Chemical evolution of photosynthesis

Area of Science:

• Astrobiology
• Biochemistry
• Geochemistry

Background:

• Biological evolution of photosynthesis is understood, but its chemical origins remain unclear.
• Photosynthesis relies on photoreceptors to absorb solar radiation.
• Studied inorganic Earth crust components, coenzymes, and abiogenic/biogenic porphyrins as potential early photoreceptors.

Purpose of the Study:

• Elucidate the chemical evolution of photosynthesis using model systems.
• Investigate the role of inorganic photosensitizers and porphyrins in early light-driven metabolism.
• Model the transition from simple light absorption to complex energy conversion.

Main Methods:

• Constructed model photosystems using inorganic photosensitizers (TiO2, ZnO).
• Synthesized porphyrins abiogenically.
• Modeled electron transfer processes using electron donors (D) and acceptors (A) with magnesium-porphyrin complexes (P).

Main Results:

• Inorganic photosensitizers modeled photosystems I and II.
• Photochemical activation of coenzymes suggested an intermediate step in metabolism evolution.
• Abiogenically synthesized porphyrins, particularly magnesium complexes, demonstrated light-driven electron transfer capabilities.
• Proposed a primary electron transfer unit (D-P-A) incorporated into membranes, enabling charge translocation.
• Hypothesized that these units were precursors to biological photosynthetic systems.

Conclusions:

• The study presents plausible steps for the chemical evolution of photosynthesis.
• Early photosynthetic systems likely involved inorganic components and evolved towards complex organic molecules like porphyrins.
• These model systems provide insights into the transition from abiogenic chemical processes to biological photosynthesis.
• Further research in Precambrian rocks and space exploration may reveal the precise sequence of these events.