Synthesis of Prebiotic Building Blocks by Photochemistry
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doi: 10.1007/s40242-020-0289-6
Review
Synthesis of Prebiotic Building Blocks by Photochemistry LIU Ziwei* MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK Abstract 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. Keywords Prebiotic chemistry; UV irradiation; System chemistry; Origin of life
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Introduction
Life needs continuously energy and materials input to keep itself far-from-equilibrium. The light coming from the Sun is a major energy source for the modern life. Because of the lack of ozone layer, young Sun delivered more UV light to Earth before life was existed[1]. Due to the high level of atmospheric carbon dioxide(>103 Pa), the far UV light(wavelengths less than 200 nm) is always weakened[2]. A huge amount of chemical reactions are investigated trying to give a clue for the origin of life problem. Suggested by planetary science, a wide range of environments and conditions could exist on early Earth. For example, Miller-Urey experiments[3] indicated the amino acids generated by discharging a reduced atmosphere. Orį½¹ et al.[4] showed adenine was simply formed by heating ammonium cyanide. The Butlerow synthesis of sugar[5] is a base-catalyzed autocatalytic process. All these reactions have different substrates, different conditions, and the products are complex mixtures with only few percentages of bio-related molecules. Before we go deeply to the geochemical details of the synthesis of prebiotic building blocks, we should glimpse from extant biology down. If a modern cell reduced to a simplest one, by conceptual or experimental way, it still remains complex system. A minimal cell can be separated to three sub-systems: (a) genetic mechanism(e.g., DNA or RNA) has the ability to process and transmit heritable information to progeny; (b) metabolic machinery(e.g., protein) can capture energy and material source, catalyze chemical reaction in cell; (c) membrane compartment(e.g., phospholipid) can keep its components together and distinguish itself from the environment[6]. Nowadays, the origin of life is considered to have occurred through a co-evolutionary process involving different subsystems together rather than through self-organization in a system made of a single biopolymer. In this point of view, herein, I will summarize a systematically prebiotic building blocks synthesis from simple basic molecules under UV irradiation(Scheme 1).
Scheme 1
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Photo-synthesis of prebiotic relate
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