Transcript Stability constants of the fungal siderophore rhizoferrin with various

Stability of Siderophore Complexes
and Other Tales
Margaret Broz, Jadon Peck
Chemistry Capstone
Spring 2002
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
Metal
Stability
Constant
Fe3+ Fe2+ Ni2+ Cu2+
Zn2+
30.7
10.1
7.2
10.9
14.1
Cd2+ Al3+
7.9
23.1
La3+
Yb3+
10.9
16.0
Stability of Desferrioxamine B (DFB)3
Stability constants for metals with DFBa
Metal
Zn2+
Pb2+
Sn2+
Cu2+
Bi3+
Stability
Constant
9.55
10.00
21.14
13.73
13.54
a
Estimated, near RT
Stability of Rhizoferrin4
Stability constants for metals with Rhizoferrin
Metal
Fe3+
Fe2+
Cu2+
Ca2+
Zn2+
Stability
Constant
19.1
7.5
6.2
6.0
4.4
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
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
Pu(IV)-DFE complex
O – red, O of H2O – maroon, N – blue,
C – black, Pu - green
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
Redox Reactivity
Iron complexes:
• Fe3+ reduced to Fe2+ in redox reactions of
siderophore complexes, freeing Fe2+
• Photochemical redox reactions of Fesiderophore 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)
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)
Redox Interactions of Actinides with Microbes8
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); 62-71.
2)
M. Ott, Desferrioxamine,
http://www.medicine.uiowa.edu/frrb/education/FreeRadicalSp01/Paper%202/OttMPaper2.pdf, 3/23/02.
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); 179-184.
4)
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.
5)
K. Barbeau, A. Butler; Photochemistry of marine bacterial siderophores. Book of Abstracts,
219th ACS National Meeting, San Francisco, CA. March 26-30, 2000.
6)
S. Lambert et. al.; A preparative, spectroscopic and equilibrium study of some phenyl-2thiazoline fluorophores for aluminum(III) detection. New J. Chem. 2000, 24, 541-546.
7)
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.
8)
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.
9)
A. Albrecht-Gary et. al.; Bacterial siderophores: iron exchange mechanism with
ethylenediaminetetraacetic acid. New J. Chem. 1995, 19(1); 105-113.
10)
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.