Université de Strasbourg

Fellows Seminar - Molecular turnstiles

March 3, 2022
From 15:30 until 17:00

By Mir Wais Hosseini, 2015 Fellow

Movements are ubiquitous in all living entities such as animals and vegetals. At the molecular level, the control of intramolecular movements, i.e. the relative motion of a part of a molecule with respect to other segments, by external stimuli has become a very important research topic over the last 60 years. In pioneer research, J.-P. Sauvage, J.F. Stoddart and V. Balzani and B.L. Feringa have designed, synthesized and studied elegant dynamic entities subject to controlled rotational or translational movements. These entities are of particular relevance to nanotechnology, in particular for translocation and/or reactivity of molecular assemblies.

Another key topic in chemistry is catalysis, which plays a central role in chemical transformation of matter. During a chemical reaction, bonds between atoms are broken and other linkages are formed. Most molecules are stable and chemical reactions often occur under rather harsh conditions requiring energy. A catalyst brings together molecules in a specific manner to maximize their interactions and thus reactions and thus to minimize energy consumption production of waste.

In his USIAS project, Mir Wais Hosseini proposed to explore the possibility of coupling these two key topics by designing dynamic molecular systems allowing to link intramolecular movements with catalysis. The hypothesis was based on the control of intramolecular movement induced by external stimuli allowing to switch between active and resting states of catalysts (open and closed states of dynamic systems).

Molecular translational or rotational motors and machines are architectures for which movements between a fixed and a mobile portion may be induced by external stimuli. As a first step towards such dynamic entities, a series of “molecular turnstiles” (molecular gates which can be open and closed in a controlled fashion) have been designed and synthesized. 

Hosseini turnstiles

The first category is based on Sn(IV)porphyrins as stators bearing at its periphery interactions sites and equipped with a handle as a rotor. The connection between stators and rotors is achieved through Sn-O bonds (fig.1).

The second design principle is based on the covalent attachment of the rotor to the stator using two opposite meso positions on the porphyrin backbone (strapped porphyrins) (fig.2). 

Finally, the third approach is based on organometallic Pt complexes as rotors and coordinating handles as stators (fig.3).

The design, synthesis and structural characterizations, both in solution by multidimensional NMR techniques and in the solid state by X-ray diffraction on single crystals, of a series of molecular gates and turnstiles will be presented, and the significance of this type of research and its future will be discussed.

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