Useful nuclei

Table 1. Nmr Parameters for Less Commonly Used Nuclei 10 ...

NMR analysis allows characterization of proteins to an atomic level. The most frequently used nuclei on protein NMR are 41, 2H, 13C, 15N, and 170 with proton NMR (Jefson, 1988). The use of NMR methods for protein sequence and conformational studies was limited to the small proteins or peptides because high magnetic fields were required but not widely available to study larger molecules and it was very time consuming with the capability of instruments in the past. 

For pedagogical and practical reasons, this chapter treats only protons. 13C NMR spectrometry is treated in Chapter 5, and other useful nuclei are treated in Chapter 7. Chapter 6 is devoted to 2-D NMR. 

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. 

We have attempted in this brief chapter to introduce a few other useful nuclei and some examples of their spectra. The emphasis in this chapter is to utilize these spectra in combination with other spectra, especially other forms of NMR. We must concede that it is neither possible nor desirable to become experts on chemical shifts of these (or other) nuclei and their coupling constants. In making this concession, we can be comfortable with these four nuclei, and furthermore, we can easily broaden our outlook to other elements throughout the periodic table. 

With respect to the important question of whether the location of the nuclei was determined by the presence of such imperfections as dislocations and impurities, the authors did not rule out such possibilities, but stressed the fact that a variable number of nuclei on an element of surface can be produced by controlling the pressure of oxygen. Thus it is impossible with the present state of knowledge to use nuclei of this type to study imperfections and to draw conclusions about their number. 

As in similar cases, where different nuclides of the same element are discussed, the chemical shifts of Li and Li (in ppm) are identical because primary isotope effects can safely be neglected, scalar spin-spin coupling constants are related by the factor y( Li)/y( Li) = 2.64, and relaxation mechanisms as well as NMR linewidths differ. Nuclear properties which are important for Li NMR experiments are collected in Table 2, where data for the widely used nuclei H and as well as N and P, which are of interest in the present context, are included for comparison. Both Li and Li possess a quadrupole moment, Q, but that of Li is the smallest one known for any nucleus. Li ium-6 NMR is, therefore, not dominated by the quadrupole moment and Li has been termed an honorary spin-1/2 nucleus [11]. Long relaxation times may sometimes cause difficulties for Li NMR measurements and this has to be taken into account by choosing a sufficiently long relaxation delay between individual... 

Although not all useful nuclei contained in organic compounds have been fully explored from the chemical point of view it is as well to point out that nuclear magnetic resonance methods can be applied to study all atoms which make up organic molecules. The resonances of the following nuclei can be observed H1, H2 and H3 (Tiers, 1964) F19 Nu and N1B O17 C13 P31 S33 B10 and B11 and Si29 (Pople et al., 1959). Many of these nuclei are present in low natural abundance (Varian Associates, 1964) and some have, in addition to a nuclear magnetic moment, a nuclear electric quadrupole moment (Pople et al., 1959). 

Multinuclear NMR is potentially a very powerful technique for defining fully the coordination sphere of platinum anti-tumour drugs in solution and upon interaction with biomolecules. The properties of some useful nuclei are listed in Table 1. In our studies we seek information about the oxidation state of platinum usually Pt(II) or Pt(IV),... 

Most of the results given in the following sections were obtained using nuclei and chromatin fragments isolated from chicken erythrocytes (CE). Rat liver nuclei and chromatin, calf thymus and yeast nuclei were also used in some experiments for... 

Using Nuclei as a Matrix to Isolate Vesicles with Chromatin-Binding Activity... 

Althou most experiments clearly indicate that early after infection ribosomal EEA is the first species of ENA to be inhibited, experiments using isolated nuclei (21, 22) from mengovirus infected L-cells and EMC virus infected mouse plasmacytoma cells indicate that the polymerase II activity (responsible for heterogeneous nuclear ENA and mENA synthesis) is inhibited 1-2 hours before ENA polymerase I and III activities (responsible for rENA and 48 and 58 ENA synthesis, respectively). No difference in activity and relative proportions of the three ENA polymerases, however was found after infection using solubilized enzymes assayed in the presence of exogeneous DNA as template (2l). It is assumed that the inhibition in whole cells results from an initiation defect, since these measurements using nuclei and solubilized enzymes do not measure true initiation. 0 he explanation as to why polymerase II should be inhibited before polymerase I when rENA synthesis is clearly the first to be inhibited in whole cells remains to be worked out. 

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