# Selective Copper(II) Complexes against Mycobacterium tuberculosis

## TL;DR

This paper reports new copper complexes with quinoline derivatives that show strong and selective activity against tuberculosis bacteria.

## Contribution

The study introduces novel copper(II) complexes with high antitubercular activity and selectivity.

## Key findings

- Cu-ACQophen complex showed potent antitubercular activity with a low MIC90 of 1.68 μmol L–1.
- Cu-ACQophen had a high selectivity index (SI = 48), indicating good safety profile.
- Structural analysis confirmed distinct coordination geometries and stoichiometries among the complexes.

## Abstract

The present paper describes the synthesis, characterization,
and
biological activity of five quinoline derivatives, DCQ; ACQ12; ACQ13;
ACQ14; ACQophen, and their respective copper­(II) complexes. The class
of organic compounds is composed of 4,7-dichloroquinoline (DCQ) and
its derivatives containing aliphatic diamines, 1,2-ethanediamine (ACQ12);
1,3-propanediamine (ACQ13); 1,4-butanediamine (ACQ14); and an aromatic
diamine, o-phenylenediamine (ACQophen), as a side
chain at the 4-position of the quinoline ring. Single-crystal X-ray
diffraction was used to determine the structure of the Cu-DCQ complex
(1:2 M:L ratio), while the structure of the Cu-ACQ12 complex (1:1
M:L ratio) was obtained from powder X-ray diffraction (PXRD) data.
Spectroscopic (IR, Raman, UV–vis) and analytical data supported
coordination through the quinoline nitrogen atom in all complexes.
DFT (M06-2X/6-31G) calculations complemented the experimental results,
revealing distinct coordination geometries and molar ratios: Cu-ACQ13
and Cu-ACQ14 exhibit a 1:1 (M:L) stoichiometry with distorted square-planar
Cu­(II) centers, while Cu-ACQophen crystallizes in a 1:2 (M:L) ratio
featuring a slightly elongated square-pyramidal geometry, consistent
with nonelectrolytic behavior in DMSO. Theoretical vibrational frequencies
showed good agreement with experimental spectra, validating the proposed
models. The organic and inorganic compounds described here showed
potent activity against Mycobacterium tuberculosis (Mtb) and selectivity indexes. The Cu-ACQophen
complex exhibited relevant antitubercular activity with a low MIC90 value, about 1.68 μmol L
–1, and a high selectivity index, SI = 48. Complexes Cu-DQC
and Cu-ACQ12 also demonstrated SI values >10.