The cucurbit[n]uril family: prime components for self-sorting systems.
We determined the values of Ka for a wide range of host-guest complexes of cucurbit[n]uril (CB[n]), where n = 6-8, using 1H NMR competition experiments referenced to absolute binding constants measured by UV/vis titration. We find that the larger homologues--CB[7] and CB[8]--individually maintain the size, shape, and functional group selectivity that typifies the recognition behavior of CB[6]. The cavity of CB[7] is found to effectively host trimethylsilyl groups. Remarkably, the values of Ka for the interaction of CB[7] with adamantane derivatives 22-24 exceeds 10(12) M(-1)! The high levels of selectivity observed for each CB[n] individually is also observed for the CB[n] family collectively. That is, the selectivities of CB[6], CB[7], and CB[8] toward a common guest can be remarkably large. For example, guests 1, 3, and 11 prefer CB[8] relative to CB[7] by factors greater than 10(7), 10(6), and 3000, respectively. Conversely, guests 23 and 24 prefer CB[7] relative to CB[8] by factors greater than 5100 and 990, respectively. The high levels of selectivity observed individually and collectively for the CB[n] family renders them prime components for the preparation of functional biomimetic self-sorting systems.
Liu
Simin
S
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
Ruspic
Christian
C
Mukhopadhyay
Pritam
P
Chakrabarti
Sriparna
S
Zavalij
Peter Y
PY
Isaacs
Lyle
L
D040761:Biomimetic Materials / Q000737:chemistry*; D001952:Bridged-Ring Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007093:Imidazoles / Q000737:chemistry*; D015394:Molecular Structure
D001952:Bridged-Ring Compounds; D007093:Imidazoles