Endergonic synthesis of Diels-Alder adducts enables non-equilibrium adaptive behaviors in chemical reaction networks

The overwhelming majority of artificial chemical reaction networks respond to stimuli relaxing towards an equilibrium state. The opposite response – moving away from equilibrium – can afford the endergonic synthesis of molecules, of which only rare examples have been reported. Here, we report six examples of Diels-Alder adducts accumulated in an endergonic process and use this strategy to realize adaptive phenomena. Indeed, systems respond to repeated occurrences of the same stimulus by increasing the amount of adduct formed, with the final network distribution depending on the number and frequency of stimuli received. Our findings indicate how endergonic processes can contribute to the transition from responsive to adaptive systems.