Organoboron compounds as Lewis acid receptors of fluoride ions in polymeric membranes.
Newly synthesized organoboron compounds - 4-octyloxyphenylboronic acid (OPBA) and pinacol ester of 2,4,6-trifluorophenylboronic acid (PE-PBA) - were applied as Lewis acid receptors of fluoride anions. Despite enhanced selectivity, the polymer membrane electrodes containing the lipophilic receptor OPBA exhibited non-Nernstian slopes of the responses toward fluoride ions in acidic conditions. Such behavior was explained by the lability of the B-O bond in the boronic acids, and the OH(-)/F(-) exchange at higher fluoride content in the sample solution. In consequence, the stoichiometry of the OPBA-fluoride complexes in the membrane could vary during the calibration, changing the equilibrium concentration of the primary anion in membrane and providing super-Nernstian responses. The proposed mechanism was supported by (19)F NMR studies, which indicated that the fluoride complexation proceeds more effectively in acidic solution leading mainly to PhBF(3)(-) species. Finally, the performances of the membranes based on the phenylboronic acid pinacol ester, with a more stable B-O bond, were tested. As it was expected, Nernstian fluoride responses were recorded for such membranes with worsened fluoride selectivity.
Department of Microbioanalytics, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland.
Martyna
M
Jańczyk
Agnieszka
A
Adamczyk-Woźniak
Andrzej
A
Sporzyński
Wojciech
W
Wróblewski
D000838:Anions / Q000737:chemistry; D001554:Benzene / Q000737:chemistry; D001889:Borinic Acids / Q000737:chemistry*; D004566:Electrodes; D005459:Fluorides / Q000737:chemistry*; D058116:Lewis Acids / Q000737:chemistry*; D008567:Membranes, Artificial; D011108:Polymers / Q000737:chemistry*; D011143:Polyvinyl Chloride / Q000737:chemistry; D011199:Potentiometry
D000838:Anions; D001889:Borinic Acids; D058116:Lewis Acids; D008567:Membranes, Artificial; D011108:Polymers; D011143:Polyvinyl Chloride; D001554:Benzene; D005459:Fluorides