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Artificial Molecular Machines.

Erbas-Cakmak S, Leigh DA, McTernan CT, Nussbaumer AL - Chem. Rev. (2015)

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.

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Hydrogen-bonding solvents have been shownto disrupt macrocycle–thread interactions in single stationrotaxanes, and here addition of 5% [D4]methanol increased the rate of shuttling 100-fold, consistentwith lowering the energy barrier to migration by disrupting station–macrocycleinteractions and thus raising ground-state energies... The effect of water on the rate of shuttlinghas been investigated and was found to be greatly superior to thatof other protic solvents... Therate of escape from the station energy well can then be modeled byan Arrhenius equation with a contribution from a distance-dependentdiffusion factor to the overall rate of shuttling... A quantum mechanicaltreatment of this system has found that, as the lengthening of thespacer has no effect on the activation for breaking the hydrogen bonds,the effect on the rate of shuttling is due to the widening of theoverall potential energy well... Molecular motion in mechanically interlocked and thus kineticallystable rotaxanes can be controlled using multiple binding sites withaffinities for the macrocycle that vary under different conditions.The conditions can be modified by electrochemical redox processes,light, pH, and environmental changes... Whenthe stilbene unit adopted the E form, the macrocyclecould move randomly along the full length of the thread by Brownianmotion, while when the Z form is adopted, the macrocyclewas trapped in one or the other of the two compartments... As the stretching of the PEOtether continued, and the force exerted by the PEO linker exceededthe hydrogen-bonding forces between the macrocycle and the fumaramidestation, the ring moved away from the fumaramide station... Tensionin the tether decreased as a result of the shuttling... Extracting useful work at the molecular scalerequires the restriction of the thermal movement of submolecular componentsor the exploitation of thermal motion with additional ratcheting.Shuttling, switching, and rotation processes in solution can be modulatedexternally, and the directionality of each motion can be controlledin single molecules... Third, to drive the walker away fromequilibrium, that is, to generate directional motion, a ratchetingprocess (either an energy or an information ratchet) must take place.In addition to the requirements of a Brownian motor, certain additionalcharacteristics are necessary for a motor to be defined as a walker... For the design of processive small molecule synthetic molecularwalkers, mechanically interlocked architectures are good candidates,because the walker (macrocycle) is mechanically bonded to the track(thread)... To perform tasks that cannot be accomplishedby conventional chemical means, it will be necessary to design systemswith multiple integrated parts, each component performing a dedicatedrole within the machine ensemble... This will not be straightforwardbecause unlike a watch where the second hand, say, does not interferewith the components in the escapement mechanism, the components ofa chemical machine are not easily isolated from each other (or theenvironment) and interference from one reactive part of a machinewith another will be a significant issue as complexity increases beyondthe current rather trivial systems. (iii) The machines we arefamiliar with in the macroscopic worldare generally stable, operating unchanged through many cycles, andby and large they do not make “mistakes”... Or it may bethat evolution just did not discover these solutions to such problemsand that mankind, with the whole of the periodic table and known syntheticchemistry to work with, can... Perhaps the most productive approachwill ultimately be found by following neither of these lines of investigationtoo closely, for example, by using chemical principles for “molecularrobotics” in which ratcheted motions of molecular components(i.e., biologically inspired mechanisms) are used to perform tasksthat have their origins in innovations introduced to advance developmentsin macroscopic technology (e.g., factory assembly lines).

