Nuclear magnetic resonance spectroscopy fine structure

Wuthrich, K Protein structure determination in solution by nuclear magnetic resonance spectroscopy. Science 243 45-50, 1989. The most effective technique for determining protein fine structure in cases where x-ray diffraction cannot be used. 

XRF = X-ray fluorescence spectroscopy, XPS = X-ray photoelectron spectroscopy, AES = Auger electron spectroscopy, XANES = X-ray absorption near edge spectroscopy, RAIR = Reflectance-absorbance infrared spectroscopy, EXAFS = X-ray absorption fine-structure spectroscopy, ECR = Electric contact resistance, NMR = Nuclear magnetic resonance spectroscopy, IPS = Imaging photoelectron spectromicroscopy. 

TPR, Temperature-programmed reaction XPS, X-ray photoelectron spectroscopy IR, infrared spectroscopy H NMR, proton nuclear magnetic resonance spectroscopy UV-vis, ultraviolet-visible spectroscopy ESR, electron spin resonance spectroscopy TPD, temperature-programmed desorption EXAFS, extended X-ray absorption fine structure spectroscopy Raman, Raman spectroscopy C NMR, carbon-13 nuclear magnetic spectroscopy. 

Different characterization techniques are used to get an insight into the location of transition metal ions in an aluminophosphate framework. Generally, the data on the cation location are collected with difficulty since the metal concentration is low. In this regard, it is necessary to use more than one method if a reliable conclusion is to be reached (ie, the simultaneous application of several physical techniques is recommended). The following characterization methods are commonly applied diffuse reflectance UV-vis spectroscopy (DRS), electron spin resonance (ESR), electron spin echo modulation (ESEM), infrared (IR), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies, as well as the nuclear magnetic resonance spectroscopy (NMR), Mossbauer spectroscopy and the X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption spectroscopy for fine structure (EXAFS) (167,168) and references therein). 

A measurement method that is often used to determine the C-labeling of metabolites is 2D [ C. H] correlation nuclear magnetic resonance spectroscopy (COSY). This method yields relative intensities of multiplets in the NMR spectra that correspond to the relative amounts of groups of isotopomers in which the observed atom is C-labeled and the adjacent carbon atoms in the carbon backbone are either C-labeled or not (Szyperski, 1995). If the compound of which the labeling pattern is measured was synthesized by a microorganism growing on a mixture of uniformly C-labeled and naturally labeled carbon substrate, then the relative intensities of NMR fine structures can be calculated from the fractions of molecules that stem from one or more substrate molecule(s) in the feed medium. This is done using so-called probability equations (Szyperski, 1995) that require as input the fraction of uniformly C-labeled medium substrate and the fraction of naturally C-labeled carbon. 

Bentley and his colleagues7 describe the structure-activity relationships of a wide variety of structures derived from Diels-Alder adducts of thebaine. Among this group are found some of the most potent analgesics known. Particular attention should be directed toward the fine application of nuclear magnetic resonance spectroscopy, by Fulmor and his associates to elucidate the stereochemical configurations of these interesting compounds. 

For bulk structural detemiination (see chapter B 1.9). the main teclmique used has been x-ray diffraction (XRD). Several other teclmiques are also available for more specialized applications, including electron diffraction (ED) for thin film structures and gas-phase molecules neutron diffraction (ND) and nuclear magnetic resonance (NMR) for magnetic studies (see chapter B1.12 and chapter B1.13) x-ray absorption fine structure (XAFS) for local structures in small or unstable samples and other spectroscopies to examine local structures in molecules. Electron microscopy also plays an important role, primarily tlirough unaging (see chapter B1.17). 

In general, several spectroscopic techniques have been applied to the study of NO, removal. X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) are currently used to determine the surface composition of the catalysts, with the aim to identify the cationic active sites, as well as their coordinative environment. 

As indicated in the previous discussion, Mossbauer spectroscopy provides information that when coupled with results using other structural techniques assists in determining the structure of the complex under analysis. The relationships between the various techniques are summarized in Table II. The Mossbauer chemical shift provides information about the 4 electron contribution to the bond between the metal and the ligands in a complex. Similar estimates can be obtained from the results of measurements on the fine structure in the x-ray absorption edge and nuclear magnetic resonance data. The number of unpaired electrons can be evaluated from magnetic susceptibility data, electron spin resonance, and the temperature coeflScient of the Mossbauer quadrupole splitting (Pr). 

Figure 1.1 The electiomagnetic spectrum, showing the different microscopic excitation sources and the spectroscopies related to the different spectral regions. XRF, X-Ray Fluorescence AEFS, Absorption Edge Fine Structure EXAFS, Extended X-ray Absorption Fine Structure NMR, Nuclear Magnetic Resonance EPR, Electron Paramagnetic Resonance. The shaded region indicates the optical range.

