Changes of paramagnetic centers (PC) concentration in dispersed petroleum systems were studied in the process of low-temperature thermolysis. The kinetic model of PC concentration dynamics based on the processes of unpaired electrons formation during singlet-triplet transitions, weak chemical bonds dissociation and recombination of free radicals is proposed.

We report the observation of pulsed electron-nuclear double resonance (ENDOR) spectrum caused by interactions of the nitrogen nuclei ¹⁴N with the unpaired electron of the paramagnetic vanadyl complexes VO²⁺ of vanadyl porphyrins in natural crude oil. We provide detailed experimental and theoretical characterization of the nitrogen hyperfine and quadrupole tensors.

[Fe(3-MeO-Qsal)₂]Y (Y = PF₆, BF₄, NCS, NO₃, BPh₄) compounds were synthesized using the diffusion method and studied by the electron spin resonance and the magnetic susceptibility methods in the temperature range (5-300) K. Coexistence of spatially separated high-spin and low-spin fractions in these compounds was observed. Low-spin fraction of all compounds reveals the antiferromagnetic correlations at low temperatures. High-spin fraction of complexes with Y = PF₆ demonstrate the weak ferromagnetic properties due to exchange interaction between complexes in whole temperature range. Influence of outer-sphere anion on the spin state, the electronic properties of low-spin Fe(III) complexes is demonstrated.

Paramagnetic properties of novel bioactive nanocomposite materials based on humic substances and the precious metals (Ag, Au) are investigated by electron paramagnetic resonance and compared to their antioxidant properties. The possible mechanisms of antioxidant activity in the light of the free radical activation or inhibition of oxidation processes are analyzed.