Wurster's Salts Research Articles

Light-driven H2O2 production over redox-active imine-linked covalent organic frameworks

Imine-linked covalent organic frameworks (COFs) provide distinctive prospects for promoting photocatalytic H2O2 production, yet the intricate involvement of imine-derived linkages chemistry under light irradiation remains incompletely elucidated. Here, imine-linked COF-LZU1 demonstrates a visible light-driven H2O2 evolution rate of 387 ​μmol ​g−1 ​h−1, particularly, negligible dependence on the sacrificial agents. By virtue of electron paramagnetic spectroscopy and solid-state nuclear magnetic resonance, we experimentally tracked the structure evolution and identified its autooxidation to Wurster's salt mimics under the photocatalytic conditioning. This finding coincides with the radical anion ·O2− governed reaction pathway and is further rationalized with additional theoretical calculations. This study provides insights into both photophysical/photochemical aspects over the imine-linkage structure.

Proton-coupled electron transfer oxidation of O-H bond by the N-radical cation of Wurster's blue salt (TMPDA˙+).

Here, we report the proton-coupled electron transfer reaction between TEMPO-H and Wurster's blue salt (TMPDA˙+). TMPDA˙+ could abstract a hydrogen atom from 2,2,6,6-tetramethyl-1-hydroxy-piperidine (TEMPO-H) via concerted electron-proton transfer and displayed a large KIE (7.05 ± 0.07 at 298 K). This work shows that a nitrogen-centered radical cation (R3N˙+) such as TMPDA˙+ is more than a weak single-electron oxidant, and can also be an effective PCET reagent for oxidative bond activation.

Chemical Mechanisms for Skin Sensitization by Aromatic Compounds with Hydroxy and Amino Groups

It is well-known that aromatic diamino-, dihydroxy-, and amino-hydroxy compounds, with NH(2) and OH groups in ortho- or para-positions relative to each other, are strong skin sensitizers. In this paper, we analyze published potency and cross-reactivity data, whereby animals sensitized to one of these compounds are challenged with other compounds. The data are consistent with two parallel chemical reaction mechanisms: oxidation to electrophilic (protein reactive) quinones or quinone imines or formation of protein-reactive free radicals such as the Wurster salt, which can be formed by para-phenylene diamine. Compounds with NH(2) and OH groups meta to each other have also been found to be skin sensitizers, in some cases quite strong sensitizers. For these compounds, direct formation of quinones or quinone imines is not possible, and free radicals of the Wurster salt type are not favored. Here, we present a molecular mechanism to rationalize the sensitization potential of such compounds and, using the results of quantum mechanics calculations, show how this mechanism can explain observed structure-potency trends.

Functions of Trace Metals in Fibers on Dyeing of Wool Fiber with Oxidation Dyes

To clarify what components of CMC contribute to the oxidation reaction, the effects of pretreatment of wool fibers using ethylenediaminetetraacetic acid (EDTA) solution and premordanting with the solution of metal salts on the dye uptake of the dinuclear oxidation dyes into wool fibers were investigated. The dye uptake of the wool samples pretreated with EDTA solutions decreased apparently compared to that of the intact wool sample. On the contrary, the wool samples premordanted with copper, iron and nickel salts allowed the dye uptake of oxidation dye inside the wool fiber to increase. These findings indicate that the metal ions presented primarily within the intercellular materials play an important role in developing the colored oxidation dye on⁄into the fiber. The presence of transition metal ions in the intercuticular material causes hydrogen peroxide to undergo radical decomposition, leading to oxidizing species by means of Haber-Weiss mechanism. They take part as initiator of oxidation reaction, where the dye precursor is electrochemically oxidized to its corresponding Wurster salt.

Colour development and luminescence phenomena in epoxy glasses

The process of colour development in aromatic-amine cured epoxy resin glasses following exposure to oxygen has been studied using electron spin resonance (ESR) and thermoluminescence (TL). Even short duration exposure to oxygen was found to produce species in glassy epoxy resins which gave rise to TL when heated from room temperature to a temperature just below the cure temperature. In some epoxy samples, oxygen exposure over longer periods was found to produce sample colouration. UV-visible spectrophotometry revealed chromophores which were believed to arise from the diaminodiphenylmethane structural unit found in epoxy systems containing the resin, N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) or the curing agent, 4,4′-diaminodiphenylmethane (DDM). The chromophore produced in TGDDM-based resins appeared to be simlar to the 'Wurster's salt'-type structure produced by photoionization of these systems. A distinctive ESR spectrum was also noted for samples exposed to oxygen. These results are indicative of both peroxide group formation on the methylene groups as well as the formation of amine centred radical cations, and are consistent with the oxidative sensitivity of these epoxy resins. The TL is believed to result from the thermally induced recombination of the 'Wurster's salt'-like cations with peroxy anions leading to the production of an electronically excited diaminobenzophenone structure

