C.M. LUCACIU*, M. DÂNŞOREANU**, G. DAMIAN***, V. MICLĂUŞ****

*Department of Biophysics, Faculty of Pharmacy, “Iuliu Haţieganu” University of Medicine and Pharmaceutics, Cluj-Napoca
**Department of Biophysics, Faculty of Medicine, “Iuliu Haţieganu” University of Medicine and Pharmaceutics, Cluj-Napoca
***Department of Biomedical Physics, Faculty of Physics, “Babeş-Bolyai” University, Cluj-Napoca,
****Department of Organic Chemistry, Faculty of Chemistry, “Babeş-Bolyai” University Cluj-Napoca

Abstract. In this paper we present the results obtained by using the EPR spin label technique for testing the inclusion of monoradical nitroxide compounds in β-cyclodextrin, in liquid phase. Different concentrations of TEMPO (2, 2, 6, 6-tetramethyl-piperidine-1-oxyl), and TEMPONE (4-Oxo-2,2,6,6-tetramethyl piperidine-1-oxyl) solutions in distilled water were mixed with a water solution of β-cyclodextrin in various ratios and the EPR spectra of the mixtures were recorded on an X-band EPR spectrometer. The mixture spectra were compared to the pure spin label spectra in water. The double integration of the spectra did not revealed significant difference between the two types of samples. However, the analysis of the spectra in terms of the rotational correlation time revealed a strong difference between the samples. For TEMPO solutions, the presence of cyclodextrin leads to a fivefold increase in the rotational correlation time, in the case of TEMPONE the rotational correlation time being around three times higher in the presence of β-cyclodextrin. These results were interpreted as an indication of the complex formation and they correlate with precipitate formation when mixing high concentrations of spin labels with cyclodextrin solutions. In the presence of the ascorbic acid the intensity of the EPR signal is strongly reduced. The remaining signal is anisotropic and can be attributed to the fraction of the spin label molecules having the nitroxide group inside the cyclodextrin cavity. These results strongly support that EPR signals of monoradical nitroxides can also bring valuable informations about host-guest interactions.

Corresponding author’s e-mail: clucaciu@umfcluj.ro

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