| 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 SO42- 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 H(n)pyrr(n+) receptor has a very high effective association constant value for the SO42- at pH 4.0 (log K-eff = 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 SO42-/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 [(H(6)pyrr)(SO4)(H2O)(3)](SO4) 2 +/- 9.3H(2)O 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-H center dot center dot center dot O, C-H center dot center dot center dot O and water-mediated ones. |
