Iron clearing efficiency

Iron clearing efficiency is a measure of how much iron excretion is promoted by a chelator. It is a comparison of actual iron excretion versus theoretical iron clearance this number is given as a percentage. For example, because DFO forms a very tight 1 1 complex with Fe(III), one millimole of DFO (636 mg as its mesylate salt) given sc to a patient should cause the excretion of one milligram-atom of Fe(III) (56 mg). Unfortunately, the efficiency of DFO in clinical use is only about 5 to 7% (25, 37). 

The animal model selected for this series of experiments was the iron-overloaded C. apella monkey. In this model, we are able to measure both total iron excretion, expressed as iron clearing efficiency, and the modes of iron clearance, that is, biliary and renal. Data are presented (Table I) as the mean standard error of the mean. For comparison of the means between two compounds, a two-sample /-test (without the assumption of equality of variances) was performed. All tests were two-tailed, and a significance level of P < 0.05 was used. 

The situation was similar with the 2, 3 -dihydroxy derivatives. When a methyl group was introduced into the 4-position of the thiazoline ring of (5)-3 -(HO)-DADMDFT (6) to afford ( -3 -(HO)-DADFT (7), both the iron clearing efficiency and the modes of excretion changed. The efficiency of compound 6... 

Finally, addition of two methyl groups to the 5-position of the thiazoline ring of 1 (DM, 5) had an obvious impact on iron clearing efficacy the efficiency was 12.3 2.7% (P < 0.005 vs 1). When 5 is compared with 3 and 4, considerably less of the iron was excreted in the feces, 64%, and 36% of the iron was in the urine (47). In general, whereas methylation did alter the modes of iron excretion, the effect on overall iron clearing efficiency was much more striking. 

In the case of the 2, 3 -dihydroxy compounds, there was also an apparent relationship between log P and iron clearing efficiency. However, what is most... 

Figure 3. Iron clearing efficiency (percent, Panel A) and fecal iron clearance (tig of stool Fe/kg of body weight, Panel B) of 4 -substituted ligands IS (open circles) and 3 -substituted analogues 6-9 (filled squares) plotted versus the respective partition coefficients of the compounds. Adaptedfrom reference 47. Copyright 2003 American Chemical Society.

The activity of some metals such as indium, zinc, and iron as efficient catalysts in Friedel-Crafts acylahon is well known, even if nof clearly explained. For example, indium metal (20% mol) shows high efficiency in the acylation of various aromafic compounds wifh BC. As an example, the indium-mediated benzoylation of aromafic compounds with electron-donating groups gives the corresponding diaryl ketones in high yield (Table 3.13). Alkylbenzenes are less reactive, and with mesitylene, the yield is 77% at 150°C. Deactivated benzenes such as chloro- and bro-mobenzene are inactive. 

Clearly, the efficiency of the EMS is dependent on the magnetic character of the transported iron oxide and other particles, and if they are not magnetic, then no filtration occurs. Unfortunately, it is not unknown for installed EMS units to be ignored or their true function to be in doubt. Consequently, they may have to operate for long periods without any effective backwash or maintenance program being provided. 

It has been suggested (Bozzi et ah, 1997 Grant et ah, 1998) that Dps and E. inocua ferritin represent examples of a family of ancestral dodecameric protein which had as function to trap, but not to mineralize, metal ions, and that the ability to oxidize and mineralize iron efficiently and to form fourfold interactions came later. The hollow-cored dodecameric motif exemplified by Dps and E. inocua ferritin has clearly been adapted to a number of functions, since in addition to DNA binding and iron storage, other family members include a novel pilin, a bromoperoxidase and several other proteins of unknown function (Grant et ah, 1998). 

This variation in the efficiency of reduction, with pse of time, is clearly illustrated in the graph. Fig. g, hich shows the carbon monoxide and carbon dioxide jntent of the water gas after passing at the rate of 300 cubic feet per hour over 4 2 tons of iron oxide, sated to 750° C. 

The mechanism of iron and heme uptake by the intestine is becoming better understood 70-72), but clearly heme-iron is more efficiently absorbed from the gastrointestinal tract than inorganic iron 73-75), and there is a receptor for heme in the duodenal brush border membrane 76). Duodenal mucosal cells efficiently catabolize heme, and iron-transferrin can be detected in the plasma of blood vessels draining the intestinal segment shortly after Fe—heme—histidine is administered (75). 

Molybdenum In its pure form, without additions, it is the most efficient catalyst of all the easily obtainable and reducible substances, and it is less easily poisoned than iron. It catalyzes in another way than iron, insofar as it forms analytically easily detectable amounts of metal nitrides (about 9% nitrogen content) during its catalytic action, whereas iron does not form, under synthesis conditions, analytically detectable quantities of a nitride. In this respect, molybdenum resembles tungsten, manganese and uranium which all form nitrides during their operation, as ammonia catalysts. Molybdenum is clearly promoted by nickel, cobalt and iron, but not by oxides such as alumina. Alkali metals can act favorably on molybdenum, but oxides of the alkali metals are harmful. Efficiency, as pure molybdenum, 1.5%, promoted up to 4% ammonia. 

An analogous behavior extends to other species having small reorganization energies and appropriate potentials such as the iron(II) complexes Fe(DMB)32 + and Fe(DTB)32 + (Ey2 0.95 V versus SCE). When used in the presence of an excess of Co(DTB)32 + and in conjunction with suitable sensitizers like the heteroleptic dye Ru(dnbpy)(H2DCB)22+ (Em = 1.25 V versus SCE) (Fig. 17.28), the iron(II) comediators clearly enhance the performance of the Co(DTB)32+ and outperform the I /I3 redox couple, at least in terms of monochromatic photon to current conversion efficiency, with maximum values close to 85%. 

DFO may easily be absorbed from the gut and parenteral use is very efficient. If administered intravenously, DFO is eliminated from the systemic circulation very rapidly and in a biphasic manner (19). Both DFO and its major metabolites are cleared by the kidney and liver. However, ferrioxamine (DFO-iron complex) is cleared exclusively by the kidneys (19) and in the case of renal disease may accumulate in plasma and must be eliminated by dialysis. 

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