Electron Paramagnetic Resonance EPR Spectra

ELECTROCHEMICAL PROPERTIES AND ELECTRON PARAMAGNETIC RESONANCE (EPR)-SPECTRA OF NITRONE RADICAL IONS... 

Electron paramagnetic resonance (EPR) spectra are also discussed by Valentine et al. in reference 21. The splitting of the gy resonance is due to hyperfine coupling between the unpaired electron on Cu(II) and the nuclear spin of the copper nucleus... 

NAH is composed of four subunits (SDS-PAGE) and contains a molybdenum cofactor (Dilworth 1983). Analysis of the electron paramagnetic resonance (EPR) spectra of the molybdenum center of NAH revealed a coordination of molybdenum to selenium (Gladyshev et al. 1994b). Apparently NAH is much like other selenium-dependent molybdenum hydroxylases such as XDH from C. barkeri and other purinolytic Clostridia. Whether or not the selenium is present as a ligand of molybdenum or is coordinated to molybdenum while being bound to another molecule (e.g., sulfur of cysteine) is still not known. The nature of the selenium cofactor and the mechanism of its incorporation into NAH are most likely similar to XDH and thus also require more study. 

In some cases large extinction coefficient allows sensitive detection Circular dichroism (CD) spectra Coordination geometry metal ligands Electron paramagnetic resonance (EPR) spectra... 

Figure 13.16 Stackplot of electron paramagnetic resonance (EPR) spectra of 2,2,6,6-tetramethylpiperidine A -oxide (TEMPO)-functionalized dendrimers with 5, 10, 25, 50, 75, 90, and 95% TEMPO.

Under basic conditions 3-hydroxyimidazole 1-oxides 267 are oxidized by bromine or Pb(OAc)4 to give quite stable radicals 322 as shown by electron paramagnetic resonance (EPR) spectra (1968CI(L)651,1967AG(E)947, 1970CB296) (Scheme 96). 

In the case of copper(II) ions, the magnetic anisotropy is small, as is easily inferred from the g values obtained from electron paramagnetic resonance (EPR) spectra (Peisach and Blumberg, 1974) that reflect the magnetic anisotropy of the electronic ground level only. As the first excited level is normally not populated at room temperature, its contribution is negligible, and the anisotropy of the squared g values can be taken as a good estimate of the x anisotropy (Bertini and Luchinat, 1996). 

The mass spectrum (MS) of chitin was recorded using a VG Micro-mass 7070 F gas chromatography mass spectrometer imit. The electron paramagnetic resonance (EPR) spectra were recorded using a Varian EPR spectrometer. The MS recorded at a temperature of 300 °C is shown in Eig. 2.22. This temperature was used to obtain a more stable and rich fragmentation pattern. Table 2.13 presents the list of fragments that can be attributed to the ions detected in the recorded mass spectra (MS). 

The ESR spectrum of a Cu complex with hydrolyzed ascidiacyclamide suggested that a ligandimetal ratio of 1 1, a single monomeric copper(ll) complex, is formed in solution while computer simulation of electron paramagnetic resonance (EPR) spectra indicated a 1 2 ratio <1996IC1095>. 

Spectroscopy. FT-IR spectra were recorded on a Nicolet F-730 spectrometer equipped with an in-situ flow-cell. Electron Paramagnetic Resonance (EPR) spectra were recorded in X-band with a Bruker ESP-300 with a fE (,4 cavity. Diffuse Reflectance Spectroscopy (DRS) spectra were recorded on a Cary-5 spectrofotometer with a BaS04 integration-sphere in the UV-VIS-NIR. Molecular graphics analysis was done with Hyperchem 3.0 for Windows (Hypercube Inc.). 

Figure 3.18 shows the time-resolved Electron Paramagnetic Resonance (EPR) spectra of the reaction center from Rba. sphaeroides 2.4.1 at low temperatures. At 65 K, the initial spectrum (0.0 ps) can be ascribed to 3P. After its decay, two different spectral patterns ascribable to the T, species of spheroidene appear they are called 3Car(I) and 3Car(II). At higher temperatures, the contribution of 3P becomes much smaller, but those triplet species of carotenoid exhibit basically the same time-resolved spectra. 

The coordination structures of enzyme-bound manganese nucleotides can in favorable cases be determined by analysis of electron paramagnetic resonance (EPR) spectra of Mn(II) coordinated to O-labeled nucleotides. When the nucleotide is stereospecifically labeled with O at one diastereotopic position of a prochiral center, either oxygen can in principle be bound to Mn(II) in the coordination complex in an enzymic site. When the coordination bond is between Mn(II) and O, the EPR signals for Mn(II) are broadened and attenuated, owing to unresolved superhyperfine coupling between the nucleus of 0 and the unpaired electrons of Mn(II) (23). No such effect is possible with 0, which has no nuclear spin. The effect is observable in samples in which all the Mn(Il) is specifically bound in one or two defined complexes of the nucleotide with the enzyme. Thus the complex Mg(Sp)-[a- 0]ADP bound at the active site of ere-... 

---