A Bit of Sugar on TiO2: Quantum Chemical Insights on the Interfacial Interaction of Glycolaldehyde over Titanium Dioxide

Among 200 molecules discovered up to now in the interstellar and circumstellar space, glycolaldehyde (GA) represents the smallest monosaccharide detected in those places. This detection comes with important clues about the origins of life in the Universe and in a primeval Earth, as GA is one of the intermediates in the formose reaction leading to ribose. Mineral surfaces, such as TiO2, have a primary role in processing simple molecules toward more complex prebiotic species. In the present work, the adsorption of GA over the surface of TiO2 anatase (1 0 1) is investigated by quantum chemical simulations, being this the first step involved in the series of reactive steps mediated by the surface. Six adsorption configurations are modeled by periodic density functional theory (DFT) calculations, and for each of them structural, energetic and vibrational properties are calculated. The results of the theoretical study are supported with measurements of the GA adsorption on TiO2 by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, in order to gain experimental evidence about their interaction. The outcomes show that the most stable adsorption configuration of GA on TiO2 involves the anchoring through both the OH and the C=O groups, with a binding energy of about 18 kcal mol(-1). In addition, GA can be activated by the interaction with the surface, which may lead to the formation of reactive species that, in turn, can undergo further chemical processing.