CSGT-DFT calculation of 13C and 15N NMR shielding of the backbone amide group, 13Cα, and 13Cβ in ω-conotoxin GVIA

Density functional theory (DFT) combined with the continuous set of gauge transformations (CSGT) method was employed to calculate chemical shielding of the carbonyl carbon (C-13(O)) and nitrogen (N-15) atoms of the backbone amide groups in omega-conotoxin GVIA, as well as alpha carbon (C-13(alpha)) and beta carbon (C-13(beta)) shielding. Experimental C-13 and N-15 chemical shifts were determined using multidimensional NMR spectroscopy. The three-dimensional solution structure of omega-conotoxin GVIA was solved using a hybrid distance geometry-simulated annealing protocol. Peptide fragments with experimentally measured bond lengths, bond angles, and torsion angles were used as model structures in the CSGT-DFT calculations. Linear correlation plots were constructed to compare theoretical data with experiment. (C) 2004 Elsevier B.V. All rights reserved.