Magnetic nuclei receptivity

Magnesium has one NMR-active isotope, Mg, which is only 10.0% naturally abundant. This is a spin 5/2 nucleus with a magnetogyric ratio of —1.639 X 10 rads T , which means it has a Larmor frequency that is 6% of that of protons in the same magnetic field and a receptivity of 72.9% of that of The relatively low Larmor frequency was one of the key factors... 

The NMR of La has recently aroused the interest of biophysicists in view of the specific binding abilities of La to certain proteins and nucleic acids. La is in fact a rather favourable magnetic resonance nucleus, comparable in receptivity to... 

Zn (/ = , Q = 0-16 barn, 41%) has a magnetic moment of 0-784/iN and therefore can be considered a low-receptivity nucleus. This together with the not very extensive chemistry of this element, is primarily responsible for the little interest that this nucleus has attracted so far. 

With its natural abundance of 93.1% and a relative receptivity of its central transition comparable to that of C, K appears to be a suitable nucleus for solid state NMR. These factors are to some extent offset by its small magnetic moment and quadrupolar characteristics which have limited the number of solid-state NMR studies to date. An early study demonstrated the success of the nuclear quadrupole double resonance... 

Nucleus Natural Abundance [%] Magnetic Moment //[ iN] Magnetogyric Ratio r[10 rad T- s-i] NMR frequency B [MHz] Standard Relative Receptivity Ef Relative Receptivity... 

Another nucleus of considerable analytical potential is deuterium, whose observation at natural abundance has been demonstrated earlier (9) but whose practicality has so far been severely limited due to its low NMR receptivity and also because of its more than six times smaller chemical shift range relative to the proton. These limitations are largely overcome at high magnetic field as illustrated by the natural-abundance deuterium spectra of camphor In Figure 8. 

For spin-1/2 nuclei, relaxation times and large anisotropies in the magnetic shielding may render data acquisition difficult even if the nucleus has a favorable receptivity. For example, a comparison of the receptivities for C and Pt would suggest that the latter nucleus is more suitable for NMR studies. Yet there have been few reports of Pt... 

Knowing the gyromagnetic ratio y of a nucleus enables the resonance frequency from Equation (I) to be calculated for any magnetic field strength. Table 2 lists useful, commonly studied nuclei and their magnetic properties. The frequencies are for a 2.35 T applied magnetic field, i.e., relative to H at 100 MHz. Table 2 gives the relative sensitivity for equal numbers of each nucleus and their relative receptivities, i.e.. the product of the relative sensitivity and natural abundance. 

Nucleus Natural abundance (%) Larmor frequency at 2.11 T (MHz) Receptivity ( H = 1) Nuclear spin Nuclear magnetic moment (wn)... 

The element aluminum-27 occurs at 100% natural abundance and its nucleus has a good receptivity, though its quadrupole moment means that its resonances are broadened relative to those of spin-1/2 nuclei. However, this amounts to only a few hertz or tens of hertz in many cases, with the result that Al has been considered worthy of study from the early days of NMR spectroscopy and has already been the subject of three reviews " and figures in a fourth, and another is to appear. Historically, the first observations were carried out in the derivative mode and with poor quality magnets, which were deemed sufficient for a quadrupolar nucleus but as increasingly improved instrumentation became available, high-resolution absorption... 

Indium has two magnetically active isotopes, " In and In, whose properties are summarized in Table 1. The quadrupole moment is large, and though this is offset by the large spin quantum number, the lines are expected to be broader than those of the other group III elements. Thus we are likely to be able to observe only the most symmetrical species. Collecting data should be very easy in the FT mode but observations will be limited by the recovery time of the equipment used. In has the larger receptivity and is the preferred nucleus. 

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