Fluorescence Response Mechanism of d-Glucose Selectivity for Supramolecular Probes Composed of Phenylboronic-acid-modified β-Cyclodextrin and Styrylpyridinium Dyes

Abstract

Saccharide sensing is a current topic of interest in molecularrecognition chemistry because of the importance of determining saccharide concentrations in physiological fluids and clarifying the functions of glycoproteins at biomembranes. 1,2 Although several types of saccharide receptors having different recognition mechanisms are available, the most well-understood receptors are arylboronic acids. [3][4][5][6][7][8][9][10] The advantage of arylboronic acids as saccharide receptors originates in the favorable stability of cyclic boronate esters that are formed on reacting arylboronic acids with saccharides, even in water. In addition, it is easy to read out photophysical signals, such as UV-visible and fluorescence signals, associated with the formation of cyclic boronate esters. However, arylboronic acids have intrinsic affinity towards D-fructose (D-fru) rather than D-glucose (D-glc), 11 the most important saccharide in physiological fluids. This disadvantage has been overcome by synthesizing ditopic arylboronic acids in which two boronic acid residues are precisely attached to a single molecule. [12][13][14][15] We recently reported a novel saccharide probe that showed a favorable fluorescent response in the presence of D-glc. 16 This novel supramolecular fluorescent probe, which is composed of β-cyclodextrin (β-CD) bearing a phenylboronic acid moiety (1) and 1-heptyl-4-(4-dimethylaminostyryl)pyridinium (C7SP), demonstrated selectivity for D-glc rather than D-fru, although the saccharide receptor 1 showed affinity towards D-fru rather than D-glc. The complicated equilibria involving the 2:1 complex formation of 1 with C7SP prevented us from clarifying the exact mechanism of the observed D-glu selectivity of the 1-C7SP system in spite of its high fluorescence response. Thus, we embarked on examining the supramolecular complex formation and the fluorescence signaling for saccharides using a much simpler system, called C1SP, which is a methyl analogue of C7SP. Although the fluorescence signals are weaker for the 1-C1SP system than for the 1-C7SP system, 1 forms only a 1:1 inclusion complex with C1SP, making precise evaluation of the saccharide sensing mechanism feasible. Here, we report on a unique mechanism of the marked fluorescence enhancement and the D-glc selectivity of the supramolecular 1/C1SP complex based on equilibrium analysis in neutral and alkaline aqueous solutions containing saccharides. Our results revealed not only the unique fluorescence enhancement mechanism of the complexes of 1 with C1SP and C7SP in response to D-glc

pH-Independent Recognition of Polyhydroxy Compounds by Niobium(V) Porphyrin Complex with Unique Sugar Selectivity

“…The value is comparable to those for the reactions with resorcinol and phenol of n = 1, so that the reaction is expressed as Eq. (11). The reactivity order of polyhydroxy compounds are as follows: catechol > sorbose, fructose > glycerin in the twophase system; sorbose, fructose > glycerin, catechol in dioxanewater.…”

“…9,10 A special host containing two boronic acids or a supramolecular assembly system was proposed to enhance the selectivity to D-glucose. 6,7,[11][12][13] For further development towards various analytes, the hosts based on Lewis acids other than boron may be promising but have scarcely been explored; only Co(II) and Cu(II) complexes were examined for sugar sensing. 14,15 We have successfully used the porphyrin complexes of zirconium(IV) for recognition and potentiometric detection of hard bases such as citrate and triphosphate.…”

Effects of Cyclodextrins on Intramolecular Photoinduced Electron Transfer in a Boronic Acid Fluorophore

“…The versatile designs of chemosensors based on supramolecular chemistry are another approach to construct novel sugar sensors. [15][16][17] We have shown that the boronic acid fluorophore (C1-APB)/β-cyclodextrin (β-CyD) complex acts as a supramolecular sugar sensor. 18 The chemical structures of C1-APB and CyDs are depicted in Fig.…”

Phenylboronic Acids-based Diagnostic and Therapeutic Applications

“…[5][6][7][8][9] Optical and electrical chemosensing applications, including those focusing on glucose detection, were the next achievement. [10][11][12] The first concept of which appeared in the late 1990s and developments in this field are still active today. [13][14][15][16][17] Later works revealed that PBA could also interact with a variety of biological membranes including cells, viruses , bacteria and fungi through the membrane-constituting carbohydrate moieties.…”