The article shows the influence of different solvents and coatings on the physical properties of magnetite nanoparticles functionalized with a nitroxide radical - 4-Amino-2,2,6,6-tetramethylpiperidine-N-oxyl. The nanoparticles studied were coated with chitosan or methoxypolyethylene glycol, and dissolved in water, toluene or chloroform. The samples studied were measured using electron spin resonance (ESR) in the temperature range of 120-280 K applying field cooling (FC) procedure. The parameters obtained for the magnetic core and the nitroxide radical (TEMPO) attached to the core were analyzed and discussed. Characteristic spectroscopic parameters (g factor value and peak to peak line width Delta H-pp) were calculated and the differences in physical properties of the core and TEMPO in a different environment (solvent and coating) were described. Additionally, the EasySpin and Gaussian software was used to confirm the nitroxide radical parameters calculated from the experimental spectra. (C) 2017 Elsevier B.V. All rights reserved.