Fluorescence Sensing of Monosaccharides by Bis-boronic Acids Derived from Quinolinium Dicarboxamides: Structural and Spectroscopic Studies

Abstract

Three new diboronic acid-substituted bisquinolinium salts were synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptors for six monosaccharides and two open-chain polyols in water at physiological pH. The dicationic pyridine-2,6-dicarboxamide-based receptors contain two N-quinolinium rings as the fluorescent units covalently linked to three different isomers of phenylboronic acid (ortho, 2; meta, 3; and para, 4) as chelating binding sites for polyols. Additions of glucose/fructose in the micromolar concentration range to receptors 2 and 3 induce significant fluorescence changes, but in the presence of arabinose, galactose, mannose, and xylose, only modest optical changes are observed. This optical change is attributed to a static photoinduced electron transfer mechanism. The meta-diboronic receptor 3 exhibited a high affinity/selectivity toward glucose (K = 3800 M −1 ) over other monosaccharides including common interfering species such as fructose and mannitol. Based on multiple spectroscopic tools, electrospray ionization high-resolution mass spectrometry, crystal structures, and density functional theory calculations, the binding mode between 3 and glucose is proposed as a 1:1 complex with the glucofuranose form involving a cooperative chelating diboronate binding. These results demonstrate the usefulness of a new set of cationic fluorescent diboronic acid receptors with a strong ability for optical recognition of glucose in the sub-millimolar concentration range.

Molecular two-point recognition of fructosyl valine and fructosyl glycyl histidine in water by fluorescent Zn(ii)-terpyridine complexes bearing boronic acids

“…34,49,54 This fact is not unexpected because it is well known that the cationic nature of the quinolinium ring covalently appended to boronic acid reduces the pK a values up to two orders of magnitude. 32,51,55 On the other hand, very low pK a values ranging from 6.70 to 7.90 have been reported previously for quinolinium 51,55 and isoquinolinium 50 nuclei-bearing isomers (ortho, meta) of phenylboronic acids. These values are consistent with those estimated for 2Zn and 3Zn.…”

“…Among different saccharide recognition techniques, fluorescence is particularly desired due to its known high sensitivity, quick and direct analytical response. 32 Arylboronic acids can form reversible covalent bonds with 1,2-diols in basic aqueous media 33 where the binding strength of boronic acid-1,2-diol ester depends on the orientation of the analyte's vicinal hydroxyl groups, 34 the acidity of the boronic acid, 35 and the influence of substituent groups to stabilize the sp 3 -boronate ester. 28 In the last few decades, phenylboronic acid fluorophores have been demonstrated to be an outstanding tool for recognizing and sensing monosaccharides, 36 catechol-based neurotransmitters, 37 nucleotides, 38 sialic acid, 39 glucosamine, 40 ginsenosides, 41 glycated hemoglobin, 42 and in general, 1,2-dihydroxy-substituted derivatives.…”

“…Among different saccharide recognition techniques, fluorescence is particularly desired due to its known high sensitivity, quick and direct analytical response. 32…”

Water-soluble fluorescent chemosensor for sorbitol based on a dicationic diboronic receptor. Crystal structure and spectroscopic studies

“…Bromide salts of 11–13 were prepared according to modified procedures reported previously. 47,53 The detailed procedure of intermediaries 9-10 and bromide salt of 12 , previously reported by us, is described in the ESI †…”

“…47,53 The detailed procedure of intermediaries 9-10 and bromide salt of 12, previously reported by us, is described in the ESI. † The mixture was slurred for 2 h. Subsequently, 12.0 mL of ethyl acetate was added and stirred vigorously for 30 min, then cooled in an ice bath.…”