Triplet quenching by onium salts in polar and nonpolar solvents

Kunze, Annett; Müller, Uwe; Tittes, Knut; Fouassier, Jean‐Pierre; Morlet‐Savary, Fabrice

doi:10.1016/s1010-6030(97)00178-0

Cited by 65 publications

(67 citation statements)

References 32 publications

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“…Most flavoproteins studied formed phenyl adducts when they were reduced prior to reaction with Ph 2 I ϩ under anaerobic conditions. Our results with reaction of free reduced flavin with Ph 2 I ϩ indicate that, in addition to the simple radical pathway of Tew (7), a substantial portion of flavin adducts formation proceeds either by direct attack of Ph 2 I ϩ on the reduced flavin or via radical recombination from a primary caged radical pair. A series of flavin-phenyl adducts have been isolated and characterized, involving the flavin C4a, N5, and C8 positions.…”

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confidence: 74%

“…The known capability of iodonium compounds to undergo radical reaction (1)(2)(3)(4), the fact that most of the known enzymes to be severely inhibited, such as neutrophil NADH oxidase (5,6), cytochrome P-450 reductase (7), xanthine oxidase (8), nitric-oxide synthase (9), and sulfite reductase (10), involve radical chemistry in their mechanisms has led to the concept that inhibition by iodonium compounds is a marker of flavoprotein enzymes functioning by radical mechanisms, particularly because other flavoproteins, such as D-and L-amino acid oxidases, glucose oxidase, and glutathione reductase, which do not involve radicals in their reaction, are not inhibited (8). Previous work has demonstrated that the enzyme flavin needs to be reduced for inhibition to occur, and that the reaction of the reduced flavin with iodonium compounds results in phenyl adducts of the flavin (8,10).…”

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confidence: 99%

“…We have reinvestigated the reaction of a number of flavoproteins with Ph 2 I ϩ , as well as the reaction of reduced FAD and FMN with Ph 2 I ϩ . Ph 2 I ϩ has been demonstrated to inhibit catalysis of several enzymes that do not operate by radical mechanisms. The main criteria for inhibition appear to be maintenance of the enzyme flavin in the reduced form during the steady state of catalysis and a system redox potential sufficiently negative to act as a reductant for Ph 2 I ϩ .…”

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confidence: 99%

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Reaction of Reduced Flavins and Flavoproteins with Diphenyliodonium Chloride

Chakraborty

Massey²

2002

Journal of Biological Chemistry

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The reaction of diphenyliodonium chloride with free reduced flavins has been studied by stopped flow spectrophotometry under anaerobic conditions, and second order rate constants were determined as a function of pH. The reactive flavin species was identified as the reduced anion, based on an observed reaction pK of 6.7. The product mixture was independent of the initial concentration of reactant and contained ϳ20% oxidized flavin. The results can be modeled quantitatively on a modification of the mechanism proposed by Tew (Tew, D. G. (1993) Biochemistry 32, 10209 -10215). The composition of the complex reaction mixture has been analyzed, and four flavin-phenyl adducts with distinctive absorbance and fluorescence characteristics have been identified, involving substitution at the flavin C4a, N5, and C8 positions. Inactivation of flavoprotein enzymes by diphenyliodonium has also been studied, and several examples were found where inactivation occurs readily, despite noninvolvement of radical intermediates in their reaction mechanisms. It can be concluded that inactivation by phenyliodonium species is not a valid indicator of catalytic mechanism involving radical intermediates. One of the several factors determining inactivation is maintenance of the enzyme flavin in the reduced form in the steady state of catalysis, the other factors being redox potential and accessibility of the inhibitor to the flavin active site.

