Molecular Pumps and Motors

TLDR

Pumps and motors—from cellular proteins to industrial machinery—are fundamental to modern life, and recent advances in artificial molecular machines now allow precise control of molecular motion through kinetically driven, non‑equilibrium chemistry. This perspective reviews the historical development of pumps and motors, emphasizing the innovations that enable the design and synthesis of artificial molecular machines. The operation of these machines is governed by trajectory thermodynamics, wherein mechanically equilibrated motions obey Onsager’s microscopic reversibility, and kinetic asymmetry in designed molecules harnesses external energy to maintain non‑equilibrium geometries.

Abstract

Pumps and motors are essential components of the world as we know it. From the complex proteins that sustain our cells, to the mechanical marvels that power industries, much we take for granted is only possible because of pumps and motors. Although molecular pumps and motors have supported life for eons, it is only recently that chemists have made progress toward designing and building artificial forms of the microscopic machinery present in nature. The advent of artificial molecular machines has granted scientists an unprecedented level of control over the relative motion of components of molecules through the development of kinetically controlled, away-from-thermodynamic equilibrium chemistry. We outline the history of pumps and motors, focusing specifically on the innovations that enable the design and synthesis of the artificial molecular machines central to this Perspective. A key insight connecting biomolecular and artificial molecular machines is that the physical motions by which these machines carry out their function are unambiguously in mechanical equilibrium at every instant. The operation of molecular motors and pumps can be described by trajectory thermodynamics, a theory based on the work of Onsager, which is grounded on the firm foundation of the principle of microscopic reversibility. Free energy derived from thermodynamically non-equilibrium reactions kinetically favors some reaction pathways over others. By designing molecules with kinetic asymmetry, one can engineer potential landscapes to harness external energy to drive the formation and maintenance of geometries of component parts of molecules away-from-equilibrium, that would be impossible to achieve by standard synthetic approaches.