First-principles electronic structure study of rhizoferrin and its Fe(III) complexes.

We have determined the structure and coordination chemistry of rhizoferrin (Rf), which is a particular type of siderophore, and its Fe(III) complexes using density functional theory calculations. Our results show that the Fe(III) ion binds in an octahedral coordination, with a low-spin (S = 1/2) charge-neutral chiral complex having the largest binding energy of the investigated complexes. We have also calculated nuclear magnetic resonance parameters, such as chemical shifts for (1)H and (13)C, and indirect nuclear spin-spin couplings for (1)H-(1)H and (13)C-(1)H in free Rf and in a low-spin neutral Rf metal complex, as well as nuclear quadrupole interaction parameters, such as asymmetry parameter and nuclear quadrupole coupling constants for (14)N. Our calculated values for the chemical shifts for free Rf are in excellent agreement with experimental data while the calculated NMR parameters for Fe(III) complexes are predictions for future experimental work.