|Part of a series of articles on|
Molecular machines are a class of molecules typically described as an assembly of a discrete number of molecular components intended to produce mechanical movements in response to specific stimuli, mimicking macromolecular devices such as switches and motors. Naturally occurring or biological molecular machines are responsible for vital living processes such as DNA replication and ATP synthesis. Kinesins and ribosomes are examples of molecular machines, and they often take the form of multi-protein complexes. For the last several decades, scientists have attempted, with varying degrees of success, to miniaturize machines found in the macroscopic world. 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.
AMMs have diversified rapidly over the past few decades and their design principles, properties, and characterization methods have been outlined better. 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. Different AMMs are produced by introducing various functionalities, such as the introduction of bistability to create switches. 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).
Several definitions describe a "molecular machine" as a class of molecules typically described as an assembly of a discrete number of molecular components intended to produce mechanical movements in response to specific stimuli. The expression is often more generally applied to molecules that simply mimic functions that occur at the macroscopic level. A few prime requirements for a molecule to be considered a "molecular machine" are: the presence of moving parts, the ability to consume energy, and the ability to perform a task. Molecular machines differ from other stimuli-responsive compounds that can produce motion (such as cis-trans isomers) in their relatively larger amplitude of movement (potentially due to chemical reactions) and the presence of a clear external stimulus to regulate the movements (as compared to random thermal motion). Piezoelectric, magnetostrictive, and other materials that produce a movement due to external stimuli on a macro-scale are generally not included, since despite the molecular origin of the motion the effects are not useable on the molecular scale.
This definition generally applies to synthetic molecular machines, which have historically gained inspiration from the naturally occurring biological molecular machines (also referred to as "nanomachines"). Biological machines are considered to be nanoscale devices (such as molecular proteins) in a living system that convert various forms of energy to mechanical work in order to drive crucial biological processes such as intracellular transport, muscle contractions, ATP generation and cell division.
What would be the utility of such machines? Who knows? 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. The advent of conformational analysis, or the study of conformers to analyze complex chemical structures, in the 1950s gave rise to the idea of understanding and controlling relative motion within molecular components for further applications. This led to the design of "proto-molecular machines" featuring conformational changes such as cog-wheeling of the aromatic rings in triptycenes. By 1980, scientists could achieve desired conformations using external stimuli and utilize this for different applications. A major example is the design of a photoresponsive crown ether containing an azobenzene unit, which could switch between cis and trans isomers on exposure to light and hence tune the cation-binding properties of the ether. 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. This was further substantiated by Eric Drexler during the 1970s, who developed ideas based on molecular nanotechnology such as nanoscale "assemblers", though their feasibility was disputed.
Though these events served as inspiration for the field, the actual breakthrough in practical approaches to synthesize artificial molecular machines (AMMs) took place in 1991 with the invention of a "molecular shuttle" by Sir Fraser Stoddart. Building upon the assembly of mechanically linked molecules such as catenanes and rotaxanes as developed by Jean-Pierre Sauvage in the early 1980s, this shuttle features a rotaxane with a ring that can move across an "axle" between two ends or possible binding sites (hydroquinone units). This design realized the well-defined motion of a molecular unit across the length of the molecule for the first time. 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. Here the two binding sites are a benzidine and a biphenol unit; the cationic ring typically prefers staying over the benzidine ring, but moves over to the biphenol group when the benzidine gets protonated at low pH or if it gets electrochemically oxidized. In 1998, a study could capture the rotary motion of a decacyclene molecule on a copper-base metallic surface using a scanning tunneling microscope. Over the following decade, a broad variety of AMMs responding to various stimuli were invented for different applications. In 2016, the Nobel Prize in Chemistry was awarded to Sauvage, Stoddart, and Bernard L. Feringa for the design and synthesis of molecular machines.
Artificial molecular machines
Over the past few decades, AMMs have diversified rapidly and their design principles, properties, and characterization methods have been outlined more clearly. A major starting point for the design of AMMs is to exploit the existing modes of motion in molecules. For instance, single bonds can be visualized as axes of rotation, as can be metallocene complexes. 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. Similarly, ring-opening and -closing reactions such as those seen for spiropyran and diarylethene can also produce curved shapes. Another common mode of movement is the circumrotation of rings relative to one another as observed in mechanically interlocked molecules (primarily catenanes). While this type of rotation can not be accessed beyond the molecule itself (because the rings are confined within one another), rotaxanes can overcome this as the rings can undergo translational movements along a dumbbell-like axis. Another line of AMMs consists of biomolecules such as DNA and proteins as part of their design, making use of phenomena like protein folding and unfolding.
AMM designs have diversified significantly since the early days of the field. A major route is the introduction of bistability to produce molecular switches, featuring two distinct configurations for the molecule to convert between. This has been perceived as a step forward from the original molecular shuttle which consisted of two identical sites for the ring to move between without any preference, in a manner analogous to the ring flip in an unsubstituted cyclohexane. If these two sites are different from each other in terms of features like electron density, this can give rise to weak or strong recognition sites as in biological systems — such AMMs have found applications in catalysis and drug delivery. This switching behavior has been further optimized to acquire useful work that gets lost when a typical switch returns to its original state. Inspired by the use of kinetic control to produce work in natural processes, molecular motors are designed to have a continuous energy influx to keep them away from equilibrium to deliver work.
Various energy sources are employed to drive molecular machines today, but this was not the case during the early years of AMM development. Though the movements in AMMs were regulated relative to the random thermal motion generally seen in molecules, they could not be controlled or manipulated as desired. 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. Chemical energy (or "chemical fuels") was an attractive option at the beginning, given the broad array of reversible chemical reactions (heavily based on acid-base chemistry) to switch molecules between different states. 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, more recently waste-free reactions such based on electron transfers or isomerization have gained attention (such as redox-responsive viologens). Eventually, several different forms of energy (electric, magnetic, optical and so on) have become the primary energy sources used to power AMMs, even producing autonomous systems such as light-driven motors.
