Sensitivity of Saturation Transfer Electron Spin Resonance Extended to Extremely Slow Mobility in Glassy Materials
✍ Scribed by Ivon J. van den Dries; P.Adrie de Jager; Marcus A. Hemminga
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 179 KB
- Volume
- 131
- Category
- Article
- ISSN
- 1090-7807
No coin nor oath required. For personal study only.
✦ Synopsis
A novel extension of the saturation transfer (ST) ESR technique peratures, using small nitroxide spin-labeled molecules as that enables the determination of extremely long rotational correprobes (4-6). Conventional ESR is sensitive in the motional lation times of nitroxide spin labels up to values around 10 4 s is region for values of the rotational correlation time t R beproposed. The method is based on the observation that the integral tween 10 011 and 10 08 s. In the motional region for t R ú of ST-ESR spectra is sensitive to the spin-lattice relaxation time 10 07 s, ST-ESR is commonly used. ST-ESR is based on of the electron of the spin label, which in turn is directly dependent the diffusion and recovery of saturation between different upon the rotational correlation time. The method is applied to the portions of the spectrum (7, 8) in competition with field spin label TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-Nmodulation. For the usual ST-ESR field modulation frequenoxyl) in glycerol. From the known viscosity data and the related cies of around 50 kHz, the upper limit of sensitivity for rotational correlation times of the TEMPOL spin label in glycerol, rotational mobility is for t R É 10 03 s (7, 9), provided that the rotational correlation times of unknown samples can be determined. The method is especially applicable to systems with a very there is sufficient recovery of saturation, which is determined high viscosity, such as glassy materials. The method is applied to by the spin-lattice relaxation time of the electron (T 1 ). At a 20 wt% glucose-water mixture in the glassy state, giving a value room temperatures, T 1 is about 1 ms for nitroxide spin labels for the highest limiting rotational correlation time of about 10 3 s (10), which is in the right range for ST-ESR spectroscopy. at a temperature of 45 K below the glass transition temperature Beyond the upper limit, the ST-ESR spectra are no longer of this system. This is an extension by six decades for the rotational sensitive for the diffusion of saturation, because the domicorrelation time, as compared to the current application of STnating effect is the recovery of saturation, as given by T 1 .
ESR.