2 research outputs found
Unusually High Selectivity of Guest Exchange in <i>tert</i>-Butylthiacalix[4]arene Clathrate Producing More Thermostable Inclusion and Memory of Guest
New properties, earlier unknown for calixarenes, were
found for <i>tert</i>-butylthiacalixÂ[4]Âarene (<b>1</b>) clathrate with
1,2-dichloroethane (DCE). Guest exchange in <b>1</b>·1.90DCE
for vapors of some organic compounds gives clathrates, which are more
thermostable at 34–59 °C than those prepared by direct
saturation of guest-free <b>1</b> with pure guests. Besides,
guest exchange may produce clathrates that cannot be formed by direct
saturation in binary host–guest systems. Some compounds, like
water, toluene, and trichloroethylene, expel DCE from its clathrate
with <b>1</b> but are not included above the trace level. Residual
contents of DCE in clathrate may be controlled by variation of water
and <b>1</b>·1.90DCE ratio in the studied system. Host <b>1</b> can remember methanol after its elimination from the guest
exchange product. This memory can be read as an exoeffect by differential
scanning calorimetry. Only methanol and only after guest exchange
is remembered giving an example of a genuine molecular recognition
Unusually High Efficiency of β‑Cyclodextrin Clathrate Preparation by Water-Free Solid-Phase Guest Exchange
An effective preparation procedure
is offered for β-cyclodextrin
(bCD) clathrates with volatile guests of moderate hydrophilicity,
which otherwise require a finely tuned optimization of the bCD/water/guest
ratio. The proposed procedure includes guest exchange in a water-free
bCD matrix. As a result, more stable clathrates with a higher inclusion
capacity can be prepared than by direct saturation of dried or hydrated
bCD. To find an optimal preparation method, the structure–property
relationships were studied for four different ways of bCD clathrate
formation with guests of varying molecular structure. The study was
much simplified by used procedures excluding direct contact of guest
and water liquids with bCD. Besides, in clathrate preparation experiments,
the thermodynamic activities of water and guest were varied independently,
which makes explicit the role of water in this process. Hydration
of bCD reduces its inclusion threshold for hydrophobic guests by their
activity (relative vapor pressure), giving favorable hydration effect
for their inclusion. Besides, water competes with hydrophilic guests
for binding sites in bCD at high water activities. Together with bCD
dehydration by excess of hydrophilic guests, these observations give
a complete thermodynamic picture, which may be fruitful for elaboration
of guest encapsulation techniques by cyclodextrins