Naslov
EPR study of diffusion of nitroxide radicals in normal and supercooled water

Autori
Merunka, Dalibor ; Perić, Miroslav

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
DSL2016 Abstract Book / DSL CONFERENCE - Split : DSL CONFERENCE, 2016, 126-126

Skup
12th International Conference on Diffusion in Solids and Liquids - DSL2016

Mjesto i datum
Split, Hrvatska, 26.06.2016. - 30.06.2016

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
electron paramagnetic resonance; Heisenberg spin exchange; dipole-dipole interaction; diffusion coefficient

Sažetak
Electron paramagnetic resonance (EPR) spectroscopy is sensitive technique for detecting radicals in liquid solution. The EPR spectrum of radicals is affected by their relative motion, which modulates the Heisenberg spin exchange (HSE) and dipole-dipole (DD) interactions between radicals. Therefore, a diffusion coefficient of radical in a given liquid can be obtained from the concentration dependence of EPR spectral parameters, such as linewidths, hyperfine splittings and coherence transfer. However, this procedure demands a reliable spectral fitting to find experimental concentration constants and a valid theoretical expression relating them to the diffusion coefficient. The effect of HSE interaction on EPR spectrum, which is dominant effect at higher temperatures, was calculated by solving kinetic equations for spin evolution of interacting radical pairs whose distance varies according to continuous diffusion model [1]. We extended the spin evolution equations by including the DD interaction, whose effect increases by lowering temperature. Since no analytical solution exists for these equations, an iterative method was applied assuming a weak effect of DD interaction. The obtained theoretical expressions were tested by measuring concentration dependences of EPR spectra of two nitroxide radicals in the normal (T>0°C) and supercooled (T<0°C) states of water. The nitroxide radicals were 14N- and 15N-labelled perdeuterated TEMPONE, which were chosen because their EPR spectra strongly differ, while their size and diffusion coefficient are expected to be the same. The experimental concentration constants derived by fitting the EPR spectra correlate with theoretical expressions, allowing us to calculate diffusion coefficients. The calculated diffusion coefficients have similar values for both radicals and the calculated Stokes-Einstein radius decreases by lowering temperature in the supercooled state. [1] K.M. Salikhov, et al., Appl. Magn. Reson., 45, 911 (2014).

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemija

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