We report herein the characterization and binding properties of a microporous crystalline host formed by the self assembly of a bis-urea macrocycle 1. Bis-urea macrocycle 1 has been designed to crystallize into stacked hollow columns. The self-assembly process is guided primarily by hydrogen bonding and aromatic stacking interactions that yield crystals of filled host 1‚acetic acid (AcOH). The AcOH guests are bound in the cylindrical cavities of the crystal. The guest AcOH can be removed by heating to form a stable crystalline apohost 1. Apohost 1 displays a type I gas adsorption isotherm with CO 2 that is consistent with an open framework microporous material. Apohost 1 binds a range of small molecule guests with specific stoichiometry. The formation of these inclusion complexes does not destroy the crystal framework and therefore apohost 1 can be reused, much like a zeolite. We investigated the structure of apohost 1 and its inclusion complexes by powder X-ray diffraction. The ability of guests to bind and their stoichiometry could be rationalized on the basis of the size, shape, and polarity of the guest molecules. Finally, the shape selectivity of these self-assembled porous materials was demonstrated in competition studies in which apohost 1 preferentially bound p-xylene from a mixture of xylene isomers.
Two novel DNA base
surrogate phosphoramidites 1 and 2, based
upon relatively electron-rich 1,5-dialkoxynaphthalene
(DAN) and relatively electron-deficient 1,4,5,8-naphthalenetetracarboxylic
diimide (NDI), respectively, were designed, synthesized, and incorporated
into DNA oligonucleotide strands. The DAN and NDI artificial DNA bases
were inserted within a three-base-pair region within the interior
of a 12-mer oligonucleotide duplex in various sequential arrangements
and investigated with CD spectroscopy and UV melting curve analysis.
The CD spectra of the modified duplexes indicated B-form DNA topology.
Melting curve analyses revealed trends in DNA duplex stability that
correlate with the known association of DAN and NDI moieties in aqueous
solution as well as the known favorable interactions between NDI and
natural DNA base pairs. This demonstrates that DNA duplex stability
and specificity can be driven by the electrostatic complementarity
between DAN and NDI. In the most favorable case, an NDI–DAN–NDI
arrangement in the middle of the DNA duplex was found to be approximately
as stabilizing as three A–T base pairs.
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