Various AMMs have been designed with a broad range of functions and applications, several of which have been tabulated below along with indicative images:
|Molecular balance||A molecule that can interconvert between two or more conformational or configurational states in response to the dynamic of multiple intra- and intermolecular driving forces, such as hydrogen bonding, solvophobic or hydrophobic effects, π interactions, and steric and dispersion interactions. The distinct conformers of a molecular balance can show different interactions with the same molecule, such that analyzing the ratio of the conformers and the energies for these interactions can enable quantification of different properties (such as CH-π or arene-arene interactions, see image).|
|Molecular hinge||A molecular hinge is a molecule that can typically rotate in a crank-like motion around a rigid axis, such as a double bond or aromatic ring, to switch between reversible configurations. Such configurations must have distinguishable geometries; for instance, azobenzene groups in a linear molecule may undergo cis-trans isomerization when irradiated with ultraviolet light, triggering a reversible transition to a bent or V-shaped conformation (see image). Molecular hinges have been adapted for applications such as nucleobase recognition, peptide modifications, and visualizing molecular motion.|
|Molecular logic gate||A molecule that performs a logical operation on one or more logic inputs and produces a single logic output. Modelled on logic gates, these molecules have slowly replaced the conventional silicon-based machinery. Several applications have come forth, such as water quality examination, food safety examination, metal ion detection, and pharmaceutical studies. The first example of a molecular logic gate was reported in 1993, featuring a receptor (see image) where the emission intensity could be treated as a tunable output if the concentrations of protons and sodium ions were to be considered as inputs.|
|Molecular motor||A molecule that is capable of directional rotary motion around a single or double bond and produce useful work as a result (as depicted in the image). Carbon nanotube nanomotors have also been produced. Single bond rotary motors are generally activated by chemical reactions whereas double bond rotary motors are generally fueled by light. The rotation speed of the motor can also be tuned by careful molecular design.|
|Molecular necklace||A class of mechanically interlocked molecules derived from catenanes where a large macrocycle backbone connects at least three small rings in the shape of a necklace (see image for example). A molecular necklace consisting of a large macrocycle threaded by n-1 rings (hence comprising n rings) is represented as [n]MN. The first molecular necklace was synthesized in 1992, featuring several α-cyclodextrins on a single polyethylene glycol chain backbone; the authors connected this to the idea of a "molecular abacus" proposed by Stoddart and coworkers around the same time. Several interesting applications have emerged for these molecules, such as antibacterial activity, desulfurization of fuels, and piezoelectricity.|
|Molecular propeller||A molecule that can propel fluids when rotated, due to its special shape that is designed in analogy to macroscopic propellers (see schematic image on right). It has several molecular-scale blades attached at a certain pitch angle around the circumference of a nanoscale shaft. Propellers have been shown to have interesting properties, such as variations in pumping rates for hydrophilic and hydrophobic fluids.|
|Molecular shuttle||A molecule capable of shuttling molecules or ions from one location to another. This is schematically depicted in the image on the right, where a ring (in green) can bind to either one of the yellow sites on the blue macrocyclic backbone. A common molecular shuttle consists of a rotaxane where the macrocycle can move between two sites or stations along the dumbbell backbone; controlling the properties of either site and by regulating conditions like pH can enable control over which site is selected for binding. This has led to novel applications in catalysis and drug delivery.|
|Molecular switch||A molecule that can be reversibly shifted between two or more stable states in response to certain stimuli. This change of states influences the properties of the molecule according to the state it occupies at the moment. Unlike a molecular motor, any mechanical work done due to the motion in a switch is generally undone once the molecule returns to its original state unless it is part of a larger motor-like system. The image on the right shows a hydrazone-based switch that switches in response to pH changes.|
|Molecular tweezers||Host molecules capable of holding items between their two arms. The open cavity of the molecular tweezers binds items using non-covalent bonding including hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, π interactions, or electrostatic effects. For instance, the image on the right depicts tweezers formed by corannulene pincers clasping a C60 fullerene molecule, termed "buckycatcher". Examples of molecular tweezers have been reported that are constructed from DNA and are considered DNA machines.|
|Nanocar||Single-molecule vehicles that resemble macroscopic automobiles and are important for understanding how to control molecular diffusion on surfaces. The image on the right shows an example with wheels made of fullerene molecules. The first nanocars were synthesized by James M. Tour in 2005. They had an H-shaped chassis and 4 molecular wheels (fullerenes) attached to the four corners. In 2011, Feringa and co-workers synthesized the first motorized nanocar which had molecular motors attached to the chassis as rotating wheels. The authors were able to demonstrate directional motion of the nanocar on a copper surface by providing energy from a scanning tunneling microscope tip. Later, in 2017, the world's first-ever nanocar race took place in Toulouse.|
Biological molecular machines
The most complex macromolecular machines are found within cells, often in the form of multi-protein complexes. Important 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. "[I]n effect, the [motile cilium] is a nanomachine composed of perhaps over 600 proteins in molecular complexes, many of which also function independently as nanomachines ... Flexible linkers allow the mobile protein domains connected by them to recruit their binding partners and induce long-range allostery via protein domain dynamics." Other biological machines are responsible for energy production, for example ATP synthase which harnesses energy from proton gradients across membranes to drive a turbine-like motion used to synthesise ATP, the energy currency of a cell. Still other machines are responsible for gene expression, including DNA polymerases for replicating DNA, RNA polymerases for producing mRNA, the spliceosome for removing introns, and the ribosome for synthesising proteins. These machines and their nanoscale dynamics are far more complex than any molecular machines that have yet been artificially constructed.
