Electron paramagnetic resonance chromium

The electron paramagnetic resonance spectrum of transition metal ions has been widely used to interpret the state of these ions in systems of catalytic interest. Major emphasis has been placed on supported chromia because of its catalytic importance in low-pressure ethylene polymerization and other commercial reactions. Earlier work on chromia-alumina catalysts has been reviewed by Poole and Maclver 146). On alumina it appears that the chromium is present in three general forms the S phase, which is isolated Cr3+ on the surface or in the lattice the 0 phase, which is clusters of Cr3+ and the y phase, which is isolated Cr5+ on the surface. The S and 0... 

DETECTION AND STRUCTURAL CHARACTERIZATION OF OXO-CHROMIUM(V)-SUGAR COMPLEXES BY ELECTRON PARAMAGNETIC RESONANCE... 

J. R. Dethlefsen, A. Dossing, and E. D. Hedegard, Electron paramagnetic resonance studies of nitrosyl and thionitrosyl and density functional theory studies of nitride, nitrosyl, thionitrosyl, and selenoni-trosyl complexes of chromium, Inorg. Chem., 49 (2010) 8769-8778. 

Microsomal reduction of chromium(VI) can also result in the formation of chromium(V), which involves a one-electron transfer from the microsomal electron-transport cytochrome P450 system in rats. The chromium(V) complexes are characterized as labile and reactive. These chromium(V) intermediates persist for 1 hour in vitro, making them likely to interact with deoxyribonucleic acid (DNA), which may eventually lead to cancer (Jennette 1982). Because chromium(V) complexes are labile and reactive, detection of chromium(V) after in vivo exposure to chromium(VI) was difficult in the past. More recently, Liu et al. (1994) have demonstrated that chromium(V) is formed in vivo by using low-frequency electron paramagnetic resonance (EPR) spectroscopy on whole mice. In mice injected with sodium dichromate(VI) intravenously into the tail vein, maximum levels of chromium(V) were detected within 10 minutes and declined slowly with a life time of about 37 minutes. The time to reach peak in vivo levels of chromium(V) decreased in a linear manner as the administered dose levels of sodium... 

Liu KJ, Shi X, Jiang JJ, et al. 1995. Chromate-induced chromium(V) formation in live mice and its control by cellular antioxidants an L-band electron paramagnetic resonance study. Arch Biochem Biophys 323(l) 33-39. 

Liu KJ, Shi X, Jiang J, Goda F, Dalai N, Swartz HM. 1996. Low frequency electron paramagnetic resonance investigation on metabolism of chromium(VI) by whole live mice. Ann Clin Lab Sci 26(2) 176-184. 

Weckhuysen BM, Schoonheydt RA, Mabbs FE, Collison D. 1996. Electron paramagnetic resonance of heterogeneous chromium catalysts. J Chem Soc, Faraday Trans 92(13) 2431-2436. 

The third principal application of the electron spin resonance technique is to the study of paramagnetic transition metal ions in biochemical systems. Most examples are complexes of copper, iron, manganese, chromium, cobalt and molybdenum. Other metals such as titanium, vanadium and nickel are sometimes employed as structural probes. Only four of these ions, Cu ", Mn, Gd " and VO ", are seen in ESR spectroscopy at room temperature under virtually all conditions. Therefore, they are of special importance. 

There are two important experimental factors that must be accounted for if we are to be successful in running 15N experiments. The 15N nucleus tends to relax very slowly Tj s of greater than 80 seconds have been measured. Thus, either long pulse delays must be incorporated into our pulse sequence or, alternatively, we could provide another route for spin relaxation. A common procedure is to add a catalytic amount of chromium (III) acetylacetonate, a paramagnetic substance, whose unpaired electrons efficiently stimulate transfer of spin. In cases where Tt s are not known (and not intended to be measured), pulse delays and pulse angles must be considered carefully because the signal from one (or more) 15N resonance can accrue too slowly or be missed altogether. 

---