Sequence‐Specific Self‐Sorting of the Binding Sites of a Ditopic Guest by Cucurbituril Homologues and Subsequent Formation of a Hetero[4]pseudorotaxane

Abstract

Ties us together: The selectivity and recognition behavior of cucurbit[n]uril (CB[n]) homologues (n=6,7,8) towards a ditopic guest containing two distinct binding sites is explored. CB6, CB7, and CB8 recognize and self‐sort the binding sites according to their size, shape, and chemical nature. In the presence of both CB6 and CB8 a hetero[4]pseudorotaxane is formed.

Kinetics Inside, Outside and Through Cucurbiturils

“…[75] Instead of using bulky or negatively charged stoppers, dethreading can also be controlled using "supramolecular valves". [84] In both cases, CB [7] or CB [8] egression is coupled to the exchange kinetics of CB [6] at the terminal stations. In the presence of an excess amount of CB [6], CB [7] slowly escapes from the axle and is replaced by CB [6], when a minute fraction of CB [6] oscillates between the terminal station and the bulk.…”

“…To the contrary, we would invoke primarily pathway 2 for the inhibition of cystamine (83) reduction to cysteamine (84) with dithiothreitol (Kaifer and coworkers), [114] and selenocystamine (85) with tris(2-carboxyethyl)phosphine to product 86 (Ren and coworkers; see Scheme 13). [115] The inhibition of the corresponding oxidation of cysteamine (84) with Fe(III) chloride or chloropicrin may be attributed to pathway 2, but pathway 1 may be at play when oxygen is the oxidizing agent, [114] when CB [6] prevents hydrogen peroxide oxidation of selenocystamine (85) to selenous acid 87, [115] or when CB [7] encapsulation of the alkanolamine form of sanguinarin 76 prevents its photo oxidation to 6-oxysanguinarine (88) by oxygen.…”

Five‐Component Self‐Assembly of Cucurbituril‐Based Hetero‐pseudorotaxanes

“…Importantly, the extended set of available affinity data for CB6, CB7, and CB8 binding to structurally diverse guests provides a solid foundation for the molecular design of complex supramolecular structures containing CB macrocycles as key elements. This might ultimately lead to complex, yet well‐defined systems that exhibit biomimetic features . In this study, we were especially interested in the use of CBs as wheel components of pseudorotaxanes.…”

Pseudorotaxanes with Self‐Sorted Sequence and Stereochemical Orientation

“…Previously, one of us reported a heteropseudo [3]rotaxane [10,11] bearing two similar crown ethers (dibenzo[24]crown-8 and benzo-[21]crown-7) in a specific sequence along a constitutionally asymmetric dialkylammonium axle. [12] To the best of our knowledge, no examples of a system that sorts among species that differ in sequence and stereochemistry exist so far.…”