Biological machines have potential applications in nanomedicine. For example, they could be used to identify and destroy cancer cells. Molecular nanotechnology is a speculative subfield of nanotechnology regarding the possibility of engineering molecular assemblers, biological machines which could re-order matter at a molecular or atomic scale. Nanomedicine would make use of these nanorobots, introduced into the body, to repair or detect damages and infections, but these are considered to be far beyond current capabilities.
Research and applications
The construction of more complex molecular machines is an active area of theoretical and experimental research. Though a diverse variety of AMMs are known today, experimental studies of these molecules are inhibited by the lack of methods to construct these molecules. In this context, theoretical modeling has emerged as a pivotal tool to understand the self-assembly or -disassembly processes in these systems.
A wide range of applications have been demonstrated for AMMs, including those integrated into polymeric, liquid crystal, and crystalline systems for varied functions. Homogenous catalysis is a prominent example, especially in areas like asymmetric synthesis, utilizing noncovalent interactions and biomimetic allosteric catalysis. AMMs have been pivotal in the design of several stimuli-responsive smart materials, such as 2D and 3D self-assembled materials and nanoparticle-based systems, for versatile applications ranging from 3D printing to drug delivery.
AMMs are gradually moving from the conventional solution-phase chemistry to surfaces and interfaces. For instance, AMM-immobilized surfaces (AMMISs) are a novel class of functional materials consisting of AMMs attached to inorganic surfaces forming features like self-assembled monolayers; this gives rise to tunable properties such as fluorescence, aggregation and drug-release activity.
Most of these applications remain at the proof-of-concept level, and need major modifications to be adapted to the industrial scale. Challenges in streamlining macroscale applications include autonomous operation, the complexity of the machines, stability in the synthesis of the machines and the working conditions.
- Carroll, GT; Pollard, MM; van Delden, RA; Feringa, BL (2010). "Controlled rotary motion of light-driven molecular motors assembled on a gold surface" (PDF). Chemical Science. 1 (1): 97–101. doi:10.1039/C0SC00162G. hdl:11370/4fb63d6d-d764-45e3-b3cb-32a4c629b942. S2CID 97346507.
- Vincenzo, V.; Credi, A.; Raymo, F. M.; Stoddart, J. F. (2000). "Artificial Molecular Machines". Angewandte Chemie International Edition. 39 (19): 3348–3391. doi:10.1002/1521-3773(20001002)39:19<3348::AID-ANIE3348>3.0.CO;2-X. PMID 11091368.
- Cheng, C.; Stoddart, J. F. (2016). "Wholly Synthetic Molecular Machines". ChemPhysChem. 17 (12): 1780–1793. doi:10.1002/cphc.201501155. PMID 26833859. S2CID 205704375.
- Huang, T. J.; Juluri, B. K. (2008). "Biological and biomimetic molecular machines". Nanomedicine. 3 (1): 107–124. doi:10.2217/174358220.127.116.11. PMID 18393670.
- Kinbara, K.; Aida, T. (2005). "Toward Intelligent Molecular Machines: Directed Motions of Biological and Artificial Molecules and Assemblies". Chemical Reviews. 105 (4): 1377–1400. doi:10.1021/cr030071r. PMID 15826015.
- Feynman, R. (1960). "There's Plenty of Room at the Bottom" (PDF). Engineering and Science. 23 (5): 22–36.
- Kay, E. R.; Leigh, D. A. (2015). "Rise of the molecular machines". Angewandte Chemie International Edition. 54 (35): 10080–10088. doi:10.1002/anie.201503375. PMC 4557038. PMID 26219251.
- Shinkai, S.; Nakaji, T.; Nishida, Y.; Ogawa, T.; Manabe, O. (1980). "Photoresponsive crown ethers. 1. Cis-trans isomerism of azobenzene as a tool to enforce conformational changes of crown ethers and polymers". Journal of the American Chemical Society. 102 (18): 5860–5865. doi:10.1021/ja00538a026.
- Drexler, K. E. (1981). "Molecular engineering: An approach to the development of general capabilities for molecular manipulation". Proceedings of the National Academy of Sciences. 78 (9): 5275–5278. Bibcode:1981PNAS...78.5275D. doi:10.1073/pnas.78.9.5275. PMC 348724. PMID 16593078.
- Baum, R. (1 December 2003). "Drexler and Smalley make the case for and against 'molecular assemblers'". C&EN. Vol. 81, no. 48. pp. 37–42. Retrieved 16 January 2023.
- Anelli, P. L.; Spencer, N.; Stoddart, J. F. (1991). "A molecular shuttle". Journal of the American Chemical Society. 113 (13): 5131–5133. doi:10.1021/ja00013a096. PMID 27715028. S2CID 39993887.
- Dietrich-Buchecker, C. O.; Sauvage, J. P.; Kintzinger, J. P. (1983). "Une nouvelle famille de molecules : les metallo-catenanes" [A new family of molecules: metallo-catenanes]. Tetrahedron Letters (in French). 24 (46): 5095–5098. doi:10.1016/S0040-4039(00)94050-4.
- Dietrich-Buchecker, C. O.; Sauvage, J. P.; Kern, J. M. (May 1984). "Templated synthesis of interlocked macrocyclic ligands: the catenands". Journal of the American Chemical Society. 106 (10): 3043–3045. doi:10.1021/ja00322a055.
- Bissell, R. A; Córdova, E.; Kaifer, A. E.; Stoddart, J. F. (1994). "A chemically and electrochemically switchable molecular shuttle". Nature. 369 (6476): 133–137. Bibcode:1994Natur.369..133B. doi:10.1038/369133a0. S2CID 44926804.
