New longwave absorbing chromogenic calix[4]arene for calcium determinationin aqueous environment

A new calcium ion selective and water-soluble calix[4]arene chromoionophore has been synthesised from the 25,27-bis[(ethoxycarbonyl)methoxyl-26,28-dih ydroxy-calix[4]arene (1) and the N4,N4-diethyl-2-methyl-1,4-phenylenediamin e-6-sulfonic acid (2). The 1,3-bis(indoaniline)-derived 2,4-bis-[(ethylcarb onyl)methoxy]-calix[4]arene (3) was obtained by introducing sulfonic groups into a phenylenediamine-derived chromophore followed by oxidative incorpor ation of two units of 2 into 1. The new chromophoric calix[4]arene 3 posses ses an absorbance maximum at 604 nm in buffered aqueous environment. Upon c omplexation of calcium a bathochromic shift of 84 nm occurs along with an i ncrease in the absorption coefficient. The dissociation constants and the c ross sensitivity to other alkali and alkaline earth ions were evaluated. (C ) 2000 Elsevier Science B.V. All rights reserved.