Vanadium activated peroxide

It is possible to measure the formation of various radicals such as reactive oxygen species in cells. Reactive oxygen species (ROS) activate the nuclear factor of activated T cell transcription factor (NFAT), which is associated with its dephosphorylation, nuclear translocation, and increased affinity for DNA binding. Vanadium activation of nuclear factor of activated T cells (NFAT) was found to correlate with formation of the ROS H202 and was dependent upon the activity of calcium channels [39], In activated human neutrophiles, vanadium(II), (III), and (IV) increased hydroxyl radical formation and attenuation of myeloperoxidase activity, whereas V(V) did not show these effects. Similar results were seen in a cell-free system [40], Increased lipid peroxidation in liver but not in kidneys was found in normal rats treated with vanadate [41]. 

Related V complexes show activity toward the oxidative decomposition of pinacol with C—C bond cleavage and aerobic oxidation of 4-methoxybenzylalcohol and other lignin model compounds." Other oxidovanadium(V) complexes with c 5-2,6-bis-(methanolate)-piperidine ligands of the type depicted on Scheme 3 were appHed as catalysts to convert prochiral alkenols into 2-(tetrahydrofiiran-2-yl)-2-propanols, 2-(tetrahydropyran-2-yl)-2-propanols, oxepan-3-ols and epoxides, upon oxidative alkenol cyclization with TBHP as oxidant (Scheme 3)." These catalysts are rather stable and possess improved chemoselectivity, e.g., epoxidation of geraniol occurs enantioselectively. It was ruled out the vanadium(V) ieri-butyl peroxy complex formation is a key step to activate peroxides. 

Depending on the peroxide class, the rates of decomposition of organic peroxides can be enhanced by specific promoters or activators, which significantly decrease the energy necessary to break the oxygen—oxygen bond. Such accelerated decompositions occur well below the peroxides normal appHcation temperatures and usually result in generation of only one usehil radical, instead of two. An example is the decomposition of hydroperoxides with multivalent metals (M), commonly iron, cobalt, or vanadium ... 

A.ctive driers promote oxygen uptake, peroxide formation, and peroxide decomposition. At an elevated temperature several other metals display this catalytic activity but are ineffective at ambient temperature. Active driers include cobalt, manganese, iron, cerium, vanadium, and lead. 

Under microwave irradiation and applying MCM-41-immobilized nano-iron oxide higher activity is observed [148]. In this case also, primary aliphatic alcohols could be oxidized. The TON for the selective oxidation of 1-octanol to 1-octanal reached to 46 with 99% selectivity. Hou and coworkers reported in 2006 an iron coordination polymer [Fe(fcz)2Cl2]-2CH30H with fez = l-(2,4-difluorophenyl)-l,l-bis[(l//-l,2,4-triazol-l-yl)methyl]ethanol which catalyzed the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as oxidant in 87% yield and up to 100% selectivity [149]. An alternative approach is based on the use of heteropoly acids, whereby the incorporation of vanadium and iron into a molybdo-phosphoric acid catalyst led to high yields for the oxidation of various alcohols (up to 94%) with molecular oxygen [150]. 

Except for Prussian blue activity in hydrogen peroxide, reduction has been shown for a number of transition metal hexacyanoferrates. The latter were cobalt [151], nickel [152], chromium [150], titanium [153], copper [154], manganese [33], and vanadium [28] hexacyanoferrates. However, as was shown in review [117], catalytic activity of the mentioned inorganic materials in H202 reduction is either very low, or is provided by impurities of Prussian blue in the material. Nevertheless, a number of biosensors based on different transition metal hexacyanoferrates have been developed. 

Haloperoxidases are peroxidases capable of halogenating substrates in the presence of halide and hydrogen peroxide [14] or other reactions such as sulfoxidation, epoxidation and aromatic hydroxylation. Here, the halide ion is initially bound to the active site which may incorporate heme or vanadium or be metal free. The halide ion is incorporated into the substrate after electron transfer... 

The incorporation of vanadium(V) into the framework positions of silicalite-2 has been reported by Hari Prasad Rao and Ramaswamy . With this heterogeneons oxidation catalyst the aromatic hydroxylation of benzene to phenol and to a mixtnre of hydroqninone and catechol conld be promoted. A heterogeneons ZrS-1 catalyst, which has been prepared by incorporation of zirconinm into a silicalite framework and which catalyzes the aromatic oxidation of benzene to phenol with hydrogen peroxide, is known as well in the literature. However, activity and selectivity were lower than observed with the analogous TS-1 catalyst. 

