title: Cytosine substituted calix[4]pyrroles: neutral receptors for 5'-guanosine monophosphate.
abstract: The synthesis and characterization of two cytosine-substituted calix[4]pyrrole conjugates, bearing the appended cytosine attached at either a beta- 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 beta-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 beta- 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 beta-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.
authors.affiliation: Department of Chemistry and Biochemistry and Institute for Cellular and Molecular Biology, University of Texas, Austin, TX 78712-1167, USA. sessler@mail.utexas.edu
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Sessler
authors.forename: Vladimír
authors.initials: V
authors.lastname: Král
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Shishkanova
authors.forename: Philip A
authors.initials: PA
authors.lastname: Gale
mesh_terms: D047250:Calixarenes; D003596:Cytosine / Q000737:chemistry*; D006151:Guanosine / Q000737:chemistry; D006157:Guanosine Monophosphate / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008956:Models, Chemical; D010710:Phosphates / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry*
chemical_list: D046911:Macromolecular Substances; D010710:Phosphates; D011758:Pyrroles; D006151:Guanosine; D047250:Calixarenes; D006157:Guanosine Monophosphate; D003596:Cytosine