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confidence: 74%

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confidence: 99%

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confidence: 99%

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Reaction of Reduced Flavins and Flavoproteins with Diphenyliodonium Chloride

Chakraborty

Massey²

2002

Journal of Biological Chemistry

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“…11,12,13 This compound is potentially useful for applications that require photosensitization in the middle region (300-400 nm) of the UV spectrum. This communication describes the discovery, that a wide variety of substituted phenothiazines are efficient photosensitizers for the photolysis of onium salts.…”

Section: Scheme Imentioning

confidence: 99%

Phenothiazine Photosensitizers for Onium Salt Photoinitiated Cationic Polymerization

Gomurashvili

Crivello

2003

ACS Symposium Series

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The syntheses of several different substituted phenothiazines are described and the ability of these compounds to photosensitize the photolysis of different onium salt cationic photoinitiators is described. These photosensitizers (PS) are generally operative in the mid-and long-range regions of the UV spectrum. The efficiencies of photosensitization of the cationic photopolymerizations of several typical epoxide and vinyl ether monomers by different substituted phenothiazine compounds were evaluated and compared. In addition, a phenothiazine-containing monomer and polymer were prepared and were shown to be effective photosensitizers.Currently, the most commonly used photoinitiators employed for photoinduced cationic polymerizations are diaryliodonium, I, and triarylsulfonium salts, Π, with the general structures shown below in which MtX n " represents a weakly nucleophilic counterion. Another promising class of photoinitiators is dialkylphenacylsulfonium salts, HI.

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“…The iodonium salts efficiently undergo photolysis with a quantum yield of 0.7 to 0.9 [64] and have a lower reduction potential than triarylsulfonium salts [65,66]. The mechanism of the photolysis first involves photoexcitation of diarylidodonium salt and then decay of the resulting excited singlet state with both heterolytic and homolytic cleavages of the carbon-iodine bond, resulting in the formation of free-radical, cationic, and cation-radical fragments [64].…”

Section: Photoelectron Transfer-induced Micellization [54]mentioning

confidence: 99%

Photo-Induced Micellization of Block Copolymers

Yoshida

Kuwayama

2010

Polymers

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Abstract:We found novel photo-induced micellizations through photolysis, photoelectron transfer, and photo-Claisen rearrangement. The photolysis-induced micellization was attained using poly(4-tert-butoxystyrene)-block-polystyrene diblock copolymer (PBSt-b-PSt). BSt-b-PSt showed no self-assembly in dichloromethane and existed as isolated copolymers. Dynamic light scattering demonstrated that the copolymer produced spherical micelles in this solvent due to irradiation with a high-pressure mercury lamp in the presence of photo-acid generators, such as bis(alkylphenyl)iodonium hexafluorophosphate, diphenyliodonium hexafluorophosphate, and triphenylsulfonium triflate. The 1 H NMR analysis confirmed that PBSt-b-PSt was converted into poly(4-vinylphenol)-block-PSt by the irradiation, resulting in self-assembly into micelles. The irradiation in the presence of the photo-acid generator also induced the micellization of poly(4-pyridinemethoxymethylstyrene)-block-polystyrene diblock copolymer (PPySt-b-PSt). Micellization occurred by electron transfer from the pyridine to the photo-acid generator in their excited states and provided monodispersed spherical micelles with cores of PPySt blocks. Further, the photo-Claisen rearrangement caused the micellization of poly(4-allyloxystyrene)-block-polystyrene diblock copolymer (PASt-b-PSt). Micellization was promoted in cyclohexane at room temperature without a catalyst. During micellization, the elimination of the allyl groups competitively occurred along with the photorearrangement of the 4-allyloxystyrene units into the 3-allyl-4-hydroxystyrene units. OPEN ACCESSPolymers 2010, 2 624

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Triplet quenching by onium salts in polar and nonpolar solvents

Cited by 65 publications

References 32 publications

Reaction of Reduced Flavins and Flavoproteins with Diphenyliodonium Chloride

Reaction of Reduced Flavins and Flavoproteins with Diphenyliodonium Chloride

Phenothiazine Photosensitizers for Onium Salt Photoinitiated Cationic Polymerization

Photo-Induced Micellization of Block Copolymers

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