Dissipative Assembly of Aqueous Carboxylic Acid Anhydrides Fueled by Carbodiimides

Biochemical systems make extensive
use of chemically fueled processes
(e.g., using ATP), but analogous abiotic systems remain rare. A key
challenge is the identification of transformations that can be adapted
to a range of applications and make use of readily available chemical
fuels. In this context, the generation of transient covalent bonds
is a fundamental tool for nonequilibrium systems chemistry. Here,
we show that carbodiimides constitute a simple class of chemical fuels
for dissipative assembly, taking advantage of their known reactivity
to produce (hydrolytically unstable) anhydrides from carboxylic acids
in water. Both aliphatic and aromatic anhydrides are formed on convenient
time scales using the common, commercially available peptide coupling
agent 1-ethyl-3-(3-(dimethyl­amino)­propyl)­carbo­diimide
(EDC). An important feature of this reaction is that no part of the
carbodiimide is incorporated into the transient species; that is,
the fuel is decoupled from the structureand thus functionof
the assembled state. We show that intramolecular anhydride formation
of oligo­(ethylene glycol) diacids gives macrocycles analogous to crown
ethers, representing minimal examples of out-of-equilibrium supramolecular
hosts. The kinetics and yields of macrocycle formation respond to
cation guests, with the presence of matched cations decreasing their
overall production.