Mechanistic Insights into the Silica-Mediated Synthesis\nof Glyceraldehyde from Glycolaldehyde and Hydroxymethylene

Minerals\nare crucial ingredients in prebiotic chemistry as they\ncould have promoted the evolution of simple organic molecules toward\nproto-biomolecules that are on the route of the emergence of self-replicating\ninformation-rich macromolecules. In this respect, the formose reaction,\ninvolving the sequential autocatalytic condensation of formaldehyde,\nis the generally accepted pathway for sugar synthesis. Although obtained\nunder controlled laboratory conditions with enhanced sugar yields\npromoted by the presence of silicate in the reaction medium, it presents\na number of limitations, and the underlying reaction mechanism remains\nan unsolved riddle. In this work, the focus is on the second step\nof the formose reaction, namely, the synthesis of glyceraldehyde,\nwhich is accomplished by considering the reaction between glycolaldehyde\nand hydroxymethylene taking place on the edingtonite mineral. The\nreaction mechanism is explored by quantum chemical simulations performed\nat various degrees of sophistication to shed light on the thermochemical\nand kinetic feasibility of the reaction. The same pathway is also\ninvestigated in the gas phase in order to disentangle the role played\nby the zeolitic mineral. The obtained results show that the exothermic\nreaction between glycolaldehyde and hydroxymethylene yields glyceraldehyde\nby a submerged reaction path, both in the gas phase and on the edingtonite\nsurface. The mineral substrate provides further stabilization, by\nabout 20 kcal mol<sup>–1</sup>, of all the species involved\nin the reaction pathway and acts as a scaffold favoring the interaction\nof the two reactants.