Dual Sensing by Simple Heteroditopic Salt Receptors Containing an Anthraquinone Unit

We
synthesized simple ion pair receptors consisting of a crown
ether cation binding site and an anthraquinone-supported thiourea
anion binding domain and studied their anion-, cation-, and salt-binding
properties using spectroscopic, spectrophotometric, and electrochemical
measurements in acetonitrile solution. Apart from carboxylate anions,
which cause deprotonation, all the anions tested were found to associate
with receptor 1 more strongly in the presence of sodium
cations, whereas in the presence of potassium or ammonium cation the
anion binding strength was greatly diminished. A homotopic anion receptor 3, lacking a crown ether unit, was unable to bind sodium salt
more strongly than tetrabutylammonium salts. Solution and solid-state
X-ray measurements revealed that strong sodium coordination with the
cation-binding domain is responsible for the salt-binding enhancement.
Electrochemical measurements showed that the addition of anions to
the receptor 1 pretreated with sodium cations resulted
in greater changes in reduction potentials compared to the addition
of anions to receptor 1 in the absence of Na+.