Vanadium-catalyzed hydrocarbon oxidation with peroxides can be carried out also by supporting the catalyst with the appropriate ligand on polymers " , on sUica " or encapsulating it in zeolites ". Similar activity has been obtained with vanadium-containing... 

Vanadium-catalyzed hydroxylation of benzene and cyclohexane has also been obtained with in situ generation of hydrogen peroxide from H2/O2 in the presence of palladium. A similar process has been settled for methane oxygenation to methyl trifluoroacetate and formic acid. Monoperoxovanadate, as well as copper hydroperoxides, have been indicated as the active species for the activation of the C—H bond of methane. 

By analogy between the oxo forms of vanadium(V) and iron(IV), the latter being the active species in oxidations by cytochrome P-450, the system constituted by vanadium oxide as the catalyst, and t-butylhydro-peroxide, as the oxidant, gives good results in the conversion of olefins to the corresponding epoxides. With the supported "clayniac" catalyst, in the presence of i-butyraldehyde as a sacrificial reducer, olefins are epoxidized in good yields by compressed air at room temperature, in a convenient procedure. 

While hydrogen peroxide cannot be employed to epoxidize C,C double bonds, its combination with boron trifluoiide is effective. Accentuation of polar character (in this case an acceptor) by an external agent through complex formation achieves the activation. Similar activation [242] of hydroperoxides by vanadium and titanium cations is now well known. 

The pentoxides of vanadium, niobium, and tantalum react with hydrogen peroxide to produce per-acids of the general formula HR04. H20. These per-acids increase in stability with increase in atomic weight. Pertantalic acid is a white solid which can be heated to 100° C. without undergoing decomposition. The oxyfluorides of these metals also take up active oxygen to yield peroxyfluorides, which are much better defined in the case of niobium and tantalum than with vanadium. 

If we consider the d0 metal-N,JV-dialkylhydroxylamino complexes (79), (80) and (81) as valid models for the reactive but unstable alkyl peroxide species Mo02(OOR)2, VO(OOR)3 or V203(00R)4, and Ti(OOR)4 presumably involved in catalytic oxidations, the low activity of vanadium and titanium for the epoxidation of simple alkenes could be interpreted by the fact that these alkenes cannot displace the O.O-bonded alkyl peroxide groups in the coordinatively saturated Vv- and Tiiv-alkyl peroxide species, whereas allylic alcohols can displace the alkyl peroxide groups by forming bidentate allylic alkoxides as in equation (75).162... 

The standard procedure for removal of active-site vanadium(V) has been to incubate V-BrPO in 0.1 Mphosphate-citrate buffer pH 3.8, containing 10 mM ethylenediaminetetra-acetic acid (edta). These conditions remove over 95% of the vanadium, which produces the inactive apo-BrPO derivative [1,45]. The essential component of the apoprotein preparation is the phosphate, without which vanadium is not completely removed and the enzyme is not completely inactivated [46], In fact phosphate in the absence of edta is sufficient for preparation of apo-BrPO [46] inactivation by phosphate is much faster at low pH (pH 4) than at neutral or higher pH. However, phosphate inactivation does not occur in the presence of dihydrogen peroxide [46],... 

In addition to bromide and iodide, V-BrPO can catalyze the oxidation of chloride [64]. As mentioned previously and discussed more fully later, a distinct enzyme, vanadium chloroperoxidase, has also been discovered. Originally it was thought that V-BrPO could only catalyze the oxidation of bromide and iodide by dihydrogen peroxide. In fact, under the standard mcd bromoperoxidase assay conditions, in which the V-BrPO concentration is ca. nanomolar, very little, if any, chlorination of mcd is observed. However, it seemed very unusual that V-BrPO could be inhibited by fluoride and bromide, but apparently not by chloride [27], In reinvestigating the halide specificity of V-BrPO, it was discovered that when the enzyme concentration is increased 100-fold to 0.1 pM, chlorination is observed at an appreciable rate [64], The specific chloroperoxidase activity is 0.76 U/mg (under conditions of 1 M certified 100% bromide-free KC1, 2 mMH202, 50 pM... 

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