Iron nitrilotriacetate

Iqbal, M. and Athar, M., Attenuation of iron-nitrilotriacetate (Fe-nta)-mediated renal oxidative stress, toxicity and hyperproliferative response by the prophylactic treatment of rats with garlic oil, Food Chem. Toxicol., 36, 485M95, 1998. 

Iron can be controlled with certain complexing agents, in particular glucono-5-lactone, citric acid, ethylenediaminetetraacetic acid, nitrilotriacetic acid, hydroxyethylethylene diaminetriacetic acid, hydroxyethyliminodiacetic acid, and the salts from the aforementioned compounds. These compounds must be added together with nitrogen-containing compounds such as hydroxylamine salts or hydrazine salts [486,643,1815]. 

Figure 17-26. Complexing agents for iron control glucono-6-lactone, nitrilotriacetic acid, hydroxyethylene diaminetetraacetic acid, and ethylenediaminetetraacetic acid.

Fe2+ is also transported by the CorA protein (Hantke, 1997), a divalent cation transporter for Mg2+, Co2+, Mn2+, and Ni2+ in E. coli and S. typhimurium. CorA may represent the often-mentioned low-affinity iron-uptake system of E. coli that is suppressed in Fe3+ uptake studies by the addition of 0.2 mM dipyridyl and 0.1 mM nitrilotriacetate. 

Iron(III)-pyrophosphate looks promising as an alternative to iron(III)-carbohydrate preparations for parenteral administration for treatment of anemia.Kinetics of removal of iron from transferrin (tf) by pyrophosphate (pp) were found to be biphasic under certain conditions, with the rapid first phase attributed to the formation of a pp—Fe—tf—CO intermediate.A later study of the kinetics of removal of iron from transferrin employed pyrophosphate and tripodal phosphonates such as nitrilotris(methylenephosphonic acid), N(CH2P03H2)3. For the tripodal ligands there are parallel first-order and saturation pathways, with the latter dominant (contrast the exclusively first-order reaction of ferritin with nitrilotriacetate) for pyrophosphate the paths are roughly equal in importance. The saturation kinetics suggest that tfiFe-phosphonate intermediates play an important role in the kinetics. 

Figure 7-5 shows the titration of 2.000 mL of apotransferrin with 1.79 X I0-3 M ferric nitrilotriacetate solution. As iron is added to the protein, red color develops and absorbance increases. When the protein is saturated with iron, no further color can form, and the curve levels off. The extrapolated intersection of the two straight portions of the titration curve at 203 p-L in Figure 7-5 is taken as the end point. The absorbance continues to rise slowly after the equivalence point because ferric nitrilotriacetate has some absorbance at 465 nm. 

Figure 7-5 Spectrophotometric titration of transferrin with ferric nitrilotriacetate Absorbance is corrected as if no dilution had taken place. The initial absorbance of the solution, before iron is added, is due to a colored impurity.

Nitrilotriacetic acid (NTA) is a constituent of various domestic and hospital detergents and is a common water contaminant. NTA forms water-soluble chelate complexes with various metal ions, including iron, at neutral pH. Its iron complex, Fe-NTA, is a known potent nephrotoxic agent. The renal toxicity is assumed to be caused by the elevation of serum free-iron concentration following the reduction of Fe-NTA at the luminal side of the proximal tubule, which generates reactive oxygen species and leads to enhancement of lipid peroxidation. 

The free ion, Cu2+, appears to be the major species of Cu taken up by plants (Graham, 1981 Jones and Jarvis, 1981). Hence Cu complexation will decrease uptake (DeKock and Mitchell, 1957) unless the complex can dissociate and/or diffuse quickly enough to maintain a constant supply of Cu2+ at the root surface. In the case of Zn, the presence of humic acid (Chen and Aviad, 1990) and carboxylic acids (EDTA, diethylenetriamine pentaacetic acid (DTPA), nitrilotriacetic acid (NTA) DeKock and Mitchell, 1957) has been found to decrease absorption but it is not known whether Zn uptake is correlated with Zn2+ in solution because Zn speciation was not estimated. Other work has shown that Zn initially complexed with citrate is taken up by barley from nutrient solutions (Chairidchai and Ritchie, 1993) and the presence of chelates (EDTA, citrate) can speed up the diffusion of Zn to a root surface in soils (Hodgson et al., 1967 Elgawhary et al., 1970). Speciation in solution is particularly important in the uptake of iron because of its extremely low solubility in the absence of complexing anions... 

