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The basic methodology and development of the spin Hamiltonian method as well as the terminology and symbols used in EPR developed out of atomic spectroscopy. Therefore it is useful to review how atomic spectroscopy of atoms and ions dealt with the Zeeman effect, which is the effect of a magnetic field on atomic spectra. This is all covered in the classic work by Herzberg [1].

Zero field NMR serves as the solution to a diverse grouping of very specific problems in solid state magnetic resonance. For some systems large magnetic fields interfere with the interesting phenomenon. In other cases high sensitivity may be achieved, paradoxically, not in high field but only where nuclear spins are transported from high to very low fields and back. And, finally, zero field NMR is of potential interest where the spectral resolution of dipole-dipole couplings and/or quadrupole couplings is limited by the broadening introduced to the spectrum when these nuclear spin interactions are observed in the presence of a large magnetic field. These couplings can be represented in their full form as H d = − Σ l < k ω l k d [ 3 ( I l ⋅ r l k ) ( I k ⋅ r l k ) r l k 2 − I l ⋅ I k ]

NMR studies of organoboron compounds usually deal with ^1H, ^13C, and ^11B nuclei, and with few exceptions focus on solutions [1–5]. The presence of the quadrupolar 11B isotope (natural abundance 80.42%; I = 3/2) can be exploited in several ways.

The NMR spectroscopic characterization of organogermanium compounds is based almost entirely on ^1H and ^13C NMR measurements in the usual way.

NMR studies of organotin compounds in solution deal in most cases with ^1H, ^13C, and ^119Sn nuclei. In some fields of organotin chemistry, solid-state ^119Sn NMR measurements become increasingly important [1]. The fact that both ^119Sn (8.58%) and ^117Sn (7.61%) are spin-1/2 nuclei with appreciable natural abundance (in contrast to ^115Sn: 0.35%; I = 1 /2), and that they are fairly sensitive toward the NMR experiment (factors 25.7 and 19.2 relative to ^13C!) creates an attractive situation for 119Sn NMR measurements [2–6], in particular if the molecules in question contain two or more tin atoms.

Oxygen offers several advantages as a paramagnetic reagent. Picosecond electron spin-lattice relaxation times, the absence of charge, and a rapid diffusion rate in water and membrane interiors, mean that oxygen is both an effective paramagnetic shift reagent (^19F or ^13C NMR applications) or spin-lattice relaxation agent (applications involving high gamma nuclei, such as ^19F and ^1H). Moreover, oxygen is well known to possess a marked solubility gradient along the immersion depth axis in lipid bilayers and detergent micelle systems. The consequent paramagnetic gradients (both in terms of spin-lattice relaxation rates and contact shifts) can be used to discern immersion depth of membrane additives (membrane peptides, drugs, or lipids). In studies of transmembrane α-helical and β-strand proteins, oxygen paramagnetic effects are used to discern information on protein topology. Applications involving studies of water-soluble proteins are also reviewed. Oxygen permeation in heme proteins, local preferences for oxygen on protein surfaces, or binding interfaces in protein-protein complexes may be uniquely studied using either chemical shift perturbations or spin-lattice relaxation rate enhancements.

Lysozymes (LYSs) are antibacterial enzyme, β- N -acetylmuramyl-hydrolase, that disrupts a glycosidic bond of the polysaccharide that is found in the cell walls of many bacteria. A number of LYSs are found in nature; in mammalian milk, tears, and egg white. The most common animal LYS is the c type, such as the chicken egg white lysozyme (EWL, 14.3 kDa), found in animal, insects, and plants [1]. LYS and α-lactalbumin (α-LA) have undoubtedly evolved from a common ancestor because of the similarity of their amino acid sequences (Figure 1) [2]. α-LA, which is a major milk component of milk whey, is a calcium-binding metalloprotein [3]. It is the so-called B component of lactose synthase and acts as a specificity modifier of galactosyltransferase to convert it to lactose synthase. The original discovery of its calcium-binding property was made when an effect of ethylenediaminetetracetic acid (EDTA) on the conformational stability of bovine α-LA was demonstrated. Then, a microanalytical method has been developed using high-performance gel-filtration chromatography together with the use of a calcium-specific fluorescent reagent [4]. Binding constants of a calcium ion to calcium-binding LYSs and bovine α-LA are 10^6-7 M^-1 [5].

Solid-state NMR has long been utilized to study biomolecular structure and dynamics ranging from applications to protein complexes [1] and nucleotides [2] to membrane proteins [3–5] and protein fibrils [6]. In the case of macroscopically oriented membrane peptides, solid-state NMR furthermore has provided structural constraints to assemble three-dimensional (3D) membrane protein structures (see Ref. [7] for a recent review). Under magic angle spinning (MAS) [8], structural investigations were focused for a long time on the determination of local structural parameters. Recently, substantial progress has been made in NMR methodology, instrumentation, and sample preparation that now permits 3D molecular structure determination under MAS from one or a limited set of NMR samples. These approaches will be discussed in the context of this chapter. The interested reader is also referred to a series of recent review articles [9–11].

NMR is a convenient tool for investigating a wide domain of polymeric properties whether investigations deal with thermodynamics or with chain dynamics. Considering here low-resolution NMR of protons attached to chains, measurements can be performed using low-cost equipment. Main magnetic interactions involved in proton relaxation in polymers are dipole-dipole interactions; for example, the magnetic interaction strength of two protons located on a methine group (-CH_2) is 10^5 rad/s in pulsation units. This interaction strength serves as a reference for characterizing dynamic polymeric properties: whether or not they are isotropic, random segmental motions detected from NMR are necessarily characterized by correlation times shorter than about 10^-5 s [1]. The spin system response exhibits an axial symmetry; the longitudinal (spin-lattice) relaxation is induced by a quasi-resonant exchange of energy between the spin system and the molecular thermal bath and is sensitive to friction effects which occur around the Larmor frequency (10^8 rad/s) whereas the proton transverse (spin-spin) relaxation mainly reflects quantum phase coherences of nuclear spins and is sensitive to deviations from isotropic random rotations of monomeric units in networks. Although they were not observed during polymer flow NMR properties are closely related to the linear viscoelastic behavior of polymers.

Ethylene copolymers are a large group of polymer material with a lot of industrial applications [1]. They usually consist of two types of monomers. One is the ethylene unit and the other one is the comonomer unit like methyl methacrylate, vinyl acetate, vinyl alcohol, etc. These two monomer units distribute, randomly in most cases, along the polymer chain, forming ethylene segments with different length. Once the length of some ethylene segments exceeds a critical value, i.e. the so-called minimum crystallizable sequence length at a certain temperature [2], these segments tend to aggregate and form crystals, while the segments with the length smaller than the minimum crystallizable sequence locate in the amorphous region. The comonomer units, which often lack the ability of crystallization, are either expelled from the crystals or embedded in the crystals as defects when the volume of the comonomer unit is small. Similar to other semicrystalline polymers, the bulk samples of ethylene copolymers usually comprise the crystalline, the amorphous, and the interfacial region, which lies between the crystalline and amorphous regions. The structures and the dynamics of these different morphological regions, which have large impact on the macroscopic properties of the material, have been the topics with a lot of research interests.