1-(d-Glucopyranosyl-2′-deoxy-2′-iminomethyl)-2-hydroxynaphthalene as chemo-sensor for Fe3+ in aqueous HEPES buffer based on colour changes observable with the naked eye

A new glucose-based C2-derivatized colorimetric chemo-sensor (L1) has been synthesized by a one-step condensation of glucosamine and 2-hydroxy-1-naphthaldehyde for the recognition of transition metal ions. Among the eleven metal ions studied, viz., Mg2+, Ca2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Hg2+, L1 results in visual colour change only in the presence of Fe2+, Fe3+and Cu2+ in methanol. However, in an aqueous HEPES buffer (pH 7.2) it is only the Fe3+ that gives a distinct visual colour change even in the presence of other metal ions, up to a concentration of 280 ppb. The changes have been explained based on the complex formed, and the composition has been determined to be 2:1 between L1 and Fe3+ based on Job’s plot as well as ESI MS. The structure of the proposed complex has been derived based on HF/6-31G calculations.