title: Sulfate recognition by a hexaaza cryptand receptor.
abstract: A hexamine macrobicycle with pyrrolyl spacers was evaluated as an anion receptor in its protonated forms. The protonation constants of the receptor, as well as its association constants with Cl(-), NO3(-), AcO(-), ClO4(-), H2PO4(-), and SO4(2-) were determined by potentiometry at 298.2 ± 0.1 K in H2O-MeOH (50 : 50 v/v) and at an ionic strength of 0.10 ± 0.01 M in KTsO. These studies revealed that the Hnpyrr(n+) receptor has a very high effective association constant value for the SO4(2-) at pH 4.0 (log Keff = 6.42), and it is selective for the uptake of this anion in the presence of the other studied anionic substrates. In particular, the receptor showed very high SO4(2-)/NO3(-) selectivity. Using the indicator-displacement approach the receptor is able to signal the presence of sulfate by a change of color. Single crystal X-ray diffraction determination of [(H6pyrr)(SO4)(H2O)3](SO4)2·9.3H2O revealed the presence of one sulfate anion inside the receptor cavity and showed that the encapsulation of the anion is favored by an array of nine hydrogen bonding interactions, including N-HO, C-HO and water-mediated ones.
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal. pmateus@itqb.unl.pt delgado@itqb.unl.pt.
authors.forename: Pedro
authors.initials: P
authors.lastname: Mateus
authors.forename: Rita
authors.initials: R
authors.lastname: Delgado
authors.forename: Vânia
authors.initials: V
authors.lastname: André
authors.forename: M
authors.initials: M
authors.lastname: Teresa Duarte
mesh_terms: D018360:Crystallography, X-Ray; D004988:Ethers, Cyclic / Q000138:chemical synthesis / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011199:Potentiometry; D062165:Receptors, Artificial / Q000138:chemical synthesis / Q000737:chemistry*; D012545:Schiff Bases / Q000138:chemical synthesis / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012996:Solutions; D013431:Sulfates / Q000032:analysis*; D014867:Water
chemical_list: D004988:Ethers, Cyclic; D062165:Receptors, Artificial; D012545:Schiff Bases; D012996:Solutions; D013431:Sulfates; C444241:cryptand; D014867:Water