Shielding tensors polypeptides

Table 6. Isotropic 15N shielding (triso) and 15N shielding tensor element (022) of solid polypeptides [Leu, X] containing 15N-labelled L-leucine residue in the a-helix...

The development of high-resolution solid-state NMR techniques has made possible the study of shielding tensors. No doubt 15N will receive more attention in the near future for a number of reasons such as the increased availability of high-field spectrometers and the development of polarization transfer techniques for solids. Recently some interesting results on the relation between l5N shielding tensors and structures of solid polypeptides have been reported. Nitrogen NMR could, therefore, be a useful intrinsic probe in 15N NMR studies of polypeptides and proteins in the solid state, particularly in cases where selective 15N labelling is possible. 

Why is the displacement of the an different for [Ala ] and [Leu ] The reason for this is not clear at present, but this is a very important question in reaching and understanding of the correlation between structures and the l5N shielding tensor. The 15N shielding tensor may be useful for conformational analysis of solid polypeptides, if the origin of the chemical shift displacements can be elucidated. 

In this paper, we aim to elucidate the correlation between the chemical shift tensors and the conformation of peptides, by carrying out NMR shielding calculations using the ab initio GIAO-CHF MO with 6-31G basis set, in order to understand the 13C chemical shift and chemical shift tensor behavior of the peptides and polypeptides. 

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