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Stability of Siderophore Complexes and Other Tales

Stability of Siderophore Complexes and Other Tales. Margaret Broz, Jadon Peck Chemistry Capstone Spring 2002. Stability of Siderophore Complexes: Desferrioxamine (DFO). Fe 3+ is the most stable metal for desferrioxamine, followed by Al 3+

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Stability of Siderophore Complexes and Other Tales

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

  2. Stability of Siderophore Complexes: Desferrioxamine (DFO) • Fe3+ is the most stable metal for desferrioxamine, followed by Al3+ • Cu2+ can be complexed by siderophores in the absence of Fe3+ (Ex. filamentous blue-green algae)1 Stability constants for metals with DFO2

  3. Stability of Desferrioxamine B (DFB)3 Stability constants for metals with DFBa a Estimated, near RT Stability of Rhizoferrin4 Stability constants for metals with Rhizoferrin

  4. Moron Complexation • Fe complexes of some marine siderophores are subject to photolytic degradation, which releases Fe2+ into the ocean5 • Photolysis may be an important loss factor for strong iron binding ligands in the upper ocean5 • Siderophore derivatives can be used to detect Al3+, due to significant UV-Vis absorbance changes upon complexation6

  5. Pu(IV)-DFE complex O – red, O of H2O – maroon, N – blue, C – black, Pu - green 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, Zn2+ and Mn2+ concentrations7 • Plutonium forms complexes with DFO regardless of its oxidation state 8

  6. Reaction Rates and Kinetics9 • 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

  7. Redox Reactivity • Iron complexes: • Fe3+ reduced to Fe2+ in redox reactions of siderophore complexes, freeing Fe2+ • Photochemical redox reactions of Fe-siderophore complexes may form Fe2+ 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 potentials10 • (pH of the ocean is 8.1)

  8. Redox Reactivity • Plutonium complexes8: • 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)

  9. Redox Interactions of Actinides with Microbes8 An stands for actinide species

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

  11. Sources • D. McKnight et. al.; Copper complexation by siderophores from filamentous blue-green algae, Limnol. Oceanogr.1980, 25(1); 62-71. • M. Ott, Desferrioxamine, http://www.medicine.uiowa.edu/frrb/education/FreeRadicalSp01/Paper%202/OttM-Paper2.pdf, 3/23/02. • B. Hernlem, et. al.; Stability constants for complexes of the siderophore desferrioxamine B with selected heavy metal cations.Inorg. Chim. Acta.1996,244(2); 179-184. • M. Shenker, et. al.; Stability constants of the fungal siderophore rhizoferrin with various microelements and calcium. Soil Sci. Soc. Am. J.1996,60(4); 1140-1144. • K. Barbeau, A. Butler; Photochemistry of marine bacterial siderophores.Book of Abstracts, 219th ACS National Meeting, San Francisco, CA. March 26-30, 2000. • 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, 541-546. • 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); 1580-1586. • C. Ruggerio et. al.; Interaction of Pu with desferrioxamine can affect bioavalibility and mobility. The Actinide Research Quarterly.2000, 2nd/3rd quarter.http://www.lanl.gov/orgs/nmt/nmtdo/AQarchive/00fall/interactions.html, 2/23/02. • A. Albrecht-Gary et. al.; Bacterial siderophores: iron exchange mechanism with ethylenediaminetetraacetic acid. New J. Chem. 1995,19(1); 105-113. • 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; 190-191.

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