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(a) Chemical structure of tris-monodentatedisk shaped ligand 3 and hexakis-monodentate ligand 4. (b) Schematicrepresentation of complex [Ag3(3)2] shown as its M-helical enantiomer. (c) X-ray structureof complex [Ag3(3)2].197 (d) Schematic representation of the flippingmotion of the rings attached to the disks and subsequent ligand exchangefrom 1-A, 3-E, and 5-C in M to 1-B, 3-F, and 5-Din P. The direction of rotation in the M to P transition is opposite to that of a subsequent P to M′ transition.200 Reprinted with permission from refs (197) and (200). Copyright 2003 and 2004Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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fig10: (a) Chemical structure of tris-monodentatedisk shaped ligand 3 and hexakis-monodentate ligand 4. (b) Schematicrepresentation of complex [Ag3(3)2] shown as its M-helical enantiomer. (c) X-ray structureof complex [Ag3(3)2].197 (d) Schematic representation of the flippingmotion of the rings attached to the disks and subsequent ligand exchangefrom 1-A, 3-E, and 5-C in M to 1-B, 3-F, and 5-Din P. The direction of rotation in the M to P transition is opposite to that of a subsequent P to M′ transition.200 Reprinted with permission from refs (197) and (200). Copyright 2003 and 2004Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mentions: The sandwich-shaped trinuclear silver(I) complex [Ag3(3)2] (Figure 10) developed by Shionoya and co-workers197−199 is an example of a different type of a rotational device. The complexconsists of two disk-shaped ligands, 3, consisting ofthree thiazolyl or 2-pyridyl ligands and three p-tolylgroups attached to a central benzene ring. The three p-tolyl groups force the neighboring ligands to adopt a nonplanararrangement with respect to the central aromatic ring, and make thecoordination sites more accessible for silver(I) cations. The exteriorrings tilt at 30° in the same sense and thus form helical structureswith P and M geometries. A changefrom P to M helicity, and vice versa,was induced by 120° relative rotation of the ligand in thesecomplexes (Figure 10). These observations were further studied using a heterotopic system[Ag3(3)(4)] consisting of a hexa-monodentateligand 4 and a tris-monodentate thiazolyl ligand 3, which complex three silver(I) cations.200 In the case of the hexa-monodentate thiazolyl ligand 4, only every second ring is coordinated to a silver cation.Correlated flipping motion of the coordinating rings (and ligand exchange)results in the conversion from M to P and a 60° rotation of the two disks (Figure 10d).


Artificial Molecular Machines.

Erbas-Cakmak S, Leigh DA, McTernan CT, Nussbaumer AL - Chem. Rev. (2015)

(a) Chemical structure of tris-monodentatedisk shaped ligand 3 and hexakis-monodentate ligand 4. (b) Schematicrepresentation of complex [Ag3(3)2] shown as its M-helical enantiomer. (c) X-ray structureof complex [Ag3(3)2].197 (d) Schematic representation of the flippingmotion of the rings attached to the disks and subsequent ligand exchangefrom 1-A, 3-E, and 5-C in M to 1-B, 3-F, and 5-Din P. The direction of rotation in the M to P transition is opposite to that of a subsequent P to M′ transition.200 Reprinted with permission from refs (197) and (200). Copyright 2003 and 2004Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585175&req=5

fig10: (a) Chemical structure of tris-monodentatedisk shaped ligand 3 and hexakis-monodentate ligand 4. (b) Schematicrepresentation of complex [Ag3(3)2] shown as its M-helical enantiomer. (c) X-ray structureof complex [Ag3(3)2].197 (d) Schematic representation of the flippingmotion of the rings attached to the disks and subsequent ligand exchangefrom 1-A, 3-E, and 5-C in M to 1-B, 3-F, and 5-Din P. The direction of rotation in the M to P transition is opposite to that of a subsequent P to M′ transition.200 Reprinted with permission from refs (197) and (200). Copyright 2003 and 2004Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Mentions: The sandwich-shaped trinuclear silver(I) complex [Ag3(3)2] (Figure 10) developed by Shionoya and co-workers197−199 is an example of a different type of a rotational device. The complexconsists of two disk-shaped ligands, 3, consisting ofthree thiazolyl or 2-pyridyl ligands and three p-tolylgroups attached to a central benzene ring. The three p-tolyl groups force the neighboring ligands to adopt a nonplanararrangement with respect to the central aromatic ring, and make thecoordination sites more accessible for silver(I) cations. The exteriorrings tilt at 30° in the same sense and thus form helical structureswith P and M geometries. A changefrom P to M helicity, and vice versa,was induced by 120° relative rotation of the ligand in thesecomplexes (Figure 10). These observations were further studied using a heterotopic system[Ag3(3)(4)] consisting of a hexa-monodentateligand 4 and a tris-monodentate thiazolyl ligand 3, which complex three silver(I) cations.200 In the case of the hexa-monodentate thiazolyl ligand 4, only every second ring is coordinated to a silver cation.Correlated flipping motion of the coordinating rings (and ligand exchange)results in the conversion from M to P and a 60° rotation of the two disks (Figure 10d).

