Prebiotic Chemistry in Aqueous Environment:A Review of Peptide Synthesis and Its Relationship with Genetic Code

Prebiotic peptide synthesis and the origin of the genetic code are central issues concerning the origin of life.The question of how they are possibly correlated on the primordial Earth remains perplexing,although numerous experiments have been carried out to explain the prebiotic chemistry of peptide synthesis and the genetic code origin.The purpose of this article is to review the chemical reactions occurred during the synthesis of peptides and the origin of the genetic code in the early Earth aqueous environment.Meanwhile,we attempt to review their relationship as well.At last,from our perspective,the chiral properties of biomolecules should be taken into account in the prebiotic chemical scenarios,which may contribute to some breakthroughs in the further research of this field.

Schreibersite on the early Earth:Scenarios for prebiotic phosphorylation

The mineral schreibersite,（Fe,Ni）_3P,provides a reactive source of phosphorus capable of forming phosphorylated molecules.These molecules may have been an important component of prebiotic chemistry,allowing their build-up and eventual commencement of autopoiesis.Discussed here are potential geochemical routes to providing schreibersite,as a potentially important prebiotic mineral,to the Hadean Earth.Two routes are identified：delivery of phosphides by meteoritic material and the reduction of phosphates to phosphides by high-temperature,low-redox conditions.About 1-10% of all crustal phosphorus is estimated to have been in schreibersite during the Hadean,making the long-term reaction of this mineral with organic-laden water plausible for many years.Ultimately,such conditions would have been conducive to the formation of life as we know it today.

Synthesis of Prebiotic Building Blocks by Photochemistry

Ultraviolet(UV)light is a very competent energy source for the synthesis of prebiotic building blocks on early Earth.In aqueous solution,hydrated electron is produced by irradiating ferrocyanide/cuprous cyanide/hydrosulfide by 254 nm UV light.Hydrated electron is a powerful reducing reagent driving the formation of prebiotic building blocks under prebiotically plausible conditions.Here we summarize the photoredox synthesis of prebiotic related building blocks from hydrogen cyanide(HCN)and other prebiotically related molecules.These results indicate biological related building blocks can be generated on the surface of early Earth.

Trimetaphosphate-induced chiral selection between amino acid and nucleoside using ^(15)N-^(31)P coupling NMR

Life on Earth uses a common set of L-amino acids(L-aa)to construct proteins and D-nucleosides(D-Nu)to form nucleic acids,which serve as the carrier of genetic information.Herein,we reveal the in-trinsic mechanism of chiral selection of L-aa and D-Nu from the perspective of chemical origin of life.This work employed^(15)N-labeled L-aa and performed one-pot synthesis of nucleotide amidate of amino acid(N-aa-NMP)using equal amounts of L-^(15)N-aa and D-^(14)N-aa with D-/L-Nu in the aqueous solution of trimetaphosphate,generating L-^(15)N-aa-NMP and D-^(14)N-aa-NMP,respectively.The ^(31)P-NMR data indicated that L-aa was preferentially selected during the formation of N-aa-NMP in the presence of D-Nu.Surpris-ingly,D-aa was preferred over L-aa in the presence of L-Nu.Further analysis revealed that L-^(15)N-aa-D-NMP vs.D-^(14)N-aa-L-NMP and D-^(14)N-aa-D-NMP vs.L-^(15)N-aa-L-NMP were mirror isomers of each other,respec-tively.These data suggest that there could be a set of chiral systems opposite to that on Earth,which infers there might be a world of life that is a mirror image of the Earth.