Systems magnetic resonance coupling parameters

Spectroscopic studies on the Fe-Mo protein by EPR and Mossbauer spectroscopy have shown six iron atoms each in a distinctive magnetic environment coupled to an overall S=3/2 spin system (6,7,8) and electron nuclear double resonance (ENDOR) studies suggest one molybdenum per spin system (8). The 5 Fe signals (five or six doublets) observed in the ENDOR spectra (8) indicate a rather asymmetric structure for the Fe/Mo/S aggregate in which the iron atoms roughly can be grouped into two sets of trios, each set having very similar hyperfme parameters. 

Nuclear magnetic resonance (NMR) is a technique of considerable versatility in polymer science. It is used universally as a probe of chemical configurations, it provides information on the dynamics and relaxation times of a polymer system and it offers a route to the determination of orientation parameters, the exact route depending on the particular nuclei employed. In principle quadrupolar, dipolar, shielding tensor and indirect spin coupling interactions can all be employed " however, in practice only the first two have any universal appeal. Dipolar coupling using proton NMR offers the simplest approach in terms of material preparation and will be considered first. 

We conclude this chapter by considering a phenomenon that has attracted a great deal of attention in the physics community, but remains almost unknown to chemists. It is an effect that arises when the constraint parameters of a nonlinear oscillator are slowly varied in a cyclic fashion. We may think of it as occurring in a situation where an oscillator is periodically forced with a frequency much less than its natural frequency, or when two oscillators with very different periods are coupled together. First pointed out by physicist Michael Berry in the context of quantum mechanical systems such as magnetic resonance and the neutron inter-... 

Autschbach has outlined some basic concepts of relativistic quantum chemistry and recent developments of relativistic methods for the calculation of the molecular properties, including important for NMR spectroscopy, nuclear magnetic resonance shielding, indirect nuclear spin-spin coupling and electric field gradients (nuclear quadrupole coupling). The author analysed the performance of density functional theory (DFT) and its applications for heavy-element systems. Finally, the author has reviewed selected applications of DFT in relativistic calculation of magnetic resonance parameters. 

Grage SL and Ulrich AS (1999) Structural parameters from homonuclear dipolar couplings, obtained by multipulse solid state NMR on static and oriented systems. Journal of Magnetic Resonance 138 98-106. 

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