Effect of the symmetry of the calix[4]pyrrole cavity on sensitivity and selectivity of potentiometric sensors for neutral nitrophenols

Lipophilic macrocyclic and acyclic derivatives of pyrrole were applied as sensory elements of liquid membrane potentiometric sensors destined for the recognition of neutral forms of nitrophenol isomers. All compounds displayed high ability for the uptake of protons. The potential of liquid membranes, containing pyrrole derivatives, strongly depended on the pH of the aqueous phase. Their potentiometric responses generated in the presence of nitrophenol derivatives were investigated at three different pH: 4.0, 6.0 and 8.0. All membranes investigated responded towards the neutral form of nitrophenol isomers. They did not respond to their anionic forms. The symmetry of the macrocyclic cavity of calix[4]pyrroles had a very mild effect on the molecular recognition of nitrophenol guests. The membranes incorporating macrocyclic pyrrole derivatives generated a higher potentiometric signal in the presence of neutral nitrophenols in comparison to membranes containing acyclic pyrrole derivatives. The sensors presented displayed high selectivity for para-nitrophenol. (C) 2001 Elsevier Science B.V. All rights reserved.