In a Review on supramolecular systems chemistry (page 111) Elio Mattia and Sijbren Otto — who are based at the Institute of University of Groningen — guide us through the major conceptual developments in the field of supramolecular chemistry, a field that has been described1 as 'chemistry beyond the molecule'. Supramolecular chemistry deals with weak, reversible molecular interactions that are harnessed to make large aggregates and the approach is a fundamental component of self-assembly techniques and bottom-up fabrication processes. Mattia and Otto first look at the initial approach to supramolecular chemistry, which has principally involved thermodynamic equilibrium assemblies, and then move on to more recent developments that exploit states in a kinetic trap (a local minimum with potential energy barriers high enough to trap a specific configuration). But perhaps the most exciting aspect of the Review comes from the discussion of far-from-equilibrium systems. These are chemical systems that cannot be defined by a single supramolecular structure; rather, their properties come from a continuous interchange among a series of different structures as the system moves along a potential energy landscape. To remain far from equilibrium, these supramolecular systems require a constant supply of energy that is then dissipated into the environment.

Alongside the supramolecular chemistry of far-from-equilibrium systems, Mattia and Otto highlight how the topic ties in with the field of systems chemistry, the ultimate goal of which is to understand the chemical basis of life2. Systems chemists look for new chemical properties that emerge from the interaction between chemical systems. And because far-from-equilibrium supramolecular chemistry studies the interplay between different states and how these interact with each other and the environment, the confluence between the two fields seems natural. Published examples of emerging properties that are sustained by a continuous supply of energy include the formation of compartments, concentration gradients and directional motion of molecular components3. If harnessed in a concerted fashion, directed molecular motion can be made to do work against the environment. An example of this is reported by Nicolas Giuseppone and colleagues at the University of Strasburg on page 161. In particular, they show that thousands of molecular rotors attached to a polymer network can work in unison under light irradiation to produce a macroscopic structural modification of a gel.

Although in the long run the fields of supramolecular chemistry and systems chemistry may provide a new angle in our understanding of life from a chemical perspective, it is not unreasonable that the collaboration between researchers in the two fields will also be useful for designing new materials that adapt, respond and exhibit different functionalities as the environmental conditions change.