- Gimzewski, J. K.; Joachim, C.; Schlittler, R. R.; Langlais, V.; Tang, H.; Johannsen, I. (1998). "Rotation of a Single Molecule Within a Supramolecular Bearing". Science. 281 (5376): 531–533. Bibcode:1998Sci...281..531G. doi:10.1126/science.281.5376.531. PMID 9677189.
- Balzani, V.; Credi, A.; Raymo, F. M.; Stoddart, J. F. (2000). "Artificial Molecular Machines". Angewandte Chemie International Edition. 39 (19): 3348–3391. doi:10.1002/1521-3773(20001002)39:19<3348::AID-ANIE3348>3.0.CO;2-X. PMID 11091368.
- Erbas-Cakmak, S.; Leigh, D. A.; McTernan, C. T.; Nussbaumer, A. L. (2015). "Artificial Molecular Machines". Chemical Reviews. 115 (18): 10081–10206. doi:10.1021/acs.chemrev.5b00146. PMC 4585175. PMID 26346838.
- Staff (5 October 2016). "The Nobel Prize in Chemistry 2016". Nobel Foundation. Retrieved 5 October 2016.
- Chang, Kenneth; Chan, Sewell (5 October 2016). "3 Makers of 'World's Smallest Machines' Awarded Nobel Prize in Chemistry". New York Times. Retrieved 5 October 2016.
- Erbas-Cakmak, Sundus; Leigh, David A.; McTernan, Charlie T.; Nussbaumer, Alina L. (2015). "Artificial Molecular Machines". Chemical Reviews. 115 (18): 10081–10206. doi:10.1021/acs.chemrev.5b00146. PMC 4585175. PMID 26346838.
- Nogales, E.; Grigorieff, N. (2001). "Molecular Machines: putting the pieces together". The Journal of Cell Biology. 152 (1): F1-10. doi:10.1083/jcb.152.1.f1. PMC 2193665. PMID 11149934.
- Jiang, X.; Rodríguez-Molina, B.; Nazarian, N.; Garcia-Garibay, M. A. (2014). "Rotation of a Bulky Triptycene in the Solid State: Toward Engineered Nanoscale Artificial Molecular Machines". Journal of the American Chemical Society. 136 (25): 8871–8874. doi:10.1021/ja503467e. PMID 24911467.
- Kai, H.; Nara, S.; Kinbara, K.; Aida, T. (2008). "Toward Long-Distance Mechanical Communication: Studies on a Ternary Complex Interconnected by a Bridging Rotary Module". Journal of the American Chemical Society. 130 (21): 6725–6727. doi:10.1021/ja801646b. PMID 18447353.
- Kamiya, Y.; Asanuma, H. (2014). "Light-Driven DNA Nanomachine with a Photoresponsive Molecular Engine". Accounts of Chemical Research. 47 (6): 1663–1672. doi:10.1021/ar400308f. PMID 24617966.
- Morimoto, M.; Irie, M. (2010). "A Diarylethene Cocrystal that Converts Light into Mechanical Work". Journal of the American Chemical Society. 132 (40): 14172–14178. doi:10.1021/ja105356w. PMID 20858003.
- Stoddart, J. F. (2009). "The chemistry of the mechanical bond". Chemical Society Reviews. 38 (6): 1802–1820. doi:10.1039/B819333A. PMID 19587969.
- Mao, X.; Liu, M.; Li, Q.; Fan, C.; Zuo, X. (2022). "DNA-Based Molecular Machines". JACS Au. 2 (11): 2381–2399. doi:10.1021/jacsau.2c00292. PMC 9709946. PMID 36465542.
- Saper, G.; Hess, H. (2020). "Synthetic Systems Powered by Biological Molecular Motors". Chemical Reviews. 120 (1): 288–309. doi:10.1021/acs.chemrev.9b00249. PMID 31509383. S2CID 202562979.
- Biagini, C.; Di Stefano, S. (2020). "Abiotic Chemical Fuels for the Operation of Molecular Machines". Angewandte Chemie International Edition. 59 (22): 8344–8354. doi:10.1002/anie.201912659. PMID 31898850. S2CID 209676880.
- Tatum, L. A.; Foy, J. T.; Aprahamian, I. (2014). "Waste Management of Chemically Activated Switches: Using a Photoacid To Eliminate Accumulation of Side Products". Journal of the American Chemical Society. 136 (50): 17438–17441. doi:10.1021/ja511135k. PMID 25474221.
- Le Poul, N.; Colasson, B. (2015). "Electrochemically and Chemically Induced Redox Processes in Molecular Machines". ChemElectroChem. 2 (4): 475–496. doi:10.1002/celc.201402399.
- Thomas, C. R.; Ferris, D. P.; Lee, J.-H.; Choi, E.; Cho, M. H.; Kim, E. S.; Stoddart, J. F.; Shin, J.-S.; Cheon, J.; Zink, J. I. (2010). "Noninvasive Remote-Controlled Release of Drug Molecules in Vitro Using Magnetic Actuation of Mechanized Nanoparticles". Journal of the American Chemical Society. 132 (31): 10623–10625. doi:10.1021/ja1022267. PMID 20681678.
- Balzani, V.; Credi, A.; Venturi, M. (2009). "Light powered molecular machines". Chemical Society Reviews. 38 (6): 1542–1550. doi:10.1039/B806328C. PMID 19587950.
