An efficient route to glyceraldehyde (HOCH2CH(OH)CHO)—the simplest aldose—via reactions of carbon-centered radicals in deep space

Abstract

The simplest sugar—glyceraldehyde (HOCH₂CH(OH)CHO)—represents a central molecule in the biochemistry of all lifeforms (glycolysis/gluconeogenesis). Linking photosynthesis and carbon fixation to sugar metabolism is fundamental to the liberation of energy from sugars and is the point at which glycolysis becomes exothermic—the pay-off phase. By exploiting isomer-selective photoionization reflectron time-of-flight mass spectrometry, glyceraldehyde and its energetic enol isomer 1,2,3-propenetriol (HOCH₂C(OH)CHOH) are identified in situ during space-simulation experiments as reaction products of radicals formed in ethylene glycol (HOCH₂CH₂OH) and carbon monoxide (CO) interstellar model ices exposed to energetic electrons as proxies for galactic cosmic rays. Isotopic substitution demonstrates the mechanism of sugar formation from molecules abundant in the interstellar medium. The stability of the carbon-centered radical intermediates formyl (HĊO) and 1,2-dihydroxyethyl (HOCH₂ĊHOH) imply that reactions of carbon monoxide and methanol derivatives like ethylene glycol represent a facile, highly active mechanism of sugar production within ice coated interstellar grains in deep space.