jo7b02846_si_005.xyz (5.85 kB)
Thermodynamics of Halide Binding to a Neutral Bambusuril in Water and Organic Solvents
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posted on 2018-01-26, 00:00 authored by Tomas Fiala, Kristina Sleziakova, Kamil Marsalek, Karolina Salvadori, Vladimir SindelarDriving forces of anion binding in
water in contrast to nonpolar
environments are of high interest because of their relevance to biology
and medicine. Here we report a neutral bambusuril macrocycle (1), soluble in both water and nonpolar solvents due to decoration
with 12 polyethylene glycol-based substituents. The new bambusuril
has the highest affinity for I– in pure water ever
reported for a synthetic macrocycle relying on hydrogen bonding interactions
rather than metal coordination or Coulombic forces. Isothermal titration
calorimetry (ITC) experiments in nine different solvents, ranging
from polar water to nonpolar carbon tetrachloride, provided insight
into the forces responsible for halide binding by bambusurils. The
different importance of anion solvation and solvent expulsion from
the cavity of the macrocycle in various solvents is illustrated by
the fact that halide binding in water and chloroform is exclusively
driven by favorable enthalpy with an entropic penalty, while in alcohols
and nonpolar solvents, both favorable enthalpy and entropy contribute
to anion encapsulation. DFT calculations and correlation of thermodynamic
data with the solvent Swain acity parameter further underscore the
importance of solvent effects on anion binding by bambusurils.