Bile Acid-Based Cyclic Bisbenzimidazolium Receptors for Anion Recognition:  Highly Improved Receptors for Fluoride and Chloride Ions

Abstract

The anion binding properties of bile acid-based cyclic bisbenzimidazolium receptors 6-8 bridged with m-xylene, p-xylene, and 2,6-dimethylpyridine have been studied. Receptors 6 and 7 exhibit much higher binding affinity for fluoride and chloride ions, respectively, as compared to the imidazolium receptors 1 and 2. Receptor 8, however, shows high selectivity but very low binding affinity for anions due to the presence of pyridyl nitrogen. The single-crystal X-ray structure of imidazolium receptor 10-(Br)2 containing pyridyl spacer reveals the binding pattern.

Facially amphiphilic polyionene biocidal polymers derived from lithocholic acid

“…They typically stay conjugated with taurine or glycine in the liver forming bile salts that serve as surfactants to solubilize dietary lipids and fats by the formation of micelles allowing digestion of food. Bile acids have been utilized in many areas including gene delivery [ 19 , 20 ], drug delivery [ 21 ], sensing [ 22 ], polymeric gels [ 23 ], antimicrobial agents [ [24] , [25] , [26] ] and other biological applications [ 27 ].…”

Steroid-based anion receptors and transporters

“…These cyclic and acyclic structures feature positively charged C-H donor units, furnished by benzimidazolium and methyl-1,2,3-triazolium groups. Halides were bound with associations as high as 20 500 M À1 (receptor 23 + chloride, in CDCl 3 ) 29 and with selectivity tuned by adjusting the size of the binding cavity. Receptors 22 29 and 24 30 show modest selectivity for fluoride over the larger halides while receptor 23 29 was selective for chloride and bromide over fluoride and iodide.…”

“…Halides were bound with associations as high as 20 500 M À1 (receptor 23 + chloride, in CDCl 3 ) 29 and with selectivity tuned by adjusting the size of the binding cavity. Receptors 22 29 and 24 30 show modest selectivity for fluoride over the larger halides while receptor 23 29 was selective for chloride and bromide over fluoride and iodide. Receptor 25 31 bound dihydrogenphosphate with a 5 to 20 fold selectivity over the halide anions.…”

Progress of 3-aminopyridinium-based synthetic receptors in anion recognition

“…These types are known as ion pair binding hosts. A survey of previous studies reveals that charged receptors based on guanidinium, 12,13 imidazolium, [14][15][16] benzimidazolium, [17][18][19][20][21][22][23][24][25] polyammonium 26,27 and thiourenium [28][29][30] motifs are known and well explored in anion recognition. Similar to these charged systems, the pyridinium motif has been noted as a useful and versatile motif in devising molecular receptors for anions.…”