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Energetic Competition Effects on Thermodynamic Properties of Association between β‑CD and Fc Group: A Potential of Mean Force Approach
journal contribution
posted on 2016-02-20, 07:55 authored by Gaëlle Filippini, Florent Goujon, Christine Bonal, Patrice MalfreytA host–guest system involving ferrocenemethanol
(FcOH) and
β-cyclodextrin (CD) in both homogeneous (free CD) and heterogeneous
conditions (gold-confined CD) is studied by applying an integrated
approach that combines energy and structure. Numerical experiments
were used to calculate the potential of mean force between the host
and guest at different separation distances. The thermodynamic properties
of association are obtained by integrating the free-energy profile.
In this study, we specially focus on the comparison of the association
process between β-CD and FcOH in both isolated and water phases.
We establish that the association process is enthalpy driven in all
conditions (homogeneous and heterogeneous systems in both isolated
and water phases). As a consequence, the driving forces involved in
the complexation by β-CD are then essentially due to van der
Waals interactions. As concerns the comparison between the isolated
and water phases, the simulations have shown that the association
constants in vacuum are significantly greater than the corresponding
ones in solution. A significant difference appears in the enthalpy
between the two conditions. From the analysis of the different energy
contributions, we have found that the more favorable free energy in
gas comes from the electrostatic contributions. The differences observed
between the thermodynamic properties are also interpreted through
an atomistic description. The ability of molecular dynamic simulations
to enable a better understanding of the role of liquid water and hydrogen
bonds on the complexation thermodynamics of β-CD is illustrated
in this paper.