IUPAC ’09: saving the planet one atom at a time
Hello from Glasgow, Scotland. Home to the deep fried mars bar, Charles Rennie Mackintosh, Gordon Brown MP, and now, for one week only, the IUPAC congress.
I’m here to delve into the finer points of chemistry and to see what is getting chemists salivating this year.
The first session I went to was about artificial photosynthesis. The process that plants carry out with ease – turning sunlight into stored energy – is causing a major headache for scientists trying to mimic the process.
Rather than try to rebuild the molecules used by nature for photosynthesis, chemists are looking at systems that they can build and understand better, and use them to do the same jobs that plants do with their complex molecular machinery.
In these systems, sunlight is used to power the separation of charge – from a neutral molecule to one with a positive and negative component. But the big problem is keeping those charged states apart from one another for any length of time. If they recombine, the charge separation, which could lead to electric current, is lost.
Today I got to see how making the molecules really long with the charged ends separate from each other in space can help. Ken Ghiggino from the University of Melbourne, Australia, uses a set of four porphyrins, which are big ring-shaped molecules. One end has a zinc atom sitting inside the ring and the other a gold atom. These two metals can shunt a charge from one end to the other. The trouble is that this kind of system is far too complicated to ever be manufactured on a large scale.
Another suggestion is simple dyad systems with one charge donating and one charge accepting part. But as Andy Benniston from Newcastle University showed us, to separate the charge with these systems is also not as easy as hoped. He suggested that when previous chemists have claimed to have a long lived charge separated state what they had actually done was form a different quantum state called a triplet state. This is something else entirely.
All this is yet more evidence that nature is unfathomably clever in its use of molecular processes to gain energy, and that humans are way behind in our understanding. But thanks to chemists who refuse to get depressed by this notion, one day we may just be able to take sunlight and produce energy that we can store and use at will, without destroying our world.