Nuclear magnetic resonance background

The aim of this text is to introduce the fascinating topic of the hyphenation of chromatographic separation techniques with nuclear magnetic resonance spectroscopy to an interested readership with a background either in organic, pharmaceutical or medical chemistry. The basic principles of NMR spectroscopy, as well as those of separation science, should previously be known to the reader. 

The reader is referred to articles by Barrow,12 Garson,1314 and Moore15 for background information on the field of marine secondary metabolite biosynthesis. Early work in this field used radiochemical tracers such as 14C or 3H recently, studies with 13C have proved popular because of the ease of detection of this stable isotope by nuclear magnetic resonance (NMR). In particular, our understanding of marine microbial biosynthesis and of de novo biosynthesis in marine molluscs has progressed significantly as a consequence of the use of 13C-labeled precursors. 

The focus of this edition remains the same as that for the first, namely, to make electrochemistry an attractive, useful characterization methodology for chemists [comparable to infrared (IR), nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS)]. The goal is to outline the basic principles and modem methodology of electrochemistry in such a way that the uninitiated may gain sufficient background to use electrochemical methods for the study of chemical systems. Thus chemical problems that are amenable to an electrochemical approach are introduced as representative examples. 

In this chapter, we lay the background for nuclear magnetic resonance in general and proceed to develop proton NMR. The objective is the interpretation of proton... 

We discuss briefly some basic topics in materials physics such as crystallography, lattice vibrations, band structure, x-ray diffraction, dielectric relaxation, nuclear magnetic resonance and Mossbauer effects in this chapter. These topics are an important part of the core of this book. Therefore, an initial analysis of these topics is useful, especially for those readers who do not have a solid background in materials physics, to understand some of the different problems that are examined later in the rest of the book. 

Virtually, all students of chemistry, biochemistry, pharmacy and related subjects learn how to deduce molecular structures from nuclear magnetic resonance (NMR) spectra. Undergraduate examinations routinely set problems using NMR spectra, and masters and doctoral theses describing novel synthetic or natural products provide many examples of how powerful NMR has become in structure elucidation. Existing texts on NMR spectroscopy generally deal with the physical background of the newer and older techniques as well as the relationships between NMR parameters and chemical structures. Very few, however, convey the know-how of structure... 

A number of nuclear magnetic resonance (NMR) textbooks and review articles that focus on the dynamics in supercooled liquids comprised of organic molecules [2,11,12,15], on polymer specific dynamics [71-75], and on ionic or inorganic glasses [76-79] exist. In these contributions, the theoretical background of NMR techniques and models of molecular motion have been comprehensively discussed. Therefore, we curtail the theoretical part and concentrate on selected NMR techniques applied most frequently to the investigation of molecular glass formers. 

An extremely sensitive technique able to detect the nature of radical pairs in a photochemical reaction is called chemically induced dynamic nuclear polarization (CIDNP), which depends on the observation of an enhanced absorption in a nuclear magnetic resonance (NMR) spectrum of the sample, irradiated in situ, in the cavity of a NMR spectrometer. The background to and interpretation of CIDNP are discussed by Gilbert and Baggott (28). 

The natural stable isotope of fluorine, fluorine-19 (19F), with a spin of one-half and a chemical shift range of around 300 ppm, is a sensitive and useful probe in nuclear magnetic resonance (NMR) studies. Fluorine substitution may be a very effective method for studying the fate of bioactive molecules. Since there are few natural fluorinated materials to create background signals, the analyses are freed from the complications often associated with proton NMR spectroscopy (65). An artificially prepared useful short-lived isotope, fluorine-18 (18F), decays by positron emission. Positron emission tomography (PET) is an especially useful non-invasive... 

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