Binding mode dependent signaling for the detection of Cu2+: An experimental and theoretical approach with practical applications

Abstract

Two amido-schiff bases (3-Hydroxy-naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide and Naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide) have been synthesized having a common structural unit and only differs by a -OH group in the naphthalene ring. Both of them can detect Cu²⁺ ion selectively in semi-aqueous medium in distinctly different output modes (one detects Cu²⁺ by naked-eye color change where as the other detects Cu²⁺ by fluorescence enhancement). The difference in the binding of Cu ²⁺ with the compounds is the reason for this observation. The detection limit is found to be micromolar region for compound which contains -OH group whereas the compound without -OH group detects copper in nano-molar region. DFT calculations have been performed in order to demonstrate the structure of the compounds and their copper complexes. Practical utility has been explored by successful paper strip response of both the compounds. The biological applications have been evaluated in RAW 264.7.

Keywords: Colorimetric sensing; Fluorescence enhancement; Ion detection; LMCT; Schiff base; Test kit.