Quercetin oxidation

Copper dioxygenase Quercetinase Fungal Quercetin oxidative cleavage... 

Quercetin- dsDNA interaction at a multi-layer DNA biosensor To study the interaction between dsDNA and the quercetin-Cu(II) ion complex, a newly prepared multi-layer dsDNA biosensor was kept for 10 min in a mixture of quercetin and Cu(II) ions. The electrode was transferred to supporting electrolyte and a DP voltammogram recorded. The quercetin oxidation peak 1 occurs followed by another peak at +0.45 V (Fig. 20.3). Comparing with the voltammogram obtained before incubation, the peaks due to dGuo and dAdo base oxidation are several... 

Fig. 9. The mechanism of reduction of quercetin oxidation with N-bromosuccinimide [34].

Table 5 shows that exposure of 15 mg of quercetin in 100 ml of pH 7.5 ethanol-buffer for 24 hours at 37 C produced an inactive product. However, activity was retained when the concentration of quercetin was increased to 30, 60, 75 mg in 100 ml of ethanol-buffer. In contrast, at pH 9.0, inactivation took place at all four concentrations. These results suggest that, in addition to the paramount importance of hydroxide ions in the destruction of quercetin, quercetin oxidation appears to be governed by concentration, at least at low concentrations. 

Study of effect of myeloperoxidase on quercetin at pH 6.0 indicated quercetin oxidation via the formation of the oxidation product. The stability of quercetin and oxidation product was investigated as a function of time by using spectrophotometric and HPLC techniques. The apparent pseudo first-order rate constants were calculated and discussed. 

The heme enzyme myeloperoxidase (MPO) is oxidant enzyme in the process of inflammation and atherogenesis [8]. Myeloperoxidase is relatively nonspecific with respect to its reducing substrates. This enzyme is able to oxidize different substrates among which anilines and phenols [9-11]. This letter deals with quercetin oxidation hy myeloperoxidase-H202 system. 

The kinetic curves that describe the quercetin degradation and the formation of the oxidation product in the presence of different MPO, concentrations are shown in Figure 2. In the presence of MPO concentration that was >15 nM oxidation product was formed at the first minute of reaction (Figure 2(a)). The overall apparent first-order rate constants for the oxidation product formation and quercetin transformation to its degradation products were determined from the kinetic curves and are presented in Table 1. For comparison, in Table 1 we also presented values for these constants obtained for quercetin oxidation by UV irradiation [17]-... 

Figure 2 Change of absorbance of quercetin in the presence of various MPO concentrations in the function of time, at pH 6.0 (a) formation of quercetin oxidation product at Inset 20 nM MPO and (b) degradation of quercetin oxidation product at...

The rate of quercetin oxidation by MPO at pH 6.0 is 3-fold faster compared with the rate of quercetin oxidation by UV irradiation at pH 10.0. Moreover, product obtained for quercetin oxidation by MPO at pH 6.0 is more stable than product of quercetin oxidation by UV irradiation at pH 10.0. 

Eosin Flavonoids Morin Flavonol, fisetin, robinetin Quercetin Rutin condensation products of urea, formaldehyde and methanol [126], pesticide derivatives [127] sweetening agents [128, 129] anion-active and nonionogenic surface-active agents [130] steroids, pesticides [29,132, 133] pesticides [134—137] vanadium in various oxidation states [138] uracil derivatives [139]... 

HAYEK T, FURHMAN B, VAYA J, ROSENBLAT M, BELINRY P, COLEMAN R, ELIS A, AVIRAM M (1997) Reduced progression of atherosclerosis in apolipoprotein E-deficient mice following consiunption of red wine, or its polyphenols quercetin or catechin, is associated with reduced susceptibility of LDL to oxidation aggregation, Arteriosclerosis, Thrombosis and Vascular Biology, 17, 2744-52. 

Fig. 16.4 Interaction between quercetin (Quer) and iron and the balance between pro-oxidative and antioxidative effects. Quercetin may reduce Fe(H20) to yield Fe(H20) active in the Fenton region forming hydroxyl radicals ( OFI) or alkoxyl radicals ( OR), in effect being pro-oxidative. In contrast, quercetin may form a complex with iron(II), inactive in reducing FI2O2 to OFI, but rather oxidised in the quercetin ligand, in effect being antioxidative. Quer (-H) is the phenoxyl radical.

In the water-like solvent tert-butyl alcohol, a-tocopherol was found to prevent lipid oxidation, showing a distinct lag-phase for oxygen consumption. This was in contrast to quercetin or epicatechin, which were only weak retarders of lipid oxidation without any clear antioxidative effect. Quercetin or epicatechin, when combined with a-tocopherol, increased the lag-phase for oxygen consumption as seen for a-tocopherol alone. The stoichiometric factor for a-tocopherol, a-TOH, as chain-breaking antioxidant has the value n = 2 according to the well-established mechanism ... 

Protection against oxidative damage of erythrocyte membrane by the flavonoid quercetin and its relation to iron chelating activity, FEBS Letters, 416, 123-9. 

Quercetin is a naturally occurring flavonoid with both antioxidant and prooxidant activities (Scheme 10.12).90 It has been demonstrated in a variety of bacterial and mammalian mutagenicity experiments that quercetin has mutagenic properties that could be related to quinoid formation.91,92 Quercetin is initially oxidized to an o-quinone, which rapidly isomerizes to di-QMs that could also be called extended... 

An extract from Lactuca indica showed significant free radical scavenging activity, and protected phixl74 supercoiled DNA against strand cleavage and reduced oxidative stress in human promyelocytic leukemia HL-60 cells. On account of protocatechulic acid, methyl p-hydroxybenzoate, caffeic acid, 3,5-dicaffeoylquinic acid, luteolin 7-O-fT glucopyranoside, and quercetin 3-0-(3-g 1 ucopyranoside are the major antioxidative constituents (111). 

Lodi, F, R Jimenez, C Menendez, PW Needs, J Buaret, and E Perez-Vizcaino. 2008. Glucuronidated metabolites of the flavonoid of quercetin do not auto-oxidize, do not generate free radicals and do not decrease nitric oxide bioavailability. Planta Med 74(7) 741-746. 

E.S.B. Ferreira, A. Quye, H. McNab, A.N. Hulme, Photo oxidation products of quercetin and morin as markers for the characterisation of natural flavonoid yellow dyes in ancient textiles, Dyes in History and Archaeology 18, 63 72 (2002). 

Jimenez M and Garcia-Carmona F. 1999. Oxidation of the flavonol quercetin by polyphenol oxidase. J Agric Food Chem 47(l) 56-60. 

Red wine contains quercetin, rutin, catechin, and epicatechin, among other flavonoids (Frankel and others 1993). Quercetin and other phenolic compounds isolated from wines were found to be more effective than a-tocopherol in inhibiting copper-catalyzed LDL oxidation. It has been determined that quercetin has also several anti-inflammatory effects it inhibits inflammatory cytokine production (Boots and others 2008), inducible NO synthase expression and activation of inflammatory transcription factors (Hamalainen and others 2007), and activity of cyclooxygenase and lipooxygenase (Issa 2006), among others. 

BSA was oxidized by the cupric quercetin complex probably through binding to tryptophan residue [26]. Iwai et al. [27] showed that the iron regulatory protein 2 (IRP2) responsible... 

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