Binding of alpha,omega-alkyldiammonium ions by cucurbit[n]urils in the gas phase
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- Binding of alpha,omega-alkyldiammonium ions by cucurbit[n]urils in the gas phase
- Yang, F; Jones, CA; Selvapalam, N; Young Ho Ko; Ki Moon Kim; Dearden, DV
- SUPRAMOLECULAR CHEMISTRY, v.26, no.9, pp.684 - 691
- TAYLOR & FRANCIS LTD
- We investigated gas-phase complexes of a,v-n-alkyldiammonium ions with cucurbituril (CB), decamethylcucurbit
uril (mc5), penta(cyclohexyl)cucurbituril (CB*), hexa(cyclohexyl)cucurbituril (CB*), cucurbituril (CB)
and cucurbituril (CB) using electrospray Fourier transform ion cyclotron resonance mass spectrometry and collisioninduced
dissociation techniques. The five-membered cucurbit[n]urils (CB[n]s) form singly charged 1:1 and doubly charged
2:1 diamine:CB[n] complexes. All dissociate via loss of neutral a,v-n-alkyldiamine with only weak dependence of
dissociation thresholds on chain length. For a given diamine, threshold energies are in the order CB , mc5 , CB*.
This is consistent with guest hydrogen bonding on the portals of the CBs with no threading into the host’s interior. The n
$ 6 CB[n]s form 1:1 complexes with doubly protonated a,v-n-alkyldiamines. These collisionally dissociate via four
channels: loss of singly protonated a,v-n-alkyldiammonium; fragmentation of the CB[n] cage; loss of neutral a,v-nalkyldiamine
and fragmentation of the a,v-n-alkyldiamine. The dissociation threshold energies and branching ratios exhibit
strong dependence on the length of the a,v-n-alkyldiamine and the size of the CB[n]. The data suggest that the optimum a,
v-n-alkyldiamine length for binding CB* is three to four methylene groups; for CB, four to five methylene groups and
for CB, five to six methylene groups, indicating an increasing tendency for the guest to span the host cavity diagonally as
the size of the CB[n] increases.
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