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 1-10(3)  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 10(7)  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.

Counterions influence three-center halogen bonds differently than coordination bonds of transition metals.

Institute of Mathematics of the Academy of Sciences of the Czech Republic provides access to digitized documents strictly for personal use. Each copy of any part of this document must contain these Terms of use. This paper has been digitized, optimized for electronic delivery and stamped with digital signature within the project DML-CZ: The Czech Digital Mathematics Library http://project.dml.cz Časopis pro pěstování matematiky, roč. 80 (1955) POZNÁMKA O EXISTENCI KONEČNÝCH GRAFŮ VÁCLAV HAVEL, Praha. (Došlo dne 23. prosince 1954.) J)T 519.5 V této poznámce je udán algoritmus, podle něhož lze rozhodnout, zdali daná přirozená čísla a x , a 2 , ..., a n lze pokládat za stupně jednotli vých uzlů nějakého konečného grafu. Grafem budeme rozumět konečnou množinu se symetrickou a nereflexivní binární relací mezi jejími prvky. Ke každému prvku přiřadíme počet všech těch prvků, které s ním stojí v grafové relaci. Z těchto přiřazených čísel sesta víme nerostoucí posloupnost a nazveme ji strukturou. Pořadí, členů struktury určuje pořadí odpovídajících prvků grafu. Položme (i, j) = 1 (resp. (i, j) = 0), když i-tý prvek je (resp. není) v relaci s /-tým prvkem. Dále nazveme r-posloupnosti konečnou nestoupající posloupnost, jejímiž členy jsou přirozená čísla, při čemž je první člen menší než počet všech členů a počet lichých členů je sudý; strukturu, která je r-posloupností, nazveme r-strukturou.

A recently discovered anion receptor is jointed by three related macrocycles differing in the number of glycoluril units and type of substitution. The synthesis is carried out in nonpolar solvents compared to aqueous media used in the case of the original macrocycle. The size of macrocycle is controlled by a template. A hexameric macrocycle with benzyl substitution binds halide anions with an affinity exceeding 10(9) M(-1) while a tetrameric analog does not bind any of the investigated anions.

Neutral and negatively charged anion receptors functioning in pure water are rare in supramolecular chemistry. Moreover, studies on adjusting the affinity of such receptors toward anions in water are absent from the literature. Two new bambusurils, 1 a and 2 a, were prepared to demonstrate that the affinity of bambusurils towards anions can be altered by the length of carboxyalkyl groups attached to the macrocycles. The stability of the bambusuril complexes was further controlled by the pH value. The crystal structure of bambusuril 1 a was described, in which two carboxyalkyl arms fold into the macrocycle cavity, thus forming the intramolecular self-inclusion complex.

Bambus[6]urils are a class of neutral anion receptors with outstanding binding properties in various solvents. The host–guest associations of bambusurils in aqueous environments have been investigated in detail, but their behavior in nonpolar solvents has not yet been reported. This paper presents isothermal calorimetry and 1H NMR data on the binding of dodecabenzylbambus[6]uril (Bn12BU[6]) to seventeen anions in chloroform. Under these conditions, anion inclusion in the macrocycle appears to be enthalpy‐driven, yielding complexes with stability constants of up to 1010 m−1. Perchlorate was optimally sized for inclusion in Bn12BU[6], while larger anions exhibited significantly lower affinity for the macrocycle. In addition, complexes of bambusuril and anions can be differentiated by NMR analysis based on the unique chemical shifts of characteristic peaks in their spectra. This finding was used to perform quantitative and qualitative analysis of multiple anion mixtures.

No abstract

No abstract