A Pulse EPR Study of Longitudinal Relaxation of the Stable Radical in γ-Irradiated L-Alanine
✍ Scribed by B. Rakvin; N. Maltar-Strmečki; P. Cevc; D. Arčon
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 96 KB
- Volume
- 152
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
The longitudinal relaxation rate of the first stable alanine radical, SAR1, was studied by employing pulse EPR technique over a wide temperature interval (5-290 K). The complex nonexponential recovery of the longitudinal magnetization in this temperature interval has been described with two characteristic relaxation times, 1/T * 1a as the faster component and 1/T * 1b as the slower component, respectively. It was shown that 1/T * 1a is strongly affected by the CH 3 group dynamics of the SAR1 center. The complete temperature dependence of 1/T * 1a was described by invoking several relaxation mechanisms that involve hindered motion of the CH 3 group from classical rotational motion to coherent rotational tunneling. It was shown that all relevant relaxation mechanisms are determined by a single correlation time with the potential barrier (∆E/k = 1570 K). On the other hand the temperature dependence of 1/T * 1b is related to the motional dynamics of the neighborly NH 3 and CH 3 groups. We found a larger average potential barrier for this motion (∆E/k = 2150 K) corresponding to smaller tunneling frequencies of the neighbor groups.