Selective Sugar Recognition by Anthracene-Type Boronic Acid Fluorophore/Cyclodextrin Supramolecular Complex Under Physiological pH Condition

Cyclodextrin Host-Guest Recognition in Glucose-Monitoring Sensors

Diabetes mellitus is a prevalent chronic health condition that has caused millions of deaths worldwide. Monitoring blood glucose levels is crucial in diabetes management, aiding in clinical decision making and reducing the incidence of hypoglycemic episodes, thereby decreasing morbidity and mortality rates. Despite advancements in glucose monitoring (GM), the development of noninvasive, rapid, accurate, sensitive, selective, and stable systems for continuous monitoring remains a challenge. Addressing these challenges is critical to improving the clinical utility of GM technologies in diabetes management. In this concept, cyclodextrins (CDs) can be instrumental in the development of GM systems due to their high supramolecular recognition capabilities based on the host-guest interaction. The introduction of CDs into GM systems not only impacts the sensitivity, selectivity, and detection limit of the monitoring process but also improves biocompatibility and stability. These findings motivated the current review to provide a comprehensive summary of CD-based blood glucose sensors and their chemistry of glucose detection, efficiency, and accuracy. We categorize CD-based sensors into four groups based on their modification strategies, including CD-modified boronic acid, CD-modified mediators, CD-modified nanoparticles, and CD-modified functionalized polymers. These findings shed light on the potential of CD-based sensors as a promising tool for continuous GM in diabetes mellitus management.

Sensitive and specific detection of saccharide species based on fluorescence: update from 2016

Increasing evidence supports the critical role of saccharides in various pathophysiological steps of tumor progression, where they regulate tumor proliferation, invasion, hematogenic metastasis, and angiogenesis. The identification and recognition of these saccharides provide a solid foundation for the development of targeted drug preparations, which are however not fully understood due to their complex and similar structures. In order to achieve fluorescence sensing of saccharides, extensive research has been conducted to design molecular probes and nanoparticles made of different materials. This paper aims to provide in-depth discussion of three main topics that cover the current status of the carbohydrate sensing based on the fluorescence sensing mechanism, including a phenylboronic acid-based sensing platform, non-boronic acid entities, as well as an enzyme-based sensing platform. It also highlights efforts made to understand the recognition mechanisms and improve the sensing properties of these systems. Finally, we present the challenge of achieving high selectivity and sensitivity recognition of saccharides, and suggest possible future avenues for exploration.

Marcus model-based analysis of the photo-quenching mechanism of a boronic acid fluorophore: water concentration dependence of electron transfer rate

The photo-quenching mechanism of 2-(4-phenylboronic acid)-1-pyrenemethamide (C1-APB), which has potential application as a saccharide-recognition sensor, was investigated. By performing temperature-dependent time-resolved photoluminescence measurements, we determined the mechanism responsible for the photo-quenching properties of C1-APB to be a photoinduced electron transfer (PET). Moreover, the dependence of the electron transfer rate (k_PET) on the solvent water concentration was explored in detail, and it was found that k_PET increased by many orders of magnitude with increasing water concentrations. This phenomenon was analyzed using the Marcus model, in which the electron transfer can be represented by a potential diagram involving the potential barrier (ΔG_a) and frequency factor (A). With the aid of temperature-dependent measurements, the contribution of ΔG_a and A to the increase in k_PET was successfully analyzed independently, which allowed us to discuss the effect of water molecule orientation and change in molecular structure of C1-APB. The temperature-dependence measurements performed in this study offer a powerful research tool for investigating the PET process, and will contribute to the development of molecular recognition fluorescent sensors.

A simple supramolecular complex of boronic acid-appended β-cyclodextrin and a fluorescent boronic acid-based probe with excellent selectivity for d-glucose in water

A simple supramolecular complex of modified cyclodextrin with a boronic acid probe enabled the highly selective detection of d-glucose in water.

Effect of Spacer Length in Pyrene-Modified-Phenylboronic Acid Probe/CyD Complexes on Fluorescence-based Recognition of Monosaccharides in Aqueous Solution

The chemical sensing of saccharides is of importance for the diagnosis of diabetes. Various enzymatic sensors have been developed, but their heat and pH instability issues need to be resolved. In this regard, the development of artificial saccharide sensors with high stability is attracting attention. We have designed a heat- and pH-stable supramolecular inclusion complex system composed of cyclodextrin (CyD) as a host and a phenylboronic acid (PB) probe possessing pyrene as a fluorescent guest. Several probes possessing alkyl spacers having various lengths between the PB and the pyrene moiety, Cn-APB (n = 1 - 4), were newly synthesized and evaluated with respect to their monosaccharide recognition ability on the basis of the fluorescence response through the cyclic esterification of monosaccharide and PB. These Cn-APB/CyD supramolecular inclusion complexes have exhibited a selective fluorescence response towards fructose in aqueous solution based on the photo-induced electron transfer mechanism. The spacer length of the alkyl group in Cn-APB significantly affects the affinity for saccharides. With respect to the complex between C4-APB and PB-modified CyD (3-PB-γ-CyD), it was found that the supramolecular inclusion complexes had high selectivity for glucose with significant fluorescence enhancement. These results indicate that the lengths of the alkyl spacers in the probe molecules are important to control the recognition of saccharides in aqueous solution.

Supramolecular Zn(II)-Dipicolylamine-Azobenzene-Aminocyclodextrin-ATP Complex: Design and ATP Recognition in Water

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.