2:55 PM - 3:10 PM
[MIS08-05] Reactive Molecular Dynamics Simulation on Fundamental Process of Synthesis of Amino Acid Precursor
Keywords:The origin of life, chemical evolution, molecular dynamics simulation, ice mantle
Proteins that constitute terrestrial life are formed by condensation polymerization of amino acids. In studies of the origin of life, it is believed that organic substances such as amino acids were first formed in an inanimate environment. Current research on the origin of life is based on the theory of “chemical evolution,” in which simple molecules are transformed into complex molecules through chemical reactions and eventually evolve into materials for life. Analysis of meteorites that have flown to Earth has revealed amino acids and high-molecular-weight organic materials, suggesting the possibility that organic materials, the building blocks of life, were synthesized in the space environment. In this study, we performed molecular dynamics simulations of the formation of polymeric organic molecules.
Molecular clouds are regions of high concentration of matter and are the birthplace of planets. Because of this high concentration of matter, stellar light does not penetrate the molecular clouds, and the extremely low temperatures inside them result in a multi-component ice called the “ice mantle” with a dust core. The ice mantle is composed of simple molecules such as water, carbon monoxide, ammonia, etc. When irradiated by cosmic rays, the ice mantle is assumed to dissolve into the interior and transform into polymeric organic matter through chemical reactions.
In this study, simulations were designed based on this chemical evolution scenario. In the simulation, a group of small molecules of water, carbon monoxide, and ammonia were placed in a simulation box, and it was assumed that the molecules acquired energy by cosmic ray irradiation. The molecules produced were further evaluated by implementing a temperature control such that the system reached a high temperature (10,000 K) and then cooled to the temperature in the molecular cloud (10 K). Reactive force fields were used in the molecular dynamics calculations to handle bond formation and cleavage between atoms.
Hybrid simulations were performed, combining canonical ensemble simulations in which the energy of the system is controlled by an external heat bath and microcanonical ensemble simulations in which, in addition, an isolated system without energy transfer is treated. The former simulation evaluated the density dependence of the produced molecules and the dependence of the starting molecular species. The results showed that the higher the density, the easier it is to unbind multiple bonds of atoms, and the more carbon atoms chain together to form larger molecules. It was also confirmed that larger molecules are easily synthesized by selecting a configuration that contains more carbon and nitrogen atoms in the starting material. The latter simulation reproduced the spatially sparse cooling process of the starting material and showed that larger molecules are synthesized as the temperature gradually decreases.
These results suggest that the formation of high-molecular-weight organic materials is likely to occur when cosmic rays irradiate regions of the ice mantle with locally high proportions of carbon and nitrogen atoms.
Molecular clouds are regions of high concentration of matter and are the birthplace of planets. Because of this high concentration of matter, stellar light does not penetrate the molecular clouds, and the extremely low temperatures inside them result in a multi-component ice called the “ice mantle” with a dust core. The ice mantle is composed of simple molecules such as water, carbon monoxide, ammonia, etc. When irradiated by cosmic rays, the ice mantle is assumed to dissolve into the interior and transform into polymeric organic matter through chemical reactions.
In this study, simulations were designed based on this chemical evolution scenario. In the simulation, a group of small molecules of water, carbon monoxide, and ammonia were placed in a simulation box, and it was assumed that the molecules acquired energy by cosmic ray irradiation. The molecules produced were further evaluated by implementing a temperature control such that the system reached a high temperature (10,000 K) and then cooled to the temperature in the molecular cloud (10 K). Reactive force fields were used in the molecular dynamics calculations to handle bond formation and cleavage between atoms.
Hybrid simulations were performed, combining canonical ensemble simulations in which the energy of the system is controlled by an external heat bath and microcanonical ensemble simulations in which, in addition, an isolated system without energy transfer is treated. The former simulation evaluated the density dependence of the produced molecules and the dependence of the starting molecular species. The results showed that the higher the density, the easier it is to unbind multiple bonds of atoms, and the more carbon atoms chain together to form larger molecules. It was also confirmed that larger molecules are easily synthesized by selecting a configuration that contains more carbon and nitrogen atoms in the starting material. The latter simulation reproduced the spatially sparse cooling process of the starting material and showed that larger molecules are synthesized as the temperature gradually decreases.
These results suggest that the formation of high-molecular-weight organic materials is likely to occur when cosmic rays irradiate regions of the ice mantle with locally high proportions of carbon and nitrogen atoms.