Crown ether

The resulting cations often form salts that are soluble in nonpolar solvents, and for this reason crown ethers are useful in phase transfer catalysis.

[3][4] In 1967, Charles Pedersen, who was a chemist working at DuPont, discovered a simple method of synthesizing a crown ether when he was trying to prepare a complexing agent for divalent cations.

This linking defines a polydentate ligand that could partially envelop the cation and, by ionization of the phenolic hydroxyls, neutralize the bound dication.

Citing earlier work on the dissolution of potassium in 16-crown-4,[7][8] he realized that the cyclic polyethers represented a new class of complexing agents that were capable of binding alkali metal cations.

[10] Affinities of a given crown ether towards the cations of lithium, sodium, and potassium can change by multiple magnitudes, which is attributed to the high differences in their charge density.

Between the cations of potassium, rubidium, and cesium changes in affinities are less notable, as their charge density varies less than the alkali metals in earlier periods.

By incorporating luminescent substituents into their backbone, these compounds have proved to be sensitive ion probes, as changes in the absorption or fluorescence of the photoactive groups can be measured for very low concentrations of metal present.

In addition, some of these compounds were screened for their antibacterial and antifungal activity on Klebsiella pneumoniae, Staphilococcus aureus, Pseudomanas aeruginosa and Candida albicans.