Lariat ethers ammonium binding

Intramolecularity in lariat ether complexation was demonstrated in three ways. First, when solution cation binding constants were determined. Kg was shown to be independent of cation and macrocycle concentrations (within certain limits). The efficacy of complexation of a single cation by two macrorings [(ML2) complex formation] should be concentration dependent. Second, ammonium cation binding constants were determined for the series (see above) of monoaza-15-crown-5 and -18-crown-6 compounds having (CH2CH20)jiClH3 (n 0 to 8) sidearms (31). 

Lariat ethers, which were designed to add dimensionality to the essentially flat crown ether, have been used as synthetic ionophores for decades. The binding properties of crown ethers are now well documented and generally well understood. Most such studies have been conducted with metal ions, although complexation of ammonium species and some neutral species (Gokel, 1973 Kyba, 1977) have also been reported. 

The anthracenylmethyl lariat ether shown as (10) was reported by de Silva and coworkers (1986) as a crown that is useful for fluorescence sensing. Binding of K+ resulted in a detectable fluorescence emission signal. Recent advances in this area include the development of compounds that can sense ion pairs. The anthracenyl crown shown as (11) was designed to simultaneously sense sodium and phosphate ions (de Silva, 2003). Excitation of the complex with ultraviolet radiation results in a fluorescent output only when Na+ is complexed in the crown and the ammonium groups are bound to the anion. The complex self-quenches in the case when either no or only one of the ions is present. 

Shultz et al (1985) 12-, 15-, and 18-Membered-ring nitrogen-pivot lariat ethers syntheses, properties, and sodium and ammonium cation binding properties. 1 Am Chem Soc 107 6659-6668... 

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