67253-23-0Relevant articles and documents
A mechanistic study on the disproportionation and oxidative degradation of phenothiazine derivatives by manganese(III) complexes in phosphate acidic media
Wisniewska, Joanna,Rzesnicki, Pawel,Topolski, Adrian
, p. 767 - 774 (2011)
The oxidative degradation of phenothiazine derivatives (PTZ) by manganese(III) was studied in the presence of a large excess of manganese(III)-pyrophosphate (P2O7 2-), phosphate (PO4 3-), and H+ ions using UV-vis. spectroscopy. The first irreversible step is a fast reaction between phenothiazine and manganese pyrophosphate leading to the complete conversion to a stable phenothiazine radical. In the second step, the cation radical is oxidized by manganese to a dication, which subsequently hydrolyzes to phenothiazine 5-oxide. The reaction rate is controlled by the coordination and stability of manganese(III) ion influenced by the reduction potential of these ions and their strong ability to oxidize many reducing agents. The cation radical might also be transformed to the final product in another competing reaction. The final product, phenothiazine 5-oxide, is also formed via a disproportionation reaction. The kinetics of the second step of the oxidative degradation could be studied in acidic phosphate media due to the large difference in the rates of the first and further processes. Linear dependences of the pseudo-first-order rate constants (k obs) on [Mn III] with a significant non-zero intercept were established for the degradation of phenothiazine radicals. The rate is dependent on [H+] and independent of [PTZ] within the excess concentration range of the manganese(III) complexes used in the isolation method. The kinetics of the disproportionation of the phenothiazine radical have been studied independently from the further oxidative degradation process in acidic sulphate media. The rate is inversely dependent on [PTZ+.], dependent on [H+], and increases slightly with decreasing H+ concentration. Mechanistic consequences of all these results are discussed.
Reduction potentials of flavonoid and model phenoxyl radicals. Which ring in flavonoids is responsible for antioxidant activity?
Jovanovic, Slobodan V.,Steenken, Steen,Hara, Yukihiko,Simic, Michael G.
, p. 2497 - 2504 (2007/10/03)
Model phenoxyl and more complex flavonoid radicals were generated by azide radical induced one-electron oxidation in aqueous solutions. Spectral, acid-base and redox properties of the radicals were investigated by the pulse radiolysis technique. The physicochemical characteristics of the flavonoid radicals closely match those of the ring with the lower reduction potential. In flavonoids which have a 3,5-dihydroxyanisole (catechins), or a 2,4-dihydroxyacetophenone (hesperidin, rutin, quercetin)-like A ring and a catechol- or 2-methoxyphenol-like B ring, the antioxidant active moiety is clearly the B ring [reduction potential difference between the model phenoxyls is ΔE(A-B ring models) > 0.1 V]. In galangin, where the B ring is unsubstituted phenyl, the antioxidant active moiety is the A ring. Even though the A ring is not a good electron donor, E7, > 0.8/NHE V, it can still scavenge alkyl peroxyl radicals, E7, = 1.06 V, and the Superoxide radical, E7 > 1.06 V. Quercetin is the best electron donor of all investigated flavonoids (measured E10.8 = 0.09 V, and calculated E7 = 0.33 V). The favourable electron-donating properties originate from the electron donating O-3 hydroxy group in the C ring, which is conjugated to the catechol (B ring) radical through the 2,3-double bond. The conjugation of the A and B rings is apparently minimal, amounting to less than 2.5% of the substituent effect in either direction. Thus, neglecting the acid-base equilibria of the A ring, and using those of the B ring and the measured values of the reduction potentials at pH 3,7 and 13.5, the pH dependence of the reduction potentials of the flavonoid radicals can be calculated. In neutral and slightly alkaline media (pH 7-9), all investigated flavonoids are inferior electron donors to ascorbate. Quercetin, E7 = 0.33 V, and gallocatechins, E7 = 0.43 V, can reduce vitamin E radicals (assuming the same reduction potential as Trolox C radicals, E7 = 0.48 V). Since all investigated flavonoid radicals have reduction potentials lower than E7 = 1.06 V of alkyl peroxyl radicals, the parent flavonoids qualify as chain-breaking antioxidants in any oxidation process mediated by these radicals.
Endor Studies of Cation Radicals from Pharmacologically Active Phenothiazines
Helle, N.,Kurreck, H.,Bock, M.,Kieslich, W.
, p. 964 - 970 (2007/10/02)
A variety of substituted phenothiazine cation radicals, including those from pharmacologically active derivatives, e.g. chloropromazine, alimemazine and laevomepromazine, have been studied by means of ENDOR and TRIPLE resonace spectroscopy.These techniques allowed accurate determinations of hyperfine coupling constants, including their signs.Conclusions concerning molecular structure (e.g. twist angles) could be drawn, supporting previous investigations of the interrelationship of molecular conformations with the pharmacological potential, i.e. neuroleptic, antihistaminic or anti-Parkinsonian.
Cation Radicals of Phenothiazines. Part 4. Electron Transfer Between Aquamanganase(III) and N-Alkylphenothiazines
Pelizzetti, Ezio
, p. 484 - 486 (2007/10/02)
The kinetics of electron transfer between aquamanganase(III) and N-alkylphenothiazines, giving rise to the corresponding cation radicals, has been investigated in the range 0.20-1.50 mol dm-3 HClO4 at different temperatures.The main reaction path has been assigned to the unhydrolysed species Mn(3+)(aq), and there is a dependence of the rate constants on the corresponding reduction potentials.
