A origem da homoquiralidade terrestre para nucleosídeos e aminoácidos

On the origin of terrestrial homochirality for nucleosides and amino acids

Ronald Breslow,1 and Zhan-Ling Cheng

+Author Affiliations

Department of Chemistry, Columbia University, New York, NY 10027

Contributed by Ronald Breslow, April 23, 2009 (sent for review April 16, 2009)

Abstract

Before life could start on earth, it was important that the amino acid building blocks be present in a predominant handedness called the L configuration and that the ribose of RNA be predominantly in the D configuration. Because ordinary chemical processes would produce them in equal L and D amounts, it has long been a puzzle how the needed selectivities could have arisen. Carbonaceous chondrites such as the Murchison meteorite, which landed in Australia in 1969, brought some unusual amino acids with a methyl group replacing their α hydrogen. They cannot racemize and have a small but real excess of those with the L configuration. We have shown that they can partake in a synthesis of normal L amino acids under credible prebiotic conditions. We and others showed that small preferences can be amplified into solutions with very high dominance of the L amino acids because of the higher solubility of the pure L form than of the more stable DL racemic compound crystal. Here, we show that such solubility-based amplification of small excesses of three D nucleosides, uridine, adenosine, and cytidine, can also occur to form solutions with very high D dominance under credible prebiotic conditions. Guanosine crystallizes as a conglomerate and does not amplify in this way. However, under prebiotic conditions it could have been formed from homochiral D ribose from the hydrolysis of amplified adenosine or cytidine.

chiral amplification Murchison meteorite transamination water solubilities
Footnotes

1To whom correspondence should be addressed. E-mail: rb33@columbia.edu

Author contributions: R.B. and Z.-L.C. designed research; Z.-L.C. performed research; R.B. and Z.-L.C. analyzed data; and R.B. wrote the paper.

The authors declare no conflict of interest.

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