Carbohydrate's Silicate Origins

Sugar-silicate complexes may be key to the origin of complex, stereospecific carbohydrates on Earth, reports a group led by Northwestern University’s Joseph B. Lambert (Science 2010, 327, 984). Scientists have long looked at the formose reaction, in which formaldehyde is converted into sugars through a series of aldol reactions in basic solution, as a possible route for prebiotic sugar synthesis. But the products are racemic and unstable. Sugars can, however, form stable aqueous complexes with silicate, the major component of Earth’s crust and mantle. Lambert and colleagues experimented with adding formaldehyde, glycoaldehyde, and glyceraldehyde to sodium silicate solutions. Although the aldehydes on their own are too small to complex with the silicate, the researchers found that the molecules can oligomerize through base-catalyzed reactions to form larger molecules such as the sugar threose (C₄H₈O₄). The larger sugars can in turn complex with and be stabilized by silicate if they have appropriate stereochemistry.