94 research outputs found
Thermodynamics of Host–Guest Interactions between Fullerenes and a Buckycatcher
<sup>1</sup>H NMR and isothermal
titration calorimetry (ITC) experiments
were employed to obtain reliable thermodynamic data for the formation
of the 1:1 inclusion complexes of fullerenes C<sub>60</sub> and C<sub>70</sub> with the buckycatcher (C<sub>60</sub>H<sub>28</sub>). NMR
measurements were done in toluene-<i>d</i><sub>8</sub> and
chlorobenzene-<i>d</i><sub>5</sub> at 288, 298, and 308
K, while the ITC titrations were performed in toluene, chlorobenzene, <i>o</i>-dichlorobenzene, anisole, and 1,1,2,2-tetrachloroethane
at temperatures from 278 to 323 K. The association constants, <i>K</i><sub>a</sub>, obtained with both techniques are in very
good agreement. The thermodynamic data obtained by ITC indicate that
generally the host–guest association is enthalpy-driven. Interestingly,
the entropy contributions are, with rare exceptions, slightly stabilizing
or close to zero. Neither Δ<i>H</i> nor Δ<i>S</i> is constant over the temperature range studied, and these
thermodynamic functions exhibit classical enthalpy/entropy compensation.
The Δ<i>C</i><sub><i>p</i></sub> values
calculated from the temperature dependence of the calorimetric Δ<i>H</i> values are negative for the association of both fullerenes
with the buckycatcher in toluene. The negative Δ<i>C</i><sub><i>p</i></sub> values are consistent with some desolvation
of the host-cavity and the guest in the inclusion complexes, C<sub>60</sub>@C<sub>60</sub>H<sub>28</sub> and C<sub>70</sub>@C<sub>60</sub>H<sub>28</sub>
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