Abstract
We synthesized novel PET (photoinduced electron transfer)-type fluorescence glucose probe 1 [(4-(anthracen-2-yl-carbamoyl)-3-fluorophenyl)boronic acid], which has a phenylboronic acid (PBA) moiety as the recognition site and anthracene as the fluorescent part. Although the PBA derivatives dissociate and bind with sugar in the basic condition, our new fluorescent probe can recognize sugars in the physiological pH by introducing an electron-withdrawing fluorine group into the PBA moiety. As a result, the pKa value of this fluorescent probe was lowered and the probe was able to recognize sugars at the physiological pH of 7.4. The sensor was found to produce two types of fluorescent signals, monomer fluorescence and dimer fluorescence, by forming a supramolecular 2:1 complex of 1 with glucose inside a γ-cyclodextrin (γ-CyD) cavity. Selective ratiometric sensing of glucose by the 1/γ-CyD complex was achieved in water at physiological pH.
Highlights
Sugars, especially monosaccharides, play important roles in various biological systems (Brewer et al, 2002; Davis, 2002; Brodesser et al, 2003)
We introduced an electron-withdrawing fluorine group into the phenyl group of the phenylboronic acid (PBA) moiety to reduce the pKa value of PBA (Figure 1)
We report the introduction of fluorine into PBA to reduce the pKa value of the probe, and selective glucose sensing at physiological pH in water, by measurements of fluorescence spectra and induced circular dichroism (ICD) spectra
Summary
Especially monosaccharides, play important roles in various biological systems (Brewer et al, 2002; Davis, 2002; Brodesser et al, 2003). As a hydrophobic sensor (or probe) is included inside the CyD cavity, the formation of a stable supramolecular complex in water is expected. We have shown an efficient dimer formation for selective glucose sensing, in which two fluorescent molecules are included inside a CyD cavity and emits dimer fluorescence at long wavelengths (Hashimoto et al, 2019) This system realizes glucose recognition only in the basic condition (pH 11) due to the high pKa value of PBA. We report the introduction of fluorine into PBA to reduce the pKa value of the probe, and selective glucose sensing at physiological pH in water, by measurements of fluorescence spectra and induced circular dichroism (ICD) spectra. To evaluate the formation of boronic acid probe/CyD supramolecular complex, UV-vis and fluorescence spectral measurements were performed. Solutions containing probe 1 (10 μM), γ-CyD (5 mM), sugar (0–30 mM), phosphate buffer (10 mM, adjusted to pH 7.4), and NaCl (100 mM) were prepared and fluorescence spectra were measured at pH 7.4 with the addition of sugar
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