Chemists have synthesized a controlled molecular brake

Russian chemists from the Institute of Physical Chemistry and Electrochemistry named after A.N. Frumkin created a molecular machine, two parts of which can rotate freely relative to each other, and when the acidity of the medium changes, this rotation is inhibited. This is due to the formation of bonds between the parts of the ensemble, and their formation and rupture are controlled and reversible. The control and management of the motion of such machines can be used in the development of optoelectronic materials operating on the principle of converting the energy of motion into an optical signal. The study was published in the New Journal of Chemistry and supported by a grant from the Russian Science Foundation (RSF) under the Presidential Program of Research Projects, received by a young chemist Ivan Meshkov. The work is part of the research carried out jointly with the laboratory by Professor
M.V. Hosseini (University of Strasbourg, F
rance) Molecular machines are molecular systems whose components undergo controlled mechanical movement, and these parts can be either individual molecules or any of their parts. The 2016 Nobel Prize in Chemistry was awarded for the development and creation of the first artificial molecular machines. Numerous molecular machines are found in living nature, in particular, several proteins at the base of the flagellum of some bacteria are similar to an electric motor. It is thanks to these proteins that the flagellum starts to move, allowing the cell to move in the environment. 
In the new work, scientists are exploring molecular machines based on porphyrins, macrocyclic molecules formed by four pyrrole rings. Such molecules are widespread in nature: they are part of chlorophyll, hemoglobin, vitamin B12 and many enzymes. The molecule used in this work is a dimer, that is, it consists of two parts – porphyrin rings. They are connected by a diacetylene bridge, which allows the two halves of the molecule to rotate freely around its axis. The introduction of special “blocker molecules” into the system inhibits this rotation. By varying the acidity of the medium, chemists managed to achieve control over this process: in the main medium, nothing interferes with the movement, and in the acidic medium, the rotation stops. 
“Why is it interesting to control such a molecular machine precisely by changing the acidity of the medium? – comments one of the authors of the work, Yulia Gorbunova. – Firstly, this is the principle of living nature, since in nature no one adds new substances, there is a regulated acid-base balance. The reversible formation of hydrogen bonds can trigger this or that process in the body, so the possibility of creating molecular machines and switches based on hydrogen bonds is very attractive. ” 
Porphyrins are brightly colored, so any changes that occur with them are conveniently monitored by electron absorption spectroscopy. In this case, this approach is sensitive to the orientation of the porphyrin macro-rings in the ensemble, which makes it possible to find out their relative position, that is, to know whether the molecule is in a hindered state
or not. “Changing the optical properties is the basis for creating smart materials with customizable properties,” Gorbunova continues. “By changing the acidity of the medium, you can adjust the optical properties or, for example, make the compound fluoresce (glow) or quench the fluorescence.” Molecu
lar machines as a field of research appeared about 30 years ago and have not yet reached the level of large-scale applications, but the first attempts are already being m
ade. what has been done on porphyrins is a demonstration of the principles of design and management of such systems, – sums up Gorbunova. – Since we have an optical response, this, of course, can be used in the development of materials. Changing the optical properties is important for a number of applications, for example, the development of materials for new optoelectronic devic

es. ”Source: www.gazeta.ru