Rotational and Vibrational Signatures of Astrophyscially relevant Gas-Phase Stereo-isomeric Species of Proteinogenic Amino acid Leucine.

The search for life-supporting molecules in outer space is an ever-growing endeavour. Towards this, the computational chemistry supporting the astronomical spectroscopic observations is becoming a valuable tool to unravel the complex chemical network in interstellar medium (ISM). In the present work, quantum-mechanical computations, accounting for anharmonic effects, are performed to obtain the rotational and vibrational line-data for the gas-phase conformers of proteinogenic amino acid Leucine and its isomeric species predicted to be involved in its stereoinversion under the extreme environment of ISM.

Gas-Phase Stereoinversion in Aspartic Acid: Reaction Pathways, Computational Spectroscopic Analysis, and Its Astrophysical Relevance.

Noncatalytic reaction pathways for the gas-phase stereoinversion in aspartic acid are mapped employing a global reaction route mapping strategy using quantum mechanical computations. The species including the transition states (TSs) traced along the stereoinversion pathways are characterized using rotational and vibrational computational spectroscopic analysis while accounting for the vibrational corrections to rotational constants and anharmonic effects. Notably, the TS structures traced along the stereochemical pathways resemble the achiral ammonium ylide and imine intermediates as observed in the Strecker synthesis of chiral amino acids.

Mechanism and Kinetics of the Gas-Phase Stereoinversion in Proteinogenic l-Threonine and Its Astrophysical Relevance.

Quantum-mechanical computations are performed to trace the mechanistic pathways for the gas-phase stereoinversion in proteinogenic l-threonine, an amino acid with two stereocenters. The pathways are explored employing density functional and coupled cluster theories along with a global reaction route mapping strategy to locate various intermediates and transition states along the stereoinversion pathways on the complex potential energy surface of l-threonine. A simultaneous intramolecular proton and hydrogen atom transfer is observed to drive the stereoinversion in threonine.