Linear artificial molecular muscles.
Two switchable, palindromically constituted bistable [3]rotaxanes have been designed and synthesized with a pair of mechanically mobile rings encircling a single dumbbell. These designs are reminiscent of a "molecular muscle" for the purposes of amplifying and harnessing molecular mechanical motions. The location of the two cyclobis(paraquat-p-phenylene) (CBPQT(4+)) rings can be controlled to be on either tetrathiafulvalene (TTF) or naphthalene (NP) stations, either chemically ((1)H NMR spectroscopy) or electrochemically (cyclic voltammetry), such that switching of inter-ring distances from 4.2 to 1.4 nm mimics the contraction and extension of skeletal muscle, albeit on a shorter length scale. Fast scan-rate cyclic voltammetry at low temperatures reveals stepwise oxidations and movements of one-half of the [3]rotaxane and then of the other, a process that appears to be concerted at room temperature. The active form of the bistable [3]rotaxane bears disulfide tethers attached covalently to both of the CBPQT(4+) ring components for the purpose of its self-assembly onto a gold surface. An array of flexible microcantilever beams, each coated on one side with a monolayer of 6 billion of the active bistable [3]rotaxane molecules, undergoes controllable and reversible bending up and down when it is exposed to the synchronous addition of aqueous chemical oxidants and reductants. The beam bending is correlated with flexing of the surface-bound molecular muscles, whereas a monolayer of the dumbbell alone is inactive under the same conditions. This observation supports the hypothesis that the cumulative nanoscale movements within surface-bound "molecular muscles" can be harnessed to perform larger-scale mechanical work.
California NanoSystems Institute, University of California, Los Angeles, California 90095, USA.
Yi
Y
Liu
Amar H
AH
Flood
Paul A
PA
Bonvallet
Scott A
SA
Vignon
Brian H
BH
Northrop
Hsian-Rong
HR
Tseng
Jan O
JO
Jeppesen
Tony J
TJ
Huang
Branden
B
Brough
Marko
M
Baller
Sergei
S
Magonov
Santiago D
SD
Solares
William A
WA
Goddard
Chih-Ming
CM
Ho
J Fraser
JF
Stoddart
D040761:Biomimetic Materials / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry; D004563:Electrochemistry; D015394:Molecular Structure; D009132:Muscles / Q000502:physiology*; D043862:Rotaxanes / Q000737:chemistry; D013057:Spectrum Analysis; D055672:Static Electricity
D004220:Disulfides; D043862:Rotaxanes