- Balzani, V.; Clemente-León, M.; Credi, A.; Ferrer, B.; Venturi, M.; Flood, A. H.; Stoddart, J. F. (2006). "Autonomous artificial nanomotor powered by sunlight". Proceedings of the National Academy of Sciences. 103 (5): 1178–1183. Bibcode:2006PNAS..103.1178B. doi:10.1073/pnas.0509011103. PMC 1360556. PMID 16432207.
- Paliwal, S.; Geib, S.; Wilcox, C. S. (1994). "Molecular Torsion Balance for Weak Molecular Recognition Forces. Effects of "Tilted-T" Edge-to-Face Aromatic Interactions on Conformational Selection and Solid-State Structure". Journal of the American Chemical Society. 116 (10): 4497–4498. doi:10.1021/ja00089a057.
- Mati, Ioulia K.; Cockroft, Scott L. (2010). "Molecular balances for quantifying non-covalent interactions" (PDF). Chemical Society Reviews. 39 (11): 4195–4205. doi:10.1039/B822665M. hdl:20.500.11820/7ce18ff7-1196-48a1-8c67-3bc3f6b46946. PMID 20844782. S2CID 263667.
- Y., Lixu; A., Catherine; Cockroft, S. L. (2015). "Quantifying Solvophobic Effects in Nonpolar Cohesive Interactions". Journal of the American Chemical Society. 137 (32): 10084–10087. doi:10.1021/jacs.5b05736. hdl:20.500.11820/604343eb-04aa-4d90-82d2-0998898400d2. ISSN 0002-7863. PMID 26159869.
- L., Ping; Z., Chen; Smith, M. D.; Shimizu, K. D. (2013). "Comprehensive Experimental Study of N-Heterocyclic π-Stacking Interactions of Neutral and Cationic Pyridines". The Journal of Organic Chemistry. 78 (11): 5303–5313. doi:10.1021/jo400370e. PMID 23675885.
- Hwang, J.; Li, P.; Smith, M. D.; Shimizu, K. D. (2016). "Distance-Dependent Attractive and Repulsive Interactions of Bulky Alkyl Groups". Angewandte Chemie International Edition. 55 (28): 8086–8089. doi:10.1002/anie.201602752. PMID 27159670.
- Carroll, W. R.; Zhao, C.; Smith, M. D.; Pellechia, P. J.; Shimizu, K. D. (2011). "A Molecular Balance for Measuring Aliphatic CH−π Interactions". Organic Letters. 13 (16): 4320–4323. doi:10.1021/ol201657p. PMID 21797218.
- Carroll, W. R.; Pellechia, P.; Shimizu, K. D. (2008). "A Rigid Molecular Balance for Measuring Face-to-Face Arene−Arene Interactions". Organic Letters. 10 (16): 3547–3550. doi:10.1021/ol801286k. PMID 18630926.
- Kassem, Salma; van Leeuwen, Thomas; Lubbe, Anouk S.; Wilson, Miriam R.; Feringa, Ben L.; Leigh, David A. (2017). "Artificial molecular motors" (PDF). Chemical Society Reviews. 46 (9): 2592–2621. doi:10.1039/C7CS00245A. PMID 28426052.
- Bandara, H. M. Dhammika; Burdette, S. C. (2012). "Photoisomerization in different classes of azobenzene". Chemical Society Reviews. 41 (5): 1809–1825. doi:10.1039/c1cs15179g. PMID 22008710.
- Wang, J.; Jiang, Q.; Hao, X.; Yan, H.; Peng, H.; Xiong, B.; Liao, Y.; Xie, X. (2020). "Reversible photo-responsive gel–sol transitions of robust organogels based on an azobenzene-containing main-chain liquid crystalline polymer". RSC Advances. 10 (7): 3726–3733. Bibcode:2020RSCAd..10.3726W. doi:10.1039/C9RA10161F. PMC 9048773. PMID 35492656.
- Hada, M.; Yamaguchi, D.; Ishikawa, T.; Sawa, T.; Tsuruta, K.; Ishikawa, K.; Koshihara, S.-y.; Hayashi, Y.; Kato, T. (13 September 2019). "Ultrafast isomerization-induced cooperative motions to higher molecular orientation in smectic liquid-crystalline azobenzene molecules". Nature Communications. 10 (1): 4159. Bibcode:2019NatCo..10.4159H. doi:10.1038/s41467-019-12116-6. ISSN 2041-1723. PMC 6744564. PMID 31519876.
- Garcia-Amorós, J.; Reig, M.; Cuadrado, A.; Ortega, M.; Nonell, S.; Velasco, D. (2014). "A photoswitchable bis-azo derivative with a high temporal resolution". Chemical Communications. 50 (78): 11462–11464. doi:10.1039/C4CC05331A. PMID 25132052.
- Hamilton, A. D.; Van Engen, D. (1987). "Induced fit in synthetic receptors: nucleotide base recognition by a molecular hinge". Journal of the American Chemical Society. 109 (16): 5035–5036. doi:10.1021/ja00250a052.
- Dumy, P.; Keller, M.; Ryan, D. E.; Rohwedder, B.; Wöhr, T.; Mutter, M. (1997). "Pseudo-Prolines as a Molecular Hinge: Reversible Induction of cis Amide Bonds into Peptide Backbones". Journal of the American Chemical Society. 119 (5): 918–925. doi:10.1021/ja962780a.
- Ai, Y.; Chan, M. H.-Y.; Chan, A. K.-W.; Ng, M.; Li, Y.; Yam, V. W.-W. (2019). "A platinum(II) molecular hinge with motions visualized by phosphorescence changes". Proceedings of the National Academy of Sciences. 116 (28): 13856–13861. Bibcode:2019PNAS..11613856A. doi:10.1073/pnas.1908034116. PMC 6628644. PMID 31243146.
