Selective colorimetric molecular probe for cyanide ion detection in aqueous solution

5-Nitro-2-hydroxybenzaldehyde (1) demonstrated to be a sensitive, and a selective molecular probe for cyanide ion (CN - ) in aqueous media. In acetonitrile, compound 1 shows sensitivity and selectivity for cyanide, acetate and fluoride, in comparison to other investigated anions using both visual and spectroscopic means. In aqueous solution, the color becomes intense yellow upon addition of cyanide, while acetate showed this effect to a much lower extent. Significant spectral changes were also detected with the appearance of two new absorption bands at 358 and 387 nm. This was accompanied by concomitant intensity decrease for the band at 314 nm. Fluoride, dihydrogen phosphate, chloride, bromide, perchlorate, and azide showed negligible color and spectral changes for the probe in aqueous solutions. On the other hand, hydrogen sulfate caused fainting of the yellow color and gave a spectrum similar to that of the sensor in polar aprotic solvents. The cyanide ion was detected at micro molar levels in aqueous solutions with a stoichiometry of 1:1 for CN: probe in acetonitrile as the solvent. Cyanide, hydroxide, acetate, fluoride and dihydrogen phosphate showed identical changes to color and spectra, indicating a hydrogen bonding and a deprotonation mechanism.