Polarization transfer cross-relaxation-induced

With the adaptation of NMR techniques for larger molecules, it becomes possible to analyze proteins with molecular weights reaching 50 kDa. These techniques include H-, N-TROSY (transverse relaxation-optimized spectroscopy, with the mutual cancellation of H-, N-dipole-dipole coupling and the N chemical shift anisotropy) and CRINEPT (Cross-correlated Relaxation-Enhanced Polarization Transfer, combining insensitive nuclei enhanced by polarization transfer (INEPT) transfer with cross-correlated relaxation-induced polarization transfer). They are used in conjunction with the N-, c-labeling of the protein for increased sensitivity. 

TROSY (transverse relaxation-optimized spectroscopy) and CRIPT (cross-correlated relaxation-induced polarization transfer) or CRINEPT (cross-correlated relaxation-enhanced polarization transfer) for the two-dimensional (2D) NMR analysis of N-. H-labeled homo-oligomeric macromolecules with masses ranging from 110-800 kDa. Practical applications of these methods are, for instance analyses of intermolecuiar interactions in supramolecular complexes or conformational changes of a single macromolecule upon interactions with other molecules. 

For hydrogenation of styrene and its derivatives over several cationic Rh complexes, in addition to the hyperpolarized multiplets of ethylbenzene the H NMR spectra contained similar polarized multiplets but shifted to a higher field [41,42]. These signals were attributed to the product molecules that have not yet detached from the metal center after the hydrogen-transfer stage was over (e.g., with the aromatic moiety r -coordinated to the Rh(I) center). The results demonstrate that the detachment process can be fairly slow on the NMR timescale. The use of chiral catalysts and/or asymmetrically substituted styrenes led to more complicated spectral patterns. Kinetic studies can be used to measure the rates of formation and decay of such catalyst-product complexes [43]. The fact that the observed product remains coordinated to the catalyst was confirmed [44] in experiments with polarization transfer from the product to the hydrogens of other ligands of the catalyst induced by cross relaxation. 

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