- Erbas-Cakmak, S.; Kolemen, S.; Sedgwick, A. C.; Gunnlaugsson, T.; James, T. D.; Yoon, J.; Akkaya, E. U. (2018). "Molecular logic gates: the past, present and future". Chemical Society Reviews. 47 (7): 2228–2248. doi:10.1039/C7CS00491E. hdl:11693/50034. PMID 29493684.
- de Silva, A. P. (2011). "Molecular Logic Gate Arrays". Chemistry: An Asian Journal. 6 (3): 750–766. doi:10.1002/asia.201000603. PMID 21290607.
- Liu, L.; Liu, P.; Ga, L.; Ai, J. (2021). "Advances in Applications of Molecular Logic Gates". ACS Omega. 6 (45): 30189–30204. doi:10.1021/acsomega.1c02912. PMC 8600522. PMID 34805654.
- de Silva, P. A.; Gunaratne, N. H. Q.; McCoy, C. P. (1993). "A molecular photoionic AND gate based on fluorescent signalling". Nature. 364 (6432): 42–44. Bibcode:1993Natur.364...42D. doi:10.1038/364042a0. S2CID 38260349.
- Lancia, F.; Ryabchun, A.; Katsonis, N. (2019). "Life-like motion driven by artificial molecular machines". Nature Reviews Chemistry. 3 (9): 536–551. doi:10.1038/s41570-019-0122-2. S2CID 199661943.
- Mickler, M.; Schleiff, E.; Hugel, T. (2008). "From Biological towards Artificial Molecular Motors". ChemPhysChem. 9 (11): 1503–1509. doi:10.1002/cphc.200800216. PMID 18618534.
- Fennimore, A. M.; Yuzvinsky, T. D.; Han, Wei-Qiang; Fuhrer, M. S.; Cumings, J.; Zettl, A. (24 July 2003). "Rotational actuators based on carbon nanotubes". Nature. 424 (6947): 408–410. Bibcode:2003Natur.424..408F. doi:10.1038/nature01823. PMID 12879064. S2CID 2200106.
- Kelly, T. Ross; De Silva, Harshani; Silva, Richard A. (9 September 1999). "Unidirectional rotary motion in a molecular system". Nature. 401 (6749): 150–152. Bibcode:1999Natur.401..150K. doi:10.1038/43639. PMID 10490021. S2CID 4351615.
- Koumura, Nagatoshi; Zijlstra, Robert W. J.; van Delden, Richard A.; Harada, Nobuyuki; Feringa, Ben L. (9 September 1999). "Light-driven monodirectional molecular rotor" (PDF). Nature. 401 (6749): 152–155. Bibcode:1999Natur.401..152K. doi:10.1038/43646. hdl:11370/d8399fe7-11be-4282-8cd0-7c0adf42c96f. PMID 10490022. S2CID 4412610.
- Vicario, Javier; Meetsma, Auke; Feringa, Ben L. (2005). "Controlling the speed of rotation in molecular motors. Dramatic acceleration of the rotary motion by structural modification". Chemical Communications. 116 (47): 5910–2. doi:10.1039/B507264F. PMID 16317472.
- Zhang, Z.; Zhao, J.; Guo, Z.; Zhang, H.; Pan, H.; Wu, Q.; You, W.; Yu, W.; Yan, X. (2022). "Mechanically interlocked networks cross-linked by a molecular necklace". Nature Communications. 13 (1): 1393. Bibcode:2022NatCo..13.1393Z. doi:10.1038/s41467-022-29141-7. PMC 8927564. PMID 35296669.
- Harada, A.; Li, J.; Kamachi, M. (1992). "The molecular necklace: a rotaxane containing many threaded α-cyclodextrins". Nature. 356 (6367): 325–327. Bibcode:1992Natur.356..325H. doi:10.1038/356325a0. S2CID 4304539.
- Wu, G.-Y.; Shi, X.; Phan, H.; Qu, H.; Hu, Y.-X.; Yin, G.-Q.; Zhao, X.-L.; Li, X.; Xu, L.; Yu, Q.; Yang, H.-B. (2020). "Efficient self-assembly of heterometallic triangular necklace with strong antibacterial activity". Nature Communications. 11 (1): 3178. Bibcode:2020NatCo..11.3178W. doi:10.1038/s41467-020-16940-z. PMC 7311404. PMID 32576814.
- Li, S.-L.; Lan, Y.-Q.; Sakurai, H.; Xu, Q. (2012). "Unusual Regenerable Porous Metal-Organic Framework Based on a New Triple Helical Molecular Necklace for Separating Organosulfur Compounds". Chemistry: A European Journal. 18 (51): 16302–16309. doi:10.1002/chem.201203093. PMID 23168579.
- Seo, J.; Kim, B.; Kim, M.-S.; Seo, J.-H. (2021). "Optimization of Anisotropic Crystalline Structure of Molecular Necklace-like Polyrotaxane for Tough Piezoelectric Elastomer". ACS Macro Letters. 10 (11): 1371–1376. doi:10.1021/acsmacrolett.1c00567. PMID 35549010.
- Simpson, Christopher D.; Mattersteig, Gunter; Martin, Kai; Gherghel, Lileta; Bauer, Roland E.; Räder, Hans Joachim; Müllen, Klaus (March 2004). "Nanosized Molecular Propellers by Cyclodehydrogenation of Polyphenylene Dendrimers". Journal of the American Chemical Society. 126 (10): 3139–3147. doi:10.1021/ja036732j. PMID 15012144.
- Wang, Boyang; Král, Petr (2007). "Chemically Tunable Nanoscale Propellers of Liquids". Physical Review Letters. 98 (26): 266102. Bibcode:2007PhRvL..98z6102W. doi:10.1103/PhysRevLett.98.266102. PMID 17678108.
