Biosynthesis of CuO nanoparticles using Acacia concinna pod and their application for the synthesis of tetra-hydrobenzo[b]pyran derivatives

Abstract

Herein, we have synthesized copper oxide nanoparticles (CuONPs) using an aqueous pod extract of Acacia concinna (A. concinna) and analyzed their catalytic activities. The phytochemicals in the pod extract of A. concinna were used as a reducing and stabilizing agent and CuSO₄·7H₂O as a precursor for forming CuONPs. The biosynthesized CuONPs were characterized using UV–visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscope (HR-TEM) for structural and morphological analysis. The synthesis of CuONPs was confirmed by the UV absorption peak at 330 nm and XRD analysis. TEM analysis has been representing the CuO nanospheres with an average size of 29 nm. The newly synthesized CuONPs exhibit greater antibacterial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The highest efficacy of biosynthesized CuONPs (200 µg/mL) was observed against S. aureus with a 36.5 mm zone of inhibition. Biosynthesized CuONPs are a basic, highly efficient, heterogeneous, and green recyclable catalyst for the multicomponent synthesis of 4H-benzo[b]pyran derivatives. Tetra-hydrobenzo[b]pyran derivatives can be synthesized through a three-component reaction involving an aldehyde, malononitrile, and either 1,3-cyclohexanedione or 5,5-dimethyl-1,3-cyclohexanedione, conducted at room temperature. This synthetic method provides several advantages such as simple work-up procedures, short reaction time, minimal byproducts, and high yields of products.

Graphical abstract