13C chemical shift tensors and secondary structure of poly-L-alanine by solid-state two-dimensional spin-echo NMR and ab initio chemical shielding calculation

✍ Scribed by Naoki Asakawa; Masatoshi Takenoiri; Daisuke Sato; Minoru Sakurai; Yoshio Inoue

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 180 KB
• Volume: 37
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199904)37:4<303::aid-mrc440>3.0.co;2-w

✦ Synopsis

Analyses of 13C chemical shielding tensors for powder samples of a-helix-rich poly-L-alanine (pALA) and the mechanically stretched b-sheet pALA Ðlms were performed by solid-state two-dimensional spin-echo (2DSE) NMR spectroscopy. From the iterative Ðtting of 2DSE spectra with spectrum simulations, information was obtained about the principal values of the chemical shift tensors (CST) for nuclei with small chemical shift anisotropy such as CH and carbons. The experimental results show that the lowest shielding component, of CH 3 d 11 , L-alanine residue aand b-carbons are sensitive to the conformational changes and responsible for the behavior of the conformation-dependent isotropic chemical shifts. Ab initio gauge-invariant atomic orbital chemical shielding calculations were carried out in order to understand the correlation between the CST and the polypeptide conformation.