Non-equilibrium chemistry

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A strong discrepancy exists in the way chemistry is carried out in the laboratory and in nature. The reaction flask of a chemist contains exclusively the reagents and additives that serve to obtain the desired reaction product. On the other hand, the reaction flask used by nature - the cell - is loaded with thousands of different molecules that are engaged in a complex interconnected reaction network characterized by numerous positive and negative feedback loops. The result is a dynamic entity that communicates, adapts, grows, divides; in short, it is alive. Our current knowledge of chemistry does not permit the creation of synthetic mixtures of molecules that can even closely mimic the complexity of the cell and the forthcoming properties. The emerging field of Systems Chemistry aims at bridging the divide that separates synthetic chemistry and the chemistry of life.

Figure 1. Chemistry in the laboratory vs chemistry in nature

In recent years, we have become particularly interested in the non-equilibrium nature of living systems. All living organisms find themselves in an entropically disfavoured state, which can only be maintained through the continuous consumption of energy. The development of synthetic molecular systems that require energy to sustain a non-equilibrium state is therefore an important step towards the design of innovative materials with life-like functions. Some time ago we illustrated how chemical energy stored in high-energy molecules, such as ATP, can be used to drive self-assembly processes away from thermodynamic equilibrium.[1] One of the key factors that govern this process is the improved ability of the assembly - compared to the unassembled components – to catalyse the conversion of fuel to waste. This installs so-called ‘kinetic asymmetry’ in the system, which permits a non-equilibrium composition to be maintained at steady-state conditions.

In this paper, Rui Chen demonstrates that kinetic asymmetry can also emerge at the macroscopic level.[2] Local UV-irradiation of a hydrogel installs concentration gradients that persist for as long as irradiation is continued. This implies that a macroscopic non-equilibrium steady state is installed in the hydrogel. Rui then made the important observation that the overall catalytic activity of the material is higher under non-equilibrium conditions. Using kinetic models, we showed that the light-sustained concentration gradients in the gel are the source of the enhanced catalytic activity.

Figure 2. Light-sustained concentration gradients in a hydrogel

The improved performance of the material under non-equilibrium conditions is an important stimulus to continue the exploration of complex systems that operate using life-like principles. It bodes well for the prospect that the entrance of synthetic chemistry in the domain of the chemistry of life will yield functional synthetic systems with unprecedented properties.

References

[1] Giulio Ragazzon, Leonard J. Prins 'Energy consumption in chemical fuel-driven self-assembly' Nat. Nanotechnol. 201813, 882-889. www.nature.com/articles/s41565-018-0250-8

[2] Rui Chen, Simona Neri, Leonard J. Prins 'Enhanced catalytic activity under non-equilibrium conditions' Nat. Nanotechnol. 2020, www.nature.com/articles/s41565-020-0734-1 

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Leonard

Chemist, University of Padova

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