"Looking to nature for clues…" she says, "we find microorganisms containing enzymes whose active sites are intricate molecular arrangements of iron, sulphur and sometimes iron and nickel, that work with great efficiency to produce hydrogen from water. Other ‘tiny factories’ might use the hydrogen as does a fuel cell to generate electrical energy."
One problem with a lot of catalysts is that they are oxygen sensitive – that is they degrade when exposed to air – and nature has an answer to this too. The enzymes that Dr Darensbourg is copying are thought to have been developed by the earliest life forms, perhaps before oxygen was a major component of the earth’s atmosphere. Over time, as oxygen became more abundant, the enzymes evolved in response, developing ways to protect themselves.
The enzymes developed two lines of defence. The first is to bury the active site (the part of the molecules that actually does the catalysis – usually based around a metal atom) deep within a protein polymer. The second is to have a large atom in the oxygen family, such as sulphur or selenium, immediately attached to the metal. Both these lines of defence help to shield the active site from attack by oxygen molecules.
In their work, Dr Darensbourg and her team have studied these enzymes using computer modelling. They explored various designs – using different metals at the active site, and using sulphur or selenium as the protecting active – and investigated the effect of different structures on protecting the active site from damage.
Dr Darensbourg explains that developing better catalysts for hydrogen production could one day contribute towards solving global warming and the looming energy crisis. "We must all try and contribute in some way to the problem of carbon management – with dreams of reducing as soon as possible humankind’s carbon footprint, which is resulting in the warming of the planet at an alarming rate."
This article is free to read in our open access, flagship journal Chemical Science: Xuemei Yang et al., Chem. Sci., 2018, Advance Article. DOI: 10.1039/C8SC044336H. You can access all of our ChemSci Picks in this article collection.