Cryptophanes for Methane and Xenon Encapsulation: A Comparative Density Functional Theory Study of Binding Properties and NMR Chemical Shifts

The
host–guest chemistry of cryptophanes is an active research
area because of its applications in sensor design, targeting small
molecules and atoms in environmental and medical sciences. As such,
the computational prediction of binding energies and nuclear magnetic
resonance (NMR) properties of different cryptophane complexes are
of interest to both theoreticians and experimentalists working in
host–guest based sensor development. Herein we present a study
of 10 known and some newly proposed cryptophanes using density functional
theory (DFT) calculations. We benchmark the description of nonbonding
interactions by different DFT functionals against spin-component-scaled,
second-order Møller–Plesset theory (SCS-MP2) and predict
novel host molecules with enhanced affinity toward methane and Xenon,
two representative systems of high interest. We demonstrate the power
and limitations of the different computational methods in describing
the binding and NMR properties of these established and novel host
systems. The results show the importance of including dispersion corrections
in the DFT functionals. The overall analysis of the dispersion corrections
indicated that results obtained from pure DFT functionals should be
used cautiously when conclusions are drawn for molecular systems
with considerable weak interactions. Proposed analogues of cryptophane-A,
where the alkoxy bridges are replaced by alkyl chains, are predicted
to display enhanced affinity toward both methane and Xenon.