Chemical shift analysis

Sensitivity of chemical shift analysis is determined by the spectral resolution of the XPS system. The resolution of a typical XPS system without a monochromator is 1.0 eV. This corresponds to the intrinsic line width of Al Ka or Mg Ka radiation. The analysing system contributes only little to the overall resolution. This resolution is sufficient to determine the binding energies of most core levels within 0.1 eV. Considerable improvement of the resolution down to 0.3 eV can be achieved by use of a monochromator. The higher resolution has to be paid for by a loss in intensity which, however, is no problem in modern instruments. 

Sophorine was isolated from Sophora alopecuroides (26). The nature of MS decay showed that sophorine is a quinolizidine alkaloid of the lupinine type. The IR spectrum suggests the presence of a franj-quinolizidine moiety (2675-2945 cm ) and an — NH—CO— group (1605 and 1683 cm ). On the basis of chemical shift analysis and signal multiplicity of H- and C-NMR spectra as well as biosynthetic considerations, structure 59 was proposed for sophorine. 

Figure 6 Chemical Shift Analysis of Cyclic p-sheet Peptides1 21...

Homans et al. [150] have analyzed the conformations of bisected structures by measuring the coupling constants 3J5 6. and 3J5 6. They conclude from a chemical shift analysis that the conformation of the 06 of the pentasaccharide is... 

Fig. 28. Conformations around the glycosidic bonds of aminoglycoside antibiotics as proposed on the basis of 13C-NMR chemical shift analysis...

Wishart, D. S and Nip, A. M. (1998) Protein chemical shift analysis a practical guide, Biochemistry and Cell Biology 76, 153-163. 

Timberlake and coworkers have studied the degenerate rearrangement of pentacyclo-propylethyl cation 56 (involving 1,2-cyclopropyl shifts) under long-lived stable ion conditions (equation 39a). The rearrangement could not be frozen even at -80 °C. However, additivity of NMR chemical shift analysis indicates the classical trivalent nature of the... 

From H-NMR spectra of l,2-dithiole-3-thiones and l,2-dithiol-3-ones it was not possible to draw conclusions concerning the pseudoaromatic character of the l,2-dithiole-3-thione system.277 Proton chemical shifts of methyl substituents are in agreement with values reported for methyl substituents in aromatic systems.278 Calculated diamagnetic and paramagnetic anisotropies for a series of l,2-dithiole-3-thiones and l,2-dithiol-3-ones have been compared with observed chemical shifts. Analysis of these data suggests that a phenyl substituent in position 5 is nearly coplanar with the dithiole nucleus and that the 1,2-dithiole nucleus is an electron-attracting group. ... 

Applying the additivity of chemical shift analysis to the 2-norbornyl cation also supports the nonclassical bridged nature of the ion. The chemical shift difference of 168 ppm between 2-norbomyl cation (C7H11+) and its parent hydrocarbon norbornane 129 is characteristic of the <200 ppm difference observed between a nonclassical ion and its parent hydrocarbon. In contrast, an ordinary classical trivalent carbocation such as the cyclopentyl cation (75) reveals a chemical shift difference of >360 ppm (between the ion and the parent hydrocarbon, cyclopentane). This is consistent with the 350ppm difference characteristic of classical carbocations and their precursor hydrocarbons. 

The model monosaccharides just listed were prepared from common precursor IV.l (Scheme 39), which was readily obtained by azidonitration of 3,4,6-tri-O-acetyl-D-galactal followed by deacetylation with sodium methoxide. Treatment of IV.l with acetone and toluene p-sulfonic acid monohydrate at room temperature led to predominant formation of the thermodynamically favored 3,4-O-isopropylidene (IV.2) in 61% yield while also producing 27% of the 4,6-O-isopropylidene derivative IV.3. The position of the isopropylidene IV.2 was verified by the use of NMR chemical shift analysis to confirm the position of the acetate group in the resultant acetylated adduct IV.4. Synthesis of the 4-O-sulfate derivative (IV.7) from IV.2 utilized a step that differentiated the 3-OH and 4-OH positions after benzylation and de-isopro-pylidination of IV.2, a selective methylation at the 3-OH of diol IV.5 was achieved via a tin procedure [91] to give methyl glycoside IV.6. Conversion of the azide into... 

Unfortunately, even in moderately complex organic solids, overlapping spectral features make chemical shift analysis of ID MAS spectra nearly impossible. In this case several approaches have been suggested for separating the isotropic and anisotropic parts of the spectra. 

In order to further characterize the key role of the 4 -amino group of ThDP for cofactor activation, the influence of the chemical environment at the active site of pyruvate decarboxylase from Zymomonas mobilis on the electronic properties of the 4 -amino group was studied by two-dimensional proton-nitrogen correlated NMR spectroscopy (Tittmann et al., 2005a). Chemical shift analysis and its pH dependence indicate that the acceleration of C2 deprotonation by 5 orders of magnitude is not mainly of thermodynamic nature caused by a significant increase in basicity... 

Evidence has also been recently obtained by NMR chemical shift analysis on the interaction of calcium-activated S100B and target proteins CapZ (74) and p53 (75). Here again, there are differences in the reported binding sites on S100B, which may be due to differences in the binding peptides. 

Fig. 56. Ingredients of the 3D homology-modelling program. The experimental dipolar couplings of the amides as well as the information about the secondary structure as derived from the chemical-shift analysis is used as experimental input. The pdb data bank is used in addition. Alignment of sec-ondary-stmcture elements while optimizing the fit of the dipolar couphngs yields the scoring function for the homology fitting.

Alonso et al. (2002) used a combination of H self-diffusion measurements and C chemical shift analysis to study the solubilization of amphiphilic additives C H, +iX (n=4, 6 X=OH, NHj) in cetyltrimethylammonium bromide (CTAB) micelles that provided complementary data on structures of micelles and conformations of alkyl chains. All the additives studied behave as cosurfactants affecting micellar structures and the degree of their solubilization was determined solely by their alkyl chain length. For different additives, the effects depend on cosurfactant penetration into micelles. 

Schleyer PvR, Manoharan M, Wang Z-X, Kiran B, Jiao H, Puchta R, Hommes NJRVE (2001) Dissected nucleus-independent chemical shift analysis of n-aromaticity and antiaromaticity. Org Lett 3 2465-2468... 

Schleyer, P.V.R. Manoharan, M. Wang, Z. Kiran, X.B. Jiao, H. Puchta, R. Eikema Hommes, N.J.R. Dissected nucleus-independent chemical shift analysis of pi-aromaticity and antiaromaticity. Org. Lett. 2001,3, 2465. 

A novel crystalline form of the boron-containing antibacterial drug (5 )-3-(aminomethyl)-7-(3-hydroxypropoxy)benzo[c][l,2]oxaborol-l(3H)-ol hydrochloride has been studied by solid-state NMR and single-crystal X-ray diffraction techniques. After determination of the crystal structure by X-ray diffraction, solid-state NMR spectroscopy of this form is performed to obtain structural information using experimental approaches based on dipolar correlation, chemical shift analysis, and quadrupolar interaction analysis. solid-state NMR experiments at 16.4 T using MAS and homonuclear dipolar decoupling, 2D solid-state NMR experiments based on and dipolar heteronuclear correlation, and DFT... 

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