Tuesday, 9 July 2013

Cold Fusion (Of Hydrogen Cyanide)

Life appeared on the planet around 3.8 billion years ago. We are certain that the first cells were bacteria and pretty sure about what structures they were built from. Yet, we are still mapping the chemical pathways which made them. Decades of research have given us parts of the picture, namely no oxygen in the atmosphere, an abundant energy source and constant flow of chemical compounds.

A simplified diagram of the Miller Urey Experiment.
Various experiments have shown us how the organic constituents of life is formed from simple chemicals. The Miller Urey experiment conducted in the 1950s formed amino acids found in proteins from carbon dioxide, water vapor, methane, ammonia and hydrogen with a spark of electricity. Bubbles of oil and blocks of clay have allowed us to create structures similar to cell membranes. Now another means of generating the building blocks of life has recently been demonstrated.

When multiple molecules of hydrogen cyanide are exposed to ultraviolet light, after multiple reaction stages, a chemical known as an imidazole intermediate, a compound vital in the formation of the nucleobases in DNA, the parts of the molecule which encode genetic information, is formed. This has been known since the 1960s. What remained unclear was how the UV light caused the formation of the imidazole intermediate?

Yet earlier this year, a computer model created by researchers from the Max Planck Institute in Germany, demonstrated something incredible: that this hydrogen cyanide reaction can occur in very common conditions rather than a precise set. 'This has nothing to do with heat, but with electrons,' said Mario Barbatti. Many organic reactions require a temperature range of between 0 and 100 degrees Celsius to occur which restricts their use in models of the origins of life to planets of such a temperature.

The reaction scheme involving hydrogen cyanide and UV light.
This reaction on the other hand, on the basis of the computer models, can actually occur at much lower temperatures, such as the vacuum of space. Each photon of UV light impacting a molecule of hydrogen cyanide boosts its energy state until it can react. This new molecule absorbs yet more photons and reacts again forming another new molecule. The problem is that this has to occur quickly as the molecule's energy state is only raised briefly before it is lost in the form of a second photon of UV light emitted from the molecule.

In order to react, each molecule must absorb hundreds of photons very quickly before the energy is dissipated. 'This is very inefficient and quite extraordinary,' said Barbatti. Finding a solution to this problem was the main challenge facing the researchers. After analyzing multiple possible intermediates, they found the imidazole intermediate, which fitted with previous research and the fast energy dissipation of the reactions. 'Some intermediates are too elusive to analyze them in the laboratory; they disappear before we may see them,' explained Barbatti.

A reaction which can occur in the depths of space is incredibly useful to the story of the origins of life. Analysis of nebulae and a number of planetary atmospheres has revealed the presence of hydrogen cyanide. Stars are powerful sources of UV radiation, meaning that this reaction could have very easily occurred in the nebula from which our solar system was formed, in the atmosphere of the early Earth and existing nebulae.