The construction of supramolecular recognition systems based on specific host–guest interactions has been studied in order to design selective chemical sensors. In this study, guest-responsive receptors for ATP have been designed with cyclodextrins (CyDs) as a basic prototype of the turn-on type fluorescent indicator. We synthesized dipicolylamine (DPA)-modified CyD–Cu²⁺ complexes (Cu·1α, Cu·1β, and Cu·1γ), and evaluated their recognition capabilities toward phosphoric acid derivatives in water. The UV-Vis absorption and fluorescence spectra revealed that Cu·1β selectively recognized ATP over other organic and inorganic phosphates, and that β-CyD had the most suitable cavity size for complexation with ATP. The 1D and 2D NMR analyses suggested that the ATP recognition was based on the host–guest interaction between the adenine moiety of ATP and the CyD cavity, as well as the recognition of phosphoric moieties by the Cu²⁺–DPA complex site. The specific interactions between the CyD cavity and the nucleobases enabled us to distinguish ATP from other nucleoside triphosphates, such as guanosine triphosphate (GTP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). This study clarified the basic mechanisms of molecular recognition by modified CyDs, and suggested the potential for further application of CyDs in the design of highly selective supramolecular recognition systems for certain molecular targets in water.

Various diboronic acid-based chemosensors for D-glucose have been developed for use in diabetes diagnostic systems. However, most of these chemosensors have limitations, such as poor water solubility, difficulties in synthesis, and inability to selectively detect D-glucose from among other saccharides. We report a simple chemosensor based on a supramolecular complex of fluorophenylboronic acid-appended β-cyclodextrin (FPB-βCyD) and an anthracene-based probe having a boronic acid moiety (1). Hydrophobic 1 is encapsulated in the cyclodextrin cavity of FPB-βCyD, making the supramolecular complex (1/FPB-βCyD) applicable in a water-rich solvent mixture (98% water). Interestingly, 1/FPB-βCyD showed a strong turn-on response to D-glucose with a 9.6-fold enhancement in fluorescence intensity, and no response to other saccharides. This study uncovers an innovative approach based on the supramolecular assembly of simple components for the development of a water-soluble D-glucose chemosensor with excellent selectivity.

Cyclodextrins (CyDs) are water-soluble host molecules possessing a nanosized hydrophobic cavity. In the realm of molecular recognition, this cavity is used not only as a recognition site but also as a reaction medium, where a hydrophobic sensor recognizes a guest molecule. Based on the latter concept, we have designed a novel supramolecular sensing system composed of Zn(II)-dipicolylamine metal complex-based azobenzene (1-Zn) and 3A-amino-3A-deoxy-(2AS,3AS)-γ-cyclodextrin (3-NH₂-γ-CyD) for sensing adenosine-5′-triphosphate (ATP). 1-Zn showed redshifts in the UV-Vis spectra and induced circular dichroism (ICD) only when both ATP and 3-NH₂-γ-CyD were present. Calculations of equilibrium constants indicated that the amino group of 3-NH₂-γ-CyD was involved in the formation of supramolecular 1-Zn/3-NH₂-γ-CyD/ATP. The Job plot of the ICD spectral response revealed that the stoichiometry of 1-Zn/3-NH₂-γ-CyD/ATP was 2:1:1. The pH effect was examined and 1-Zn/3-NH₂-γ-CyD/ATP was most stable in the neutral condition. The NOESY spectrum suggested the localization of 1-Zn in the 3-NH₂-γ-CyD cavity. Based on the obtained results, the metal coordination interaction of 1-Zn and the electrostatic interaction of 3-NH₂-γ-CyD were found to take place for ATP recognition. The “reaction medium approach” enabled us to develop a supramolecular sensing system that undergoes multi-point interactions in water. This study is the first step in the design of a selective sensing system based on a good understanding of supramolecular structures.

Guest-induced supramolecular chirality: the guest ion selectivity was dramatically altered by a slight change in the spacer length of (15C5-Azo-n-dpa)₂–γ-CyD complexes in water.