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

Abstract Density functional theory (DFT) combined with the continuous set of gauge transformations (CSGT) method was employed to calculate chemical shielding of the carbonyl carbon ( 13 C O ) and nitrogen ( 15 N) atoms of the backbone amide groups in ω-conotoxin GVIA, as well as alpha carbon ( 13 C α ) and beta carbon ( 13 C β ) shielding. Experimental 13 C and 15 N chemical shifts were determined using multidimensional NMR spectroscopy. The three-dimensional solution structure of ω-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.