Spectral simplification

Ease of manipulation of nuclear spin Hamiltonians (spectral simplification)... 

The spectrum simplification in the SEA-TROSY (Fig. 21.2) is dramatic, as is also evident from the ID traces taken from a crowded region of the spectra. The SEA-TROSY spectrum (Fig. 21.2) exhibits a loss in signal-to-noise ratio by a factor of only 0.7 on average. This small loss, however, is largely compensated for by the spectral simplification achieved. The cross-peak intensity is modulated by Eq. (1), so that a best compromise between spectral simplification and signal-to-noise ratio can be empirically derived by com-... 

Hager, J. W. (2003). Product ion spectral simplification using time-delayed fragment ion capture with tandem linear ion traps. Rapid Commun. Mass Spectrom. 17 1389-1398. 

Cross-polarization in tilted frame has been proposed.275 In this scheme, the two effective fields matching the Hartmann-Hahn condition have a large offset comparable to two RF fields. This method was named SPECIFIC CP (spectrally induced filtering in combination with cross-polarization Fig. 20) because the matching depends on the resonance offset of the involved nuclei. This method is clearly useful for spectral simplification, as demonstrated in Fig. 21. Under fast spinning conditions, 7-coupling-mediated CP can be observed as shown by Verhoeven et al.216... 

The three sequences shown in Fig. 19 demonstrate that the decrease of the specific surface area is accompanied by a dramatic decrease in intensity of the spectra and by a drastic spectral simplification. In particular, all bands in the 2120-1100 cm interval, attributed to species formed at very reactive three-fold and four-fold coordinated oxygen sites located on edges and steps (O4J) and on corners (Of ) are strongly affected by sintering and are nearly totally absent on MgO smoke (Fig. 19c). A similar effect was discussed in Section III.C for the H2 adsorption and splitting on the same MgO samples (Fig. 11) and on the chemistry of CO adsorbed on Mg sites (spectral region not reported in Fig. 19) (12,26,177). 

As described in previous reports, (1-3) all multiple resonance experiments (without noise modulation) can be used to determine chemical shifts indirectly even if the primary objective is spectral simplification, assignment, or a study of coupling constants. It must be remembered that the different applications of multiple resonance cannot necessarily be pursued independently and that in chemical shift determinations care must be taken, especially in complex spin systems, to ensure that the centre of the total spectrum and not of a subspectrum is found. 

One major advantage of using NMR spectroscopy to study complex biomixtures is that measurements can often be made with minimal sample preparation (usually with only the addition of 5-10% D2O) and a detailed analytical profile can be obtained on the whole biological sample. Hence, much effort has been expended in discovering efficient new NMR pulse sequence techniques for spectral simplification and water suppression especially for biofluids. ... 

The axial or equatorial positions of protons on a cyclitol ring (or of acetoxy methyl protons) may also be deduced from chemical-shift data. Geometric (or spectroscopic) proton equivalence produces characteristic spectral simplification, often serving to distinguish more symmetrical from less symmetrical configurations. Variable-temperature spectra are useful for studying equivalence due to time-averaging they reveal many other kinds of equilibria if these exist in the solution of the sample. " ... 

This spectral simplification, however, produces a serious drawback in signal assignments since valuable coupling information is destroyed. Thus, a variety of assignment methods have been developed some of which are introduced in this chapter. There are five main areas experimental NMR techniques, coupling constants, solvent effects, presence of auxiliaries and derivatization. 

These lanthanide complexes produce spectral simplifications in the NMR spectrum of any compound with a relatively basic pair of electrons (an unshared pair) which can coordinate with Eu ". Typically, aldehydes, ketones, alcohols, thiols, ethers, and amines all interact ... 

Even when Raman spectroscopy is used primarily as a means for the differentiation of polymorphs or solvates, the degree of spectral simplification associated with Raman data permits a more facile generation of band assignments. This feature has been successfully exploited in the cases of spironolactone [128], losartan [138], 3-(p-thioanisoyl)-l,2,2-trimethyl-cyclopentanecarboxylic acid [139], and tra 5-3,4-dichloro-A-methyl-A-[l,2,3,4-tetrahydro-5-methoxy-2-(pyrrolidin-l-yl)]-naphth-1 -ylbenzeneacetamide [ 140]. 

R. Tycko, G. Dabbagh, Double-quantum filtering in magic-angle-spinning NMR spectroscopy an approach to spectral simplification and molecular strucmre determination, J. Am. Chem. Soc. 113 (25) (1991) 9444—9448. 

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