Hemin, catalyst

Oxene is the active form of the hemin catalyst. It oxidizes two fatty acid hydroperoxide molecules to peroxy radicals that will then initiate lipid peroxidation. 

Many chemiluminescent compounds emit light only in neutral or, better in alkaline solution, e.g. luminol and lucigenin. Thus these can be used as neutralization indicators in acid-base titrations. Used in an end-point titration, light can be detected from strongly coloured or turbid or opaque solutions where colorimetric titrations are difficult. For example in the determination of the acidity of milk, of red wine, or mustard [4] or of dark coloured fats and oils [5,6]. It seems that luminol-fluorescein mixtures are better than luminol alone, because a hemin catalyst is not required here [7]. The system luminol - hemin leads to an irreversible destruction of hemin and is, therefore, not reversible with respect to the catalyst - in contrast to the luminol-fluorescein system [7]. 

The luminol dianion Lum2< > does not exist in appreciable quantities in aqueous solvents hydrogen peroxide and a catalyst such as hemin are required. Thus another mechanism seems to be at work here. Perhaps a hydrogen atom is abstracted from the luminol monoanion Lum( > to yield a luminol radical anion 55 which then reacts with oxygen or a radical ion derived from hydrogen peroxide according to 3,4,109)... 

A sterically protected, water-soluble synthetic iron porphyrin could provide a readily available biomimetic catalyst for both basic research and potential industrial applications. Such a synthetic hemin might be superior to the enzyme, in that being a small molecule it could interact, with the polymeric lignin molecule more readily than can ligninase. 

The CLD methods for HPLC using isoluminol (190) with microperoxidase catalysis, for determination of lipid hydroperoxides in clinical fluids, have been reviewed. Determination of phospholipids hydroperoxides by luminol (124) CL has been reviewed . A fast RP-HPLC method (retention times 1 to 2 min) for determination of hydroperoxides and other peroxide compounds includes UVD, which is not always effective, and CLD, attained on injection of luminol (124), the CL reagent (Scheme 3), hemin (75a), a catalyst, and NaOH to raise the pH of the solution. A FLD cell may act as CLD cell if the excitation source is turned off. The selectivity of CLD is of advantage over UVD in industrial analysis thus, for example, UVD of a sample from a phenol production line based on cumene oxidation (equation 13) shows peaks for cumyl hydroperoxide (27), unreacted cumene, cumyl alcohol and acetophenone, whereas CLD shows only the 27 peak. The... 

A procedure for determination of lipid hydroperoxides in human plasma is based on kinetic measurement of the CL of luminol (124) with hemin (75a) catalysis . CLD of microperoxidase-catalyzed oxidation of luminol (124) or isoluminol (190) was applied to detection and determination of amino acid hydroperoxides after exposure to UV and y-irradiation A method for determination of hydroperoxides in the phospholipids of cultured cells uses isoluminol (190) and microperoxidase as catalyst " . Simultaneous determination of phosphatidylcholine hydroperoxides and cholesteryl ester hydroperoxides in human serum is carried out by quantitative extraction of the lipids, HPLC separation by column switching and CLD using isoluminol (190) with microperoxidase catalysis . ... 

Acetylation and formylation are classical reactions in porphyrin chemistry. H. Fischer s synthesis of hemin, for which he was awarded the 1930 Nobel prize, required treatment of deuterohemin (49) with acetic anhydride (or acetyl chloride) in the presence of tin(IV) chloride as a Friedel-Crafts catalyst the product, 3,8-diacetyldeuterohemin-IX (50), was obtained in high yield. Fischer also accomplished formylation of iron porphyrins using dichloromethyl methyl ether and a Friedel-Crafts catalyst (B-37MI30700). Both of Fischer s examples resulted in peripheral substitution of unsubstituted iron porphyrins. However,... 

As mentioned above, both the point-mutation on the distal side of the Mb and the modification of the heme-propionate side chains are effective to convert the Mb into peroxidase and peroxygenase. Thus, one can imagine that the combination of an amino acid mutation and a modified-heme reconstitution may more effectively allow us a new catalyst by oxygen storage. Recently, two examples, which demonstrated the hybrid modification of Mb, have been reported. One is the T67R/S92D Mb reconstituted with the modified hemin where a histidine is linked at the terminal of the heme-propionate side chain (108). The peroxidase activities toward p-hydroxyphenylpropionic acid and tyramine oxidations by the reconstituted mutant Mb are increased by 24- and 2.3-fold, respectively, based on the kciJKm value compared to those observed for the native Mb. 

