Details of photosynthetic water splitting revealed
A study by an international team of researchers led by Johannes Messinger from the Max Planck Institute for Bioinorganic Chemistry in Mühlheim an der Ruhr now provides more detailed information on how plants use sunlight to split water. To do this, the researchers analyzed in detail the geometric structure of the manganese-calcium complex in photosystem II, a collection of molecules that is said to play a crucial role in generating energy through photosynthesis. Using a combination of X-ray technology and computer calculations, the scientists were able to filter out the correct arrangement of the atoms from the 18 discussed so far.
The manganese-calcium complex consists of four manganese, one calcium and at least five oxygen atoms, which - as the research team has now discovered - form a structure of three connected diamonds. With their help, under the influence of sunlight, plants split water into its components oxygen and hydrogen.
According to the researchers, it was necessary to determine the distances between the individual manganese atoms for a more precise understanding of the actual construction plan. Previous studies failed again and again because the high radiation dose of the X-ray structure analysis destroyed the sensitive molecule - a problem that the researchers countered with the further development of the significantly gentler EXAFS measurement method (Extended X-Ray Absorption Fine Structure). However, it remains uncertain where the individual calcium atom is positioned within the complex and in which orientation the entire complex fits into photosystem II.
With their work, the researchers are contributing to a deeper understanding of the processes involved in photosynthesis, fueling the hope of one day being able to imitate the photosynthetic splitting of water in the laboratory. Should this succeed, the hydrogen released during the reaction would provide an ideal source of energy, obtained from pure solar energy.