A case of oxoanion recognition based on combined cationic and neutral C–H hydrogen bond interactions

Abstract

A novel bidentate bis-(benzimidazolium) receptor containing pyrene as fluorescent signaling units has been synthesized. Fluorescence and NMR spectroscopy studies reveal that this receptor exclusively recognizes sulphate and hydrogenpyrophosphate in the competitive water-DMSO (1 : 9) medium; significant downfield shifts were observed for the C(2)-H protons of both the imidazolium groups, and appreciable downfield shifts were also observed for the inner naphthalene protons indicating their participation in hydrogen bonding with anions along with the C(2) imidazolium protons. The calculated association constants from (1)H NMR and fluorescence titrations demonstrate that the receptor binds sulphate stronger than hydrogenpyrophosphate anions.

Utilizing a pH‐Sensitive Dye in the Selective Fluorescent Recognition of Sulfate

“…Compound 6 (tert-Butyl N-{2-amino-4- [8-(2-methoxyethoxy)-2,4dioxo-3-azatricyclo-[7.3.1.0 5,13 ]trideca-1(12), 5,7,9(13),10-pentaen-3yl]phenyl}carbamate): The Boc-protected nitroamine 5 (2.35 g, 5mmol) was dissolved in dry THF (100 mL). In another flask, Pd/C 10 %( 230 mg) was suspended in THF (100 mL) and saturated with hydrogen for 30 min.…”

“…The reaction mixture was filtered from the catalyst and evaporated. The product was purified by column chromatography in 1, 58.3, 68.5, 70.0, 78.8, 106.9, 114.6, 115.9, 116.6, 122.4, 122.9, 123.4, 124.4, 126.3, 128.3, 128.9, 131.0, 132.5, 133.1, 141.53, 153.6, 159.5, 163.1, 163.7;E SI-MS calcd for M + H + : 478.1973, found 478.1979. Compound 3 (3-(3,4-diaminophenyl)-8-(2-methoxyethoxy)-3-azatricyclo-[7.3.1.0 5,13 ]trideca-1(12), 5,7,9(13),10-pentaene-2,4-dione): N-(p-Amino-m-nitrophenyl)-4-(2'-methoxyethoxy)-1,8-naphthalimide 4 (1.53 g, 3.75 mmol)and 10 %P d/C powder (0.15 g) were mixed in THF (300 mL) and saturated with hydrogen gas for 2h.T hen water (50 mL) was added and the reaction mixture was stirred under hydrogen atmosphere at r.t. overnight. The catalyst was filtered off and the solution was evaporated.…”

“…[2] This emphasis reflectsagrowingi nterest fors uch systemsi nm odeling the functions of naturala nion binding proteins,a sw ell as in ad emand of their use in analyticala pplications.T ypically,as ynthetic receptor that binds anionsi no rganic solvents show much lower or almost no affinity for anions in aqueous mediumb ecause of the competition between anions and molecules of water. [2a] Generala pproaches to retain or introduce the property to bind anions in aqueous mediumi nclude the construction of molecular cages [3] or the introduction of positive charges [4,5] and solubilizing groups [6] in the structure of ahost.…”

Imidazolium Based Probes for Recognition of Biologically and Medically Relevant Anions

“…Caballero, Molina and coworkers have studied the detection of oxoanions SO 4 2− and HP 2 O 7 3− in highly competitive aqueous media through NMR and fluorescence studies. The solution of probe 127 in DMSO‐H 2 O (9:1) gave only weak emission due to both monomer and excimer emission bands of pyrene moiety (λ ex 360 nm).…”

Amide‐Triazolium‐Appended Anthracenes for Turn‐On Fluorescence Sensing of Anions in Noncompetitive and Competitive Solvents

“…There has been growing interest in anion recognition because anions play ubiquitous roles in chemical and biochemical processes, and some are also of great environmental and medical concern . In particular, the binding of fluoride and phosphate ions represents an important part of this field, because fluoride ions show duplicitous clinical nature, and phosphates play important roles in biology in signaling, energy transduction, and information storage and expression . Therefore, many man‐made receptors incorporating different anion‐binding sites and signaling subunits have been developed to realize the sensitive and selective detection of these anions.…”