Applications of NMR Spectroscopy

Polyphenols have been recognized as one of the largest and most widespread groups of plant secondary metabolites with marked antioxidant properties as well as recently recognized specific biological properties associated with prevention of chronic diseases such as cardiovascular disease, various cancers and type II diabetes. Within plant kingdom, over 50,000 of structurally diverse polyphenols are present, and their characterization stands as a challenge. In recent years, renewed interest in extraction, isolation and identification of polyphenols especially flavonoids from plant sources have become the core research in food chemistry, pharmacognosy and modern medicinal biochemistry. The NMR spectroscopy, which provides a rapid and nondestructive method for profiling of polyphenols by identification of the characteristic structural features through structural assignments, has been addressed in this chapter.

Magnetic resonance imaging (MRI) has become the imaging modality of choice for most questions in neuroradiology. However, MR spectroscopy (MRS) has been used in both in vitro and in vivo long before the wide distribution of MRI in a clinical setting. The techniques are similar as a RF pulse with Larmor frequency is used to excite the hydrogen nuclei, in MRS, however, there is no read-out gradient. Instead of acquiring the spatial information of a probe, the frequency information is used to identify different chemical compounds. The different peak intensities change according to the molecular composition of the sample, which may be different depending on the underlying disease. This provides different information about basic metabolic processes, such as energy metabolism, neuronal integrity, cell proliferation and degradation and necrotic changes in the tissue. The scope of this chapter is to give an overview on the physical background of the technique and typical clinical applications of MRS, such as brain development, noxa during pregnancy, developmental delay, mitochondrial disorders, leukodystrophias, neurodegenerative diseases, infections, stroke and brain tumors.

Nuclear magnetic resonance (NMR) is a well-established analytical method used for qualitative and quantitative analyses in various areas and applications. It utilizes a phenomenon where nuclei of a certain atom is resonating at a specific secondary oscillating magnetic field under a strong static magnetic field. The energy absorbed during resonance is highly specific and governed by the micro magnetic environment of the nuclei. During the early stage of development, NMR analyses were performed in laboratory by placing the sample of interest inside a strong stationary magnet. Then it followed by monitoring the absorption frequency occurred on the secondary radio-wave directed to the sample. In order to obtain high resolution in the absorption frequency, high magnetic field is required and often generated using superconductor wire surrounded with cooling coils. Although the configuration produces accurate results, the instrument is rather large, heavy, and non-portable. This has made the practical utilization less possible for on-site applications or for samples having sizes larger that the core of the permanent magnet. Continuous development based on the fundamental principle of NMR has resulted in great advancement in hardware and the detection sensitivity. One of the most remarkable achievements will be the development of portable NMR-based sensors. This class of sensor is far more flexible due to its smaller size and suits on-site in situ measurements. Furthermore, such sensors are cheaper to develop and less costly to maintain as compared to the conventional instruments. However, the sensors have lower resolution as due the weaker magnetic field generated from smaller permanent magnets. Despite this, the results recorded are still significantly useful. Data analysis and optimization of the sensor configuration can be employed to achieve better resolution. For instance, the NMR-MOUSE is one of the portable NMR-based sensor types that can be used for bio-imaging and characterization of polymers. This chapter discusses some fundamental developments of the portable NMR-based sensors and its practical application in the field of medical diagnosis. Future prospects and challenges faced in this area are highlighted.

NMR spectroscopy is the most versatile technique for the investigation of structural and dynamic aspects of biological molecules and their interactions in solution. In addition, recent advances in the NMR instrumentation and methodology have allowed to overcome problems relating to macromolecule size and have made NMR a very feasible technique also for the investigation of highly dynamic, partially inhomogeneous molecules and heterogeneous complexes.

NMR has been widely employed to study molecular interactions that take place between biomacromolecules and their ligands at different levels of complexity. The characterization of the fine structural details of the recognition processes is essential to understand fundamental mechanisms underlying phenomena of biological and biomedical relevance and can be exploited for the rational design of new therapeutic and diagnostic strategies. In fact, ligands can be represented both by macromolecules, such as other proteins, nucleic acids or lipids, and small molecules (MW less than 1000 kDa), such as allosteric effectors, cofactors, substrates and their analogues, drugs.

Depending on the complex features, the interaction strength and the chemical nature of the interacting species, different experimental approaches can be chosen.

In this chapter we will describe the most important NMR techniques developed to study molecular recognition processes involving proteins and nucleic acids also focusing on their application to drug discovery and development. The most significant examples provided in literature will be also reported in details.

Recent advances in the field of structural biology, with relatively new biophysical techniques such as solid-state nuclear magnetic resonance that holds promise for determining the structures of peptides and proteins located within the cell membrane, facilitate the collection of data on the atomic structures of the biological molecules. Classical methods such as X-ray diffraction (XRD) and liquid-state NMR spectroscopy suffer from difficulties in crystallizing functional proteins in membrane environments (XRD) or too slow molecular motion for averaging of anisotropic nuclear spin interactions (liquid-state NMR) [1]. These problems have motivated the search for alternative methods such as solid-state NMR (SS-NMR). In the solid state NMR, the nuclear spin interactions are typically governed by anisotropic (orientation dependent) components in addition to the isotropic (orientation independent) components known from liquid-state NMR [2-4]. The method (SS-NMR) elucidates molecular structure and dynamics in systems not amenable to characterization by any other way. The importance of the technique stands in its ability to determine accurately intermolecular distances and molecular torsion angles. The technique has been used in systems including both microscopically ordered preparations such as membrane proteins, nanocrystalline proteins, amyloid fibrils, and also disordered or amorphous systems such as glasses. This chapter presents a view of algorithm formulation of structural biology with the mathematical foundation of the determination of protein structure from orientation constraints which highlight the solid-state NMR used as probe for the determination of peptide and protein structures. We also review the continuity conditions and torsion angles from solid-state NMR orientational restraints. Tools such as vector algebra, Gram matrices, and determinants, are used.