Spectroscopy produces spectra which arise as a result of interaction of electromagnetic radiation with matter. The type of interaction (electronic or nuclear transition, molecular vibration or electron loss) depends upon the wavelength of the radiation (Tab. 7.1). The most widely applied techniques are infrared (IR), Mossbauer, ultraviolet-visible (UV-Vis), and in recent years, various forms ofX-ray absorption fine structure (XAFS) spectroscopy which probe the local structure of the elements. Less widely used techniques are Raman spectroscopy. X-ray photoelectron spectroscopy (XPS), secondary ion imaging mass spectroscopy (SIMS), Auger electron spectroscopy (AES), electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopy. 

Thanks to the extensive literature on Aujj and the related smaller gold cluster compounds, plus some new results and reanalysis of older results to be presented here, it is now possible to paint a fairly consistent physical picture of the AU55 cluster system. To this end, the results of several microscopic techniques, such as Extended X-ray Absorption Fine Structure (EXAFS) [39,40,41], Mossbauer Effect Spectroscopy (MES) [24, 25, 42,43,44,45,46], Secondary Ion Mass Spectrometry (SIMS) [35, 36], Photoemission Spectroscopy (XPS and UPS) [47,48,49], nuclear magnetic resonance (NMR) [29, 50, 51], and electron spin resonance (ESR) [17, 52, 53, 54] will be combined with the results of several macroscopic techniques, such as Specific Heat (Cv) [25, 54, 55, 56,49], Differential Scanning Calorimetry (DSC) [57], Thermo-gravimetric Analysis (TGA) [58], UV-visible absorption spectroscopy [40, 57,17, 59, 60], AC and DC Electrical Conductivity [29,61,62, 63,30] and Magnetic Susceptibility [64, 53]. This is the first metal cluster system that has been subjected to such a comprehensive examination. 

The spectroscopic techniques described in this section include IR, Raman, and UV-visible spectroscopy, nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. Techniques based on particle scattering, transitions in the nucleus, and radioisotope techniques that produce radiation that is a measure of the chemical environment are described in Sections IV.B and C. Some of these techniques, such as IR and UV-visible spectroscopy, have been applied to studies of catalysts for more than 30 years, whereas others, such as EXAFS, are relatively new to catalytic studies. 

Among the techniques ideally suited for in situ studies are infrared, Raman, and nuclear magnetic resonance (NMR) spectroscopies and extended x-ray absorption fine structure (EXAFS). While still relatively new, the scanning tunneling and atomic force microscopes are expected to play an increasingly important role in catalyst characterization. Both instruments permit visualization of a catalyst surface at the atomic level and hold the potential of showing how atoms and molecules interact with a surface. 

Although they may be part of a catalyst testing [1-3] programme, investigations focused on revealing the reaction mechanism, such as in-situ Fourier transform infrared (FTIR) in transmission or reflection mode, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), X-ray absorption fine-structure spectroscopy (EXAFS), X-ray photoelectron spectroscopy (XPS), electron microscopy (EM), electron spin resonance (ESR), and UV-visible (UV-vis) and the reaction cells used are not included. For the correct interpretation of the results, however, this chapter may also provide a worthwhile guide. 

Another contribution to variations of intrinsic activity is the different number of defects and amount of disorder in the metallic Cu phase. This disorder can manifest itself in the form of lattice strain detectable, for example, by line profile analysis of X-ray diffraction (XRD) peaks [73], 63Cu nuclear magnetic resonance lines [74], or as an increased disorder parameter (Debye-Waller factor) derived from extended X-ray absorption fine structure spectroscopy [75], Strained copper has been shown theoretically [76] and experimentally [77] to have different adsorptive properties compared to unstrained surfaces. Strain (i.e. local variation in the lattice parameter) is known to shift the center of the d-band and alter the interactions of metal surface and absorbate [78]. The origin of strain and defects in Cu/ZnO is probably related to the crystallization of kinetically trapped nonideal Cu in close interfacial contact to the oxide during catalyst activation at mild conditions. A correlation of the concentration of planar defects in the Cu particles with the catalytic activity in methanol synthesis was observed in a series of industrial Cu/Zn0/Al203 catalysts by Kasatkin et al. [57]. Planar defects like stacking faults and twin boundaries can also be observed by HRTEM and are marked with arrows in Figure 5.3.8C [58],... 

P. aer. = Pseudomonas aeruginosa A. den. = Alcaligenes denitrificans MCD = magnetic circular dichroism EPR = electron paramagnetic resonance XAS = X-ray absorption spectroscopy NMR = nuclear magnetic resonance EXAFS = extended X-ray absorption fine structure. 

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