Inclusion Complexation of Organic Micropollutants with β‑Cyclodextrin

Recently, β-cyclodextrin
(βCD)-based polymers with
enhanced adsorption kinetics and high removal capacity of organic
micropollutants (OMPs) and uptake rates have been synthesized and
tested experimentally. Although the exact physical–chemical
mechanisms via which these polymers capture the various types of OMPs
are not yet fully understood, it is suggested that the inclusion complex
formation of OMPs with βCD is very important. In this study,
the inclusion complex formation of OMPs with βCD in an aqueous
solution is investigated by using the well-established attach–pull–release
method in force field-based molecular dynamics simulations. A representative
set of OMPs is selected based on the measured occurrences in surface
and ground waters and the directives published by the European Union.
To characterize the formation of the inclusion complex, the binding
free energies, enthalpies, and entropies are computed and compared
to experimental values. It is shown that computations using the q4md-CD/GAFF/Bind3P
force field combination yield binding free energies that are in reasonable
agreement with the experimental results for all OMPs studied. The
binding enthalpies are decomposed into the main contributing interaction
types. It is shown that, for all studied OMPs, the van der Waals interactions
are favorable for the inclusion complexion and the hydrogen bond formation
of the guest with the solvent and βCD plays a crucial role in
the binding mechanism. Our findings show that MD simulations can adequately
describe the inclusion complex formation of βCD with OMPs, which
is the first step toward understanding the underlying mechanisms via
which the βCD-based polymers capture OMPs.