Copper- and Zinc-Based Coordination Polymers toward the Development of More Efficient Agrochemicals

Abstract

Inorganic agrochemicals have been used by the food industry for thousands of years to maximize production and quality, with copper(II) sulfate being one of the main used pesticides. Given the increasing global population (expected to reach 9.6 billion by 2050) and the challenges facing agricultural production, there is a pressing need to address the impact of intensified agrochemical use (e.g., soil and water contamination, human health risk, pesticide resistance, etc.). Coordination polymers (CPs) as agrochemicals offer several significant advantages compared to traditional agrochemicals, such as the controlled release of the active ingredients in the target zone and reduced toxic doses released to environment. In this work, the plant growth regulator 3-indolepropanoic acid (IPA), which stimulates root initiation and elongation, is used as a chelating agent of Cu²⁺ and Zn²⁺ metal ions, both known for their antibacterial and antifungal properties, to obtain two crystalline CPs, named Cu-IPA [Cu(H₁₀C₁₁NO₂)₂]_n and Zn-IPA [Zn(H₁₀C₁₁NO₂)₂(H₂O)]_n. Their role as potential antibacterial agents was evaluated. First, the stability of these materials was studied, showing a fast release of both cations (100% after 8 and 3 h for Cu-IPA and Zn-IPA, respectively) in aqueous solution. The antibacterial test against Escherichia coli, a bacterium involved in many farm animal infections, evidenced a notable growth inhibition, with values of inhibition of the colony forming unit (CFU) for Cu-IPA of 10.2 and 26.2% and for Zn-IPA of 2.1 and 5.3% at 500 and 1500 ppm, respectively. This study highlights the potential of CPs for enhancing efficiency and sustainability of inorganic agrochemicals in agriculture.