Thiazole containing benzo crown ethers: A new class of ammonium selective ionophores

A new class of crown ethers containing heterocyclic units has been designed to develop synthetic NH4+-selective ionophores whose resulting potentiomet ric properties in solvent polymeric membranes are superior or at least comp arable to those of nonactin. It was found that the derivatives of thiazole containing dibenzo-18-crown-6 (1; TDB18C6) incorporated in PVC-based membra nes provide enhanced NH4+ selectivities over alkali metal cations, especial ly over Na+, compared to those of the nonactin-doped membranes: for example , the selectivity coefficients, log K-NH4+J(POT) (J = Li+, Na+, K+), for th e 2-nitrophenyloctyl ether (NPOE) plasticized PVC membranes doped with the hexyl chain-substituted TDB18C6 (2) were -4.9, -3.9, and -1.3, while those for the same type of membranes with nonactin -4.4, -3.0, and -1.0, respecti vely. Unlike other synthetic NH4+-selective neutral carriers reported to da te, TDB18C6-type compounds result in potentiometric performance highly comp arable to that of the nonactin-based ones except their slightly higher dete ction limits (similar to 3 x 10(-6) vs 7 x 10(-7)). The complex formation b etween TDB18C6 and NH4+ was identified from H-1 NMR spectra. The 1:1 comple x formation constant of TDB18C6 with NH4+ in solvent polymeric membranes es timated using the method suggested by Bakker et al. and the NH4+ selectivit y coefficient over K+ (K-NH4+,K+(POT)) are similar to 200 times smaller tha n that of nonactin (1.8 x 10(7) vs 3.6 x 10(9)).