Stability of Siderophore Complexes and Other Tales Margaret Broz, Jadon Peck Chemistry Capstone Spring 2002

MetalFe 3+ Fe 2+ Ni 2+ Cu 2+ Zn 2+ Cd 2+ Al 3+ La 3+ Yb 3+ Stability Constant Stability of Siderophore Complexes: Desferrioxamine (DFO) Stability constants for metals with DFO 2 Fe 3+ is the most stable metal for desferrioxamine, followed by Al 3+ Cu 2+ can be complexed by siderophores in the absence of Fe 3+ (Ex. filamentous blue-green algae) 1

Stability of Desferrioxamine B (DFB) 3 MetalZn 2+ Pb 2+ Sn 2+ Cu 2+ Bi 3+ Stability Constant Stability constants for metals with DFB a a Estimated, near RT Stability of Rhizoferrin 4 MetalFe 3+ Fe 2+ Cu 2+ Ca 2+ Zn 2+ Stability Constant Stability constants for metals with Rhizoferrin

Moron Complexation Fe complexes of some marine siderophores are subject to photolytic degradation, which releases Fe 2+ into the ocean 5 Photolysis may be an important loss factor for strong iron binding ligands in the upper ocean 5 Siderophore derivatives can be used to detect Al 3+, due to significant UV-Vis absorbance changes upon complexation 6

Other Interesting Bits High molybdate concentrations lead to selective formation of protochelin to the exclusion of other siderophores in A. vinelandii (terrestrial bacterium) 7 Protochelin also accumulates with high vanadate, tungstate, Zn 2+ and Mn 2+ concentrations 7 Plutonium forms complexes with DFO regardless of its oxidation state 8 Pu(IV)-DFE complex O – red, O of H 2 O – maroon, N – blue, C – black, Pu - green

Reaction Rates and Kinetics 9 Iron exchange kinetics studied for three bacterial siderophores using EDTA as a model Exchanges kinetics show first order dependence Results interpreted as a three-step mechanism First step – fast – protonation of Fe-siderophore complex Second step – fast – ternary complex formation with ferric complex and EDTA Third step – RDS – dissociation of the ternary complex

Redox Reactivity Iron complexes: Fe 3+ reduced to Fe 2+ in redox reactions of siderophore complexes, freeing Fe 2+ Photochemical redox reactions of Fe- siderophore complexes may form Fe 2+ at ocean surface It is difficult to reduce these complexes under physiological conditions using typical biological reducing agents (i.e. NADH), due to very large reduction potentials 10 (pH of the ocean is 8.1)

Plutonium complexes 8 : Pu(IV)-DFO complexes form from any oxidation state of Pu (III, IV, V, or VI) Above pH=6, Pu (VI) is reduced irreversibly to Pu(IV), and reduction is assisted by higher DFO concentrations Surprisingly, Pu(IV)-DFO complex is still reactive, since Pu(VI) will be reduced even though the DFO is already complexed NMR shows that these complexes are highly fluxional and may undergo ligand exchange, which helps to explain the previous phenomenon Siderohpores “steal” Pu and keep it solubilized and mobile, as they have higher formation constants with Pu than other chelators (EDTA, NTA) Redox Reactivity

Redox Interactions of Actinides with Microbes 8 An stands for actinide species

Acknowledgements Alison Butler Gustavus Adolphus College SciFinder Scholar Google the mysterious ocean depths Jacques Cousteau

Sources 1)D. McKnight et. al.; Copper complexation by siderophores from filamentous blue-green algae, Limnol. Oceanogr. 1980, 25(1); )M. Ott, Desferrioxamine, Paper2.pdf, 3/23/02. Paper2.pdf 3)B. Hernlem, et. al.; Stability constants for complexes of the siderophore desferrioxamine B with selected heavy metal cations. Inorg. Chim. Acta. 1996, 244(2); )M. Shenker, et. al.; Stability constants of the fungal siderophore rhizoferrin with various microelements and calcium. Soil Sci. Soc. Am. J. 1996, 60(4); )K. Barbeau, A. Butler; Photochemistry of marine bacterial siderophores. Book of Abstracts, 219 th ACS National Meeting, San Francisco, CA. March 26-30, )S. Lambert et. al.; A preparative, spectroscopic and equilibrium study of some phenyl-2- thiazoline fluorophores for aluminum(III) detection. New J. Chem. 2000, 24, )A. Cornish, W. Page; Role of molybdate and other transition metals in the accumulation of protochelin by Azotobacter vinelandii. Appl. Environ. Microbiol. 2000, 66(4); )C. Ruggerio et. al.; Interaction of Pu with desferrioxamine can affect bioavalibility and mobility. The Actinide Research Quarterly. 2000, 2 nd /3 rd quarter. 2/23/ )A. Albrecht-Gary et. al.; Bacterial siderophores: iron exchange mechanism with ethylenediaminetetraacetic acid. New J. Chem. 1995, 19(1); )K. Matsumoto et. al.; Crystal structure and redox behavior of a novel siderophore model system: a trihyroxamato-iron(III) complex with intra- and interstrand hydrogen bonding networks. Inorg. Chem. 2001, 40;