Total correlated spectroscopy

TOCSY Total correlation spectroscopy, in the homonuclear COSY format, e.g. HH TOCSY traces out all proton-proton coimectivities of a partial structure in addition to the coimectivities (V, V, V, J) as detected by HH COSY... 

A related experiment TOCSY (Total Correlation Spectroscopy) gives similar information and is relatively more sensitive than the REIAY. On the other hand, intensity of cross peak in a NOESY spectrum with a short mixing time is a measure of internuclear distance (less than 4A). It depends on the correlation time and varies as . It is positive for small molecules with short correlation time (o r <<1) and is negative for macromolecules with long correlation time (wr >>l) and goes through zero for molecules with 1 Relaxation effects should be taken into consideration for quantitative interpretation of NOE intensities, however. 

Homonuclear Hartmann-Hahn Spectroscopy or Total Correlation Spectroscopy 267... 

HOMONUCLEAR HARTMANN-HAHN SPECTROSCOPY (HOHAHA), OR TOTAL CORRELATION SPECTROSCOPY (TOCSY)... 

The HOHAHA spectrum (100 ms) of podophyllotoxin is presented. The HOHAHA, or TOCSY (total correlation spectroscopy), spectrum (100 ms) shows coupling interactions of all protons within a spin network, irrespective of whether they are directly coupled to one another or not. As in COSY spectra, peaks on the diagonal are ignored as they arise due to magnetization that is not modulated by coupling interactions. Podophyllotoxin has only one large spin system, extending from the C-1 proton to the C4 and 015 protons. Identify all homonuclear correlations of protons within this spin system based on the crosspeaks in the spectrum. 

We now want to turn to another experiment which, we must make clear at the start, does not have any relationship in theory to NOE experiments. In fact the theory is so complicated that we shall not say anything about it at all, but just refer you to one of the books in the Appendix. We are including this experiment because of its unique advantages when the spectrum has overlapping multiplets. It is called TOCSY, which stands for Total Correlation SpectroscopY (it has a second, more amusing name HOHAHA, standing for HOmonuclear HArtmann-HAhn), and is of particular use when oligosaccharides or peptides are under study. 

The total correlation spectroscopy (TOCSY) techniques, which come in both 1- and 2-D versions, offer an alternative to 1-D spin decoupling and COSY methods for establishing through-bond connectivities. The important difference between the two is that TOCSY methods allow easy identification of isolated spin systems. For example, using our trusty morpholine compound once more, you can see that it is possible to identify the -CH2-CH2- spin system between the nitrogen and the oxygen atoms, these hetero-atoms, effectively isolating the protons from all others in the molecule. 

TOCSY Total correlation spectroscopy. One and two-dimensional techniques that are analogous to COSY but which differ in that it shows couplings within specific spin systems. 

Total correlation spectroscopy (TOCSY) is similar to the COSY sequence in that it allows observation of contiguous spin systems [35]. However, the TOCSY experiment additionally will allow observation of up to about six coupled spins simultaneously (contiguous spin system). The basic sequence is similar to the COSY sequence with the exception of the last pulse, which is a spin-lock pulse train. The spin lock can be thought of as a number of homonuclear spin echoes placed very close to one another. The number of spin echoes is dependent on the amount of time one wants to apply the spin lock (typically 60 msec for small molecules). This sequence is extremely useful in the identification of spin systems. The TOCSY sequence can also be coupled to a hetero-nuclear correlation experiment as described later in this chapter. 

We have characterized a resin-bound pentasaccharide by HR-MAS techniques. A comparison of the solution spectrum of the resin-cleaved pentasaccharide with the HR-MAS spectrum of the resin-bound pentasaccharide is shown in Figure 8.5. It is immediately obvious that the HR-MAS technique provides data of a quality similar to that of the solution technique, but in both cases, only four of the five anomeric protons are visible. However, a 2D homonuclear total correlation spectroscopy (TOCSY) spectrum (Fig. 8.6) of the resin-bound pentasaccharide allowed us to clearly observe the overlapped anomeric protons (demonstrating a resolution of 4.4 Hz). 

SQ TOCSY TROSY ZQ ZQC single quantum total correlation spectroscopy transverse relaxation-optimized spectroscopy zero quantum zero-quantum coherence... 

TOCSY Two-dimensional total correlation spectroscopy To elucidate structure of organic molecules To establish proton coupling network and molecular connectivity... 

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. 

The 2D homonuclear TOCSY (Total Correlation SpectroscopY) experiment... 

By 2D TOCSY NMR spectroscopy (TOCSY - total correlated spectroscopy), the structure of a biosynthetic intermediate of PQQ was shown to be 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid 15, not its constitutional isomer 16 <2004JA3452>. This result shows that the last enzyme on the biosynthetic pathway of PQQ facilitates a pyrrole ring closure and an unprecedented eight-electron oxidation of 15. 

Fig. 5.4.15a,b Parts of two-dimensional total correlated spectroscopy spectra of human bile (a) and a mixture of standard solutions of GCA, GDCA, TCA and TDCA (b). These spectra show the connectivity of amide proton signals to H-25 and/or H-26 protons of glycine and/or taurine conjugated bile acids (reprinted from [40])... 

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