Acetohydroxamic acid complexation

For example, the specific reaction of yellow Fe with acetohydroxamic acid to form a purple complex is therefore assumed to correspond to the scheme in equation 3. 

A large volume of work64 has been published on the determination of stability constants for complexes of hydroxamic acids, e.g. acetohydroxamic acid.65 The stability of 3d transition metal ions (Mn2+ to Zn2+) with salicylhydroxamic and 5-methyl-, 5-chloro-, 5-bromo-, 5-nitro-, 4-chloro-, 4-bromo- and 3-chloro-salicylhydroxamic acids,66 as well as with methyltolylbenzohydroxamic acid,67 has been studied potentiometrically. Stability constants of iron(III) with a number of hydroxamic acids have been determined by redox potential studies.68... 

As U is the major component of a SNF see Table 1.2, its initial separation in reprocessing alleviates the mass burden of following steps and is considered preferable. The UREX process developed in the AFCI program of the United States is based on the PUREX process (30 vol % TBP in n-dodecane) and suppression of extractions of Pu and Np by reduction/complexation (175-182). Plutonium and Np are reduced by acetohydroxamic acid (AHA, CH3CONHOH) to Pu(III), Np(V), and Np(IV). U is kept in an extractable U(VI) state. Although Np(IV) is also extractable, AHA forms a complex with Np(IV) that is soluble in the aqueous phase. In the case where reoxidation of Pu(III) occurs, the Pu(IV) also transfers to the aqueous phase by forming a Pu(IV)-AHA complex. Thus, U is exclusively extracted. AHA decomposes to hydroxylamine and acetic acid (176). 

The major drawback of phenyl derivatives of BNOPCs is that they are only scarcely soluble in classical hydrocarbon diluents without the addition of massive amounts of phase modifiers, such as TBP or TOPO. They are, however, soluble in halogenated and nitro-halogenated organic diluents (130). Furthermore, the anomalous aryl strengthening effect also increases the extraction of other fission products, such as Zr, Mo, Tc, and Fe, which can only be avoided by introducing specific hydrophilic complexants (e.g., acetohydroxamic acid). 

UREX [URanium Extraction] A solvent extraction process for extracting uranium and technetium from used nuclear fuel, while rejecting all the transuranic elements. Based on the Purex process, which uses tributyl phosphate in a hydrocarbon mixture, but incorporating acetohydroxamic acid, which complexes the Pu and Np and thereby prevents them from being extracted. Developed by the Westinghouse Savannah River Company in 2003. Associated processes are NPEX, TRUEX, and Cyanex 301. 

The two five-membered rings of this spirocyclic X. Si-silicon(IV) complex each contain two oxygen atoms, one nitrogen atom, one carbon atom, and one (pentacordinate) silicon atom. As shown in Scheme 8, this compound was prepared by analogy to the synthesis of the related A, Si-silicates 10-16. Thus, treatment of (MeO)3SiCH2NMe2 with two mole equivalents of acetohydroxamic acid in acetonitrile at room temperature yielded 28 in 80 % yield as a crystalline solid [5]. The formation of this compound can be understood in terms of a reaction of (MeO)3SiCH2NMe2 with the 1,2-diol acetohydroximic acid, which is a tautomer of acetohydroxamic acid. 

Acetohydroxamic acid (AcHA) is CH3CNHOH. Sketch the structure expected for a complex of AcHA and Fe, including the possible resonance structures. 

Acetyl and Feruloyl Esters in Pectin. A colorimetric method for determining degrees of acetylation in pectins from various sources ( ), has been shown to be rapid and quite sensitive. Hydroxy-lamine is reactive toward both the methyl and acetyl esters in pectin, and ferric ion complexes with the resulting hydroxamic acids are red. The pectin complex is insoluble and removed by filtration the intensity at 520nm in the soluble fraction, consisting of the ferric complex with acetohydroxamic acid, is a measure of acetyl content. The accuracy of the method was demonstrated in determinations of 0-acetyl levels in standard per-ace-tylated polysaccharides. Another method ( ) involves alkaline hydrolysis of the acetyl groups from pectin, followed by distillation of acetic acid and its titration with standard base. 

The stabilities of Fe" complexes of hydroxamates are much lower than those of Fe " for the bis Fe" complex of acetohydroxamic acid = 3 x 10 ). It is thought, therefore, that the mechanism of release of iron from hydroxamate siderophores may occur via reduction of Fe " to the much more weakly bound Fe" state, as also proposed for the tris(catecholato) siderophores. Cyclic voltammetry has shown that the Fe" hydroxamate complexes undergo reversible or quasi-reversible one-electron reductions under suitable conditions. The observed formal potential E( is pH dependent, decreasing from —0.388 mV (ys. SCE) at pH 7 by 60 mV per pH unit, for the case of tris(acetohydroxamato)iron(III), consistent with progressive deprotonations of the coordinated ligand. Thus, deprotonation stabilizes the Fe " vs. the Fe state. ... 

Acetic acid, trimethylenediaminetetra-metal complexes equilibrium constants, 784 synthesis. 779 Acetohydroxamic acid metal complexes spectroscopy, 506 Acetohydroxamic acid, A -phenyl-metal complexes, 507 as metal precipitants, 506 Acetone oximes... 

Fig. 1. Structural models of urease from Bacillus pasteurii in the native state (panel A), and its complexes with /3-mercaptoethanol (BME panel B), acetohydroxamic acid (AHA panel C), phosphate (PHO panel D), diamidophosphate (DAP model E), and boric acid (B(0H>3 panel F). The Ni atoms in the active site are shown as filled circles.

High resolution structures of urease from B. pasteurii complexed with /3-mercaptoethanol (13) (BME Fig. IB) and acetohydroxamic acid (14) (AHA Fig. 1C) indicate the presence of bridging/chelating coordination to the Ni ions, highlighting the importance of both metal ions in the reactivity of the enzyme. The structures of B. pasteurii urease crystallized in the presence of phosphate... 

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