Molecular machine

A molecule or molecular assembly that performs a controlled mechanical-like function through changes in structure or position. Its operation can use chemical energy, light, or other inputs to produce directed motion or work.

Brownian ratchet: A mechanism that rectifies random thermal motion into directed movement using an energy-consuming or time-varying constraint. It explains how machines at molecular scales can achieve directed motion amid constant thermal fluctuations.
Molecular self-assembly: The spontaneous organization of molecules into ordered structures through noncovalent interactions. Self-assembly builds many molecular machines from components without step-by-step fabrication.
Rotaxane: A mechanically interlocked molecule consisting of a ring threaded onto a linear molecular component. Rotaxanes can be designed so the ring shuttles between positions as a controlled molecular motion.
Molecular motor: A molecule or molecular assembly that converts energy into directional movement or force. A motor is a narrower kind of molecular machine, defined by producing motion or force.
Allostery: A change in a molecule's activity caused by a structural change at a different site. Allostery shows how binding at one site can control motion or action elsewhere.
Noncovalent interaction: An interaction between atoms or molecules that does not involve sharing electron pairs through a covalent bond. Reversible noncovalent forces often let machine components bind, release, and rearrange.
Catenane: A molecule composed of two or more interlocked rings that cannot be separated without breaking a covalent bond. Catenanes provide interlocked components for molecular switches and motors.
Molecular switch: A molecule that reversibly changes between distinguishable states in response to an external stimulus. A switch changes state, but need not perform repeated work or a mechanical cycle.
Conformational change: A change in a molecule's three-dimensional arrangement that preserves its chemical connectivity. Structural rearrangements often provide the moving parts of molecular machines.
Molecular recognition: Selective binding between molecules based on complementary chemical and structural features. Recognition supplies the selective binding events that trigger many machine cycles.

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