Key principles of NMR

This section deals with basic quantum mechanical theory in NMR. For some readers, this may be surplus to requirements. However, in our view, an appreciation of the quantum mechanical theory behind NMR spectroscopy is essential in order to understand the subsequent principles of biological NMR spectroscopy. So unless the reader is truly familiar with the quantum level NMR theory, please read on  

The inherent magnetic field strength associated with any given spin state is represented by a magnetic moment, //.z, that is proportional to the component of spin angular momentum, /z, which each spin state projects upon the reference z-axis, defined above as the direction of the externally applied magnetic field. Since spin angular momentum is quantised in terms 

Magnetic moment relates directly to the allowed z-axis component of angular momentum of any given spin state of a nucleus according to 

The energy differences between different spin states are created by the differential way in which the magnetic moments of given spin states interact with the applied magnetic field, Bz. The interaction energy attributable to any given spin state, Em, is defined by the product given in 

Isotope Spin (1) Natural Abundance (%) 10 X y rad Relative sensitivity NMR frequency (vl) at 2.35 T (field strength) 

---

Abstract The principle of chromatographic NMR, a version of NMR diffuso-metry devised for a facilitated study of mixtures using the addition of a selectively retarding agent, is illustrated. The technical requirements for acquiring exploitable H NMR diffusometry spectra for a heterogeneous solution/solid mix are described. Applications of the technique to test mixtures for several choices of solvents/ interacting phase are reviewed. Key Words Mixtures, Porous materials, Diffusion, HRMAS, DOSY. 

The key challenge for the successful use of NMR velocity-imaging techniques to characterize fluid flow properties is the interpretation of the measured parameters. Different experimental strategies provide information about flow processes at different spatial and dynamic scales in porous media. In principle, the flow velocity can be probed either as a local quantity with an image resolution below the pore level,2425 or as a macroscopic flow property corresponding to local volume and temporal averages of fluid molecular displacements.26 One must develop a suitable methodology to correctly determine the parameters that best describe the properties of interest. 

An MRI scanner is an NMR machine large enough to accommodate a human being, has a powerful magnet, operates in the pulse-FT mode, and detects protons—usually the protons in water and, to a lesser extent, lipids. The principles are the same as those of conventional FT-NMR spectroscopy but, because the goal is different, the way the data are collected and analyzed differs too. Some key features of MRI include ... 

This chapter reviews all aspects of the 2D NMR of relaxation and diffusion. Firstly, numerous pulse sequences for the 2D NMR and the associated spin dynamics will be discussed. One of the key aspects is the FLI algorithm and its fundamental principle will be described. Applications of the technique will then be... 

In principle there is no label, if not set by the user, to identify the given DISNMR file as an FID or spectrum, or if the NMR data is from a H or C experiment. However the Bruker automation software, primarily developed to connect older type spectrometers (AC, AM) to a sample changer, allows the user to structure the name in such a way that it carries additional information with respect to the type of experiment. The user is referred to the corresponding automation manual available from Bruker and to the name conventions set by the key NMR operator at your site. 

A bit of explanation is required here for those readers unfamiliar with the condensation concept, a key notion to describe polyelectrolytes. Consider as here a polyanion. If the charges are brought closer to one another, on the average, below a critical distance their mutual repulsion is such that — in order to continue to obey first principles electrostatics such as the Poisson equation — they screen themselves with an atmosphere of counterions. This atmospheric condensation, which can coexist with ionic binding at the individual sites, boosts the local concentration of counterions in the space surrounding the polyelectrolyte by as much as three orders of magnitude. The nmr measurements analyzed here focus on these water hydration molecules coordinated to condensed sodium counterions, next to the surface of the tactoids (see Fripiat s chapter). 

Fig. I The typical metabolomics workflow has three key steps the isolation of metabolites, detection of the metabolites, and data analysis. The isolation step is typically determined by the class of metabolite being measured because of the physicochemical properties of different metabolite classes (i.e., hydrophobic, hydrophilic), which require different enrichment protocols. Two principle methods for metabolite detection are NMR- and MS-based methods. Finally, the data analysis can be performed in a variety of ways depending on the problem...

While mass spectrometry cannot provide the detailed structural information that is obtained by NMR and X-ray crystallography, it can, in principle, provide valuable information on the formation and stoichiometry of nonco-valent complexes. There are several key questions that need to be addressed before we can decide whether the advantages of mass spectrometry (sensitivity, speed, and specificity) can be successfully applied to the study of nonco-valent interactions. These questions are... 

---