Pyridoxal derivatives as probes for water concentration in non-aqueous solvents

Abstract

In order to provide a basis for the design of spectofluorimetric indicators for water activity or concentration in organic solvents a series of O- and N-alkylated pyridoxal derivatives has been prepared. The compounds were examined for their ability to exhibit a shift in fluorescence emission wavelength on complexation with water. The shift in fluorescence on complexation with water previously observed (Yunxiang and Xin, Talanta, 1984, 31, 556) was confirmed for pyridoxal itself but alkylation of the oxygen functionalities blocked the fluorescence shift. In contrast, a strong enhancement in emission intensity but no shift in emission wavelength was observed with the N-methylpyridoxal. From these studies, it appears that modification at the nitrogen or, presumably, at C-2 or C-6 are the only available sites for the development of useful compounds from the pyridoxal prototype.