Field strength, experiment design

In a magnetic resonance experiment designed to record the rotational spectrum, the fixed radiation frequency would be close to the resonant zero-field frequency, with the mismatch being tuned with a swept magnetic field. Equation (9.95) enables us to calculate the behaviour of the levels as a function of magnetic field strength we show the results for both the TV = 1 and 2 rotational levels in figure 9.25, appropriate for the CN radical where yv=0 has the value 217.5 MHz [55]. 

Protein concentrations in solution are often limited by solubility and aggregation (and, of course, protein availability) to a maximum of 0.5-5 mM. Today most NMR structural studies are performed at 1-2 mM protein concentrations, although it can be expected that new technologies leading to increased sensitivity in NMR experiments (increased field strength, improved probe design, cryo-probes etc.) will lower the concentration requirements to the 100-mM range within the next few years. 

The suggestion by Cain that the effect occurs through an actual dipolar reorientation would require unusually large field strengths or extremely large dipole moments. The prediction of an inhibitory effect due to membrane hyperpolarization because of increased steady-state potassium conductance concomitant with decreased steady-state sodium conductance certainly should merit enough attention to design experiments to test the existence of such a response. 

Probe construction materials were investigated for their signal contribution to ultrashort echo time spectroscopy and imaging. H-1, C-13, and P-31 spectra were obtained at a field strength of 9.4 T for 16 materials considered for use in probe and holder design and construction. Four of the materials were found to be suited for the construction of NMR probes, housing of RF coils, and holders for in vivo experiments. 

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