To date, the composition of active sites is known for many enzymes, the most probable action mechanisms are suggested, and comparison data exist on catalytic group properties in enzymes and free molecules in solutions. Note also that the chemical composition of catalytic active sites of enzymes is independent of the presence of any specific compounds. Moreover, the majority of them are the well-known compounds for homogeneous catalysis histidine imidazole, carboxylic groups of aspartic and aminoglutaric acids, flavins, hemins, etc. However, as homogeneous catalysts, they possess rather moderate or even poor catalytic activity in appropriate reactions. 

Note that the monooxygenase model reactions described above are performed in non-aqueous diluters. Therefore, hematin form is absent and only hemin is present, of which, apparently, formation of an intermediate shaped as Hm=0 is typical. Model catalysts of cytochrome P-450 operate in liquids, similar to enzymes themselves. Their activity depends on many factors, including diluter origin, reaction mixture pH and cell effects. As indicated [1], the gas-phase version of the oxidation process is much freer from these effects. 

Figure 7.31 Resonance Raman spectra (a) free hemin chloride, (b) 1% biomimic (catalyst) and (c) biomimic after reaction with H202. Soret band at 406.7 nm laser power equals 80mW and resolution is 2cm 1.

Attempts were made to increase the catalase activity of synthesized hemin-containing catalysts by the thermoactivation method, where the time of thermal treatment and temperature were varied. The positive role of thermoactivation was observed catalase activity and atomic catalytic activity (ACA) increased in activated samples and the growth of hemin-containing catalyst stability was observed (the lifetime increased almost 2-fold compared with inactivated samples) [88]. 

As can be seen from the works analyzed, modification of hemin-containing heterogeneous catalyst synthesis has been developed gradually. At present, catalysts obtained by the methods designed are being applied to complex production processes on pilot units and are approaching industrial use. 

II. Ikariyama, Y., Suzuki, S., andAizawa, M., Luminescence immunoassay of human serum albumin with hemin as labeling catalyst. Anal. Chem. 54, 1126-1129 (1982). 

The oxidation is catalyzed by various heavy metal ions such as Cu , Fe (hemin complex), Ni and Co and their complexes,and more importantly, the addition of these ions leads to the selective formation of disulfides without any overoxidized products. The cluster (Bu"4N)2[Fe4S4(SR)4], the analog of the active site of nonheme iron-sulfur proteins, catalyzed extremely smooth oxidation of thiols by oxygen to disulfides in acetonitrile at 0 C (equation 4), while in the case of FeCb or FeCb catalysts oxygen uptake was very slow." The catalysis by AI2O3 for aerobic oxidation is also common. Thus, by stirring thiols in benzene with exposure to air at room temperature for 4-6 h disulfides were obtained almost quantitatively except in the hindered case of Bu SH. 

The four-coordinate sqnare planar iron(n) porphyrins discussed above are not only of great valne in heme protein model chemistry, but also in chemical applications, since they undergo a wealth of ligand addition reactions. For example it has been shown that TPPFe complexes are active catalysts for important carbon transfer reactions in organic chemistry and are found to catalyze the stereoselective cyclopropanation of aUcenes, olefin formation from diazoalkanes, and the efficient and selective olefination of aldehydes and other carbonyl compounds. The active species in these carbon transfer reactions are presumably iron porphyrin carbene complexes. " It was also found that ferrous hemin anchored to Ti02 thin films reduce organic halides, which can pose serious health problems and are of considerable environmental concern because of their prevalence in groundwater. ... 

P. S. Traylor, D. Dolphin, T. G. Traylor, Sterically protected hemins with electronegative substituents Efficient catalysts for hydroxylation and epoxidation, /. Chem. Soc. Chem. Commun. (1984) 279. 

As an application of an oligonucleotide catalyst, we immobilized DNAzyme carrying peroxidase activity with hemin on gold particles using a thiol modification of the DNAzyme s end to detect peroxide 116). Usually, horseradish peroxidase is immobilized on a solid support. Compared with protein enzymes, the DNAzyme is advantageous because of its thermal stability and convenience of preparation. 

Haematoporphyrin derivative is synthesised from porcine hemine by treating a hematoporphyrin chlorhydrate with acetic acid in presence of sulfuric acid used as a catalyst [8], The resulting mixture is then filtered, neutralised and dried. The final step of HPD preparation, involving the product solubilisation in a diluted alkaline solution (pH adjusted at 7.4), provokes a wide variety of unexpected reactions with the formation of dimers and even oligomers of superior degrees (n < 7). 

Metalloporphyrins consist of porphyrin ring structures complexed to a central atom. Among them, hemin structures with central iron atoms at different oxidation states and chlorophyll pigments containing magnesium are most abundant The interest in their spectroelectrochemical studies is multiple. Thus, their adsorption and electrochemical behaviour at the electrode surface can be used not only to model their functions in a biological matrix but also to improve the practical application of porphyrin coated electrodes as catalysts or sensitizers in photoelectrochemical cells... 

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