A molecular complex based on iron has been developed to break down nitrate, a stable form of nitrogen that contributes to harmful algal blooms and groundwater contamination. Researchers at the University of Michigan, led by chemist Nathaniel Szymczak, have published a study in Nature Chemistry that details a method to reduce nitrates into compounds that could be reused as fertilizer or otherwise recycled. This development could help address environmental issues caused by excess nitrates in water systems. Nitrates are essential components of fertilizers, but their stability makes them difficult to remove from the environment. In nature, the nitrogen cycle involves processes such as lightning in the atmosphere or bacterial activity in soil, which convert nitrogen into ammonia or nitrates that plants and other organisms can use. However, overuse of fertilizers has led to excessive nitrate runoff into water bodies, disrupting ecosystems and creating pollution that biological systems struggle to manage. To understand how nitrates can be effectively reduced, the research team examined nitrate transporter proteins in plants. These proteins use hydrogen bonds to bind nitrates, and the team focused on a "secondary sphere" — a halo of surrounding molecules that interact with the nitrate. Inspired by this natural mechanism, they created an iron complex surrounded by a secondary sphere of hydrogen bonds, which they tuned to selectively bind nitrates and prepare them for chemical reactions. When the researchers used heat to drive the reaction, the iron complex removed oxygen atoms from nitrate, reducing it to nitric oxide. Using light instead, the complex removed all oxygen atoms, converting nitrate to ammonia. Nitric oxide has medical applications, such as reducing blood pressure, while ammonia can be reused as fertilizer. Szymczak emphasized that these findings offer a foundation for developing methods to remove nitrates from the environment. Understanding how nitrates behave and can be reduced is crucial for creating devices that could be used in wastewater treatment plants, potentially leading to more sustainable environmental management solutions in the future.