Potassium cavity binding site

One constant problem for crown ether based sensors in vivo is the ubiquitous presence of chemical species that will compete with the target analyte for the sensor binding site. For sensors incorporating [18]crown-6 this especially problematic as sodium, potassium, ammonium and hydronium (H30+) cations are all attracted to the threefold symmetry of the crown s cavity. Protonated terminal amines, including amino acids and peptides, can also interfere with analyte detection. It is therefore all the more pleasing when a crown ether based sensor is developed that does not bind to biologically common cations. This is the case for a saxitoxin chemosensor reported by Gawley, LeBlanc and co-workers [24],... 

Crown Ether Complexes In Chapter 6, we encountered the use of crown ethers, large cyclic polyethers that specifically solvate metal cations by complexing the metal in the center of the ring. Different crown ethers solvate different cations, depending on the relative sizes of the crown ether and the cation and the number of binding sites around the cation. The EPM of 18-crown-6 shows that the cavity in the center of the molecule is surrounded by electron-rich oxygen atoms that complex with the guest potassium cation. 

In fact, self-assembly of 5 -GMP depends critically on the caption present Pinnavia et al. using nmr(36) and Laszlo et al. (34,37-39) using 23 a and nmr showed a potassium-selective interaction of alkali metal cations with the central cavity in the 5 -GMP tetramers. When sodium and potassium ions are present in conjunction, an organized structure [(G, K , G ), 4 Na ] forms(40). Potassium ions bind selectively to the inner (cavity) site, where they are sandwiched in between two GMP tetramers(40). These are maintained at a spacing close to 3.3 A which is characteristic of base stacking (41), while the oxygen distances... 

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