Intramolecular Spin Exchange in Flexible PEG-based Nitroxide Biradicals in Aqueous Solutions

• DOI: 10.1007/s00723-014-0636-1
• Publication Date: 2015-01-09T08:59:58Z
• Authors: G. Ionita; G. A. Vorobieva; V. Chechik; A. I. Kokorin
• Keywords: 0103 physical sciences; 01 natural sciences

Intramolecular spin exchange in four flexible PEG-based bis-nitroxides was studied by X-band electron paramagnetic resonance (EPR) spectroscopy as a function of temperature and solvent viscosity. A series of biradicals with different lengths of the ethylene glycol bridge connecting the two nitroxide groups was investigated in aqueous and mixed 1:1 i-propanol:water solutions. Conformational transitions in liquid solutions of the biradicals were analyzed, and thermodynamic parameters of the conformational reorganization were calculated from the EPR spectra. Intramolecular distances r between paramagnetic >N–O• fragments in biradicals in frozen solutions were calculated and compared with dynamic properties of the biradicals.