Interaction of Actinide Species with Microorganisms & Microbial Chelators: Cellular Uptake, Toxicity, & Implications for Bioremediation of Soil & Ground Water. Page: 8 of 12
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_6 B5 B4 B3 B2 B1 pHKa6
COHOm Ser Gly fDab OHAsp Orn Asp0
pKa2
pKa3 NH
NHa" CH2
OH CH2 . H2 NH NH
CHHO C H CH2
pKa4 o Hp a H
HO,\ 'I " N om 'uN N
N \ N N CH C .i
H; GH2
HOQC OH: ~
pKa8 pKao - OH HO
pKa5 pKal
Y1 Y2 Y3 Y4 Y5 Y6 pKa7
The structure of pyoverdine (Figure), shows that this siderophore has a mixed functionalities,
catecholate, hydroxamate and a carboxylic acid group. The binding groups bearing hard oxygen donor
atoms are expected to enhance pyoverdin's blinding for hard metal ions like Fe(III) and Pu(IV).
Electochemical behavior of Pu(IV/III)-siderophore complexes. The cyclic voltammogram of
Pu(IV/III) couple in 0.5 M HCl (shown in the previous section) shows a quasireversible behavior with
Eva2= 935 mV(vs NHE), which is consistent with the formal potential for Pu(IV)-Pu(III) couple from
literature data (953 mV, in 1 M HCl). We have shown that EDTA forms a strong complex with Pu(IV)
and considerably less stable complexes with Pu(III). The cyclic voltammograms of Pu-EDTA show a
quasi reversible couples with Ev2 = 342 at pH 3.2. The shift in the redox potential of Pu(IV/III) upon
EDTA binding (593 mV) is attributed to the differences in the affinity of EDTA toward Pu(IV)
binding, which is attributed to the hard character of the oxygen donor groups on EDTA carboxylic acid
binding groups. Similarly, siderophores are known for their hard oxygen donor groups character,
favoring strong complexes formation with iron(III) and considerably less stable complexes with
iron(II). The differences in siderophores binding for Fe(III)-Fe(II) result in redox potentials for
Fe(III/II)-siderophore complexes in the range -350 to -700 mV depending on the structure of the
siderophore. Pu(III)-siderophore complexes are considerably less stable than Pu(IV)-siderophore
complexes. The cyclic voltammograms of Pu-siderophore complexes measured when one equivalent of
siderophore is added to a solution of containing Pu(IV) shows an irreversible behavior. A reduction
wave is observed around -200 mV(NHE) without its reoxidation counter part. The presence of excess
siderophore is necessary to obtain a reversible voltammograms. The cyclic voltammograms of Pu(IV)
complexes with the natural siderophores desferrioxamine E and B (DFB and DFE), pyoverdin,
rhodotorulic acid and the synthetic aceto hydroxamic acid recorded in large excess of siderophore at
neutral pH are shown in Figure (Figure). For comparison purposes, cyclic voltammograms of Pu-
ferrioxamine B, Ferrioxamine E, Rhodotorulic acid, and Acido hydroxamic acid were also recorded
under similar conditions. In all cases excess siderophore was used for cyclic votametry measurements.
The redox potentials of the iron-siderophores and Pu-siderophore complexes shown in Table ? indicate
that Pu-siderophore complexes undergo redox changes at potentials slightly lower than the iron
complexes.
Most siderophores are hexavelent, and a single molecule ensures full iron coordination. The
tetra valent siderophores like rhodotorulic acid were a single molecules can not satisfy full iron
coordination, complexes with a 2:3 Fe:Siderophore stoichiometry are formed. Pu which can
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Hakim Boukhalfa Mary, P. Neu Alvin Crumbliss. Interaction of Actinide Species with Microorganisms & Microbial Chelators: Cellular Uptake, Toxicity, & Implications for Bioremediation of Soil & Ground Water., report, March 28, 2006; United States. (https://digital.library.unt.edu/ark:/67531/metadc877623/m1/8/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.