Synthesis and evaluation of colorimetric chemosensors for monitoring sodium and potassium ions in the intracellular concentration range

The azo-dye based colorimetric chemosensors 1 and 2 were designed for the detection of intracellular concentrations of Na+ and K+ respectively. The two sensors were synthesised from the o-anisidine based receptors 3 and 4 in a one step synthesis. Both displayed good selectivity and sensitivity for the relevant group I cations in the appropriate physiological conditions, with 1 displaying large changes in the absorption spectra upon Na+ recognition with λmax being shifted from 488 nm to 377 nm in the absorption spectra when measured in 50 ∶ 50 MeOH–H2O buffered pH 7.4 solutions and in the presence of high ionic strength. Similarly, 2 showed both a hypsochromic shift and hypochromic effect upon titration with K+. These changes were clearly visible; with red to yellow colour changes taking place upon ion recognition.