Electron paramagnetic resonance spectroscopy spin interactions

Electron paramagnetic resonance spectroscopy has proved a valuable tool in the study of AdoCbl-dependent enzymes. AdoCbl itself is EPR-silent, but upon homolysis to form Cbl(II), two spins are formed, one on the cobalt (which now has low-spin d configuration) and one on the organic radical. Typically, the two unpaired electrons remain close enough in the enzymeis active site that they interact with one another to give complex, but informative, EPR spectra. 

Electron paramagnetic resonance spectroscopy is one of the primary tools in studying the electronic structure of polynuclear complexes (341). Whereas magnetic susceptibility studies are capable of detecting electronic interactions as small as a wavenumber (discussed earlier), the EPR spectrum of a polynuclear complex may be sensitive to intramolecular exchange couplings as small as 0.001 cm even at room temperature. Additionally, the °Mn nucleus has a nuclear spin... 

Electron-nuclear double resonance (ENDOR) spectroscopy A magnetic resonance spectroscopic technique for the determination of hyperfine interactions between electrons and nuclear spins. There are two principal techniques. In continuous-wave ENDOR the intensity of an electron paramagnetic resonance signal, partially saturated with microwave power, is measured as radio frequency is applied. In pulsed ENDOR the radio frequency is applied as pulses and the EPR signal is detected as a spin-echo. In each case an enhancement of the EPR signal is observed when the radiofrequency is in resonance with the coupled nuclei. 

ESR spectroscopy is a sensitive detection method designed to provide information on radicals. This method, also known as electron paramagnetic resonance (EPR) spectroscopy, is naturally a good choice for coupling to electrochemistry as radicals can easily be electrogenerated. ESR involves the detection of unpaired electrons which are affected by nearby nuclei. Radical spin states are modified by interaction with a magnetic field, equation (17). ... 

Electron paramagnetic resonance (EPR) spectroscopy (also called electron spin resonance (ESR) spectroscopy), is used to study paramagnetic species with one or more unpaired electrons, e.g. free radicals, diradicals, metal complexes containing paramagnetic metal centres, defects in semiconductors and irradiation effects in solids. While diamagnetic materials are EPR silent, paramagnetic species always exhibit an EPR spectrum. This consists of one or more lines, depending on the interactions between the unpaired electron (which acts as a probe ) and the molecular framework in which it is located. Analysis of the shape of the EPR spectrum (the number and positions of EPR lines, their intensities and line widths) provides information... 

The pulse Fourier transform approach to magnetic resonance spectroscopy has been extensively developed and successfully applied to systems of one-half spin and their mutual interactions. But resonance spectroscopy of spin systems with the higher half- and integer spin quantum numbers is commonplace, for example, in the case of alkali metal nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) of transition metal compounds involving multi-quantum transitions. Similarly, magnetic resonance at zero field entails the observation of multi-quantum transitions. 

---