Macroscopic transport by synthetic molecular machines 

Prof. Dr. Petra Rudolf
Materials Science Centre, University of Groningen


Biological motors, both singularly and cooperatively, are capable of
transporting objects many times more massive than themselves and have
been used to power prototypical hybrid mechanical devices. However,
performing macroscopic mechanical tasks with the rudimentary early
generations of wholly synthetic molecular machines has proved more
elusive. Here we shall report on the macroscopic (millimeter scale)
transport of a droplet on a photo-responsive surface created using the
nanometer displacement of the components of light-switchable molecular
shuttles to expose or conceal fluoroalkane residues and thereby modify
surface tension. 
Stimuli-responsive molecular shuttles are rotaxanes
in which the macrocycle can be translocated from one position
('station') on the thread to a second site through an external trigger
(e.g. light, electrons, temperature, pH, nature of the environment,
reversible covalent bond formation etc.). When the rotaxanes are grafted
onto the surface and a drop is deposited on this surface, one can change
the wettability of the surface in front of the drop by light-induced
movement of the macrocycles.  The collective operation of a monolayer of
the shuttles is sufficient to power the movement of a microlitre droplet
of diiodomethane up a twelve degree incline.