Rotaxane

Catalysis

Supramolecular chemistry

Engineering

Chemical physics

Conformational isomerism

Polymer chemistry

Biology

Ratchet

Molecule

Carbodiimide

Stereochemistry

Mechanical engineering

Thermodynamics

Physics

Organic chemistry

Work (physics)

Carboxylate

Chemistry

Biophysics

Steric effects

Journal of the American Chemical Society

We report a rotaxane-based information ratchet in which the macrocycle distribution is pumped away from equilibrium using a carbodiimide fuel. A carboxylate group on the axle, nonequidistant between two macrocycle binding sites, efficiently catalyzes the hydration of a carbodiimide fuel to the corresponding urea waste, with >80% of the fuel molecules reacting through the machine-catalyzed pathway. The energy of the reaction is harnessed by kinetic differentiation of the mechanical states of the machine driving the macrocycle to the binding site distal to the catalyst. Steric hindrance between the macrocycle and the fuel slows the reaction of the carboxylate group (to form a barrier to macrocycle movement) in the proximal co-conformer, whereas hydrogen bonding between the macrocycle and the barrier accelerates hydrolysis of the activated ester proximal isomer. The two directionally biased processes reinforce each other's effect, resulting in a doubly kinetically gated ratchet that achieves 1:18 directionality, an exceptional degree of selectivity for a synthetic chemically fueled molecular motor.

A Doubly Kinetically-Gated Information Ratchet Autonomously Driven by Carbodiimide Hydration