Quantum-Chemical Modeling of the First Steps of the Strecker Synthesis: From the Gas-Phase to Water Solvation.

The two first steps of the Strecker synthesis of glycine, namely (a) addition of ammonia to formaldehyde to give aminomethanol and (b) its dehydration leading to methaneimine, is studied using high level quantum chemistry computations (G3B3). Water solvation is modeled by considering the effect of adding a discrete number of active or passive molecules of water (up to four) and by immersing the identified water-solute complexes in a conductor-like polarizable continuum solvent model. Activation of the reactants by protonation is also examined. Exhaustive search of microhydrated neutral and protonated aminomethanol has been performed using a combination of hierarchical and genealogical approaches. Critical energies associated with all the elementary reaction steps were estimated using the accurate G3B3 composite method thus providing benchmarks to discuss the possible occurrence of Strecker synthesis in prebiotic chemistry.