NMR Properties of Nuclei

Isotope Spin (/) Natural abundance (%) Relative sensitivitya 8i 

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The effects of the hyperfine interaction on NMR properties of nuclei can be exploited to obtain information on molecular structure beyond what is available nsing traditional restraints snch as NOEs and conphng constants. 

Table 1. NMR properties of nuclei included in present chapter.

The Hamiltonian to consider for the theoretical analysis of the NMR properties of nuclei in an open-shell system contains a field- and nuclear spin-free electronic part TYq, the nuclear and electron Zeeman parts and and an interaction term Tfint ... 

In addition to the standard constraints introduced previously, structural constraints obtainable from the effects of the paramagnetic center(s) on the NMR properties of the nuclei of the protein can be used (24, 103). In iron-sulfur proteins, both nuclear relaxation rates and hyperfine shifts can be employed for this purpose. The paramagnetic enhancement of nuclear relaxation rates [Eqs. (1) and (2)] depends on the sixth power of the nucleus-metal distance (note that this is analogous to the case of NOEs, where there is a dependence on the sixth power of the nucleus-nucleus distance). It is thus possible to estimate such distances from nuclear relaxation rate measurements, which can be converted into upper (and lower) distance limits. When there is more than one metal ion, the individual contributions of all metal ions must be summed up (101, 104-108). If all the metal ions are equivalent (as in reduced HiPIPs), the global paramagnetic contribution to the 7th nuclear relaxation rate is given by... 

The NMR signal arises from a quantum mechanical property of nuclei called spin . In the text here, we will use the example of the hydrogen nucleus (proton) as this is the nucleus that we will be dealing with mostly. Protons have a spin quantum number of V . In this case, when they are placed in a magnetic field, there are two possible spin states that the nucleus can adopt and there is an energy difference between them (Figure 1.1). 

The particular NMR properties of Pt caused an additional problem. Due to the presence of surfaces near most of the nuclei, the NMR line is very broad (approximately 4 kG wide). This means that only a small fraction of the nuclear spins can be excited by an rf pulse and thus contribute to any given NMR signal. Given these various constraints, our NMR studies of platinum catalysts required 1-gram samples containing 5-10% Pt by weight. 

The NMR phenomenon is based on the magnetic properties of nuclei and their interactions with applied magnetic fields either from static fields or alfemaling RF fields. Quanfum mechanically subatomic particles (protons and neutrons) have spin. In some nuclei these spins are paired and cancel each other out so that the nucleus of the atom has no overall spin that is, when the number of protons and neutrons is equal. However, in many cases the sum of the number of protons and neutrons is an odd number, giving rise to... 

TABLE 1 Selected NMR properties of the NMR active quadrupolar halogen nuclei... 

The NMR properties of the most commonly used nuclei in in vivo NMR are listed in Table 1. 

Note NMR properties of the most commonly used nuclei in in vivo NMR. The relative sensitivity derives from the physical properties of the nucleus, whereas the absolute sensitivity is the product of the relative sensitivity and the natural abundance of the isotope. 

H NMR spectrometry is the foundation upon which we will build an understanding of the magnetic resonance of other nuclei, especially 13C, which leads to the important advanced correlation experiments. We began by describing the magnetic properties of nuclei, noting the special importance of spin 1/2 nuclei. For practical... 

NMR spectroscopy exploits the magnetic properties of nuclei to give important qualitative and quantitative information on biological samples. There are various different forms of this important technique, but in each case NMR spectroscopy relies on fundamental NMR theory discussed earlier. 

While complete X-ray analysis will establish the structure in the solid state, it is useful to have NMR data on the solution state that illustrate the increase of the coordination number of silicon. It would seem that NMR spectroscopy of nuclei participating directly in donor-acceptor interaction is especially important in investigating silicon compounds with an expanded coordination sphere. This requires the use of Si NMR spectroscopy since the electron shell of the silicon atom, the bond angles and lenghts are strongly affected upon complexation. Valuable information could also be obtained with by " N, N, 0, F NMR data since these elements act as donors. Chemical shifts of nuclei other than hydrogen are determined by various factors and not yet understood well anough to provide easily applied correlations of other physical properties of the molecules. 

The key properties of nuclei that allow them to be probed by NMR are nuclear magnetism and nuclear spin. Quantum mechanics dictates that the angular momentum of any system is quantized and can take only the values ... 

Finally, 29xe is a very suitable and sensitive isotope for probing the pore architecture of zeolitic materials. The extended Xe electron cloud is easily deformable due to interactions between, e.g. the Xe atoms and the channel wall of a zeolitic ftamewoik, and deformation results in a large low-field shift of the Xe resonance. In addition, 129xe NMR can be used to study metal particles in zeolites, while reduction-oxidation reactions can be monitored (13). Table 2 summarizes the NMR properties of a number of nuclei which have been used in NMR investigations of zeolitic materials (11). 

In the following sections we will illustrate the use of these new fluids in NMR spectroscopy with examples taken from the literature and also from the results of our own research. Table 2 lists the NMR properties of the nuclei to be discussed in the remainder of this review. 

Table 1.2. NMR properties of the quadrupolar and integei -spin nuclei. ...

Table 2.1.1 NMR properties of some important spin-1/2 nuclei including the magnetically active tin isotopes and...

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