Electron Paramagnetic Resonance for Chemistry, Materials Science and Biology
Classical magnets are composed of atoms of metals, whereas the molecule-based magnets, as follows from the name, are prepared from molecules.The unpaired electrons may strongly interact with each other (exchange interaction), providing for the alignment of their magnetic moments on a molecular scale. Electron Paramagnetic Resonance plays a crucial role for determination of the properties of molecule-based magnets due to its ability to probe directly the electron spin states, measure the basic magnetic interactions and provide insight into their origin.
We study novel compounds, which are perspective as the bases for various molecular spin and magneto-mechanical devices. These compounds of family Cu(hfac)2LR are called “breathing crystals”, since they undergo the reversible structural rearrangements with temperature accompanied by the changes of their magnetic moment. On lowering temperature, the distances between unpaired electrons residing on two oxygen and one copper atoms decrease, leading to a strong increase of exchange interaction. As a result, the magnetic moment of this three-spin unit changes reflecting the coupling of two electrons of three. The reversible change of the elementary cell volume during rearrangements (“breathing”) reaches ca. 13% for some crystals Cu(hfac)2LR and is accompanied by ca. 30% change in magnetic moment. It was found recently, that the change of the magnetic moment can also be achieved by the irradiation with light. Therefore “breathing crystals” can be used as magneto-mechanical nano-switches operated by temperature or light. Using the EPR at different microwave frequencies (9, 35 GHz and higher) we characterize the magnetic properties of breathing crystals and their changes under temperature or light, providing for necessary information for further synthetic research on the way to molecule-based magnetic devices.
|The other systems of our recent interest include complexes with large zero-field splitting, which are promising for the design of single-molecule magnets.|
|Representative publications: Coord. Chem. Rev. 289–290 (2015) 341-356 (10.1016/j.ccr.2014.11.015), Angew. Chem. Int. Ed. 53 (2014) 10636 –10640 (10.1002/anie.201403672), J. Amer. Chem. Soc. 136 (2014) 10132–10138 (10.1021/ja504774q), J. Amer. Chem. Soc. 134 (2012) 16319-16326 (10.1021/ja306467e), J. Amer. Chem. Soc. 132 (2010) 13886-13891 (10.1021/ja105862w), Angew. Chem. Int. Ed. 47 (2008) 6897-6899 (10.1002/anie.200801400), J. Amer. Chem. Soc. 130 (2008) 2444-2445 (10.1021/ja710773u).|
|Metal−organic frameworks (MOFs) made up of clusters or chains of metal ions connected by organic linkers are intensively studied since past two decades. Three-dimensional (3D) porous frameworks, which may include 1D, 2D, and 3D channel systems, have intriguing structures, diverse topologies, and many potential applications, such as gas separation and storage, catalysis, ion exchange, microelectronics, and so forth.|
|In our lab we apply EPR to investigate properties of MOFs and their guest-host interactions with adsorbed molecules. For this sake, we employ spin probes (nitroxide radicals) adsorbed into the pores of MOFs and acting as EPR-active reporters, or paramagnetic dopants incorporated into the naturally diamagnetic MOFs.|
|Representative publications: J. Phys. Chem. Lett. 5 (2014) 20-24 (doi: 10.1021/jz402357v), J. Phys. Chem. C 120 (2016) 10698-10704 (10.1021/acs.jpcc.6b02966).|
We are also interested in MOF catalysis and elucidation of reaction mechanisms using EPR.
|Representative publications: En. Environ. Sci. 8 (2015) 364-375 (10.1039/c4ee02853h), Sci. Rep. 6 (2016) 23676 (10.1038/srep23676).|
|Since a few years we are intersting in application of ionic liquids as unusual media for photochemical reactions. In particular, we actively apply Time-Resolved EPR on photoexcited triplets dissolved in the ionic liquid to study the effects of nano/microstructuring.|
|Representative publication: J. Phys. Chem. B 119 (2015) 13440−13449 (10.1021/acs.jpcb.5b06792).|
|Spin labeling and distance measurements in biopolymers|
|In collaboration with NIOCh SB RAS and ICBFM SB RAS we investigate biopolymers and their complexes using new advanced spin labels and spin labeling approaches. As a rule, Double Electron-Electron Resonance (also known as PELDOR) spectroscopy is applied to obtain distance distributions between incorporated spin labels and draw conclusions on structure and dynamics of the biomolecule under study. We focus on new spin labels (advanced nitroxides and trityls), new immobilization approaches, RNAs and their ribosomal complexes, and DNAs.|
Representative publications: J. Amer. Chem. Soc. 136 (2014) 9874–9877 (10.1021/ja505122n), J. Phys. Chem. Lett. 7 (2016) 2544-2548 (10.1021/acs.jpclett.6b01024), Nucleic Acids Reseach 44 (2016) 7935–7943 (10.1093/nar/gkw516).