Switchable Cucurbituril–Bipyridine Beacons

Abstract

4-Aminobipyridine derivatives form strong inclusion complexes with cucurbit[6]uril, exhibiting remarkably large enhancements in fluorescence intensity and quantum yields. The remarkable complexation-induced pK(a) shift (DeltapK(a)=3.3) highlights the strong charge-dipole interaction upon binding. The reversible binding phenomenon can be used for the design of switchable beacons that can be incorporated into cascades of binding networks. This concept is demonstrated herein by three different applications: 1) a switchable fluorescent beacon for chemical sensing of transition metals and other ligands; 2) direct measurement of binding constants between cucurbit[6]uril and various nonfluorescent guest molecules; and 3) quantitative monitoring of biocatalytic reactions and determination of their kinetic parameters. The latter application is illustrated by the hydrolysis of an amide catalyzed by penicillin G acylase and by the elimination reaction of a beta-cabamoyloxy ketone catalyzed by aldolase antibody 38C2.

Applicable Properties of Cucurbiturils

“…The specific case discussed below involves an effort to create interconnected networks of non‐covalent binding equilibria where one binding event triggers a cascade of other binding phenomena 10. Such equilibria cascades, which can give rise to specific functional outputs, represent very common regulatory mechanisms in biological systems.…”

Supramolecular Assemblies for Information Processing

“…The list of CB-derived systems with logic gate functionality on application of chemical input signals could be surely extended. For example, a recent work by the Keinan group [60], in which chemically switchable CB6-bipyridine beacons (see 4-aminobipyridine structures 24 and 25 in Scheme 6.12) are demonstrated, bears potential in this direction. However, the herein discussed few case studies are meant to just illustrate the general idea.…”

Single and Double Binding of 1,10‐Phenanthroline and 4,7‐Dimethyl‐1,10‐phenanthroline to HMeQ[7]: Contrasting pKa Shifts Induced by HMeQ[7]

“…In the past decade, several literature reports have demonstrated the supramolecular p K a shift of guests induced by Q[ n ]s . For example, Bhasikuttan group presented large upward p K a shifts in two bichromophoric coumarin laser dyes induced by Q[7], and established their supramolecular structure‐property relationship .…”

“…For example, Bhasikuttan group presented large upward p K a shifts in two bichromophoric coumarin laser dyes induced by Q[7], and established their supramolecular structure‐property relationship . Keinan and co‐workers investigated the binding interactions of series of aminobipyridine derivatives with Q[6], found that their inclusion complexes exhibit remarkably large enhancements in fluorescence intensity and quantum yields as well as remarkable complexation‐induced p K a shifts . In particular, Nau and Pal et al studied the interaction of Q[7] with neutral red and the photophysical properties of the dye, revealing an exceptionally large p K a shift ( ∼2 units) for neutral red upon complexation with Q[7] …”