas-phase and the solution environment.
In the absence of solvent, both the stabilization of charged sites and the Coulomb repulsion of
nearby charges are accentuated.
In a way, the conundrum of supramolecular mass spectrometry revolves around the problem that
ions are easily manipulated in the gas-phase where a high analytic resolution
power is available, to then face the question if the obtained results still reflect the
solution environment.
Therefore, it is very convincing to see that in three of the five presented studies, the solution
environment is reflected in a quantitative fashion: In the quantification of the enantiomeric excess
(first study), the quantification of photoisomer content (second study), and the quantitative
determination of equilibrium constants for redox-controlled dethreading (third study).
Together with these five studies, and the detailed description in the subsequent chapters,
I expect the treatment to be useful also from the practitioner's point of view.
It is my hope that the performance, speed, and reliability
with which measurements can be performed with modern instrumentation
will make IM-MS a routine analytical tool in the repertoire of the working
supramolecular chemist.
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