Poly(vinyl chloride) (PVC)-derived ion-selective electrodes (ISEs) have been prepared from a neutral anion binding receptor, meso-octamethylcalix [4]pyrrole (1). Analogous systems were also prepared from the novel pyridine-containing analogues of 1, namely dichlorocalix[2]pyrrole[2]pyridine (2) and tetrachlorocalix-[4]pyridine (3). At lower pH values (i.e., 3.5 and 5.5), ISEs derived from 1 display strong anionic (negative slope) responses toward Br -, Cl -, and H 2 PO 4 -and, to a much lesser extent, F -. By contrast, at high pH (i.e., pH 9.0) ISEs derived from 1 not only display cationic (positive slope) responses toward chloride and bromide anions but also selectivities (i.e., Br -< Cl -< OH -≈ F -< HPO 4 2-) that are non-Hofmeister in nature. This is considered consistent with the PVC-supported receptor 1 behaving as a direct anion binding agent at low pH but acting, at least in part, as an hydroxide-complexing receptor at higher pH. For the ISEs based on 2 and 3, no special non-Hofmeister selectivity is observed at pH 9.0. However, at lower pH values both increased anionic responses and improved selectivities for hydrophilic anions (e.g., F -and H 2 PO 4 -) are observed. These observations are rationalized in terms of protonation effects involving the pyridine-containing receptors from which these ISEs are derived. For all the receptors discussed in this paper, the addition of tridodecylmethylammonium chloride (TDDMA), a known lipophilic additive, serves to increase the magnitude of the ISE response but only at the price of greatly reduced anion selectivity.

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The ion selective electrode (ISE)-based potentiometric approach is shown to be an effective means of characterizing the anion recognition sites in the molecular receptor calix[2]pyridino[2]pyrrole (CPP). In particular, potentiometric pH-measurements involving the use of experimental PVCmembranes based on CPP revealed the existence of both mono-and diprotonated forms of the receptor under readily accessible conditions. Based on these analyses, apparent surface protonation constants for this heterocalixarene were found to lie between 8.5-8.9 (pK B1 ) and 3.3-3.8 (pK B2 ). CPP was found to interact with targeted anionic analytes based on both coulombic and hydrogen bond interactions, as inferred from varying the kinds of ionic sites present within the membrane phase. Potentiometric selectivity studies revealed that CPP preferred "Y-shaped" anions (e.g. acetate, lactate, benzoate) over spherical anions (e.g. fluoride and chloride), fluoride over chloride within the set of spherical anions, and the ortho-isomer over the corresponding meta-and para-isomers in the case of hydroxybenzoate (salicylate and congeners). In the context of this study the advantages of potentiometric determinations of acetylsalicylic acid using optimized PVC-membranes based on CPP relative to more conventional PVC-membrane ISEs based on traditional anion exchanger were also demonstrated.

The synthesis and characterization of two cytosine-substituted calix[4]pyrrole conjugates, bearing the appended cytosine attached at either a ␤-or meso-pyrrolic position, is described. These systems were tested as nucleotide-selective carriers and as active components of nucleotide-sensing ion-selective electrodes at pH 6.6. Studies of carrier selectivity were made using a Pressman-type model membrane system consisting of an initial pH 6.0 aqueous phase, an intervening dichloromethane barrier containing the calix[4]pyrrole conjugate, and a receiving basic aqueous phase. Good selectivity for the Watson-Crick complementary nucleotide, 5-guanosine monophosphate (5-GMP), was seen in the case of the meso-linked conjugate with the relative rates of through-membrane transport being 7.7:4.1:1 for 5-GMP, 5-AMP, and 5-CMP, respectively. By contrast, the ␤-substituted conjugate, while showing a selectivity for 5-GMP that was enhanced relative to unsubstituted calix[4]pyrrole, was found to transport 5-CMP roughly 4.5 times more quickly than 5-GMP. Higher selectivities were also found for 5-CMP when both the ␤-and meso-substituted conjugates were incorporated into polyvinyl chloride membranes and tested as ion selective electrodes at pH 6.6, whereas near-equal selectivities were observed for 5-CMP and 5-GMP in the case of unsubstituted calix[4]pyrroles. These seemingly disparate results are consistent with a picture wherein the meso-substituted cytosine calix[4]pyrrole conjugate, but not its ␤-linked congener, is capable of acting as a ditopic receptor, binding concurrently both the phosphate anion and nucleobase portions of 5-GMP to the calixpyrrole core and cytosine ''tails'' of the molecule, respectively, with the effect of this binding being most apparent under the conditions of the transport experiments.