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 H-1 NMR in DMSO-d(6).