Interstellar glycolaldehyde: The first sugar

Interstellar glycolaldehyde (CH2OHCHO) has been detected in emission toward the Galactic center source Sagittarius B2(N) by means of millimeter-wave r otational transitions. Glycolaldehyde is an important biomarker since it is structurally the simplest member of the monosaccharide sugars that heretof ore have gone undetected in interstellar clouds. There is no consensus as t o how any such large complex molecules are formed in the interstellar cloud s. It may be that the typical environment of dense interstellar clouds is f avorable to glycolaldehyde synthesis by means of the polymerization of form aldehyde (H2CO) molecules either on grain surfaces or in the gas phase. Alt ernatively, we speculate that glycolaldehyde and other complex molecules ma y undergo assembly from functional molecular groups on grain surfaces. Util izing common chemical precursors, a chance process could account for the hi gh degree of isomerism observed in complex interstellar molecules (e.g., me thyl formate, acetic acid, and glycolaldehyde). This work suggests that the phenomenon of isomerism be investigated further as a means of potentially constraining interstellar chemistry routes for those individual sources whe re the condition of good source-beam coupling can be achieved.