A Bambusuril Macrocycle that Binds Anions in Water with High Affinity and Selectivity

Abstract

Synthetic receptors that function in water are important for the qualitative and quantitative detection of anions, which may act as pollutants in the environment or play important roles in biological processes. Neutral receptors are particularly appealing because they are often more selective than positively charged receptors; however, their affinity towards anions in pure water is only in range of 1–103 L mol−1. The anion‐templated synthesis of a water‐soluble bambusuril derivative is shown to be an outstanding receptor for various inorganic anions in pure water, with association constants of up to 107 L mol−1. Furthermore, the macrocycle discriminates between anions with unprecedented selectivity (up to 500 000‐fold). We anticipate that the combination of remarkable affinity and selectivity of this macrocycle will enable the efficient detection and isolation of diverse anions in aqueous solutions, which is not possible with current supramolecular systems.

Prospects and Challenges in Anion Recognition and Transport

“…. Contemporaneously, Pittelkow and co-workers reported the anion-binding properties of biotin [6]uril 5 in 100 mM phosphate-buffered solution (Figure 1). 7 Again, this receptor shows selectivity for hydrophobic anions, such as SCN À under aqueous conditions.…”

“…The following year, Sindelar and co-workers reported the anion receptor properties of a bambusuril macrocycle 4 (Figure 1). 6 This compound has a hydrophobic cavity lined with CH groups and in 20 mM K 2 DPO 4 solution at pD 7.1 shows selectivity for anions at the hydrophobic end of the Hofmeister series, such as ClO 4…”

Fluorinated Bambusurils as Highly Effective and Selective Transmembrane Cl−/HCO3− Antiporters

“…40 Bambus [6]urils are macrocycles structurally related to the biotin [6]urils and are known for their high affinity toward inorganic anions in both organic solvents and aqueous environments. [41][42][43] Recently, a semi-thiobambus [6]uril was shown to function as an anion carrier, albeit not as efficiently as the biotin [6]uril macrocycles. 44 Based on the high anion affinities found for bambusuril 1 (Scheme 1), 45 high selectivities observed in binding, 46 the high degree of encapsulation of anions, and their polarized but non-acidic CH groups involved in anion binding, 47 we expected bambus [6]urils to be potentially very selective anion carriers.…”

Chemical Sensors Based on Cucurbit[n]uril Macrocycles

“…[32] Inorganic anions can be efficiently bound in water with the CBn-related bambus[n]uril macrocycles, introduced by Sindelar and co-workers. [33,34,35,36,37,38,39,40] Their use as anion-chemosensors awaits an improved signal transduction besides 1 H NMR.…”