ORGN 793 |
| The conformational dynamics of biological molecules is of prime importance in modulating their molecular recognition, and can affect the active site accessibility and have an impact on the catalytic reactivity. Adapted to supramolecular chemistry, this concept will allow the preparation of artificial receptors capable to regulate molecular recognition and reactivity in unnatural settings. We synthesized a resorcinarene-based cavitand 1, containing four identical aromatic “flaps” capable to form hydrogen bonds along the upper rim of the structure, and studied its conformational behavior using variable temperature 1H NMR spectroscopy (Scheme 1). This new kind of molecular cavitand has been fully characterized by NMR spectroscopy and mass spectrometry. As follows from the 1H NMR and IR measurements, 1 adopts the “vase” conformation wherein two neighboring aromatic “arms” interact in pairs, and form hydrogen bonds via amide groups leaving all four methoxy groups free and uncomplexed. The molecule has C2 symmetry with two enantiomers 1a and 1b slowly exchanging on the 1H NMR time scale (Scheme 1). Using line-shape analysis and two-dimensional exchange spectroscopy (EXSY) methods we determined the rate constants for the exchange of enantiomers at various temperatures and in the presence of variable amounts of a proton source – trifluoroacetic acid (TFA). Importantly, we discovered that the rate of 1a to 1b exchange can be regulated with an external stimulus, i.e., the interconversion dynamics can be operated at two levels (fast without and slow with TFA present). Computational methods are currently employed in exploring the mechanism for the interconversion of the two enantiomers, followed by attempts to modulate the rate of molecular recognition of guests using principles developed in this work.
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Total Synthesis, Materials, Molecular Recognition, Process R&D, and Physical Organic Chemistry
8:00 PM-10:00 PM, Wednesday, 13 September 2006 Moscone Center -- Hall D, Poster
Division of Organic Chemistry |
