Actinide complexes hydroxamates

Hydroxamate. Hydroxamate complexes of trivalent actinides can be prepared directly in aqueous solution and other polar solvents and extracted into organic solvents, but due to the high thermodynamic stability of the corresponding tetravalent actinide complexes they are rapidly oxidized. They can also be prepared in solution via electrochemical reduction of the tetravalent complexes. These complexes have been studied for their role in separating high and low valent actinides in nuclear fuel processing schemes. ... 

Hydroxamates have been observed in the water in the Bay of Quinte, a eutrophic bay of Lake Ontario, and are believed to be produced by blue-green algae (76). Simpson and Neilands (77) have identified schizokinen, a hydroxamic acid derivative of citric acid as an extracellular product of the blue-green algae, Anabaena sp. However, not all Anabaena produce hydroxamates, Walsby (78) has shown that Anabaena cylindrica releases a large pigmented, peptide-containing material which complexes iron. As yet these peptides have not been examined for ability to complex the actinides. 

It is significant that oat plants, which are known to contain the Fe3+ complexor, 2,4-dihydroxy-7-methoxy-l,4-benzoxazin-3-one (128), do not show any significant accumulation of plutonium, or the other actinides. It is possible that this complexing agent is located within plant cells which do not come into contact with the cation transporting mechanisms. Although there is evidence of the existence of microbial hy-droxamates in soil and that hydroxamates do become concentrated in plants (129), there has been no evidence presented yet that hydroxamates are the agents responsible for plutonium uptake into plants. On the other hand there is evidence that EDTA and DTPA can stimulate actinide concentration in plants (See Table 6). 

The known complexes, MIVL4 (Table 43), precipitate from aqueous solutions of actinide(IV) compounds on addition of the ligand. Somewhat surprisingly, one hydroxamic add, (PhCO)NHOH, behaves as a neutral ligand, and the complex Th(N03)4-2(PhC0)NH0H... 

Table 43 Actinide(IV) Complexes with Hydroxamates, Cupferron and Related ligands ...

Hydroxamates and their monothio and dithio analogues form chelate complexes usually. They have been much studied because hydroxamates are present in sidero-phores, the microbial iron transport systems (Section 17-E-10) and also because of their use in sequestering agents for actinide ions and in analytical studies. 

Hydroxamates, cupferron, and related ligands. As anionic oxygen donor ligands, hydroxamates have a strong affinity for the oxophilic tetravalent actinides, with solution complex formation constants generally greatest for Pu and decreasing as follows Pu > Np > > U. ... 

Hydroxamate. Similar to trivalent hydroxamates, pentavalent actinide hydroxamate complexes are generally unstable relative to tetravalent and/or hexavalent complexes. Pu or Pu hydroxamate complexes can be prepared however, at near-neutral and basic pH they rapidly reduce to Pu complexes. ... 

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