Exploration Of Evolution Of Micromolecules And Origin Of Chirality In Hydrothermal Environment

When, where and how did life arise on the primitive earth? Many people are interested in it and pay attention to it, but no one knows the answer so far. Origin of life is one of the important and unsolved questions in modern science. We cannot find the answer by observation or doing experiment. Some hypotheses were put forward from the old. There are still many unknown question about origin of life, so the exploration will go on forever. As the development of science and the discovery of evidence, people are more passionate to explore the origin of life. The aim of study is to understand the history of the origin of life before billions of years. By this study, we can obtain much knowledge about life and environment, macrocosm and part, structure and function, individual and system, matter and energy; we can explain the mechanism of genetic variation, reproduce, metabolism, sport, controllability and so on; we can know and illustrate the essence of life.From view of modern science, the origin of life should be studied following the law of matter and motion. The life on the earth is evolved from the inorganic matter by endless chemical evolution. A variety of evidences show that life on the earth may originate from the submarine hydrothermal vents on the primitive earth. Scientists have done much and deep study on chemical evolution under hydrothermal condition to simulate the process of origin of life on the primitive earth.In the present study, we simulate the reaction under the primitive earth hydrothermal environment, in order to understand the evolution of micromolecules and origin of homochirality in the process of origin of life. We investigate the abiotic fixation of carbon dioxide under hydrothermal condition, which achieves the conversion from inorganic matter to organic matter and provides necessary organic matter for origin of life. We also investigate the symmetry breaking of racemic system and the stability of chiral molecule under hydrothermal environment, which offer a clue for origin of biohomochirality.1. We study the hydrothermal reduction reaction of carbon dioxide in the presence of different catalyst, which can provide necessary organic matter for origin of life. Iron can play a key role in the prebiotic chemical evolution, so we use iron as catalyst. Phenol is synthesized from carbon dioxide in the presence of common iron powder, whose highest yield is 1.21%. Then we use phenol as raw material and attempt to synthesize complex bioorganic molecule, which is still going on. Formic acid and acetic acid are synthesized from carbon dioxide in the presence of iron nano-particles, whose highest yields are 8.5mmol/L and 3.5mmol/L, respectively. We propose the possible reaction mechanism. The iron nano-particles have double functions in the reaction system, which not only act as the reducing agent, but also catalyze the reduction of CO2. We think the amount of rapid formation of H2 plays an important role in the selectivity of product.We demonstrate a mild hydrothermal route for reducing CO2 to formic acid, acetic acid and phenol, which are necessary organic molecules in chemical evolution and important raw material in chemical industry. These reactions offer a possibility to synthesize organic matter from inorganic matter and provide necessary precursor for origin of life.2. We demonstrate symmetry breaking in the course of polymerization of racemic D, L-alanine in the hydrothermal system. We find that the chirality of the dipeptides changes with time: at the beginning, the yields of the four dipeptides are almost equal; as the time increases, the yield of D-D-dipeptide decreases while the yield of L-L-dipeptide increases; the yield of L-L-dipeptide is four times as high as that of D-D-dipeptide when the reaction achieves balanced. The reaction brings clear enantiomeric excess and break the symmetry of the system,, which makes asymmetric prebiotic molecules synthesized from equal amounts of L- and D-enantiomers. We think that the symmetry breaking is induced by the parity-violating energy difference between enantiomers. This is a recycled autocatalysis reaction, which can amplify the small difference. The system can spontaneously evolve to and remain in a stable asymmetric state by recycled reversible chemical reactions.In the chemical evolution from amino acid to peptides, the preference of L-amino acid appears spontaneously, which is the predominant amino acid in organism. The spontaneous symmetry breaking is very significant to origin of biohomochirality. The asymmetric hydrothermal peptide formation reaction not only gives a route from amino acids to oligopeptides in the prebiotic condition, but also provides a valuable clue for the origin of homochirality. Therefore, it could play a key role in the origin of life.3. We investigate the racemization and dimerization of L-alanine under hydrothermal condition and the effect of different temperature and reaction time on the reaction. We find that in the hydrothermal system the starting temperature of dimerization of L-alanine is lower than that of racemization of L-alanine, so L-L-dipeptide is easier to form than D-alanine from the hydrothermal reaction of L-alanine. The racemization reaction of L-alanine obviously occurs only above 100°C. As soon as D-alanine is formed, L-D-dipeptide, D-L-dipeptide and D-D-dipeptide are generated from the dimerization of L-alanine and D-alanine. At 120°C, the longer the reaction time is, the more the D-alanine is formed, and the higher the ratios of the L-D-dipeptide, D-L-dipeptide and D-D-dipeptide.The result indicates that the chirality of the L-alanine can be preserved in the chemical evolution from monomers to dipeptides under mild hydrothermal condition (below 100°C) which is a possible prebiotic environment. In such environment, the racemization of L-alanine hardly takes place and the dimerization of L-alanine only generates L-L-dipeptide. Therefore the chirality of the L-alanine can be preserved.In summary, we explore the evolution of micromolecules and origin of homochirality, and obtain some progress. Our research offers a possibility to synthesize organic matter from inorganic matter and a clue for origin of biohomochirality. However, it is just a start. We realize clearly that origin of life is a worldwide problem. There are few evidences about origin of life because it happened billions of years ago. We must do more for exploring origin of life.