Homonuclear two-dimensional

NOESY NMR spectroscopy is a homonuclear two-dimensional experiment that identifies proton nuclei that are close to each other in space. If one has already identified proton resonances in one-dimensional NMR spectroscopy or by other methods, it is then possible to determine three dimensional structure through NOESY. For instance, it is possible to determine how large molecules such as proteins fold themselves in three-dimensional space using the NOESY technique. The solution structures thus determined can be compared with solid-state information on the same protein obtained from X-ray crystallographic studies. The pulse sequence for a simple NOESY experiment is shown in Figure 3.23 as adapted from Figure 8.12 of reference 19. 

Although the first NMR spectra of deuterated proteins were published already in 1968, the deuteration was mainly employed for the purpose of simplifying one-dimensional proton spectra.53,54 Later in the 1980s, LeMaster and co-workers employed random fractional deuteration for the assignment of thioredoxin using homonuclear two-dimensional spectroscopy.55 However, it was realized that deuteration significantly improves the spectral quality of homonuclear multidimensional NMR experiments. 

Selecting the C-bound protons before performing a homonuclear two-dimensional experiment enables to measure small heteronuclear coupling constants [16]. Such an experiment with a sample of natural isotopic abundance was first published by Otting and Wuthrich in 1990, where the half-filter element with spin-lock purge pulse was used to select the C-bound protons in a small protein in aqueous solution [6]. Later applications illustrated the usefulness of the same half-filter element with smaller molecules [17, 18]. 

Under the idealized zero-quantum coupling topologies (see Section V.B), the transfer of magnetization between two spins 1 /2 that are part of an arbitrary coupling network is identical in both directions (see Section VI). This symmetry with respect to the direction of the transfer is related to the symmetry of homonuclear, two-dimensional Hartmann-Hahn spectra with respect to the diagonal (Griesinger et al., 1987a). In Hartmann-Hahn experiments, the properties of the multiple-pulse sequence can induce additional symmetry constraints (Ernst et al., 1991). 

Broadband Hartmann-Hahn transfer can also be of assistance in alternative approaches to determine coupling constants that do not rely on E.COSY-type multiplets that are separated by large one-bond couplings. The homonuclear two-dimensional PICSY (pure in-phase correlation spectroscopy) experiment (Vincent et al., 1992, 1993), which is based on selective Hartmann-Hahn transfer using doubly selective irradiation, can... 

Eesik, S.W. Zuiderweg, E.R.P. Heteronuclear three-dimensional NMR spectroscopy. A strategy for the simplification of homonuclear two-dimensional NMR spectra. J. Magn. Reson. 1988, 78, 588-593. 

Efforts are currently underway to expand the utility of "P NMR to qualitative and quantitative analysis of much more complex oligophosphate mixtures. A novel application of homonuclear two-dimensional J-resolved (2DJ) spectroscopy of sodium polyphosphate glass is shown to effectively yield "p-"p decoupled spectra. Used in conjunction with Lorentzian lineshape analysis and curve deconvolution, semiquantitative analyses of these mixtures has been achieved. 

H-NMR analysis allows the elucidation of GSL structures, without the use of destructive methods and requires small amounts (nmole) of material. In addition to one dimensional 1 H-NMR, other methods such as two-dimensional 1H-NMR shift correlations spectroscopy (COSY), two-dimensional nuclear Overhauser 1 H-NMR spectroscopy (NOESY) and homonuclear two-dimensional spin-echo J-resolved 1 H-NMR spectroscopy. The introduction of1 C-NMR into the field of glycosphingolipid research should give useful information on the stereochemical conformation of molecules. This is of coniderable interest, as they most probably contribute to the immunological specificity of glycosphingolipids (37). 

The basic heteronuclear experiments are easy to combine with the two-dimensional homonuclear experiments to produce three- or four-dimensional edited spectra. In this terminology editing means selection of the protons that are attached to the heteronucleus. The main purpose of these experiments is to reduce the signal overlap of the homonuclear two-dimensional experiments. 

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