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A 2 nm helical molecular gear with an unidirectional rotation

by PREVOTS Evelyne - published on

Claire Kammerer, Lecturer and Gwénaël Rapenne, Professor at Toulouse III University - Paul Sabatier, CEMES-CNRS laboratory, and at the Institute of Science and Technology of Nara (NAIST) in Japan and Saw-Wai Hla, professor at the University of Ohio, USA, have designed a molecular helix intended to be deposited on a solid surface and studied by scanning tunneling microscopy (STM). The chirality of this molecular machine makes it possible to control its direction of rotation once set in motion by a supply of electrical energy and this rotation could be transmitted to a neighboring molecule. This work was recently published in Nature Communications.

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(a) Chemical structure of the molecular gear deposited on a gold surface; (b) STM images of the unidirectional rotation of each helix
© G. Rapenne (UT3 Paul Sabatier, NAIST, CEMES-CNRS) and S.W. Hla (Ohio University).

Synthetic molecular machines designed to work on surfaces are today able to convert energy into unidirectional movement but also under certain conditions, to transfer this movement to other molecules. In this study, ruthenium complexes designed to mimic gears deposited on a gold surface are in the form of a mixture of left and right helices in equal amounts. In figure (a), the heavily congested lower part (stator, in blue) is attached to the surface, it becomes helical and it transfers its helicity to the upper part (rotor, green) consisting of three blades that twist to satisfy the steric constraints of the stator part. The ruthenium atom plays a similar role to a ball-bearing. These propellers can be rotated in a highly unidirectional manner by providing energy via the tip of the STM. The left helical molecules rotate preferentially clockwise while the right helical molecules preferentially rotate in the opposite direction, as shown in the figure (b). Finally, when a right helical molecule is placed at an appropriate distance from a left helical molecule, the rotational movement of a gear molecule could be transmitted to the neighboring molecule as shown in the video below. This observation could pave the way for the transfer of energy or information over long distances.



A chiral molecular propeller designed for unidirectional rotations on a surface,
Y. Zhang, J.P. Calupitan, T. Rojas, R. Tumbleson, G. Erbland, C. Kammerer, T.M. Ajayi, S. Wang, L.C. Curtiss, A.T. Ngo, S.E. Ulloa, G. Rapenne, S.W. Hla,
Nature Commun. 2019, 10, article n° 3742.



Gwénaël Rapenne