All photochemical processes lead to the formation of free radicals. For example, we sunbathe, and under the influence of sunlight, free radicals of biomolecules are formed in our body, which leads to the destruction of DNA. Radical pairs are the subject of spin chemistry, a fairly new science with Siberian roots. Academic Renad Sagdeev, founder of the International Tomography Center (ITC) of SB RAS, was among the laureates of the Lenin Prize awarded in 1986 “for the discovery of magnetic and rotational effects in chemical reactions”. The spins of unpaired electrons in radical pairs can be in the single (omnidirectional) or triple (directional) state. Interacting with magnetic fields, radicals sometimes change the direction of the spins, that is, they move from the singlet state to the triplet state and vice versa. These alternations (oscillations) are theoretically known, but it was impossible to distinguish them by optical methods during photochemical exposure until the creation of a special technology proposed by ITC SB RAS employees in collaboration with scientists from the Universities of Konstanz and Würzburg (Germany), published in December 2021 in the journal Science .
Two beats for the Trinity
“Organic chemists from the University of Würzburg have synthesized triple molecules consisting of an electron donor and a solid molecular bridge and an electron acceptor,” says Nikita Loczen, Senior Investigator at ITC SB RAS, Ph.D. in Physical and Mathematical Sciences. After the laser pulse is stimulated, the donor donates its electron to the receiver. In a normal geomagnetic field, such a radical pair has a lifetime of about 0.5 microseconds and ends with recombination (reverse electron transfer). By increasing the magnetic field to 2 Tesla, we extend the life of the pair by 80 times – up to 40 microseconds, which makes it possible to study it. After the first pulse, quantum strikes (alternating between singular and triplet state) are still indistinguishable, but Ulrich Steiner of the University of Konstanz and Christoph Lambert of the University of Würzburg have proposed adding a second laser pulse to the technology some time after the first, bringing the radicals into a more excited state. This makes it possible to detect and repair oscillations. Together with Ulrich Steiner, she developed the theory of the method and then compared the calculations with experiment. In the publication, our method was called pump spectroscopy (pump thrust – “pump thrust”). The charge separation control principle can find practical application in organic photovoltaics. In addition, by studying oscillations, one can understand how to create and discover the coherence inherent in quantum phenomena.
Interestingly, the alternation of single states and triple states during irradiation of nonpolar solutions was first discovered in 1983 in the Novosibirsk Akademgorodok. The experiment was conducted by Academician Yuri Mulin (Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences) and his colleagues. One of the authors of the article was Nikita Luksin. However, no one has yet been able to “catch” the oscillations in photochemical experiments.
“Such studies are a direct path to lower electronics and the creation of “smart” materials,” says ITC SB RAS Director, Professor of the Russian Academy of Sciences Matvey Vidin. – Together with colleagues from the Institute of Problems of Chemical Physics of the Russian Academy of Sciences (Chernogolovka), the Institute of Chemistry Public and Inorganic of the Russian Academy of Sciences (Moscow), the Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences (Moscow) and Southern Federal University (Rostov), we are participating in a one hundred million project of the Ministry of Science and Higher Education of the Russian Federation “Fundamentals of Spin and Design Technologies Guide for ‘Smart’ Multifunctional Materials for X-ray Electronics and Molecular Electronics.
How to improve an MRI
Chemically induced dynamic nuclear polarization is one of the main approaches to spin chemistry, which is used to dramatically improve the NMR signal. Obtaining images of optically opaque objects using MRI is a very useful method, especially for medical diagnosis. However, the spatial resolution and sensitivity of the MRI must be improved so that patients do not have to lie in the scanner for 20-30 minutes.
Why is MRI image acquisition so slow compared to faster computed tomography (CT) scans? The contrast in MRI images depends on the difference in the relaxation properties of the spins of hydrogen nuclei, and the interaction energy of these spins with the magnetic field is very small, therefore, even in a strong magnetic field, the difference in explains Alexandra Yurkovskaya, head of the ITC Laboratory for Photochemical Reactions, Ph.D. In physical and mathematical sciences, the number of nuclear spins of aligned protons along and against the domain is very small: it is about 1 per 100,000. – but only this difference gives a useful indication. The use of spin hyperpolarization makes it possible to increase the signal and, as a consequence, the sensitivity of the NMR by thousands and tens of thousands of times. In the West, to create hyperpolarization, an approach is being developed based on the use of expensive and technically complex equipment – a rather slow and painstaking method of dynamic nuclear polarization (DNP). We are developing much cheaper and simpler methods based on establishing chemically induced polarization in reversible photoreactions involving biomolecules, and methods based on the use of parahydrogen, a long-lived nuclear spin isomer of the hydrogen molecule.
