ao0c00523_si_001.pdf (1.39 MB)
Guest/Host Complexes of Octa Acid and Amphiphilic Benzylidene-3-methylimidazolidinones Exchange Hosts within the NMR Time Scale
journal contribution
posted on 2020-03-31, 14:33 authored by Shampa
R. Samanta, Anthony Baldridge, Laren M. Tolbert, Vaidhyanathan RamamurthyCavitand octa acid
(OA) is established to form a stable capsular
assembly with one or two hydrophobic guest molecules (1:2 or 2:2 guest/host
complex). Examples are known in which the guest molecule tumbles within
the capsule without disrupting the structure of the capsuleplex. This
process makes the two OA molecules that form the capsule magnetically
equivalent. In this study, we have examined the dynamics of capsules
that host amphiphilic benzylidene-3-methylimidazolidinone molecules
as guests. In these capsuleplexes, although the guest does not tumble,
the two OA molecules become magnetically equivalent because the two
OA molecules that form the capsule exchange their positions in the
NMR time scale. This is equivalent to the content of the capsule remaining
stationary while the capsule swirls around it. Benzylidene-3-methylimidazolidinones
form both 1:1 and 1:2 supramolecular complexes with cavitand OA. Two-dimensional
NMR, ROESY, and NOESY data suggest that in a 300 ms time scale, the
two halves of the capsule exchange between themselves and with free
OA. The conclusion drawn here provides valuable information concerning
the stability of the OA capsuleplex and cavitandplex that is used
as the well-defined space to control the excited-state chemistry and
dynamics of confined guest molecules.