Accurate and effective calculation of amide proton magnetic shieldings in a calcium binding peptide

Abstract

NMR amide proton chemical shifts of the calcium complex with the bicyclic nonapeptide BCP2, cyclo-(Glu¹–Ala²–Pro³–Gly⁴–Lys⁵–Ala⁶–Pro⁷–Gly⁸)-cyclo-(1γ → 5ε)Gly⁹ were calculated by means of Hartree–Fock and DFT methods within the GIAO framework. Calculated results yielded a good agreement with experimental data: computed chemical shifts well reproduced the strong changes induced by the presence of the metal. The nature of the metal–peptide interaction, as well as other non-local effects on magnetic shielding, were discussed. Further, different hybrid methods have been tested to set up an affordable approach to study magnetic properties in metal–protein complexes.