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

A new calcium ion selective and water-soluble calix[4]arene chromoionophore has been synthesised from the 25,27bis[(ethoxycarbonyl)methoxy]-26,28-dihydroxy-calix[4]arene (1) and the N4,N4-diethyl-2-methyl-1,4-phenylenediamine-6-sulfonic acid (2). The 1,3-bis(indoaniline)-derived2,4bis-[(ethylcarbonyl)methoxy]-calix[4]arene (3) was obtained by introducing sulfonic groups into a phenylenediamine-derived chromophore followed by oxidative incorporation of two units of 2 into 1. The new chromophoric calix[4]arene 3 possesses an absorbance maximum at 604 nm in buffered aqueous environment. Upon complexation of calcium a bathochromic shift of 84 nm occurs along with an increase in the absorption coefficient. The dissociation constants and the cross sensitivity to other alkali and alkaline earth ions were evaluated