Nitrogen gas (𝑁2) is everywhere; it makes up nearly 80% of Earth’s atmosphere, but its triple bond is so strong that most living organisms can’t use it directly. Only certain microbes, armed with enzymes called nitrogenases, can split nitrogen and convert it into ammonia, a form essential for life.
There are three classes of nitrogenases, distinguished by the metals they contain: molybdenum (Mo), vanadium (V), or iron (Fe). Among them, molybdenum-based nitrogenases are the most efficient, and two new studies from MIT finally explain why.
The MIT team discovered that molybdenum doesn’t bind nitrogen directly. Instead, it helps nearby iron atoms grip nitrogen more tightly, making it easier to start breaking the nitrogen-nitrogen triple bond.
“It’s that initial binding step that’s really the hard part. Once you’ve started to break the nitrogen-nitrogen triple bond and make some new nitrogen-hydrogen bonds, it’s pretty easy to get the rest of the way,” said Daniel Suess, Arthur Amos Noyes Associate Professor of Chemistry at MIT.
This insight shows how molybdenum acts as a kind of silent partner, enabling iron to do the heavy lifting.
In the first study, led by Tong Wu and Madeleine Ehweiner, researchers swapped different metals into simplified iron-sulfur clusters. Only large atoms like molybdenum or tungsten allowed strong nitrogen binding. Smaller metals (vanadium, chromium, iron) failed to bind 𝑁2.
In the second study, led by Alexandra Brown, the team showed how molybdenum’s large orbitals overlap with iron’s, enabling electron back-bonding. This makes it easier for iron to donate electrons to nitrogen, kickstarting the reaction.
Together, these findings explain why molybdenum-containing nitrogenases outperform their cousins.
Agriculture: Engineered enzymes could help crops generate their own ammonia, reducing reliance on fertilizers.
Industry: Synthetic catalysts inspired by these enzymes could produce ammonia more efficiently than the energy-intensive Haber-Bosch process.
Biochemistry: The work reveals how nature solved one of life’s toughest chemical challenges billions of years ago.
“The primary result of these findings is to teach us about the natural world and how nature accomplishes this really important and miraculous reaction. And, maybe that can be translated into new processes,” Suess said.
This research shows how a single atom, molybdenum, can tip the balance in one of life’s most fundamental reactions. It’s a reminder that the tiniest details in molecular machinery can have planetary-scale consequences.
Journal Reference:
- Tong Wu, Madeleine A. Ehweiner, Alexandra C. Brown, Alex McSkimming, Daniel L.M. Suess. The influence of heterometals on dinitrogen binding at synthetic iron-sulfur clusters. Chem. DOI: 10.1016/j.chempr.2026.103133
- Alexandra C. Brown, Samantha N. MacMillan, et al. Molybdenum doping enhances backbonding at neighboring iron centers in iron-sulfur clusters. Chem. DOI: /10.1016/j.chempr.2026.103134
