ASSESSMENT OF 3 AZOPHENOL CALIX[4]ARENES AS CHROMOGENIC LIGANDS FOR OPTICAL-DETECTION OF ALKALI-METAL IONS

Three novel chromogenic cone conformational calix[4]arene tetraesters bearing nitrophenylazophenol residues (mono-, di- and tetra-substitute d) in the ester portion of the molecules have been synthesized and sho wn to display a dramatic change in absorbance spectrum upon complexati on with lithium, and to a lesser extent sodium, in the presence of a b ase. An instantaneous colour change from yellow to red corresponding t o a lambda(max) shift from 380 to 520 nm, is noted upon the addition o f lithium perchlorate to a solution containing any of the three ligand s with the intensity of the colour being concentration dependent. The best selectivity for lithium against sodium and potassium was exhibite d by the mono-substituted derivative, ligand 4, (approximately 70-fold selectivity in both cases). Although this is somewhat less than that required for clinical applications, it is anticipated that it can be f urther improved using a variety of approaches, which are the subject o f further investigations. The interference from potassium is too small to be measured.