title: Highly selective optical-sensing membranes, containing calix[4]arene chromoionophores, for Pb2+ ions.
abstract: Plasticized poly(vinyl chloride) (PVC) optode membranes containing novel calix[4]arene chromoionophores 1 or 2 and one equivalent of a lipophilic anion respond to Pb2+ ions with high selectivity over alkali, alkaline-earth, and other heavy metal ions. This selectivity stems from the combination of ligand specificity and a unique ion exchange scheme that employs both monovalent metal ions and protons as the exchanged ions. Complexation of Pb2+ ions inside the membrane is accompanied by deprotonation of the chromoionophores, which causes a bathochromic shift of the absorption maximum lambda(max). The response to Pb2+ ions is modulated by pH and alkali metal ions in a fashion that is consistent with the proposed ion-exchange mechanism. Of all of the other metal ions tested, only Cs+ and Ag+ produce a color change. However, these monovalent metal ions cause hypsochromic shifts of lambda(max) instead of the bathochromic shift caused by Pb2+, because the chromoionophores remain protonated upon complexation.
authors.affiliation: Department of Supramolecular Chemistry and Technology and MESA Research Institute, University of Twente, Enschede, The Netherlands. smct@ct.utwente.nl
authors.forename: N J
authors.initials: NJ
authors.lastname: van der Veen
authors.forename: E
authors.initials: E
authors.lastname: Rozniecka
authors.forename: L A
authors.initials: LA
authors.lastname: Woldering
authors.forename: M
authors.initials: M
authors.lastname: Chudy
authors.forename: J
authors.initials: J
authors.lastname: Huskens
authors.forename: F C
authors.initials: FC
authors.lastname: van Veggel
authors.forename: D N
authors.initials: DN
authors.lastname: Reinhoudt