2 research outputs found
Metal–Organic Cage Receptors for Encapsulation and Sensing of Bile Acids
Developing synthetic supramolecular receptors to solubilize,
scavenge,
recognize, encapsulate, and sense steroids is challenging. Despite
a limited number of receptors having affinity with steroids, none
exists to bind steroidal bile acids selectively. Herein, we report
a C2-symmetric metal–organic cage
[Pd6L24]12+ and an expanded
version of the Fujita cage [Pd6L14]12+, built with a conformationally flexible ligand L2, accessed through coordination-driven self-assembly. We
examined both cages for steroid recognition in water: both have certain
shared characteristics and distinctive features. [Pd6L14]12+ binds hydrophobic bile acids
and other steroids by forming a 1:1 complex. In contrast, the expanded
[Pd6L24]12+ cage exhibits
an affinity for amphiphilic bile acids and selective steroids to encapsulate
them as dimers, promoted by cooperative interguest hydrogen bonding.
[Pd6L24]12+ has a 5
times stronger solubility enhancement ability for cholic acid compared
to [Pd6L14]12+. Further,
the expanded [Pd6L24]12+ cage can selectively sense bile acids in nanomolar detection limits
through indicator displacement assay by employing sulforhodamine 101
(SR101)
Tunable Porous Organic Crystals: Structural Scope and Adsorption Properties of Nanoporous Steroidal Ureas
Previous
work has shown that certain steroidal bis-(<i>N</i>-phenyl)Âureas,
derived from cholic acid, form crystals in the <i>P</i>6<sub>1</sub> space group with unusually wide unidimensional
pores. A key feature of the nanoporous steroidal urea (NPSU) structure
is that groups at either end of the steroid are directed into the
channels and may in principle be altered without disturbing the crystal
packing. Herein we report an expanded study of this system, which
increases the structural variety of NPSUs and also examines their
inclusion properties. Nineteen new NPSU crystal structures are described,
to add to the six which were previously reported. The materials show
wide variations in channel size, shape, and chemical nature. Minimum
pore diameters vary from ∼0 up to 13.1 Å, while some of
the interior surfaces are markedly corrugated. Several variants possess
functional groups positioned in the channels with potential to interact
with guest molecules. Inclusion studies were performed using a relatively
accessible tris-(<i>N</i>-phenyl)Âurea. Solvent removal was
possible without crystal degradation, and gas adsorption could be
demonstrated. Organic molecules ranging from simple aromatics (e.g.,
aniline and chlorobenzene) to the much larger squalene (<i>M</i><sub>w</sub> = 411) could be adsorbed from the liquid state, while
several dyes were taken up from solutions in ether. Some dyes gave
dichroic complexes, implying alignment of the chromophores in the
NPSU channels. Notably, these complexes were formed by direct adsorption
rather than cocrystallization, emphasizing the unusually robust nature
of these organic molecular hosts