Limits...
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.

AUTOMATICALLY GENERATED EXCERPT
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.


(a) Operation of DNA-basedwalker. (b) AFM images of walker. Reprintedwith permission from ref (1455). Copyright 2010 Nature Publishing Group.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4585175&req=5

fig76: (a) Operation of DNA-basedwalker. (b) AFM images of walker. Reprintedwith permission from ref (1455). Copyright 2010 Nature Publishing Group.

Mentions: Stimuli-dependent positional DNAswitches1934,1935 and DNA-based devices performingmultistep organic synthesis whilemigrating along a track have been reported.1447 An in silico “tumbleweed” walker design has also beenproposed.1936 The first DNA-based walkerwas nonautonomous and bipedal and was reported by Sherman and Seeman.1834 High dilution conditions were used to preventthe walker from scrambling betwen different tracks. Sequential additionof two different anchor and fuel strands in an aqueous buffer at 16°C led to the desired walking motion being obtained. The productswere characterized by polyacrylamide gel electrophoresis (PAGE). Theenergy required for directional walking was provided by the additionalbase-pairing in the waste duplex (red toehold region, Figure 74). Mechanistically, this walkeris an inchworm walker because the leading foot remains the same throughoutthe operation. A hand-over-hand DNA walker (the mechanism of operationof kinesin) has been published by Shin and Pierce who used a similardesign.1833 Transport of a cargo over aDNA origami tile and the synthesis of nanoparticle sequences havebeen reported. It used a DNA origami walker unit with four “feet”for controlled movement, and three “arms” for pickingup cargo, each consisting of single strands of DNA (Figures 75 and 76).1455,1937,1938 Fuel strands(Fi) were used to drive the motion and to remove the anchorstrands (Ai). Each station was loaded with a distinct goldnanoparticle cargo and could be switched between states where cargodelivery was possible and where it was not. By manipulating the selectiverelease of each foot from complementary strands of DNA on the DNAtile, the movement of the walker could be controlled. When coupledto the ability of the stations to be switched “on” or“off”, this allowed the formation of eight, differentlycomposed, noncovalently bound products from the full operational sequence.This remarkable level of control on the nanoscale shows that the forcesof Brownian motion can be exploited to great effect in the synthesisof complex supramolecular products. Transportation of a DNA cargoon a DNA origami tile over 16 consecutive steps has also been reported.1939


Artificial Molecular Machines.

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

(a) Operation of DNA-basedwalker. (b) AFM images of walker. Reprintedwith permission from ref (1455). Copyright 2010 Nature Publishing Group.
© Copyright Policy
Related In: Results  -  Collection

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

fig76: (a) Operation of DNA-basedwalker. (b) AFM images of walker. Reprintedwith permission from ref (1455). Copyright 2010 Nature Publishing Group.
Mentions: Stimuli-dependent positional DNAswitches1934,1935 and DNA-based devices performingmultistep organic synthesis whilemigrating along a track have been reported.1447 An in silico “tumbleweed” walker design has also beenproposed.1936 The first DNA-based walkerwas nonautonomous and bipedal and was reported by Sherman and Seeman.1834 High dilution conditions were used to preventthe walker from scrambling betwen different tracks. Sequential additionof two different anchor and fuel strands in an aqueous buffer at 16°C led to the desired walking motion being obtained. The productswere characterized by polyacrylamide gel electrophoresis (PAGE). Theenergy required for directional walking was provided by the additionalbase-pairing in the waste duplex (red toehold region, Figure 74). Mechanistically, this walkeris an inchworm walker because the leading foot remains the same throughoutthe operation. A hand-over-hand DNA walker (the mechanism of operationof kinesin) has been published by Shin and Pierce who used a similardesign.1833 Transport of a cargo over aDNA origami tile and the synthesis of nanoparticle sequences havebeen reported. It used a DNA origami walker unit with four “feet”for controlled movement, and three “arms” for pickingup cargo, each consisting of single strands of DNA (Figures 75 and 76).1455,1937,1938 Fuel strands(Fi) were used to drive the motion and to remove the anchorstrands (Ai). Each station was loaded with a distinct goldnanoparticle cargo and could be switched between states where cargodelivery was possible and where it was not. By manipulating the selectiverelease of each foot from complementary strands of DNA on the DNAtile, the movement of the walker could be controlled. When coupledto the ability of the stations to be switched “on” or“off”, this allowed the formation of eight, differentlycomposed, noncovalently bound products from the full operational sequence.This remarkable level of control on the nanoscale shows that the forcesof Brownian motion can be exploited to great effect in the synthesisof complex supramolecular products. Transportation of a DNA cargoon a DNA origami tile over 16 consecutive steps has also been reported.1939

View Article: PubMed Central - PubMed

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

AUTOMATICALLY GENERATED EXCERPT
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.