Interstellar prebiotic formation of glycine delivery to Earth and polymerization on feldspars

Reactions of simple molecules (H2CO, NH3, HC-N) occurring at the surface of interstellar icy-based particles to give glycine, its capture on defects at a silica matrix simulating a meteoritic grain and its delivery to primordial Earth and, finally, its polymerization catalyzed by feldspar surfaces have been dealt with by molecular modeling approach based on density functional theory in a cluster approach. Two reaction channels were studied for the glycine formation in the interstellar medium: i) a Strecker-like mechanism involving H2CO, NH3 and HC-N molecules catalyzed by neutral icy particles; ii) a mechanism involving CO and H2CNH catalyzed by radical neutral/cation icy particles. Whereas channel i) was found to be hindered by too high kinetic barriers for the conditions found in the interstellar medium[1], channel ii) provided much easier paths towards glycine formation[2]. The delivery of glycine to primordial Earth was then studied by its reaction with defects at the silica grains, modeling the surface of meteoritic/cometary particles. When the grain finally reached a warm water-rich pool present on the primordial Earth, glycine is easily released[3] and becomes available for polymerization. This last step was found to be catalyzed when glycine is adsorbed on the surfaces of common feldspars, particularly abundant on the early Earth, showing that the interplay between a surface Brönsted acidic site and a nearby Lewis one was essential to activate the peptide bond formation[4, 5]. References [1] Rimola, A., Sodupe, M., Ugliengo, P., Deep-space glycine formation via Strecker-type reactions activated by ice water dust mantles. A computational approach, Physical Chemistry Chemical Physics, 12 (2010) 5285-5294. [2] Rimola, A., Sodupe, M., Ugliengo, P., Computational Study of Interstellar Glycine Formation Occurring at Radical Surfaces of Water Ice Dust Particles ApJ, submitted. [3] Rimola, A., Ugliengo, P., The role of defective silica surfaces in exogenous delivery of prebiotic compounds: clues from first principles calculations, Physical Chemistry Chemical Physics, 11 (2009) 2497-2506. [4] Rimola, A., Sodupe, M., Ugliengo, P., Aluminosilicate surfaces as promoters for peptide bond formation: An assessment of Bernal's hypothesis by ab initio methods, Journal of the American Chemical Society, 129 (2007) 8333-8344. [5] Rimola, A., Ugliengo, P., Sodupe, M., Formation versus Hydrolysis of the Peptide Bond from a Quantum-mechanical Viewpoint: The Role of Mineral Surfaces and Implications for the Origin of Life, International Journal of Molecular Sciences, 10 (2009) 746-760.