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 s ensory elements of liquid membrane potentiometric sensors destined for the recognition of neutral forms of nitrophenol isomers. All compounds displaye d high ability for the uptake of protons. The potential of liquid membranes , containing pyrrole derivatives, strongly depended on the pH of the aqueou s phase. Their potentiometric responses generated in the presence of nitrop henol derivatives were investigated at three different pH: 4.0, 6.0 and 8.0 . All membranes investigated responded towards the neutral form of nitrophe nol isomers. They did not respond to their anionic forms. The symmetry of t he macrocyclic cavity of calix[4]pyrroles had a very mild effect on the mol ecular recognition of nitrophenol guests. The membranes incorporating macro cyclic pyrrole derivatives generated a higher potentiometric signal in the presence of neutral nitrophenols in comparison to membranes containing acyc lic pyrrole derivatives. The sensors presented displayed high selectivity for para-nitrophenol. (C) 2001 Elsevier Science B.V. All rights reserved.