A thorough investigation of biomimetic polydopamine (PDA) by Electron Paramagnetic Resonance (EPR) is shown. In addition, temperature dependent spectroscopic EPR data are presented in the range 3.8-300 K. Small discrepancies in magnetic susceptibility behavior are observed between previously reported melanin samples. These variations were attributed to thermally acitivated processes. More importantly, EPR spatial-spatial 2D imaging of polydopamine radicals on a phantom is presented for the first time. In consequence, a new possible application of polydopamine as EPR imagining marker is addressed.

Spin-lattice relaxation time T1 was determined by the electron spin echo (ESE) method in the temperature range 4-60 K in a series of Tutton salt crystals MI2MII(SO4)2·6X2O (MI = NH4, K; MII = Zn, Mg; X = H, D) weakly doped (⩽1018 ions cm-3) with the 63Cu2+ isotope. The ESE signal was undetectable at higher temperatures. The relaxation rate increases over the six decades in the studied temperature range with T1 equal to 1 s at 4 K and 0.5 µs at 50 K. Various possible relaxation mechanisms are discussed with the conclusion that the relaxation is governed by two-phonon Raman processes without a noticeable contribution from the reorientations of Cu(H2O)6 octahedra between Jahn-Teller distorted configurations. Deuteration of the crystal has no effect in spin-lattice relaxation. For a few crystals, having the largest Cu2+ concentration among the studied crystals, a strong and linear in temperature contribution to the relaxation rate was found below 15 K. Possible explanations are discussed with the final conclusion that this effect is due to a non-uniform Cu2+ distribution in the host lattice producing effective relaxation via pairs and triads of the Cu2+ ions. From the T1(T) dependence the Debye temperature ΘD was determined for the all crystals studied. This varies from ΘD = 166 K for K2Zn(SO4)2·6H2O to ΘD = 238 K for (NH4)2Mg(SO4)2·6H2O. The ΘD values are discussed and used for calculation of the sound velocity which was found to be similar in all crystals and equal to ν = 4150(±150) m s-1.

The X-band EPR and magnetic susceptibility in the temperature range 4.2-300 K study of the shungite-I, natural nanostructured material from the deposit of Shunga are reported. Obtained results allow us to assign the EPR signal to conduction electrons, estimate their number, N P , and evaluate the Pauli paramagnetism contribution to shungite susceptibility. A small occupation (*5%) of the localized nonbonding p states in the zigzag edges of the open-ended graphene-like layers and/or on r (sp 2?x) orbitals in the curved parts of the shungite globules has been also revealed. The observed temperature dependence of the EPR linewidth can be explained by the earlier considered interaction of conduction p electrons with local phonon modes associated with the vibration of peripheral carbon atoms of the open zigzag-type edges and with peripheral carbon atoms cross-linking different nanostructures. The relaxation time T 2 and diffusion time T D are found to have comparable values (2.84 9 10-8 and 1.73 9 10-8 s at 5.2 K, respectively), and similar dependence on temperature. The magnetic measurements have revealed the suppression of orbital diamagnetism due to small amount of large enough fragments of the graphene layers.