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density functional calculations
fluorinated pyridines
heterocycles
non-bonding interactions
tandem mass spectrometry
Abstract:
Aseries of mono- and divalent fluorinatedpyri-
dine derivatives is investigated by electrospray ionization
(tandem) mass spectrometry and quantum chemical calcula-
tions with respect to their capability to bind anions in the
gas
phase.
The
pyrid
ine
derivativ
es
differ
not
only
in
valency
,
but also with regard to the degree of fluorination of the pyr-
idine rings, the positions of the fluorine atoms, the rigidity
of the spacers connec ting the two pyridines in the divalent
compounds, and the relative configuratio n. While the mono-
valent compounds did not form anioncomplexes, the diva-
lent analoguesexhibit anion binding even to weakly coordi-
nating anionssuch as tetrafluoroborate.Three different
tandem mass spectrometric experimentswereappliedto
rank the gas-phase binding energies:(i) collision-induceddis-
sociation (CID)experiments in aFourier transform ion-cyclo-
tron-resonance (FTICR) mass spectrometer on two different,
simultaneously mass-selected complexes with different re-
ceptors, (ii)determination of the collisionenergy required to
fragment 50 %ofthe mass-selected complexes in an ESI-
QToF mass spectrometer,and (iii)CID of heterodimers
formed from two different, competing pyridine receptor s
and indigo carmine,adianionwith two identical binding
sites. All three experimentsresult in consistent binding
energyranking. This ranki ng reveals surprising features,
whichare not in agreement with binding through anion–p
interactions. Densityfunctionaltheory (DFT) calculations
comparing different potentialbinding modes provide evi-
dencethat the ranking can insteadnicely be explained,
when C@H···anion interactions with the spacers are invoked.
Theseresults are supported by gas-phase IR spectroscopy
and ion mobility-mass spectrometry (IM-MS)onaselected
set of chloridepyridine comp lexes.
