Design of a Fluorescent Dye for Indicator Displacement from Cucurbiturils: A Macrocycle-Responsive Fluorescent Switch Operating through a pK_a Shift

Abstract

The derivatization of 3-amino-9-ethylcarbazole with a diamino-alkyl anchor affords a fluorescent dye suitable for indicator displacement from cucurbituril macrocycles. The novel compound 1 shows, due to a complexation-induced pKa shift, a large and predictable dual fluorescence response (100-fold increase at 375 nm and 9-fold decrease at 458 nm) upon supramolecular encapsulation and a strong affinity for cation-receptor macrocycles, in particular cucurbit[6]uril (CB6). A direct application is presented by monitoring the enzymatic activity of lysine decarboxylase.

Switching Properties of a Spiropyran–Cucurbit[7]uril Supramolecular Assembly: Usefulness of the Anchor Approach

“…[12,16,18,21,23] Invariably, the complexation by CBs leads to higher guest pK a values. In the present case the phenolic moiety has a pK a of 4.2 for the uncomplexed guest which shifts to pK a ' = 5.0 for the CB7 complex, i.e., pK a = pK a '  pK a = 0.8 ( Figure 5).…”

“…Cucurbiturils (CBs) are a recently widely explored class of water-soluble macrocyclic host compounds [1] with applications in chemosensing assemblies, [2][3][4][5][6][7] label-free enzyme assays, [8] nanovalves, [9] molecular self-sorting, [10] dye encapsulation and stabilization, [11][12][13] supramolecular catalysis, [14,15] drug delivery, [5,[16][17][18][19][20][21] molecular logic and switches, [22][23][24][25] etc. CBs are composed of a variable number of n glycouril units (n = 5,6,7,8,10) which are linked by methylene bridges.…”

“…Given an appropriate molecular design, anchor and fluorophore can communicate via internal charge transfer or photoinduced electron transfer and thus, enable the fluorescence monitoring of the host-guest complexation. [23,24,29] The use of photochromic compounds in the context of cucurbituril chemistry has been rarely investigated. Recently, the partial inclusion of a spiropyran photochrome [30,31] in cucurbit[n]urils (n = 7 and 8, CB7 and CB8, respectively) was reported.…”

Pillararene-based fluorescent indicator displacement assay for the selective recognition of ATP

“…These changes are usually more significant than the effects observed in direct sensing that makes FID assays more desirable. The macrocyclic components in the majority of these systems are cyclodextrins [5], calixarenes [6][7][8] and cucurbiturils [9][10][11][12].…”

pH-responsive molecular assemblies of pyridylbutadiene derivative with cucurbit[7]uril

“…It is known that the interaction with cucurbituril host increases pK a of aromatic amines. [39][40][41][42] From the pK a curves, it is anticipated that DABP encapsulated in CB7 have higher propensity to remain in the protonated form than DABP in aqueous solution. Such differential binding affinity of the dye with the host molecules have been utilized for several chemical and biological applications.…”