DFT and TD-DFT studies of free and iron(III)-coordinated vibrioferrin.

Vibrioferrin (VF) is a photoreactive, borate-binding siderophore produced by Vibrio parahaemolyticus and other pathogenic bacteria-but also by a number of marine bacteria. This study addresses hitherto unresolved questions about the stereochemistry of the iron(III)-VF complex (FeVF), based upon spectral data. Density functional theory (DFT) was used to determine relative energies for two stereoisomers of the VF, and for four different FeVF coordination configurations. The most stable ligand was also determined to yield the most stable coordination structures. Time-dependent DFT was then used to compute the absorbance spectra of the iron complexes for comparison to the experimental spectrum. The most stable FeVF configuration also had the closest matching UV-vis spectra, indicating that this is the most likely coordination structure in nature. With one stereocenter experimentally determined to be labile, it is possible that the computationally established preference for one ligand structure and configuration speaks to the structure of the siderophore receptor on vibrioferrin producing species.