An Iron Complex Reaction Powered by Light Can Reduce Nitrate to Ammonia, Mitigating Groundwater Pollution: Powered by Heat, It Yields Nitric Oxide: Manipulation of Hydrogen Bonds is the Key

     Researchers at the University of Michigan published a paper in the journal Nature Chemistry that shows how they were able to develop an iron complex that can break down leftover groundwater nitrate from fertilizer, which is typically very stable in the environment. Nitrates are notoriously difficult to chemically reduce and remove from the environment. They are also responsible for harmful algal blooms, promoting cyanobacteria growth, inducing eutrophication, and death of marine life. The new method can reduce nitrate into components that can be recycled for fertilizer.

     According to Phys.org, lead author and chemist Nathaniel Szymczak noted:

"Now we tend to overfertilize crops, and a huge majority of the fertilizer we apply actually leaches away with runoff into streams, groundwater, lakes and oceans," Szymczak said. "Human impacts have basically caused an imbalance, and it's impossible for biological systems to compensate for as much nitrate as we're dumping into them."

     They first studied nitrogen transport and chemical interactions in the environment. They found that hydrogen bonds were the key to binding nitrates as well as to enhancing the chemical reduction of them.

“They found that nitrate transporter proteins—proteins that help plants use nitrates—bind to nitrates using hydrogen bonds. These hydrogen bonds are found in a halo of surrounding molecules called the "secondary sphere."

"When we look at this problem of how we actually tackle nitrate reduction, we look to the enzymes, we look to biology, and what we've found is nature has provided cues about how to bind and reduce nitrate," he said. "We found that just by having well-positioned hydrogen bonds, you can actually change the bonding structure in nitrate and force a subsequent reduction step."

     They began with an iron complex surrounded by a secondary sphere of hydrogen bonds. They were then able to turn hydrogen bonds on, essentially targeting the binding sites on nitrates, in order to prime, or ready them for the next chemical reaction in the reduction process.   

     The researchers note that there are two types of reduction sequences for nitrates: stoichiometric reduction and catalytic reduction.

“Nature’s solution to achieve binding/activation of nitrate is to use networks of hydrogen-bonding (H-bonding) interactions, amino acid residues that are critical to the function of nitrate transport proteins and nitrate reductases.”

     The researchers compared the use of heat and light to power the chemical reaction and got two different chemical results.

“When the researchers used heat to drive the chemical reaction, the iron complex was able to grab oxygen atoms from nitrate, reducing it to nitric oxide. When the researchers used light, the iron complex was able to remove oxygen atoms from nitrate altogether, converting it to ammonia.”

     The ammonia can be reused as fertilizer, and the nitric oxide has medical and industrial uses. The experiments should be considered to be an early step in the development of chemical remediation of nitrates in water, which is needed where fertilizer use is heavy. It should be combined with more efficient, better targeting, timing, and overall optimization of fertilizer applications. Devices would need to be built that could facilitate and control the reduction step. The method could one day be used at facilities like wastewater treatment plants.

"The timeframe for development of solutions to big picture problems has a large time horizon, and they require fundamental studies to develop principles and invent new ways to do molecular transformations that are societally important," Szymczak said. "We are giving people a roadmap of how to achieve the difficult reduction step that we hope could be translated to engineered systems that might be used down the road."

    

References:

 

Iron complex breaks down stubborn pollutant using light-powered reaction. University of Michigan. edited by Sadie Harley, reviewed by Robert Egan. Phys.org. September 22, 2026. Iron complex breaks down stubborn pollutant using light-powered reaction

Secondary-sphere hydrogen bonding promotes catalytic nitrate reduction at iron. Writhabrata Sarkar, Andrew R. LaDuca, Riley W. Kazukiewicz & Nathaniel K. Szymczak. Nature Chemistry (2026). Secondary-sphere hydrogen bonding promotes catalytic nitrate reduction at iron | Nature Chemistry