Activation by iron

Dr. Moeller In our plant, we investigated our catalyst after 4000 and 5000 hrs of operation and we found no trace of iron on our catalysts. But we know that if you take no precautions against iron carbonyl formation, then you will destroy some part of your activity by iron deposition on your catalyst. And we found that the iron carbonyl is formed mainly at the mild steel tube walls or at the tube in the temperature range of 150°-200°C. So, if you enter this range and you have to heat up your gas, which has a high CO content and steam in it, you have to... 

Stahl, S. S. Lippard, S. J. Dioxygen and Alkane Activation by Iron-Containing Enzymes, Iron Metabolism Eds. Ferreira, G. C. Moura, J. J. G. Franco, R. 1999,... 

The mechanism of action for such peroxidic compounds involves a reductive activation by iron in haem, released as a result of hemoglobin digestion by Plasmodium. This irreversible redox reaction affords carbon-centered free radicals causing the alkylation of haem and of proteins. One such protein (the sarcoplasmic-endoplasmic reticulum ATPase PfATP6) appears to be critical for parasite survival, and there is no indication for resistance by the parasite. However, treatment is expensive and recrudescence of malaria occurs often. Moreover, it was found that at high doses such compounds are neurotoxic. 

Bollinger JM, Krebs C. Stalking intermediates in oxygen activation by iron enzymes Motivation and method. J Inorg Biochem. 2006 100 586-605. 

Toluenes can be oxidized by Caro s acid (H2S05) activated by iron(II) salts.286... 

Drug activation by iron and heme may explain why endoperoxides are selectively toxic to malaria parasites. The malaria parasites live in a milieu of heme iron, which the parasite converts into insoluble hemozoin. Chloroquine, which binds heme, antagonizes the antimalarial activity of artemisinin. 

The metals can be activated toward alkalies by coupling them with other metals, just as they are activated toward water and acids. When zinc is in contact with iron the former reacts rapidly with a warm solution of sodium hydroxide. Hydrogen is evolved from the iron and the zinc passes into solution as sodium zincate, NagZnOg. Tin behaves in a similar way and sodium stannite, NagSnOa, is formed. It should be noted that in these cases the metal that dissolves is the one which forms a hydroxide soluble in sodium hydroxide. When two metals are coupled in neutral or acid solution hydrogen is evolved from the metal having the lower solution pressure— that is, the one lower in the electromotive series. When the solution contains an alkali, this is not always the case. Zinc is above and tin is below iron in the electromotive series, but when activated by iron in the presence of an alkali they each dissolve. The solubility of the hydroxide in alkalies is the determining factor in the reaction. The zinc that passes into solution is not presnt in the form of zinc ions, but as zincate ions, ZnOo— which result from the ionization of the salt formed. 

Dioxygen and alkane activation by iron-containing enzymes... 

Figure 3 Environment of iron in the active sites of oxidases and hydroxylases with related transformations performed upon reaction with O2. Inset proposed pathways for dioxygen activation by iron (P stands for porphyrin).

A group of scientists attached a protein that absorbs iron to a porous silica material. F. Carmona et al. A bioinspired hybrid silica-protein material with antimicrobial activity by iron uptake. 2013. Metallomics 5(3), p. 193. DOI 10.1039/c3mt2021 la. 

A typical detector system in FIA usually records the signal against time in a continuous flow and must be sensible to variations of sample concentration. The most frequently used detector systems are potentiometric and spectrophotometric ones (Table 30.1) due to ease of assembly and their specificity, once the potential is proportional to concentration as well as to absorbance. Potentiometric detection was used by Shpigun et al. (2006) to assess antioxidant activity by iron reduction. The potential of the [Fe(CN)g] was measured against time, when an antioxidant sample was injected, the potential decreased due to iron reduction to [Fe(CN)g] a negative peak height (H) (measured in mV) has a logarithmic proportion to antioxidant concentration. 

Moreover, Tyr-fragment may be involved in substrate hydrogen binding in step of 02-activation by iron catalyst, and this can decrease the oxygenation rate of the substrate, as it is assumed in the case of homoproto-catechuate 2,3-dioxygenase. ... 

In analogy to aromatic C-H bonds, alkenyl C-H bonds can also be activated by iron(III) salts in coupling reactions with magnesium or zinc organyls (Scheme 4-250). The reaction requires a pyridine or an imine moiety in proximity to the double bond that supports the C-H bond activation step by chelation of the intermediate iron complex. Tris(acetylacetonato)iron is employed in catalytic amounts and l-bromo-2-chIoroethane or l,2-dichloro-2-methylpropane functions as oxidant. In addition, in most cases a diamine base is added. The reaction results in the stereospecific substitution of the olefinic C-H bond syn to the coordinating group. ... 

Most interestingly, also C-H bonds at a-positions of aliphatic amines can be activated by iron(III) catalysts and subjected to C-C bond formation reactions with Grignard or organozinc reagents (Scheme 4-251). As a catalyst, tris(acetylacetonato)iron is employed. The reaction requires an iodoarene substituent in appropriate distance to the amine. A mechanistic proposal involves the formation of an aryl radical by a reduced iron species, hydrogen abstraction from the a-position of the amine, ligation of the alkyl radical to the iron complex, and subsequent reductive elimination to provide the substituted pyrrolidine. ... 

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