A wavelength?ratiometric fluoride-sensitive probe based on the quinolinium nucleus and boronic acid moiety

Abstract

We report a new water-soluble fluorescent probe sensitive to aqueous fluoride. The probe shows spectral shifts and intensity changes in the presence of fluoride, in a wavelength ratiometric and colorimetric manner, enabling the detection of fluoride concentrations at visible wavelengths, in the concentration range ≈1-300 mM. The probes response is based on the ability of the boronic acid group to interact with fluoride, changing from the neutral form of the boronic acid group [R-B(OH) 2 ] to the anionic trifluoro form [R-B-F 3 ], which is an electron donating group. The presence of an electron-deficient quaternary heterocyclic nitrogen center and a strong electron donating amino group in the 6position, on the quinolinium backbone, provides for the spectral responses observed upon fluoride binding to the boronic acid group. Interestingly, the presence of the amino group on the 6-position of the quinolinium backbone suppresses the response of the boronic acid containing fluorophore towards monosaccharides, such as glucose and fructose, which are present in biological fluids and food stuffs, potentially allowing for the predominant fluoride sensitivity. In addition to physiological sugars, we discuss the response of aqueous halides as potential interferents, or indeed analytes to be sensed, and show that the new probe responds well to aqueous fluoride in the presence of a high background of other species, such as in a biological cocktail of 50 mM glucose, 50 mM aqueous Cl − and 5 mM fructose.

Cyanide-sensitive fluorescent probes

“…This important find expands on our recent reports of cyanide-sensitive probes based on the boronic acid moiety [11,12], and suggests the widespread application of BAFs to cyanide sensing. With regard to physiological cyanide sensing and safeguard, other anions such as OH ÿ [26] and F ÿ [27,28] are also known to complex with boronic acid. However, fluoride levels in blood are very low, and not thought to vary much, 20e60 mg/L [28], while the concentration of OH ÿ in blood is 10 ÿ7 M, with most physiologies not experiencing any notable changes in pH.…”

“…With regard to physiological cyanide sensing and safeguard, other anions such as OH ÿ [26] and F ÿ [27,28] are also known to complex with boronic acid. However, fluoride levels in blood are very low, and not thought to vary much, 20e60 mg/L [28], while the concentration of OH ÿ in blood is 10 ÿ7 M, with most physiologies not experiencing any notable changes in pH. Finally, with regard to the sensing mechanism of boronic acid with cyanide, a recent report by us has suggested that traditional dynamic fluorescence quenching [29] has no or little effect on probe fluorescence at these mM cyanide concentrations of interest [30], further confirming our boronic acidecyanide complexation interaction for sensing.…”

Carbohydrate biomarkers for future disease detection and treatment

“…Among all the carbohydrate sensors, boronic acid emerges as the most commonly used functional group for recognition, due to its strong interactions with diols [51-55, 231, 239, 250-263], aminoalcohols [264][265][266], α-aminoacids [267], α-hydroxyl acids [268][269][270][271], alcohols [55,233,[272][273][274][275][276][277][278][279][280][281][282][283][284][285][286][287] as well as cyanide [288,289] and fluoride [290][291][292][293][294]. The intrinsic ability for boronic acids to interact with nucleophiles is described in Scheme 2.…”

Anionic chromogenic chemosensors highly selective for cyanide based on the interaction of phenyl boronic acid and solvatochromic dyes

“…Another component of the chemosensor set is comprised of boronic acids which are used in supramolecular devices as efficient recognition units, especially for monosaccharides and anionic species, such as F − and CN − [15,[44][45][46][47][48][49]. Therefore, a displacement strategy involving compound 2 and phenyl boronic acid (PBA) was studied for the development of a chromogenic chemosensor which is highly selective toward F − among other anionic species [35].…”

“…In other related study, Cha et al developed a chromogenic chemosensor for F − based on a displacement assay using a merocyanine as the signalizing unit and PBA [50]. Although boronic acids have been utilized as recognition units in optical chemosensors for the detection of CN − [48,49,[51][52][53], this anion was not studied in the previous reports that make use of PBA-merocyanine displacement assays. In this paper, compounds 1 and 2 (Scheme 1) and PBA were used to study an anionic chromogenic chemosensor based on the displacement of the dye from the boron center caused by the nucleophilic attack of the anion on the boron center of the intermediate.…”