Nanocomposites and nanomaterials
Paramagnetic properties of gold-containing nanoclusters incorporated into organic polymer matrix studied by EPR. 
Melnyk A.K.1, Kislyuk V.V.2, Trachevskij V.V.3
1Institute for Sorption and Problems of Endoecology of the NAS of Ukraine. Naumov str.,13, Kyiv- 03164, Ukraine 
E-mail: mak106@ukr.net
2G.V. Kurdyumov Institute for Metal Physic of the NAS of Ukraine. Vernadsky blvd.,36, Kyiv- 03142, Ukraine 
3Technical centre, NAS of Ukraine. Pokrovska str.,13, Kyiv- 04070, Ukraine  
Magnetic nano-sized systems have found a wide range of applications in various fields including biology, medicine, chemistry and semiconductor technology as well. On the other hand, gold nanoparticles (AuNPs) are of particular importance for biomedical applications. Nowadays, one of the most prospective trends in this area are composite materials with self-organized NPs, stabilized within a matrix.
     There are numerous experimental evidences of the paramagnetism in relatively small Au containing clusters. Our current research concerns the nature of the magnetic properties we observed previously in such objects [1], which suggests conceptually two possibilities: i) gold ion stabilization at Au2+ intermediate state; ii) tannin- and/or citrate-based radical formation. Introducing aluminum compound into the system of reducing gold can provide fine adjustment both for rate and degree of Au ion reduction while the synthesis process.
      EPR spectra of all samples studied contain signal with g=2.062 regardless of a preparation route. We associate the origin of this band with the paramagnetic state of the 5d106s1 residual gold nanoparticle with an odd number of atoms. The evidence of weakly resolved fine structure in this line is attributed to quantum confinement of the NP’s electron structure. Additional substantially wider line could be explained due to the strong exchange interaction that occurs between closely spaced nanoclusters. Other lines with g-factor values of 2.17 and 2.0048, could be attributed respectively to the formation of the intermediate incompletely reduced paramagnetic state of Au2+ corresponding to [Xe]4f145d9 electron configuration and a radical state related to the supporting environment lability preventing (due to chelate effect) mechanical stress. In contrary, the latter can be the reason which suppresses the radical state appearance within the supporting matrix for the case of the stabilization at the zeolite surface.

1.	V.V.Kislyuk, A.K.Melnyk, N.I.Buryak, V.V.Trachevskij. An approach to the formation of paramagnetic particles of noble metals // J. Electr. Eng. - 2019. (in press).