Computational Study of Caspian Sea Nodularin

Geometry, and C-13 NMR chemical shielding tensors of nodularin from Caspian sea were determined via density functional theory. We optimized the structure using B3LYP/cc-PvDZ approach. According to computational results, the most striking structural feature of nodularin is the saddle-shaped backbone with the Ada side chain protruding behind it. However, this feature is in good agreement with most of the published 3D structures of both hepta and penta peptides. In addition, study of the trends in C-13 chemical shielding isotropy, sigma(iso) and anisotropy, Delta sigma values are explained in terms of the both geometrical and electronic effects. We anticipate that the results presented here stimulate further interest in structural studies of nodularin from Nodularia spumigena of Caspian sea by C-13 NMR spectroscopy and encourage the future use of quantum chemical approach for analysis of spectra from nodularin.