- Wang, B.; Král, P. (2007). "Chemically Tunable Nanoscale Propellers of Liquids". Physical Review Letters. 98 (26): 266102. Bibcode:2007PhRvL..98z6102W. doi:10.1103/PhysRevLett.98.266102. PMID 17678108.
- Bissell, Richard A; Córdova, Emilio; Kaifer, Angel E.; Stoddart, J. Fraser (12 May 1994). "A chemically and electrochemically switchable molecular shuttle". Nature. 369 (6476): 133–137. Bibcode:1994Natur.369..133B. doi:10.1038/369133a0. S2CID 44926804.
- Chatterjee, M. N.; Kay, E. R.; Leigh, D. A. (2006). "Beyond Switches: Ratcheting a Particle Energetically Uphill with a Compartmentalized Molecular Machine". Journal of the American Chemical Society. 128 (12): 4058–4073. doi:10.1021/ja057664z. PMID 16551115.
- Kassem, S.; van Leeuwen, T.; Lubbe, A. S.; Wilson, M. R.; Feringa, B. L.; Leigh, D. A. (2017). "Artificial molecular motors". Chemical Society Reviews. 46 (9): 2592–2621. doi:10.1039/C7CS00245A. PMID 28426052.
- Chen, C. W.; Whitlock, H. W. (July 1978). "Molecular tweezers: a simple model of bifunctional intercalation". Journal of the American Chemical Society. 100 (15): 4921–4922. doi:10.1021/ja00483a063.
- Klärner, Frank-Gerrit; Kahlert, Björn (December 2003). "Molecular Tweezers and Clips as Synthetic Receptors. Molecular Recognition and Dynamics in Receptor−Substrate Complexes". Accounts of Chemical Research. 36 (12): 919–932. doi:10.1021/ar0200448. PMID 14674783.
- Sygula, A.; Fronczek, F. R.; Sygula, R.; Rabideau, P. W.; Olmstead, M. M. (2007). "A Double Concave Hydrocarbon Buckycatcher". Journal of the American Chemical Society. 129 (13): 3842–3843. doi:10.1021/ja070616p. PMID 17348661. S2CID 25154754.
- Yurke, Bernard; Turberfield, Andrew J.; Mills, Allen P.; Simmel, Friedrich C.; Neumann, Jennifer L. (10 August 2000). "A DNA-fuelled molecular machine made of DNA". Nature. 406 (6796): 605–608. Bibcode:2000Natur.406..605Y. doi:10.1038/35020524. PMID 10949296. S2CID 2064216.
- Shirai, Yasuhiro; Osgood, Andrew J.; Zhao, Yuming; Kelly, Kevin F.; Tour, James M. (November 2005). "Directional Control in Thermally Driven Single-Molecule Nanocars". Nano Letters. 5 (11): 2330–2334. Bibcode:2005NanoL...5.2330S. doi:10.1021/nl051915k. PMID 16277478.
- Kudernac, Tibor; Ruangsupapichat, Nopporn; Parschau, Manfred; Maciá, Beatriz; Katsonis, Nathalie; Harutyunyan, Syuzanna R.; Ernst, Karl-Heinz; Feringa, Ben L. (10 November 2011). "Electrically driven directional motion of a four-wheeled molecule on a metal surface". Nature. 479 (7372): 208–211. Bibcode:2011Natur.479..208K. doi:10.1038/nature10587. PMID 22071765. S2CID 6175720.
- "NanoCar Race : la course de petites voitures pour grands savants" [NanoCar Race: the race of small cars for great scientists]. La Dépêche du Midi (in French). November 30, 2017. Retrieved December 2, 2018.
- Donald, Voet (2011). Biochemistry. Voet, Judith G. (4th ed.). Hoboken, NJ: John Wiley & Sons. ISBN 9780470570951. OCLC 690489261.
- Satir, P.; Christensen, S. T. (2008). "Structure and function of mammalian cilia". Histochemistry and Cell Biology. 129 (6): 687–693. doi:10.1007/s00418-008-0416-9. PMC 2386530. PMID 18365235.
- Kinbara, Kazushi; Aida, Takuzo (2005-04-01). "Toward Intelligent Molecular Machines: Directed Motions of Biological and Artificial Molecules and Assemblies". Chemical Reviews. 105 (4): 1377–1400. doi:10.1021/cr030071r. ISSN 0009-2665. PMID 15826015.
- Bu Z, Callaway DJ (2011). "Proteins MOVE! Protein dynamics and long-range allostery in cell signaling". Protein Structure and Diseases. Advances in Protein Chemistry and Structural Biology. Vol. 83. Academic Press. pp. 163–221. doi:10.1016/B978-0-12-381262-9.00005-7. ISBN 9780123812629. PMID 21570668.
- Amrute-Nayak, M.; Diensthuber, R. P.; Steffen, W.; Kathmann, D.; Hartmann, F. K.; Fedorov, R.; Urbanke, C.; Manstein, D. J.; Brenner, B.; Tsiavaliaris, G. (2010). "Targeted Optimization of a Protein Nanomachine for Operation in Biohybrid Devices". Angewandte Chemie. 122 (2): 322–326. Bibcode:2010AngCh.122..322A. doi:10.1002/ange.200905200. PMID 19921669.
- Patel, G. M.; Patel, G. C.; Patel, R. B.; Patel, J. K.; Patel, M. (2006). "Nanorobot: A versatile tool in nanomedicine". Journal of Drug Targeting. 14 (2): 63–7. doi:10.1080/10611860600612862. PMID 16608733. S2CID 25551052.
