Development of a calix[4]arene sensor for soft metals based on nitrile functionality

The current work is amongst the first to examine the potential usefulness of the nitrile functional group in potentiometric analytical sensors for soft metals. Nitrile functionality has hereby been incorporated into a calix[4]arene skeleton to give a series of new cation selective hosts. The analytical sensing behaviour of these hosts was examined by Ion Selective Electrode (ISE) based potentiometry. In all cases a preference for soft metals was observed, explained primarily in terms of soft-soft compatibility between calix[4]arene nitrile hosts and metal guests in combination with a classical 'lock and key' best fit mechanism. Hosts 2, 3 and 4 showed very strong responses towards Hg(II) ions, with Ag(I) being the main interferant. The introduction of electron delocalising aromaticity proximal to the nitrile functionality was thought to reduce the availability of negative charge for cation coordination, apparently affecting the Hg(II) cation in particular. An acute fall in Hg(II) response coupled with the emergence of Ag(I) as the primary ion was observed for 7 and 8.