Iron absorption design

Table VI. Experimental design of the iron absorption study.

Several other organic acids which modify iron absorption are also listed in Table V. EDTA has received much attention for it forms a highly stable iron chelate, and one would expect it to inhibit iron absorption. When sodium ferric EDTA (NaFeEDTA) was fed directly as a liquid, inhibition of iron absorption was observed both in rats (A) and in man (40, 48). Inhibition increased with Increasing chelate concentration. This effect was also observed when NaFeEDTA was added to a diet, but only when the molar ratio of disodium EDTA to iron was 2 1 or greater (33). The inhibition was observed when NaFeEDTA was added to a standard meal described as "a typical American dinner," or when it was added to a semisynthetic meal (a diet designed to yield low iron bioavailability) (33). 

For IDA, IV iron, though costly, has superior bioavailability compared with oral preparations. In select individuals the bioavailability advantage of parenteral iron over oral iron can be the difference in the achievement of a successful outcome. The benefits of using combination oral iron products designed to enhance absorption is probably not warranted. 

Fig. 16. Magnetic Mossbauer spectra of 3B at 4.2 K and 60 kOe. The overbars designate splitting of the outermost absorption lines of the diamagnetic (Fen, Fe(l) and Fe(2)) and paramagnetic (Fep, Fe(3)) iron sites. The solid line represents a least-squares fit of the experimental data to Lorentzian lines. (Reproduced from Ref. 5b. Copyright 1987 American Chemical Society.)...

Extended X-ray absorption fine structure (EXAFS) studies on the Fe/Mo/S aggregate in nitrogenase have made available structural data that are essential in the design of synthetic analog clusters. Analyses of the Mo K-edge EXAFS of both the Fe-Mo protein and the FeMoco (9) have shown as major features 3-4 sulfur atoms in the first coordination sphere at 2.35 A and 2-3 iron atoms further out from the Mo atom at 2.7 A. The Fe EXAFS of the FeMoco (10,11) shows the average iron environment to consist of 3.4 1.6 S(C1) atoms at 2.25(2) A, 2.3 +0.9 Fe atoms at 2.66(3) A, 0.4 0.1 Mo atoms at 2.76(3) A and 1.2 1.0 0(N) atoms at 1.81(7) A. In the most recent Fe EXAFS study of the FeMoco (11) a second shell of Fe atoms was observed at a distance of 3.75 A. 

However, spectroscopic studies of activated BLM indicate that it is not an Fev=0 species. It exhibits an S - 1/2 EPR spectrum with g values at 2.26, 2.17, and 1.94 [15], which is typical of a low-spin Fe111 center. This low-spin Fem designation is corroborated by Mossbauer and x-ray absorption spectroscopy [16,19], Furthermore, EXAFS studies on activated BLM show no evidence for a short Fe—0 distance, which would be expected for an iron-oxo moiety [19], These spectroscopic results suggest that activated BLM is a low-spin iron(III) peroxide complex, so the two oxidizing equivalents needed for the oxidation chemistry would be localized on the dioxygen moiety, instead of on the metal center. This Fe(III)BLM—OOH formulation has been recently confirmed by electrospray ionization mass spectrometry [20] and is supported by the characterization of related synthetic low-spin iron(III) peroxide species, e.g., [Fe(pma)02]+ [21] and [Fe(N4py)OOH]2+ [22], The question then arises whether the peroxide intermediate is itself the oxidant in these reactions or the precursor to a short-lived iron-oxo species that effects the cytochrome P-450-like transformations. This remains an open question and the subject of continuing interest. 

Allotropy of Iron.—When a bar of pure iron is allowed to cool from its melting-point to 0° C., its time-temperature cooling curve exhibits three breaks,4 or arrests, designated by the symbols Ar4, Ar3, and Ar2 respectively.5 These arrests are due to evolution of a small amount of heat consequent upon some internal alteration in the metal, whereby the rate of cooling is retarded. Indeed, the evolution of heat at the Ars point is sufficient to raise the temperature of the iron by a very appreciable amount. The phenomenon is termed recalescence.6 Similarly, on reheating the metal, three arrests, due to heat absorption, are... 

At room temperature, flash absorption studies revealed that an electron acceptor designated Aj was functioning under conditions where F and Fg were presumably reduced [37]. The state (P-700, A2 ) is formed upon flash excitation and recombines with tiu — 250 jUS. The difference spectrum due to its formation was analysed into contributions of P-700 and A2. The latter includes mainly a small and broad bleaching around 430 nm, and perhaps some absorption shifts in the red. These absorption properties, together with the disappearance of the A2 absorption signal when iron-sulfur proteins are denatured [38,39], indicate that Aj may be an iron-sulfur centre. 

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