Nanochemistry and nanobiotechnology
Solvent-dependent intramolecular spin-spin interactions in the paramagnetic derivatives of adamantane. 
Melnyk A.K.1,2, Khilchevskyi O.M.1, Vovk A.I.1 
1Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine. Murmanska str.,1,Kyiv- 02094, Ukraine
E-mail: mak106@ukr.net
2Institute for Sorption and Problems of Endoecology of the NAS of Ukraine. Naumov str.,13, Kyiv- 03164, Ukraine 

Nitroxide biradicals are promising compounds which could find applications in different physical, chemical and biological studies for the creation of organic molecular magnets, polarizing agents and spin labels and probes as well. Such factors as solvent nature, temperature, molecular conformation and linker length could seriously affect spin exchange interaction between radical moieties and therefore magnetic properties of the whole compound.  
In our current research, we used cw EPR spectroscopy to study the bis-nitroxide adamantane-based stable radicals which previously were applied as spin probes [1]. It was shown that organic solvent choice is crucial for intensity of intramolecular spin-spin interaction of two nitroxide fragments of adamantane-1,3-diacetic acid derivatives, leading to three-line spectrum in the case of low (J~0) and five-line spectrum for high (J>>AN) exchange integral value. Integrated EPR spectra revealed an additional singlet line, caused by the superposition of spin density distributions for the neighboring nitroxide moieties. In the series of water-ethanol solutions spectral shape changes with increase of ethanol content, leading to lowering of singlet line intensity and finally transformed to a pure quintet for 96% ethanol solution.
 Temperature dependencies recorded for DMSO, acetonitrile and ethylene glycol, indicated the symbate increase in the magnitude of exchange coupling constants. Molecular structure play an important role in such processes because the adamantane-1,3-diacetic acid derivatives demonstrated stronger electron spin exchange than adamantane dicarboxylic acid ones in the whole temperature range. 

1.	Melnyk A.K., Sukhoveev O.V., Kononets L.A., Khilchevsky O.M., Shulga S.M., Kukhar V. P., Vovk A. I.  An EPR spin probe study of liposomes from sunflower and soybean phospholipids // J. Liposome Res. - 2016. – 26 - P. 80-86.