Quantum Chemical Study of the Fe(III)-Desferrioxamine B Siderophore Complex-Electronic Structure, Vibrational Frequencies, and Equilibrium Fe- Isotope Fractionation

摘要

This study presents molecular orbital/density functional theory (MO/DFT) calculations of the electronic structure, vibrational frequencies, and equilibrium isotope fractionation factors for iron desferrioxamine B (Fe-DFO-B) complexes in aqueous solution. In general, there was good agreement between the predicted properties of Fe(III)-DFO-B and previously published experimental and theoretical results. The predicted fractionation factor for equilibrium between Fe(III)-DFO-B and Fe(III)-catecholate at 22 C, 0.68 0.25, was in good agreement with a previously measured isotopic difference between bacterial cells and solution during the bacterial-mediated dissolution of hornblende Brantley S. L., Liermann L. and Bullen T. D. (2001) Fractionation of Fe isotopes by soil microbes and organic acids. Geology 29, 535.538. Conceptually, this agreement is consistent with the notion that Fe is first removed from mineral surfaces via complexation with small organic acids (e.g., oxalate), subsequently sequestered by DFO-B in solution, and ultimately delivered to bacterial cells by Fe(III)- DFO-B complexes. The ability of DFO-B to discriminate between Fe(III) and Fe(II)/Al(III) was investigated with Natural Bond Orbital (NBO) analysis and geometry calculations of each metal-DFO-B complex. The results indicated that higher affinity for Fe(III) is not strictly a function of bond length but also the degree of Fe-O covalent bonding.