Croft et al. [15] reported significant increases in kt when iron was chelated by DTPA, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and several aminophosphonic acids. Compared to aqueous Fe2+, increases in /cj from 1000-fold to 50,000-fold were indicated. They also note that DTPA inhibits reaction (3). Graf et al. [10] suggest that reaction (3) is completely inhibited by DTPA, EHPG, phytate, and desferal. These two studies are not entirely consistent in their findings, possibly due to the... 

Aluminium, ammonia, antimony, arsenic, barium, beryllium, cadmium, carbon tetrachloride, cyanide, dichloromethane, di(2-ethylhexyl)-adipate, di(2-ethylhexyl)-phthalate, EDTA, epichlorohydrin, ethylbenzene, hexachlorobutadiene, iron, lead, manganese, mercury, molybdenum, monochlorobenzene, nickel, nitrilotriacetic acid, sodium, sulfate, tetrachloroethene, toluene, trichlorobenzenes,... 

Antimony, boron, bromoform, chloral hydrate, chloroform, iron, lindane, mercury, nitrilotriacetic acid, trichloroethene, zinc... 

When ferric iron (preferably as ferric nitrilotriacetate) is added to egg white, with a little salt, and the mixture is shaken, a vivid red color develops. This simple experiment introduces the protein ovotransferrin (formerly known as conalbumin) and the most striking property of transferrins, their ability to rapidly and tightly bind iron. 

The rise in the 465-nm absorbance as Fe3+ is added to the apoprotein (generally as a ferric nitrilotriacetate or ferric citrate complex) can be used to monitor iron binding and forms the basis of iron titrations that demonstrate the presence of two specific sites per molecule (Fig. 17). 

In vivo uptake of iron by transferrins usually involves its addition as a ferric-chelate complex, to prevent hydrolytic attack on the ferric ion (211). Complexes such as ferric citrate and ferric nitrilotriacetate are commonly used. Under these conditions, kinetic schemes for the uptake of iron by transferrins have identified five steps in the formation of the specific metal-anion-transferrin ternary complex (120). These may be summarized as follows. 

Evidence that the anion binds first comes from kinetic data (119) and from spectroscopic results, in which both XH NMR (118) and UV difference (177) spectra indicate that the anion binds to the apoprotein. Strong support comes from the 3D structural data the positive charge at the anion site should deter metal binding until it is neutralized by a suitable anion (78,85). Suggestions that nitrilotriacetate transiently occupies the anion site when iron is added as a Fe3+-NTA complex (212) may imply that the early steps can vary depending on the form of the added iron, but the key point probably remains that the anion site must be occupied as a first step. Spectroscopic evidence for the... 

In aspect of its toxicity, any pathway leading to abatement of chromate(VI) pollution arouse a vivid interest. One of such pathways seems to be created by cooperations between the iron and chromium photocatalytic cycles, which were reported as effectively converting chromate(Vl) into Cr(III) species. Photochemical coupling reactions between polycarboxylate Fe(III) complexes and chromate(Vl) were studied and strong collaboration between both photocatalysts was demonstrated, which was significantly affected by the oxygen concentration (16,17,95,261). On the other hand, chromium(Vl) reduction pho-toinduced by iron(lll) nitrilotriacetate accompanied by nta degradation was found to be independent of the O2 concentration, whereas the oxidation state of the chromium product depended on the pH (257). 

Iron Oxides. Chelated iron oxide, using nitrilotriacetic acid [139-13-9] and EDTA, has been studied as an alternative oxygen source (35). Iron oxide which is often difficult for the microbes to access, is made more available by chelating agents. 

Most kinetic studies of iron release have focused on pathways involving the use of chelate ligands such as EDTA (217), pyrophosphate 218-220), phosphonates 220,221), catecholates 108,216), hydroxa-mates 120), and nitrilotriacetate (221). In many cases, simple saturation kinetics are observed, and interpreted in terms of the formation of a quaternary complex, ligand-Fe-transferrin-COs (120,122). The failure to observe this complex spectroscopically [in contrast to iron uptake studies (120)] has been explained in terms of a rate-limiting conformational change, giving a basic three-step mechanism, which is essentially the reverse of that given for iron uptake (Section V.A.l). 

A class of tripodal ligands such as (131), synthesized by reaction of 3,5-dimethylaniline and nitrilotriacetic acid with triphenylphosphite, has been reported and its coordination chemistry toward iron nitrosyl acceptors has been investigated. When bonded to a metal ion, they form cavities around vacant coordination sites on metal ions.210... 

---