Recognition and Sensing of Biologically Relevant Anions in Alcohol and Mixed Alcohol–Aqueous Solutions Using Charge Neutral Cleft-Like Glycol-Derived Pyridyl–Amidothiourea Receptors

In this paper, the synthesis and the spectroscopic investigation
of new colorimetric receptors for anions 3–6, possessing a glycol chain at the 4-position of the pyridyl
ring, and 1 and 2, which lack such a chain,
and the X-ray crystal structure of 2 is presented. Structures 3–6 are able to bind to anions in competitive
media, such as alcohol or in a mixture of methanol and water, where
the anion recognition gives rise to changes in the absorption spectra,
which is red-shifted, in 1:1 or 1:2 (sensor/anion) stoichiometry.
The anion recognition for 1 and 2 was also
investigated in organic solvents and in a 4:1 mixture of DMSO/H2O. The binding of 1 to anions such as acetate,
phosphate, and fluoride was also evaluated using 1H NMR
in DMSO-d6.