Double nuclear-coherence transfer

In the HYSCORE experiment only nuclear frequencies in different manifolds belonging to the same paramagnetic center are eorrelated with each other. For multinuclear spin systems the assignment of nuelear frequencies is often not straightforward, since some of the correlation peaks may not be observed in the HYSCORE speetrum due to the small intensity of the nuelear transitions in one of the two Ws manifolds. Additional information can be gained if correlations of nuclear frequencies within the same manifold can be obtained. Cross-peaks that represent such correlations can be created by replacing the nonselective transfer n pulse in the HYSCORE sequence by the double nuclear-coherence transfer (DONUT) mixer % - t - n [58]. This DONUT-HYSCORE experiment with the pulse sequence ji/2 -ti nil - echo results in crosspeaks and (twp i, copj). The presence of these cross-peaks in the DONUT-... 

Goldfarb D, Kofman V, Libman J, Shanzer A, Rahmatouline R, Van Doorslaer S, Schweiger A. 1998. Double nuclear coherence transfer (DONUT)-HYSCORE a new tool for the assignment of nuclear frequencies in pulsed EPR experiments. J Am Chem Soc 120 7020-7029. 

Freeman, D., Hurd, R. Metabolic Specific Methods Using Double Quantum Coherence Transfer Spectroscopy. Vol. 27, pp. 199-222 Freeman, R., Robert, J.B. A Brief History of High Resolution NMR. Vol. 25, pp. 1-16 Freude, D., Haase, J. Quadrupole Effects in Solid-State Nuclear Magnetic Resonance. 

At the qualitative level, NMR studies devoted to this issue exploit heteronuclear dipolar recoupling to correlate resolved MAS NMR signals of the nuclear species associated with different network formers. This information comes from the dephasing of the observe nuclei in REDOR, TRAPDOR, or REAPDOR experiments, or from one- or two-dimensional correlation spectroscopy involving coherence transfer via TEDOR (transferred echo double resonance) or... 

The most commonly used 2D nmr technique applied to through-bond interactions is termed (7 ) correlated spectroscopy (COSY), others are total correlation spectroscopy (TOCSY), which allows somewhat longer-range through-bond connectivities to be observed than with COSY, spin echo coherence transfer spectroscopy (SECSY), relayed coherence transfer spectroscopy (RELAY), double quantum spectroscopy (DQNMR) and homonuclear Hartmann-Hahn spectroscopy (HOHAHA). The most commonly used 2D nmr technique applied to through-space interactions is termed nuclear Overhauser effect spectroscopy (NOESY) also used is the closely related rotating-frame NOESY (ROE-SY). 

Figure 3 Coherence transfer pathway diagram for homo-nuclear double-quantum selection with gradients.

COSY = homonuclear chemical shift correlation spectroscopy NOESY = 2D nuclear Overhauser effect (NOE) spectroscopy HMQC = heteronuclear mulltiple-quantum coherence RELAY = relayed coherence transfer COLOC = correlation via long-range coupling HMBC = heteronuclear long-range coupling INADEQUATE = incredible natural abundance double quantum transfer experiment. 

The first heteronuclear Hartmann-Hahn transfer in the liquid state preceded the homonuclear analogs of the experiment by about two decades. In their seminal paper on nuclear double resonance in the rotating frame, Hartmann and Hahn (1962) focused on heteronuclear polarization transfer in the solid state with the help of two matched CW rf fields with However, in the same paper, Hartmann and Hahn also discussed the coherent heteronuclear transfer of polarization for pairs of /-coupled heteronuclear spins in liquids and reported polarization-transfer experiments between H and P in hypophosphorous acid. Heteronuclear Hartmann-Hahn transfer in liquids with CW irradiation was applied by several groups (Maudsley et al., 1977 Muller and Ernst, 1979 Bertrand et al., 1978a, b Murphy et al., 1979 Chingas et al., 1979a, b, 1981). A detailed analysis of the experiment was presented by Muller and Ernst (1979) and by Chingas et al. (1981). Matched CW irradiation at the... 

NMR is the tool most widely used to identify the structure of triterpenes. Different one-dimension and two-dimension techniques are usually used to study the structures of new compounds. Correlation via H-H coupling with square symmetry ( H- H COSY), homonuclear Hartmann-Hahn spectroscopy (HOHAHA), heteronuclear multiple quantum coherence (HMQC), heteronuclear multiple bond correlation (HMBC), distortionless enhancement by polarisation transfer (DEPT), incredible natural abundance double quantum transfer experiment (INADEQUATE) and nuclear Overhauser effect spectroscopy (NOESY) allow us to examine the proton and carbon chemical shift, carbon types, coupling constants, carbon-carbon and proton-carbon connectivities, and establish the relative stereochemistry of the chiral centres. 

FIGURE 8.2. Flowchart for structure elucidation of purified compounds. DEPT Distortionless Enhancement by Polarization Transfer, HMBC Heteronuclear Multiple Bond Correlation, HSQC Heteronuclear Single Quantum Coherence, HMQC Heteronuclear Multiple Quantum Correlation, DQF-CQSY Double Quantum Filtered Correlated Spectroscopy and NOSEY Nuclear Overhauser effect spectroscopy. 

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