Nuclear magnetic resonance spectroscop structural information

Specinfo, from Chemical Concepts, is a factual database information system for spectroscopic data with more than 660000 digital spectra of 150000 associated structures [24], The database covers nuclear magnetic resonance spectra ( H-, C-, N-, O-, F-, P-NMR), infrared spectra (IR), and mass spectra (MS). In addition, experimental conditions (instrument, solvent, temperature), coupling constants, relaxation time, and bibliographic data are included. The data is cross-linked to CAS Registry, Beilstein, and NUMERIGUIDE. 

Mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy are techniques of structure determination applicable to all organic molecules. In addition to these three generally useful methods, there s a fourth—ultraviolet (UV) spectroscopy—that is applicable only to conjugated systems. UV is less commonly used than the other three spectroscopic techniques because of the specialized information it gives, so we ll mention it only briefly. 

Structural investigations into the degree of branching and into the position and nature of glycosidic bonds and of non-carbohydrate residues in polysaccharides may include periodate oxidation and other procedures such as exhaustive methylation. X-ray diffraction and spectroscopic techniques such as nuclear magnetic resonance and optical rotatory dispersion also give valuable information especially relating to the three-dimensional structures of these polymers. 

Nuclear magnetic resonance (NMR) spectroscopy In NMR technique, a sample is placed in a magnetic field which forces the nuclei into alignment. When the sample is bombarded with radiowaves, they are absorbed by the nuclei. The nuclei topple out of alignment with the magnetic field. By measuring the specific radiofrequencies that are emitted by the nuclei and the rate at which the realignment occurs, the spectroscope can obtain the information on molecular structure. 

The hyphenation of capillary electromigration techniques to spectroscopic techniques which, besides the identification, allow the elucidation of the chemical structure of the separated analytes, such as mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR) has been widely pursued in recent years. Such approaches, combining the separation efficiency of capillary electromigration techniques and the information-rich detection capability of either MS or NMR, are emerging as essential diagnostic tools for the analysis of both low molecular weight and macromolecular compounds. 

Nuclear magnetic resonance (NMR) spectroscopy is the most widely used spectroscopic technique in synthetic chemistry [1], One main reason for the dominance of NMR is its versatility—by variation of only a few experimental parameters, a vast number of different NMR experiments can easily be performed, giving access to very different sets of information on the substance or the reaction under investigation. Today, NMR is dominant in structure elucidation, and in situ NMR spectroscopy can conveniently give insight into chemical reactions under real turnover conditions (in contrast to, e.g., x-ray crystallography, which can only provide a solid-state snapshot of a molecular conformation). 

Several spectroscopic techniques, namely, Ultraviolet-Visible Spectroscopy (UV-Vis), Infrared (IR), Nuclear Magnetic Resonance (NMR), etc., have been used for understanding the mechanism of solvent-extraction processes and identification of extracted species. Berthon et al. reviewed the use of NMR techniques in solvent-extraction studies for monoamides, malonamides, picolinamides, and TBP (116, 117). NMR spectroscopy was used as a tool to identify the structural parameters that control selectivity and efficiency of extraction of metal ions. 13C NMR relaxation-time data were used to determine the distances between the carbon atoms of the monoamide ligands and the actinides centers. The II, 2H, and 13C NMR spectra analysis of the solvent organic phases indicated malonamide dimer formation at low concentrations. However, at higher ligand concentrations, micelle formation was observed. NMR studies were also used to understand nitric acid extraction mechanisms. Before obtaining conformational information from 13C relaxation times, the stoichiometries of the... 

Due to the complexity of DOM fractionation has revealed more detailed information on the structural subunits prior to the application of advanced analytical methods. Most effective is the combination of different spectroscopic methods using UV-vis absorbance, fluorescence, 1H- and 13C-nuclear magnetic resonance, and Fourier transform-infrared (FT-IR) spectroscopy. In some studies, also electron paramagnetic resonance spectroscopy (EPR) is used (e.g., Chen et al., 2002). 

GAs of previously unknown structure have been fully characterized and their structure determined by a combination of chemical and spectroscopic methods. Proton Nuclear Magnetic Resonance (NMR) spectroscopy provides a great deal of structural information (1+). 13c NMR promises to be a very powerful technique for both structure determination and metabolism studies of GAs ( UO,Ul). Yamaguchi et al. ( Ug) used a combination of proton and 13c NMR to determine the structure of GA o (2 -hydroxy GAg), a minor metabolite of G. fujlkurol. 

The elucidation and confirmation of structure should include physical and chemical information derived from applicable analyses, such as (a) elemental analysis (b) functional group analysis using spectroscopic methods (i.e., mass spectrometry, nuclear magnetic resonance) (c) molecular weight determinations (d) degradation studies (e) complex formation determinations (f) chromatographic studies methods using HPLC, GC, TLC, GLC (h) infrared spectroscopy (j) ultraviolet spectroscopy (k) stereochemistry and (1) others, such as optical rotatory dispersion (ORD) or X-ray diffraction. 

In fact, a tremendous amount of information is available on the structures of biological macromolecules descriptions of structures of proteins and nucleic acids make up major portions of modern textbooks in biochemistry and molecular biology. The Protein Data Bank and the Nucleic Acid Database are online archives that contain sequence and structural data on thousands of specific molecules and complexes of molecules. This structural information comes from in vitro experiments, with structures inferred from the x-ray diffraction patterns of crystallized molecules, spectroscopic measurements using multi-dimensional nuclear magnetic resonance, and a host of other methodologies. 

As an analytical spectroscopic technique, EPR is similar in concept to the more widely used nuclear magnetic resonance (NMR) spectroscopy [see NMR Overview of Applications in Chemical Biology]. In fact, EPR and NMR are complementary to each other. Both techniques detect magnetic moments, hut NMR determines the chemical stmctures in solution, whereas EPR describes more precisely the electronic and chemical structures of a particular region of the biological system, such as electron transfer centers, metal ions, and an intermediate state of the enzyme or substrate. It is not possible to present a full description of the theory of EPR in an article with this scope. Therefore, only sufficient information is provided here to enable the readers to understand the practical aspects of this analytical tool in enzymology. 

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