Making ribose in interstellar ices: Astrobiologists have long speculated on the origin of prebiotic molecules such as amino acids and sugars. Meinert et al. demonstrated that numerous prebiotic molecules can be formed in an interstellar-analog sample containing a mixture of simple ices of water, methanol, and ammonia. They irradiated the sample with ultraviolet light under conditions similar to those expected during the formation of the solar system. This yielded a wide variety of sugars, including ribose—a major constituent of ribonucleic acid (RNA). Science , this issue p. 208

Significance: In molecular clouds out of which stars and planetary systems form, simple solid-state molecules made in large part of H ₂ O, CO, CO ₂ , CH ₃ OH, and NH ₃ are abundantly present. In these environments, energetic and thermal processes on these ices, which can be simulated in the laboratory, lead to complex organic matter. Possibly at the origin of the organic matter in our Solar System and incorporated into planetesimals, this material may be considered as a potential source for prebiotic chemistry on telluric planets, following a process that may be quite universal. The composition of these laboratory-evolved ices includes potentially prebiotic species such as amino acids and, as presented in this paper, aldehydes and sugars.

Kinetic modeling using nonlinear differential equations is proposed to analyze the spontaneous generation of enantiomeric excess in the autocatalytic addition of diisopropylzinc to prochiral pyrimidine carbaldehydes (Soai reaction). Our approach reproduces experimentally observed giant chiral amplification from an initial enantiomeric excess of 60%, high sensitivity and positive response to the presence of minute amounts of chiral initiator at concentrations <10^–14M, and spontaneous absolute asymmetric synthesis from achiral starting conditions. From our numerical simulations using kinetic schemes derived from the Frank model, including stereospecific autocatalysis and mutual inhibition, we have shown that it is possible to reproduce the mirror-symmetry-breaking behavior of the Soai reaction under batch conditions leading to a bimodal enantiomeric product distribution. Mirror-symmetry breaking was found to be resistant to a loss of stereoselectivity up to 30%. While the mutual inhibition between enantiomers seems to originate from the presence of dimerization equilibria, the exact nature of the autocatalytic stereoselective process still remains to be revealed. From the kinetic viewpoint, simple autocatalysis involving monomers as the catalytic species is consistent with all reported experimental effects of the Soai reaction.

Chiral symmetry breaking in stirred crystallization of sodium chlorate ( ${\mathrm{NaClO}}_3$) occurs via the production of secondary crystals from a single “mother crystal.” Martin, Tharrington, and Wu [Phys. Rev. Lett. 77, 2826 (1996)] investigated this phenomenon and concluded that it was mechanical crushing of a crystal by the stir bar, not convection, that produces secondary crystals from a single crystal. Here we report the generation of secondary crystals of sodium chlorate when a saturated solution of sodium chlorate is simply made to flow over a sodium bromate ( ${\mathrm{NaBrO}}_3$) crystal. This clearly shows that fluid flows alone can generate and disperse secondary nuclei.