Decoupling heteronuclear, 192 also

By analogy with homonuclear decoupling above, selective heteronuclear decoupling is also possible. The decoupling of a single proton resonance could in... 

We have so far looked at the NOE only in a homonuclear manner, but of course there is also a heteronuclear NOE. Theory tells us that when we are dealing with C-H fragments in small molecules, the decoupling of the proton leads to an increase in the carbon signal intensity by up to almost 200% So signals of protonated carbons should be stronger than those of non-proton-ated carbons. 

The 140-residue protein AS is able to form amyloid fibrils and as such is the main component of protein inclusions involved in Parkinson s disease. Full-length 13C/15N-labelled AS fibrils and AS reverse-labelled for two of the most abundant amino acids, K and V, were examined by homonuclear and heteronuclear 2D and 3D NMR.147 Two different types of fibrils display chemical shift differences of up to 13 ppm in the l5N dimension and up to 5 ppm for the backbone and side-chain 13C chemical shifts. Selection of regions with different mobility indicates the existence of monomers in the sample and allows the identification of mobile segments of the protein within the fibril in the presence of monomeric protein. At least 35 C-terminal residues are mobile and lack a defined secondary structure, whereas the N terminus is rigid starting from residue 22. In addition, temperature-dependent sensitivity enhancement is also noted for the AS fibrils due to both the CP efficiency and motional interference with proton decoupling.148... 

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