Refolding Foldamers:  Triazene-Arylene Oligomers That Change Shape with Chemical Stimuli

Abstract

We describe the preparation of five triazene-arylene oligomers (3, 4, 7, 8, and 11) and investigations of their folding properties in aqueous solution. These oligomers contain four 2-fold rotors and populate a conformational ensemble comprising at least 10 states. Extensive 1D and 2D NMR studies as well as X-ray crystallography establish that the presence of three members of the cucurbit[n]uril family (CB[n]), CB[10], CB[7], and CB[8], results in the selective population of the (a,a,a,a)-, (a,s,s,a)-, and (a,a,a,s)-conformers. As a result of the high affinity and highly selective binding properties of the CB[n] family, it is possible to fold a single foldamer strand (3) into the CB[8].(a,a,a,s)-3 conformer by the addition of CB[8], then unfold and refold it into the CB[7].(a,s,s,a)-3.CB[7] conformer by addition of CB[7] and 3,5-dimethylaminoadamantane (17), then unfold and refold it again into the CB[10].(a,a,a,a)-3 conformer by addition of CB[10].CB[5] and aminoadamantane (18). The transformation of CB[8].(a,a,a,s)-3 into CB[7].(a,s,s,a)-3.CB[7] proceeds through the intermediacy of CB [8].(a,a,s,a)-3.CB[7], which enhances the rate of dissociation of strand 3 from CB[8].

Efficient Preparation of Separable Pseudo[n]rotaxanes by Selective Threading of Oligoalkylammonium Salts with Cucurbit[7]uril

“…Our detailed studies disclosed that the threading process showed high selectivity and only a limited number of CB units can be located at very specific sites on the cationic thread. At the same time, by taking advantage of the high binding constant between the CBs and the p-xylene diammonium units [14][15][16][17][18] and the unique solubility of CBs in protonic acid, [19] we found that these well-defined pseudo [n]rotaxanes could also be separated as pure and stable compounds from the complex systems by simple counterion exchange.…”

“…[14][15][16][17][18] Furthermore, cucurbiturils have also been used in the preparation of polyrotaxanes and pseudopolyrotaxanes [19] by diversified approaches as reported by Kim and co-workers, [20] Steinke and Tuncel, [21] Liu, [22] and others. [23] One general method is to utilize the unique click chemistry of alkyne and azide in the inner cavity of cucurbituril.…”

“…The upfield shift of the resonance peaks for aromatic protons (H b , H c ) and methylene protons (H a , H d ) suggested that one of the xylene units was encircled with CB [7], and the resonance assigned to the uncomplexed xylene unit showed a downfield shift because of the effect of adjacent carbonyl oxygen atoms on CB [7] (see detailed assignment in Figure 3C). [16,28,29] Interestingly, addition of more CB [7] (2 equiv) did not change the spectrum, and the approximate 1:1 integration ratio of the resonances for the complexed and uncomplexed phenyl rings indicated that only one CB [7] ring threaded onto the 2·A C H T U N G T R E N N U N G (PF 6 ) 3 to form a pseudo [2]rotaxane. Addition of an excess of aqueous NH 4 PF 6 to the solution resulted in precipitation of the asformed pseudo [2]rotaxane with PF 6 À as counterions, whereas the excess CB [7] still remained in the acidic solution.…”

The Delivery of Triamterene by Cucurbit[7]uril: Synthesis, Structures and Pharmacokinetics Study

“…Recently, cucurbit [n]urils (CB [n], Scheme 1) have attracted much attention due to their wide applications in chemistry, 20 material, 21 biology, 22,23 and medicine science, 24,25 following the discovery of CB [n] homologues (CB [5], CB [6], CB [7], CB [8], CB [5]@CB [10], CB [10] and CB [14]). 26−30 Cucurbituril (Scheme 1) contains a hydrophobic cavity with two uniform hydrophilic portals composed of carbonyl functional groups.…”

Deconvolution of a multi-component interaction network using systems chemistry

“…Subsequent work by our group has shown that thermodynamic self-sorting processes can be designed to occur in water using cucurbit[n]uril (CB[n]) molecular containers as hosts and can even be engineered to create systems that slowly transform from kinetic self-sorted to thermodynamic self-sorted states [37,38]. Most recently, we have begun to study the ability of such systems to respond to suitable chemical stimuli (guest addition) which resulted in artificial chaperones for folding of non-natural oligomers, pH controlled inter-aggregate molecular shuttles, metal-ion triggered folding and assembly of a heterochiral double helical structure, and as a method to control enzymatic catalytic processes [39][40][41][42].…”