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.

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Please rate it.

Hydrogen-bonding solvents have been shownto disrupt macrocycle–thread interactions in single stationrotaxanes, and here addition of 5% [D4]methanol increased the rate of shuttling 100-fold, consistentwith lowering the energy barrier to migration by disrupting station–macrocycleinteractions and thus raising ground-state energies... The effect of water on the rate of shuttlinghas been investigated and was found to be greatly superior to thatof other protic solvents... Therate of escape from the station energy well can then be modeled byan Arrhenius equation with a contribution from a distance-dependentdiffusion factor to the overall rate of shuttling... A quantum mechanicaltreatment of this system has found that, as the lengthening of thespacer has no effect on the activation for breaking the hydrogen bonds,the effect on the rate of shuttling is due to the widening of theoverall potential energy well... Molecular motion in mechanically interlocked and thus kineticallystable rotaxanes can be controlled using multiple binding sites withaffinities for the macrocycle that vary under different conditions.The conditions can be modified by electrochemical redox processes,light, pH, and environmental changes... Whenthe stilbene unit adopted the E form, the macrocyclecould move randomly along the full length of the thread by Brownianmotion, while when the Z form is adopted, the macrocyclewas trapped in one or the other of the two compartments... As the stretching of the PEOtether continued, and the force exerted by the PEO linker exceededthe hydrogen-bonding forces between the macrocycle and the fumaramidestation, the ring moved away from the fumaramide station... Tensionin the tether decreased as a result of the shuttling... Extracting useful work at the molecular scalerequires the restriction of the thermal movement of submolecular componentsor the exploitation of thermal motion with additional ratcheting.Shuttling, switching, and rotation processes in solution can be modulatedexternally, and the directionality of each motion can be controlledin single molecules... Third, to drive the walker away fromequilibrium, that is, to generate directional motion, a ratchetingprocess (either an energy or an information ratchet) must take place.In addition to the requirements of a Brownian motor, certain additionalcharacteristics are necessary for a motor to be defined as a walker... For the design of processive small molecule synthetic molecularwalkers, mechanically interlocked architectures are good candidates,because the walker (macrocycle) is mechanically bonded to the track(thread)... To perform tasks that cannot be accomplishedby conventional chemical means, it will be necessary to design systemswith multiple integrated parts, each component performing a dedicatedrole within the machine ensemble... This will not be straightforwardbecause unlike a watch where the second hand, say, does not interferewith the components in the escapement mechanism, the components ofa chemical machine are not easily isolated from each other (or theenvironment) and interference from one reactive part of a machinewith another will be a significant issue as complexity increases beyondthe current rather trivial systems. (iii) The machines we arefamiliar with in the macroscopic worldare generally stable, operating unchanged through many cycles, andby and large they do not make “mistakes”... Or it may bethat evolution just did not discover these solutions to such problemsand that mankind, with the whole of the periodic table and known syntheticchemistry to work with, can... Perhaps the most productive approachwill ultimately be found by following neither of these lines of investigationtoo closely, for example, by using chemical principles for “molecularrobotics” in which ratcheted motions of molecular components(i.e., biologically inspired mechanisms) are used to perform tasksthat have their origins in innovations introduced to advance developmentsin macroscopic technology (e.g., factory assembly lines).

No MeSH data available.