New stable phases of glycine crystals

Temperature driven transformations of glycine molecules embedded in interstellar ice

The formation of glycine amino acid on ice grains in space raises fundamental questions about glycine chemistry in interstellar media. In this work, we studied glycine conformational space and the related tautomerization mechanisms in water media by means of QM/MM molecular dynamics simulations of four glycine conformational isomers (cc, ct, tc, and tt). Interstellar low density amorphous (LDA) ice and T = 20 K were considered as representative for a cold interstellar ice environment, while temperatures of 250 and 450 K were included to model rapid local heating in the ice. In addition to the LDA environment, water clusters with 4, 17, and 27 H2O molecules were subjected to QM/MM dynamics simulations that allowed glycine tautomerization behaviour to be evaluated in water surface-like environments. The tautomerization processes were found to be strongly dependent on the number of water molecules and specific isomer structure. All the glycine isomers mostly preserve their canonical "neutral" conformations under interstellar conditions.

Glycine amino acid transformation under impacts by small solar system bodies, simulated via high-pressure torsion method

Impacts by small solar system bodies (meteoroids, asteroids, comets and transitional objects) are characterized by a combination of energy dynamics and chemical modification on both terrestrial and small solar system bodies. In this context, the discovery of glycine amino acid in meteorites and comets has led to a hypothesis that impacts by astronomical bodies could contribute to delivery and polymerization of amino acids in the early Earth to generate proteins as essential molecules for life. Besides the possibility of abiotic polymerization of glycine, its decomposition by impacts could generate reactive groups to form other essential organic biomolecules. In this study, the high-pressure torsion (HPT) method, as a new platform for simulation of impacts by small solar system bodies, was applied to glycine. In comparison with high-pressure shock experiments, the HPT method simultaneously introduces high pressure and deformation strain. It was found that glycine was not polymerized in the experimental condition assayed, but partially decomposed to ethanol under pressures of 1 and 6 GPa and shear strains of < 120 m/m. The detection of ethanol implies the inherent availability of remaining nitrogen-containing groups, which can incorporate to the formation of other organic molecules at the impact site. In addition, this finding highlights a possibility of the origin of ethanol previously detected in comets.

A molecular twist on hydrophobicity

A thorough exploration of the molecular basis for hydrophobicity with a comprehensive set of theoretical tools and an extensive set of organic solvent S/water binary systems is discussed in this work. Without a single exception, regardless of the nature or structure of S, all quantum descriptors of bonding yield stabilizing S⋯water interactions, therefore, there is no evidence of repulsion and thus no reason for etymological hydrophobicity at the molecular level. Our results provide molecular insight behind the exclusion of S molecules by water, customarily invoked to explain phase separation and the formation of interfaces, in favor of a complex interplay between entropic, enthalpic, and dynamic factors. S⋯water interfaces are not just thin films separating the two phases; instead, they are non-isotropic regions with density gradients for each component whose macroscopic stability is provided by a large number of very weak dihydrogen contacts. We offer a definition of interface as the region in which the density of the components in the A/B binary system is not constant. At a fundamental level, our results contribute to better current understanding of hydrophobicity.

Notwithstanding the very weak nature of individual contacts, it is the cumulative effect of a large number of interactions (green NCI surfaces) which provides macroscopic stability to the interfaces.