Hydroxamate complex, ferric

Hassib et al. [29] determined mefenamic acid by ferric hydroxamate complex formation and measurement of the absorbance of the colored complex at 530 nm. The method is applicable to mefenamic acid amounts varying from 0.5 to 74.5 mg/25 mL, and Ponstan capsules were successfully determined using this method. 

Figure 1 Representative siderophores of the hydroxamate and catecholate classes. The hydroxamates are synthesized from the amino acid ornithine that has been modified through hydroxylation and acetylation. Ferrichrome (a) is a prototypical example of the tri-hydroxamate class. Structurally, ferrichrome is a cyclic hexapeptide that consists of three modified ornithine residues (each of which has a hydroxamate side chain) and three glycines. Ferrichrome coordinates ferric iron through its three bidentate hydroxamate side chains. Triacetylfusarinine C (b) is also a cyclic tri-hydroxamate, but the three modified ornithine residues are joined by ester linkages rather than by peptide linkages. Ferrioxamine B (c) is a linear tri-hydroxamate consisting of three peptide-huked modified ornithine residues. Enterobactin (d) is a prototypical example of a catecholate siderophore. It consists of a tri-ester ring from which extend three side chains of chhydroxybenzoyl serine. Each of these siderophores binds ferric iron in a hexadentate manner, which results in full saturation of d orbitals and a very stable complex. Ferric forms are shown in (a) and (b). Desferri-forms are shown in (c) and (d)...

Detection with iodine vapour before quantitative determination has been used frequently, e.g. analysis of lipid esters in conjunction with gas chromatographic determination [187] or with colorimetric determination after conversion to ferric hydroxamate complexes [731] to detect analgesic drugs [215] (cf.Fig. 79) and steroids [217, 437] with subsequent spectrophotometric determination in the visible or UV regions to detect phospholipids, where phosphorus determination followed [6, 79, 637]. 

Hydroxyurea is an amidohydroxamic acid, which like other hydroxamic acids, gives a red or violet water-soluble inner complex ferric compound in weak acid solutions (compare the test for hydroxylamine, page 345). 

The formed aldehyde, treated by phenylsulfohydroxamic acid in the presence of a ferric salt, offers the usual ferric hydroxamate complex. Phenylsulfohydroxamic acid gives sulfinic acid and nitroxyl (unstable intermediary of structure HNO) in basic medium. Nitroxyl is a nucleophilic species that attacks the carbonyl group of carboxaldehyde. A hydroxynitroso derivative forms. It is in tautomeric equilibrium with hydroxamic acid responsible for the color ... 

As esters are usually difficult to detect, this test is of considerable value. In general esters react when heated with hydroxylamine to give a hydroxamic acid (I). The latter gives a coloured complex (II) with ferric salts in acid solution. 

Esters react witli hydroxylamine to form an alcohol and a hydroxamic acid, RCONHOH. All hydroxamic acids, in acid solutions, react with ferric chloride to form coloured (usually violet) complex salts ... 

TOA were determined, in the supernatant prepared as described by Hissett et al (25), by the method of Montgomery et al (26). The organic acids were esterified with acidified ethylene glycol. The esters were then reacted with hydroxylamine and the hydroxamic acids thus formed were converted to their ferric complexes and their concentrations were determined by optical density measurements at 500u. 

Mixed donor ligands. Tris(acetylhydrazine)iron(iii) trichloride has been pre-pared. ° The effect of pressure on ferric hydroxamates is to cause reduction to iron(ii), the amount of reduction being correlated with the position of the metal-> ligand charge-transfer band. Fe " complexes of A-hydroxyurea have been isolated. 8-Amino-7-hydroxy-4-methylcoumarin (58) forms the complex [FegLjCl ], in which the Fe " ions are in octahedral environments. A magnetic and Mossbauer study of [FeX(ox)2] and [FeX2(ox)] (X = Cl or... 

Once the siderophore-iron complexes are inside the bacteria, the iron is released and utilized for vital cell functions. The iron-free hydroxamate siderophores are commonly re-excreted to bring in an additional iron load (Enterobactin is at least partially degraded by a cytoplasmic esterase This cycle is repeated until specific intracellular ferric uptake regulation proteins (Fur proteins) bind iron, and signal that the intracellular iron level is satisfactory, at -which point ne-w siderophore and siderophore-receptor biosynthesis are halted and the iron-uptake process stops. This intricate feedback mechanism allows a meticulous control over iron(III) uptake and accumulation against an unfavorable concentration gradient so as to maintain the intracellular iron(III) level within the required narrow window. Several excellent reviews concerning siderophore-iron transport mechanisms have been recently published i.3,i6, is,40,45,60-62 ... 

This method is based on the fact that only esters, but not free carboxylic acids, react with hydroxylamine to form hydroxamic acids, which can be determined colorimetrically as complex with ferric chloride (8). The method—in contrast to most other procedures—measures the concentration of remaining substrate instead of products of hydrolysis. It also requires purified enzymes because of the interference of colored contaminants in the colorimetric measurements. 

Moxalactam is also amenable to the popular hydroxyl amine assay for g-lactam antibiotics. In this procedure the -lactam is reacted with hydroxyl amine to cleave the e-lactam moiety and form a hydroxamic acid. The hydroxamic acid will in turn react with acidified ferric ion to form a colored complex which is measured at 480 nm. A blank correction for non-e-lactam impurities which react with hydroxyl amine is incorporated by adding hydroxylamine to an acidified sample where the acid is used to destroy all e-lactam species. 

Cupric ion is said to give highly insoluble precipitates and this has been suggested as a test for the —CON(OH)— bond (146). In the case of iron it is apparent that the number of hydroxamate anions coordinated to the ferric ion is mainly a function of pH, and this in turn has a profound effect on the wavelength maximum and the intensity of absorption. In general, at about pH 1 to 2 the 1 1 complex is favored, the color is purple (maximum 5100 A) and the amM is about 1.0 (Table 2). (35, 116, 142). 

Using two cooled bubblers connected in series and charged with ethanol, 0.5-1 L of air was sampled at a flow of 0.3 L/min. The vinyl acetate was converted to N-hydroxyacetamide by the addition of hydroxylamine hydrochloride and sodium hydroxide. After 30 minutes, the hydroxamic acid was complexed with iron by the addition of hydrochloric acid and ferric chloride. The intensity of the color which developed in 10 minutes was compared to the intensities of standards. The lower limit of detection for this method was reported to be 0.3 yg/mL. 

However, despite large differences in ligand molecular structure, all of the hydroxamate siderophores whose structures have been determined to date have been found to be cis complexes with a coordination geometry about the ferric ion which is substantially identical to the simple tris-(benzhydroxamato)-Fe(III) complex. Thus, while ferrioxamine E is racemic but with a cis geometry (13), x-ray structure analyses of ferrichrome A (14) and ferrichrysin (15) have shown both to be A-cis isomers. 

Application and Principle This procedure is used to determine transglutaminase activity in preparations derived from Streptoverticillium mobaraense var. The assay is based on the enzymatic formation of a glutamic acid y-hydroxamate in a glutaminyl residue in the substrate peptide with another substrate, hydroxylamine. The amount of the glutamic acid y-hydroxamate formed as a red complex with ferric ion in acidic conditions at 37° is measured spectrophotometrically. 

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