Paramagnetic trap

In the work of Xiao et al. the resonance of a single electronic spin is observed directly in a field-effect transistor (FET). After creating a paramagnetic trap, they observe the source/drain current in the FET, as a function of the ESR frequency. Under a magnetic field, the Fermi level of the channel electrons is adjusted to lye between the two electronic states of the paramagnetic trap. The idea is that, if only the lower spin state is occupied, then no electron can jump from the channel to the trap. But if only the upper spin... 

Connor, H.D., Gao, W., Nukina, S., Lemasters, J.J., Mason, R.P. and Thurman, KG. (1992). Evidence that free radicals are involved in graft failure following orthotopic liver transplantation in the rat an electron paramagnetic resonance spin trapping study. Transplantation 54, 199-204. 

A second type of defect is associated with boron or aluminum impurities that are present in SiCh- In porous glass Muha (129) observed a rather complex spectrum which results from hyperfine interaction with 10B and UB isotopes. The spectrum is characterized by g = 2.0100, g = 2.0023, an = 15 and a a. = 13 G for nB. The paramagnetic defect is apparently a hole trapped on an oxygen atom which is bonded to a trigonally coordinated boron atom. This center is irreversibly destroyed upon adsorption of hydrogen. 

Special spin-trapping techniques are also available for the detection of short-lived radicals in both homogeneous and heterogeneous systems. For instance, a-phenyl A-ferf-butyl nitrone (PBN), ferf-nitrosobutanc (f-NB), -(4-pyridyl A-oxidc) A-ferf-butyl nitrone (4-POBN), or 5,5-dimethyl-l-pyrroline A-oxidc (DMPO) can be made to react with catalytic intermediates to form stable paramagnetic adducts detectable by ESR [135], Radicals evolving into the gas phase can also be trapped directly by condensation or by using matrix isolation techniques [139],... 

This article concerns a simple expedient whereby short-lived reactive free radicals may be transformed into more persistent paramagnetic species, thus enabling esr techniques to be applied to systems in which the concentration of the reactive radical remains below normal detection limits. The principle is a simple one. It depends upon the addition to the reaction system of a small quantity of a diamagnetic substance (the spin-trap ) having a particularly high affinity for reactive radicals the product of this trapping reaction must be a particularly persistant free radical (the spin adduct ) whose concentration will build to readily detectable levels (>ca. 10—7—10-6 M). The general reaction is represented by equation (1). 

Registration of ROS was carried out by electron paramagnetic resonance (EPR) technique using spin trap l-hydroxy-2,2,6,6-tetramethyl-piperidine-4-OH (2 x 10 3 M). EPR spectra in the samples were registered at room temperature in quartz cuvette with the volume of 200 pi (Burlaka et al., 1994). 

Buettner, G. R., KeUey, E. E., and Bums, C. P., 1993, Membrane hpid free radicals produced from LI 210 murine leukemia ceUs by photofrin photosensitization an electron paramagnetic resonance spin trapping study. Cancer Res. S3 3670-3673. 

Panchenko, A., Dilger, H., Kerres, J., Hein, M., Ullrich, A., Kaz, T. and Roduner, E. 2004. In situ spin trap electron paramagnetic resonance study of fuel ceU processes. Physical Chemistry Chemical Physics 6 2891-2894. 

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