VOLTAMMETRIC ANION RESPONSIVE SENSORS BASED ON MODULATION OF ION PERMEABILITY THROUGH LANGMUIR-BLODGETT-FILMS CONTAINING SYNTHETIC ANION RECEPTORS

Voltammetric sensors responsive to anionic guests were constructed that are based on ordered membrane assemblies containing anion receptors deposited directly on glassy carbon electrodes by the Langmuir-Blodgett (LB) method. The anion receptors used were lipophilic derivatives of macrocyclic polyamine (15-hexadecyI-1,4,7,10,13-pentaazacyclohexadecane, 1) and cyclodextrin polyamine (6A,6B,6cf6D,6el8,lf60-heptadeoxy-6A,6B,6c,6D,6£,6F,6G-heptakis(dodecylamlno)-β-cyclodextrin, 2), capable of binding with anionic guests in multiprotonated forms. Binding of organic anions such as nucleotides and dicarboxylates as well as inorganic anions to these receptors Induced a decrease (or increase) of the ion permeability of the membrane, as detected by cyclic voltammetry (CV) using [Fe(CN)6]4-, L-ascorbic acid, or [Ru(bpy)3]2+ as a marker ion. Such a mode of response can be explained on the basis of the charge-charge interaction involving the membraneous receptor, guest (analyte), and marker ion. Calculation of the molecular response ratio, defined as the ratio of the permeated marker ions per membraneous receptor molecule, indicates that the amount of the permeated marker ions thus detected is an amplified measure of the analyte. The response selectivity was determined for each guest on the basis of the decrease percentage of the peak current in cyclic voltammetry using [Fe(CN)d]4- as a marker ion. Comparing the selectivities for the LB membrane sensors containing host 1 and 2 (sensors 1 and 2, respectively), a similar trend of selectivities was observed for most of the anionic guests examined, reflecting the expected order of electrostatic attraction between the protonated polyamine hosts and anionic guests. On the other hand, the selectivity was different between the two sensors for the positional isomers of phthalate, i.e., response orders of ortho > meta > para and meta > para > ortho were observed with sensors 1 and 2, respectively. The characteristic selectivity observed with sensor 2 is possibly due to the host-guest interaction Involving the cyclodextrin cavity. © 1990, American Chemical Society. All rights reserved.