3-[2-(2-Quinoxalinyl)benzoxazol-5-yl]alanine derivative – A specific fluoroionophore for Ni(II)

The synthesis of N-Boc-3-[2-(2-quinoxalinyl)benzoxazol-5-yl]alanine methyl ester (1) and 3-[2-(2-quinoxalinyl)benzoxazol-5-yl]alanine (2), useful in peptide chemistry, are described. The influence of metal ions and pH on spectroscopic properties of compounds studied is presented. The compounds studied are very weak bases in the ground state and their basicity increases in the excited state. Among ions studied, in the ground state only Cu(II) and Al(III) and Pb(II) ions form stable complexes with (1), whereas in the excited state – only Ni(II) ion. Contrary to the most fluoroionophores the fluorescence intensity of ligand (1) in acetonitrile increases with the increase of Ni(II) ion concentration, whereas the fluorescence intensity of (2) in water is totally quenched by H3O+ ion.