Work began in 2014 thanks to a grant from the Russian Science Foundation “Chemical and rotational dynamics of hyperpolarization formation in the SABER method”. The then director of ITC RAS Konstantin Lvovich Ivanov, who, unfortunately, passed away a year ago, managed to gather a team of young scientists and begin work on a unique installation. They are only now trying to repeat a similar installation in the UK, and the Ivanov-Shuttle project is named after Konstantin Lvovich.
“We were able to create and test an unparalleled setup for obtaining NMR signals with high spectral resolution using magnetic field switching,” says Alexandra Yurkovskaya. – We have learned to change the magnetic field by 9 orders of magnitude – from 10 Tesla to 5 nano Tesla. The principle of operation of this setup consists in precise positioning and mechanical movement of the ampoule with the sample along the axis of the solenoid coil of a superconducting magnet. We added a multi-layer “magnetic shield” to the installation. With its help, we can study spin motions in a hyperfine field, where the spin ordering and polarization of different types of nuclei last much longer (Setup Developer, Candidate of Chemical Sciences Alexei Kiryutin). In 2021, we patented a new method for obtaining multidimensional NMR correlation spectra of nuclei of different types in an extremely weak magnetic field, using magnetic fields a thousand times weaker than Earth’s. The new method was then implemented by a graduate student, now a candidate of physical and mathematical sciences, Ivan Zhukov.
The international project of the Russian Science Foundation and the DFG (Deutsche Forschungsgemeinschaft, German research community) “Development and application of new methods for amplifying NMR signals with parahydrogen” (2019-2021) allowed to continue the work and improve the methodology. Methods have been developed by which proton polarization can be transferred to other useful nuclei, such as the C-13 carbon isotope, to obtain information using magnetic resonance imaging in functional processes, and to trace the transformation of the carbon structure of molecules during biochemical reactions. This could lead to the emergence of new scientific directions.
As part of a Russian-German project, Ivan Zhukov and Alexei Keryutin built an illustrative sample of a field switch installation at the Darmstadt University of Technology, but they did not reveal all the secrets. The device working in the ultra-high-resolution field is still only available in Novosibirsk.
– In June 2021, we started work on the project “Nuclear Polarization in Frequently Changing Magnetic Fields”, with the support of a huge grant from the Ministry of Education and Science, the research is led by the pioneering French scientist Geoffrey Bodenhausen (Ecole Normale Superior – École Normale Supérieure, Paris), Student of Nobel Prize laureate Richard Ernst (the prize was awarded for the development of multidimensional NMR methods), Alexandra Yurkovskaya follows. – One of the project’s goals is related to the creation of so-called long-lived spin states, whose magnetic field dependence will be used for drug screening (using hyperpolarization methods).
Our synthesis is critical for creating complex nuclear polarization manipulation schemes. After completing all these methods in the laboratory, we will be able to increase the information content of MRI for practical medical diagnosis. In particular, we will be able to monitor the metabolic processes that occur in a cancerous tumor in real time, and thus control the effect of drugs on it. Together with Jeffrey Bodenhausen, the recognized “NMR expert” and one of the authors of Every Specialist’s Handbook on Nuclear Magnetic Resonance, we organize educational trips for young researchers. Moreover, we signed an agreement on the exchange of students and the establishment of a joint graduate school between ITC, Novosibirsk State Research University and the Ecole Normale Supérieure in Paris with the support of the French government. Bogdan Rodin, a PhD student, is currently doing research for the DPJ in Paris.
“The development of our research is progressing,” said ITC SB RAS Director Matvey Fedin. From Reporters Without Borders’ core grants, we’ve moved on to more applied mega grants that lead to new technologies and materials. It is important that up to 70% of the team for each project will be young scientists. Our institute was and remains one of the “youth” of SB RAS. This gives confidence that Siberian spin chemistry will continue to set the tone for the world.
Image courtesy of ITC SB RAS
Pictured: Alexey Keryutin and Ivan Zhukov