A common question Professors ask in science lectures revolves around the following phrasing: ’but how does x know...’. Three common examples include →

Physics: How does light know what path has the least action in determining the trajectory it takes? We care about this question since the principle of least action explains why light travels through space and matter as observed. We care as we hope to see what the answer is.

Chemistry: How does a molecule in a reaction mechanism know to break one specific bond over the other to reach a product? Sometimes the choice of bond breaking is counter-intuitive and critical for the reaction’s success. Particularly for synthesis, this question becomes a tease to the mind, capable of unlocking new chemistry thus new technology.

Biology: How does a virus without sensors or even a metabolism adapt to its environment and evolve? If Corona means more to you than the name of a beer from Mexico, you’re probably sufficiently curious enough to watch a Youtube video on this whilst scrolling on your phone. Whilst the nuance of the question is wildly different, the crux remains the same as does the answer: it doesn’t know. Instead, something far more interesting is going on!

My Summer 1 deals with exactly this type of question. The research project focuses on the mysteries of a protein called Photosystem 2 (PSII). This protein plays a pivotal role in the breakdown of water to oxygen during photosynthesis in plants, bacteria and algae. PSII is highly conserved in nature which tells us that Earth’s best chemist (nature) was only able to crack the code once given the difficulty in the problem. So far chemists have not been able to follow in nature’s footsteps leaving us out of understanding related chemical phenomena. But perhaps we can peek at nature’s notes to facilitate our understanding of nature’s secrets · · ·

Our approach in Prof. Aidan McDonald’s research group at Trinity College Dublin is to downscale the complexity of the problem. Instead of isolating or synthesising the entirety of PSII, we focus on one reaction site called P680. This site converts light energy into chemical energy that drives the breakdown of water and formation of oxygen. Exactly how that energy conversion takes place remains a mystery though there are some indicators. By making simpler synthetic molecules of P680 and probing them with existing techniques, the reaction mechanism might become evident from these indicators thus unlocking the chemistry of proteins like PSII.

The indicators can be summarised from the effects by peripheral charges^[1] surrounding the structural components of P680. Four chlorophyll molecules constitute P680 with each individual chlorophyll molecule having a standard redox potential around 0.8 V describing the ease at which chlorophyll accepts and loses electrons. In P680 however the chlorophyll molecules each have a standard redox potential around 1.3 V indicating a change in their chemistry. Whilst the change seems small, it is worth noting that the standard redox potential is a constant for a particular compound. As an analogy, if a steel support has a maximum capacity of 0.8 ton, it would be surprising to see an identical steel support suddenly holding 1.3 ton without any sign of fatigue. Chlorophyll surprises us with exactly this and in the McDonald’s group the leading hypothesis involves explaining the cause of this through the peripheral charges surrounding the chlorophyll molecules. At the end of Summer 1 we should be able to say more about this!

By synthesising simple ‘mimic’ molecules that mimic the structure of chlorophyll, the effect of peripheral charges can be investigated. Through varying the attachments of metal ions and the type of metals attached, the effect of peripheral charges is expected to alter the standard redox potential, increasing the potential as observed in P680. Once a threshold standard redox potential is achieved or can be designed, not only can the chemistry of PSII be unlocked but also that of other enzymes involved in reactions that Chemists struggle with. Energy expensive processes such as the Haber-Bosch process for nitrogen fixation that currently account for around^[2] 2% of energy consumption globally could in principle become fully solar powered. Apart from similar analogies, new chemistry might be unlocked through the increased understanding of chemistry. Instead of perceiving chemistry through structure only, a new methodology could be developed for design and synthesis via peripheral charges that offers beneficial and contemporary chemistry.

Supervisor: Prof. Aidan McDonald & co-supervisor: Oscar Kelly at the Trinity Biomedical Sciences Institute, Trinity College Dublin, Ireland.

References

[1] S. A. Siddiqui, T. Stuyver, S. Shaik & D. Dubey, ’Journal of the American Chemical Society Au’, 3, 12, p. 3259–3269, (2023).

[2] V. Kyriakou, I. Garagounis, A. Vourros, E. Vasileiou & M. Stoukides, ’Joule’, 4, 1, p. 142-158, (2020).