First principle calculations of 113Cd chemical shifts for proteins and model systems

Cd-113 isotropic NMR shieldings are calculated for a number of metal ion binding sites in proteins, using the GIAO-B3LYP and GIAO-HF methods with the uncontracted (19s15p9d4f) polarized basis set of Kello and Sadlej on cadmium and 6-31G(d) on the ligands. The results compare favorably with experimental data, indicating that first principle calculations are a useful tool for structural interpretation of Cd-113 chemical shift data from metal ion containing proteins. The effect of different ligand types (thiolate, imidazole, water, and monodentate carboxylate), coordination number, and deviations of the coordination geometry from ideal structures is evaluated. In particular, the ligand type and coordination number are important factors, but also changes in cadmium-ligand bond lengths may cause significant changes of the chemical shift.