- Balasubramanian, S.; Kagan, D.; Jack Hu, C. M.; Campuzano, S.; Lobo-Castañon, M. J.; Lim, N.; Kang, D. Y.; Zimmerman, M.; Zhang, L.; Wang, J. (2011). "Micromachine-Enabled Capture and Isolation of Cancer Cells in Complex Media". Angewandte Chemie International Edition. 50 (18): 4161–4164. doi:10.1002/anie.201100115. PMC 3119711. PMID 21472835.
- Freitas, Robert A. Jr.; Havukkala, Ilkka (2005). "Current Status of Nanomedicine and Medical Nanorobotics" (PDF). Journal of Computational and Theoretical Nanoscience. 2 (4): 471. Bibcode:2005JCTN....2..471K. doi:10.1166/jctn.2005.001.
- Golestanian, Ramin; Liverpool, Tanniemola B.; Ajdari, Armand (2005-06-10). "Propulsion of a Molecular Machine by Asymmetric Distribution of Reaction Products". Physical Review Letters. 94 (22): 220801. arXiv:cond-mat/0701169. Bibcode:2005PhRvL..94v0801G. doi:10.1103/PhysRevLett.94.220801. PMID 16090376. S2CID 18989399.
- Drexler, K. Eric (1999-01-01). "Building molecular machine systems". Trends in Biotechnology. 17 (1): 5–7. doi:10.1016/S0167-7799(98)01278-5. ISSN 0167-7799.
- Tabacchi, G.; Silvi, S.; Venturi, M.; Credi, A.; Fois, E. (2016). "Dethreading of a Photoactive Azobenzene-Containing Molecular Axle from a Crown Ether Ring: A Computational Investigation". ChemPhysChem. 17 (12): 1913–1919. doi:10.1002/cphc.201501160. hdl:11383/2057447. PMID 26918775. S2CID 9660916.
- Ikejiri, S.; Takashima, Y.; Osaki, M.; Yamaguchi, H.; Harada, A. (2018). "Solvent-Free Photoresponsive Artificial Muscles Rapidly Driven by Molecular Machines". Journal of the American Chemical Society. 140 (49): 17308–17315. doi:10.1021/jacs.8b11351. PMID 30415536. S2CID 207195871.
- Iwaso, K.; Takashima, Y.; Harada, A. (2016). "Fast response dry-type artificial molecular muscles with [c2]daisy chains". Nature Chemistry. 8 (6): 625–632. Bibcode:2016NatCh...8..625I. doi:10.1038/nchem.2513. PMID 27219709.
- Orlova, T.; Lancia, F.; Loussert, C.; Iamsaard, S.; Katsonis, N.; Brasselet, E. (2018). "Revolving supramolecular chiral structures powered by light in nanomotor-doped liquid crystals" (PDF). Nature Nanotechnology. 13 (4): 304–308. Bibcode:2018NatNa..13..304O. doi:10.1038/s41565-017-0059-x. PMID 29434262. S2CID 3326300.
- Hou, J.; Long, G.; Zhao, W.; Zhou, G.; Liu, D.; Broer, D. J.; Feringa, B. L.; Chen, J. (2022). "Phototriggered Complex Motion by Programmable Construction of Light-Driven Molecular Motors in Liquid Crystal Networks". Journal of the American Chemical Society. 144 (15): 6851–6860. doi:10.1021/jacs.2c01060. PMC 9026258. PMID 35380815.
- Terao, F.; Morimoto, M.; Irie, M. (2012). "Light-Driven Molecular-Crystal Actuators: Rapid and Reversible Bending of Rodlike Mixed Crystals of Diarylethene Derivatives". Angewandte Chemie International Edition. 51 (4): 901–904. doi:10.1002/anie.201105585. PMID 22028196.
- Vogelsberg, C. S.; Garcia-Garibay, M. A. (2012). "Crystalline molecular machines: function, phase order, dimensionality, and composition". Chemical Society Reviews. 41 (5): 1892–1910. doi:10.1039/c1cs15197e. PMID 22012174.
- van Dijk, L.; Tilby, M. J.; Szpera, R.; Smith, O. A.; Bunce, H. A. P.; Fletcher, S. P. (2018). "Molecular machines for catalysis". Nature Reviews Chemistry. 2 (3): 0117. doi:10.1038/s41570-018-0117. S2CID 139606220.
- Neal, E. A.; Goldup, S. M. (2014). "Chemical consequences of mechanical bonding in catenanes and rotaxanes: isomerism, modification, catalysis and molecular machines for synthesis". Chemical Communications. 50 (40): 5128–5142. doi:10.1039/C3CC47842D. PMID 24434901.
- Corra, S.; Curcio, M.; Baroncini, M.; Silvi, S.; Credi, A. (2020). "Photoactivated Artificial Molecular Machines that Can Perform Tasks". Advanced Materials. 32 (20): 1906064. Bibcode:2020AdM....3206064C. doi:10.1002/adma.201906064. PMID 31957172. S2CID 210830979.
- Moulin, E.; Faour, L.; Carmona‐Vargas, C. C.; Giuseppone, N. (2020). "From Molecular Machines to Stimuli‐Responsive Materials" (PDF). Advanced Materials. 32 (20): 1906036. Bibcode:2020AdM....3206036M. doi:10.1002/adma.201906036. PMID 31833132. S2CID 209343354.
- Zhang, Q.; Qu, D.-H. (2016). "Artificial Molecular Machine Immobilized Surfaces: A New Platform To Construct Functional Materials". ChemPhysChem. 17 (12): 1759–1768. doi:10.1002/cphc.201501048. PMID 26717523.
- Aprahamian, I. (2020). "The Future of Molecular Machines". ACS Central Science. 6 (3): 347–358. doi:10.1021/acscentsci.0c00064. PMC 7099591. PMID 32232135.