Meteorites burning through the atmosphere could have seeded life on Earth - which could explain why natural proteins are all 'left handed', say researchers in The Netherlands.

Amino acids come in two, mirror image forms (enantiomers); L and D. But nature only makes proteins from the L enantiomer. Among the simple self-replicating molecules scientists have proposed as the beginnings of life on Earth, how did this preference for left handers emerge?

Recent research suggests sublimation could be the key. Ben Feringa and colleagues at the University of Groningen have now shown that a wide variety of amino acids, under gentle sublimation conditions, will form vapours highly enriched in the L-amino acid.¹ This follows work by Graham Cooks and co-workers at Purdue University, US, who found a similar effect with the amino acid serine.² Cooks had suggested this enrichment may be a property particular to serine, a proposal that Feringa's findings contradict.

'Sublimation has been proposed as a mechanism by which volatile organic compounds [on meteorites] survive atmospheric entry,' said Feringa. 'If the enantiomorph preferentially sublimes due to atmospheric heating, not only would the higher ee material be separated from the racemic material, but continued heating of the material not sublimed may serve as a mechanism to destroy the racemate,' he said.

'The different behaviour of racemic and homochiral condensed phases in phase transitions is something that must be expected,' said Josep Ribo, an expert in the emergence of chirality at the University of Barcelona. 'However, this type of work is necessary to avoid other research teams arriving at errors or badly designed experiments. In this respect the work has consequences in the design of experiments in space missions directed to the detection of optically active amino acids,' he said.

James Mitchell Crow