DEVELOPMENT OF METAL ION SENSORS BASED ON DIAZO PSEUDOCROWN ETHER DERIVATIVES

Abstract

Five novel pseudocrown ether derivatives terminating with azobenzene moieties were synthesized via azo coupling of oligoethylenediaminobenzene with ethyl-2-aminobenzoate or 4-nitroaniline, and characterized by 1H, 13C-NMR, and mass spectroscopies. The presence of metal ions in the solution of ester derivatives displayed indistinguishable color changes whereas D3N, a nitro derivative showing light brown in DMSO with λmax at 404 nm, turned to light orange with a new peak around 490 nm in the presence of transition or heavy metal ions (Cu2+, Zn2+, Cd2+, Hg2+, Pb2+). The presence of strong basic anion (OH-, F-, CN-) also produced dark purple solution with a new absorption band around 570-576 nm, which turned to orange upon adding transition or heavy metal ions. These color changes could be used for naked-eye detection of these metal ions in the presence of 2 equivalents of hydroxide ion. Although D3N solution could not selectively change color toward any particular ion, a calibration curve employing the absorption intensity of 20 µM D3N in DMSO at 574 nm could be constructed to determine trace quantity of CN- with a linear range between 2 to 10 µM with R2 = 0.9956. In addition, calibration curves for transition or heavy metal ions were constructed under a basic condition with excellent correlation coefficient, e.g. R2 = 0.9968 for Cd2+. Thus D3N could be employed as chromogenic sensor for strong basic anions and transition or heavy metal ions.