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. 2022 May 3;27(9):2908.
doi: 10.3390/molecules27092908.

A Quinoxaline-Naphthaldehyde Conjugate for Colorimetric Determination of Copper Ion

Sutapa Sahu  1 , Yeasin Sikdar  1   2 , Riya Bag  1 , Michael G B Drew  3 , José P Cerón-Carrasco  4 , Sanchita Goswami  1
Affiliations

A Quinoxaline-Naphthaldehyde Conjugate for Colorimetric Determination of Copper Ion

Sutapa Sahu et al. Molecules. .

Abstract

This work facilitates detection of bivalent copper ion by a simple Schiff base probe QNH based on a quinoxaline-naphthaldehyde framework. The detailed study in absorption spectroscopy and theoretical aspects and crystal study of the probe and probe-copper complex has been discussed. The detection limit of the probe in the presence of Cu2+ is 0.45 µM in HEPES-buffer/acetonitrile (3/7, v/v) medium for absorption study. The reversibility of the probe-copper complex has been investigated by EDTA. The selective visual detection of copper has been established also in gel form.

Keywords: Cu2+ colorimetric detection; ab initio calculations; absorption study; quinoxaline−naphthaldehyde conjugate.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Visible colour change of QNH after addition of cations in HEPES−buffer/acetonitrile (3/7, v/v) medium. The concentration of the metals in all vials is 10−4 M.
Figure 2
Figure 2
UV–Visible titration of QNH (10–5 M) in the presence of various concentrations of Cu2+. (Upward arrow indicates gradual increase in absorption at 552 nm with increasing concentration of externally added Cu2+). (Inset: absorbance of QNH at 552 nm as a function of [Cu2+]).
Figure 3
Figure 3
The left panel shows the computed absorption spectra of QNH and QNH in the presence of Cu2+, plotted with blue and black lines, respectively. The right panel shows computed frontier molecular orbitals (HOMO and LUMO) for QNH and QNH−Cu2+ model systems. Values in parenthesis are the theoretical absorption wavelengths in nm. Surfaces are generated with an isovalue of 0.02.
Figure 4
Figure 4
Absorption spectrum of QNH–Cu2+ complex in the presence of different amino acids in (3:7 v/v) HEPES buffer: acetonitrile medium.
Scheme 1
Scheme 1
Schematic representation of QNH–Cu2+ complex in the presence of histidine.
Figure 5
Figure 5
Proposed sensing mechanism of Cu2+ by QNH. The displayed chemical structures shown as ball and sticks correspond to the DFT-optimized models. Colour code: C = grey; H = white; N = blue; O = red; Cu = brown.
See this image and copyright information in PMC

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