TOCSY spectra

In Problems 41,43,45 and 50 we have recorded one-dimensional NOESY and TOCSY spectra (see Section 1.1.6.2 for details). 

The TOCSY spectra, as we have said above, contain enhancements connected with spin systems and not with distances. So the answers to the irradiation are different. You should be able to interpret them when you have solved the problem ... 

In principle, spin label effects can be observed in both homonuclear and heteronuclear spectra. When no isotope-enriched peptide is available, integration of TOCSY spectra in the presence and in the absence of spin label gives information of spatial proximity of... 

The most important two-dimensional NMR experiments for solving stmctural problems are COSY (Correlation SpectroscopY), NOESY (Nuclear Overhauser Enhancement SpectroscopY), HSC (Heteronuclear Shift Correlation) and TOCSY (Total Correlation SpectroscopY). Most modem high-held NMR spectrometers have the capability to routinely and automatically acquire COSY, NOESY, HSC and TOCSY spectra. 

Fig. 3. (Continued) (b) Spectrum of peracetylated triglucose 1 dissolved in CDCI3 (bottom) and ID TOCSY spectra A, B and C of the corresponding three glucose subunits, simultaneously acquired with pulse sequence I.

By applying the NOESY step first, this experiment allows us to jump from one spin system to another or to overcome a bottleneck in TOCSY transfer caused by an occurrence of a small coupling constant in the chain of J-connectivities. Both these features are illustrated in ID NOESY-TOCSY spectra of the type VI group B Streptococcus capsular polysaccharide (1). 

Fig. 15. ID COSY-TOCSY spectra of the oligosaccharide 5 acquired using the pulse sequence of fig. 13(b) with the initial polarization transfer from overlapping anomeric protons of two terminal glucoses, (a) Partial H spectrum of 1 at 600 MHz after 8 scans. The summation (b) and subtraction (c) of two ID COSY-TOCSY spectra acquired using the following parameters for the original spectra (not shown) = 50 ms, to = 39 ms, Tr = 28 ms,...

Figure 3 TOCSY Spectra (600 MHz, 300K, DMSO-d6) of the Cyclic Pentapeptide Sequence c[-Asn-Glu-D-His-Ala-Gly-]...

Overlap from resin signals, mentioned previously, can be overcome in several ways, and is particularly important when following reactions involving aromatic groups attached to polystyrene based resins. Spin echo MAS NMR was applied to follow the progress of a reduction of a resin-bound methyl benzoate to the alcohol.45 One-dimensional H as well as COSY and TOCSY spectra were used to elucidate the reaction products, although transformations were readily apparent in the ID spectra alone. 

TOCSY spectra usually give no information about direct coupling interactions and hence details of J-coupling networks. This missing information is commonly obtained either from ID homodecoupling or more efficiently from 2D COSY spectra. 

Fig. 3.7 Expansion of the ID TOCSY spectra of peracetylated glucose with long (top trace), medium (central trace) and short mixing times (bottom trace). Proton H-C( 1) with resonance at 5.7 ppm has been selectively perturbed.

Hint Use the multiple display option and display each of the NOE (ROE) difference spectra together with the ID TOCSY spectra of the individual monomer units to recognize and assign intra- and inter-residue NOEs (ROEs) respectively. Use different colours to differentiate between the spin systems of the individual monomers and use a special colour to mark NOEs among different monomers on your hardcopy. Cross check your findings with the conclusions extracted from previous data and carefully check the consistency of your H assignments in all the spectra. 

ID Hf H TOCSY Spectra OHTO FREQ 001001-003001 OHTO TMIX 001001-030001... 

NMR spectroscopy was carried out using a Varian Unity 300MHz spectrometer. Peptides were dissolved in 500 pL of 90% H,O/10% D20 (or 100% D20) giving a sample concentration of 1-2 mM and the pH adjusted to 5.5. H DQF-COSY (double quantum filtered two-dimensional correlated spectroscopy), ROESY, and TOCSY spectra were collected at 25 °C and processed as described.1 6-281... 

TOCSY spectra are critical to perform on paramagnetic systems when the required spectral window is large, because of the need to irradiate the spectral window efficiently with each component of a long train of many pulses (like for instance the MLEV17 sequence [49], Fig. 9.1L). Overheating of the sample can... 

Figure 7.3.2.5 Stop-flow 1H-1 H TOCSY spectra of (a) peak 1, and (b) peak 2 from the black beetles cHPLC-NMR separation...

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