Titanium dioxide crystals might have helped trigger life on earth
18 January 2006
Titanium dioxide crystals could have played a central role in establishing life on Earth, say two New Zealand chemists. They report that the crystals can catalyse the transformation of formamide (NH2CHO) into complex organic compounds, including DNA bases.
Sanjaya Senanayake and Hicham Idriss at the University of Auckland deposited formamide onto the surface of a TiO2 crystal and exposed it to low levels of UV light for 15 minutes. Light at this level stimulated reactions between the TiO2 surface and the formamide, but did not break apart any larger compounds produced.
Analysis of the crystal surface using mass spectrometry and x-ray spectroscopy revealed the formation of a range of complex organic compounds, including all the DNA and RNA bases. The researchers postulate that these compounds were produced by the action of OH radicals, produced by the UV light, on formamide polymers that had formed on the TiO2 surface.
TiO2 occurs naturally as the minerals rutile and anatase, and one of the most popular theories for the origin of life holds that mineral surfaces catalysed the formation of the first RNA strands, as well as acting as a template and store for the strands. The weakness in the theory has been determining how the nucleotide bases formed on the mineral surfaces in the first place. This research now suggests a possible process.
Nevertheless, Matthew Genge, a geoscientist who studies the origin of life at Imperial College, London, is sceptical that TiO2 played a major role. Rutile and anatase are most common in igneous granite rocks, which were probably rare on the early Earth, says Genge, and the researchers conducted their experiment in a vacuum, whereas the early Earth probably had a thick, wet atmosphere.
Genge says these reactions are more likely to occur in the depths of space. 'Perhaps in the low vacuum, dry, UV-irradiated environment of giant molecular clouds, rutile has been busily turning formamide into the building blocks of life for the last 10 billion years, and life as we know it really did come from the stars,' he told Chemistry World.
S D Senanayake and H Idriss, Proc. Natl. Acad. Sci. USA (DOI: 10.1073/pnas.0505768103)