Chromogenic reagents

Abstract

A number of compounds are described which are highly selective chromogenic reagents for cations of biological importance including Li⁺, Na⁺, K⁺, and Ca²⁺. These reagents are based upon phenolic cryptands with an azophenol chromophore incorporated into their structures, metal complexation is accompanied by deprotonation of the phenolic group and a substantial change in the wavelength of maximum light absorption. The cryptand structures are generally prepared by a novel synthetic route involving reaction of a diaza crown ether with 2,6-bisbromomethylanisole although in one case, for K⁺ selection, a bridged calix[4]arene is used. Two of the new phenolic cryptands are also highly sensitive reagents for Pb²⁺. A further variation in the structure to give a phenolic cryptand analogous to the well known solvatochromic Reichardt's dye reagent provides a reagent which is highly selective for Na⁺ and a response that depends upon solvent polarity.