Molecular machine

Naturally occurring or biological molecular machines are responsible for vital living processes such as DNA replication and ATP synthesis.

The first example of an artificial molecular machine (AMM) was reported in 1994, featuring a rotaxane with a ring and two different possible binding sites.

A major starting point for the design of AMMs is to exploit the existing modes of motion in molecules, such as rotation about single bonds or cis-trans isomerization.

A broad range of AMMs has been designed, featuring different properties and applications; some of these include molecular motors, switches, and logic gates.

A wide range of applications have been demonstrated for AMMs, including those integrated into polymeric, liquid crystal, and crystalline systems for varied functions (such as materials research, homogenous catalysis and surface chemistry).

I cannot see exactly what would happen, but I can hardly doubt that when we have some control of the arrangement of things on a molecular scale we will get an enormously greater range of possible properties that substances can have, and of the different things we can do.Biological molecular machines have been known and studied for years given their vital role in sustaining life, and have served as inspiration for synthetically designed systems with similar useful functionality.

[7] In his seminal 1959 lecture There's Plenty of Room at the Bottom, Richard Feynman alluded to the idea and applications of molecular devices designed artificially by manipulating matter at the atomic level.

[5] This was further substantiated by Eric Drexler during the 1970s, who developed ideas based on molecular nanotechnology such as nanoscale "assemblers",[8] though their feasibility was disputed.

[6] In 1994, an improved design allowed control over the motion of the ring by pH variation or electrochemical methods, making it the first example of an AMM.

[22] Bending or V-like shapes can be achieved by incorporating double bonds, that can undergo cis-trans isomerization in response to certain stimuli (typically irradiation with a suitable wavelength), as seen in numerous designs consisting of stilbene and azobenzene units.

This led to the addition of stimuli-responsive moieties in AMM design, so that externally applied non-thermal sources of energy could drive molecular motion and hence allow control over the properties.

[28] However, this comes with the issue of practically regulating the delivery of the chemical fuel and the removal of waste generated to maintain the efficiency of the machine as in biological systems.

Though some AMMs have found ways to circumvent this,[29] more recently waste-free reactions such based on electron transfers or isomerization have gained attention (such as redox-responsive viologens).

[78] Examples of biological machines include motor proteins such as myosin, which is responsible for muscle contraction, kinesin, which moves cargo inside cells away from the nucleus along microtubules, and dynein, which moves cargo inside cells towards the nucleus and produces the axonemal beating of motile cilia and flagella.

[87][88] Possible applications have been demonstrated for AMMs, including those integrated into polymeric,[89][90] liquid crystal,[91][92] and crystalline[93][94] systems for varied functions.

Kinesin walking on a microtubule is a molecular biological machine using protein domain dynamics on nanoscales .
The first example of an artificial molecular machine (a switchable molecular shuttle). The positively charged ring (blue) is initially positioned over the benzidine unit (green), but shifts to the biphenol unit (red) when the benzidine gets protonated (purple) as a result of electrochemical oxidation or lowering of the pH.
The first example of an artificial molecular machine (a switchable molecular shuttle). The positively charged ring (blue) is initially positioned over the benzidine unit (green), but shifts to the biphenol unit (red) when the benzidine gets protonated (purple) as a result of electrochemical oxidation or lowering of the pH . [ 10 ]
Some common types of motion seen in some simple components of artificial molecular machines. a) Rotation around single bonds and in sandwich-like metallocenes. b) Bending due to cis-trans isomerization. c) Translational motion of a ring along the dumbbell-like rotaxane axis. d) Rotation of interlocked rings in a catenane
Some common types of motion seen in some simple components of artificial molecular machines. a) Rotation around single bonds and in sandwich-like metallocenes . b) Bending due to cis-trans isomerization. c) Translational motion of a ring (blue) between two possible binding sites (red) along the dumbbell-like rotaxane axis (purple). d) Rotation of interlocked rings (depicted as blue and red rectangles) in a catenane.
A ribosome performing the elongation and membrane targeting stages of protein translation . The ribosome is green and yellow, the tRNAs are dark blue, and the other proteins involved are light blue. The produced peptide is released into the endoplasmic reticulum .