Study of the new electron transfer mediators in glucose oxidase catalysis

The steady-state oxidation of glucose oxidase from Aspergillus niger by phenothiazines, phenoxazines, Wurster's salts, dithia- and tetrathiaaromatic compounds, and nickelocene was investigated spectrophotometrically and electrochemically. At pH 7.0 the determined oxidation rate constants (TN/ K m) vary in the range 10 3 to 10 8 M −1·s −1. For phenothiazines, phenoxazine and Wurster's salts oxidation constants depend on the redox potential of the electron acceptors, and results were interpreted in the framework of the outer sphere electron transfer theory (Marcus and Sutin, Biochim. Biophys. Acta, 811 (1985) 265). The interpretation of the kinetic results concerning thiaaromatic compounds and metallocenes are complicated due to complex formation with the enzyme active center and aggregation of their oxidized form in buffer solution.

Capto‐dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)

AbstractThe 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto‐dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd‐Substitution has synthetically useful applications: cd‐substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross‐conjugated cd‐substituents are “radicophilic” and permit twofold carbon radical addition. cd‐Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd‐substituted molecules appear to involve radicals.

Titrimetric Determination of N,N′-Disubstituted p-Phenylenediamines

Abstract Three types of p-phenylenediamine derivatives used extensively as antioxidants and antiozonants in rubber compounds are N,N′-di-sec-alkyl-, N-sec-alkyl-N′-aryl-, and N,N′-diaryl-p-phenylenediamines. Available methods for these compounds are based mainly on a colorimetric determination of their colored oxidation products, the Wurster's salts or the p-quinonediimines. The deep coloration of the Wurster's salts was used as the basis of a spot test for the rapid detection of these diamines in rubber compounds. This test permits one to differentiate the three types of p-phenylenediamines. An investigation of the neutralization of p-phenylenediamines in nonaqueous solvents showed that N,N′-di-sec-alkyl- and N-sec-alkyl-N′-aryl-p-phenylenediamines could be determined readily in this way. The N,N′-diaryl derivatives did not give satisfactory titration curves because of their low basicity. By the addition of chloranil, however, diaryl-p-phenylenediamines were oxidized to the Wurster's salts with the formation of one equivalent of base which could be neutralized by acid. A similar procedure was applicable to the determination of N,N′-diaryl-p-quinonediimines, or mixtures of these diamines and diimines.

Titrimetric Determination of N,N'-Disubstituted p-Phenylenediamines.

Abstract Three types of p-phenylenediamine derivatives used extensively as antioxidants and antiozonants in rubber compounds are N,N′-di-sec-alkyl-, N-sec-alkyl-N′-aryl-, and N,N′-diaryl-p-phenylenediamines. Available methods for these compounds are based mainly on a colorimetric determination of their colored oxidation products, the Wurster's salts or the p-quinonediimines. The deep coloration of the Wurster's salts was used as the basis of a spot test for the rapid detection of these diamines in rubber compounds. This test permits one to differentiate the three types of p-phenylenediamines. An investigation of the neutralization of p-phenylenediamines in nonaqueous solvents showed that N,N′-di-sec-alkyl- and N-sec-alkyl-N′-aryl-p-phenylenediamines could be determined readily in this way. The N,N′-diaryl derivatives did not give satisfactory titration curves because of their low basicity. By the addition of chloranil, however, diaryl-p-phenylenediamines were oxidized to the Wurster's salts with the forma...

Visible Absorption Spectrum and Electron Spin Resonance of Wurster's Salt Adsorbed on Silica Alumina.

,シウカアルミナ表面の Lewis 型酸性点の存在を,吸者した p-フェニレンジアミンが Lewis 型酸性点と反応して Wurster 塩(セミキノン型ラジカル)を生成することによって証明した。 吸着表面におけるセミキノンの存在は,可視吸収スペクトルが水溶液のセミキノンの吸収帯 462mμ とほぼ一致して 470mμ に吸収帯を示すこと,および電子スピン共鳴スペクトルの出現から,遊離基の存在が確認されたことによって示された。種々の温度処理したシリカアルミナについてその全表面酸性度の相対量を,吸収した Wurster 酸の吸収スペクトルの吸収強度から定量した。そして,処理温度の上昇による Lewis 型酸性点の増加量は,全酸性点の増加量にほぼ比例することを見出した。

A Polarographic study of some Wurster salts

Four related Wurster salts are subjected to a polarographic investigation. In the case of Wurster's blue, results from the dropping mercury electrode, stationary platinum electrode, and rotated platinum electrode are compared. The Wurster salt of p-phenylenediamine is unstable in aqueous solution but is fairly stable in a mixture of methanol, acetic acid, and water and the decrease of diffusion current with time indicates a disproportionation. Wurster's red is also unstable in aqueous solution. In the solvent methanol, acetic acid, and water, a wave is observed with the stationary platinum electrode whose E� compares favourably with the potentiometric E?0. Evidence from the three types of electrodes mentioned previously indicates two one-electron waves for Wurster's blue. The semiquinone formation constant qualitatively appears much greater than that reported from potentiometric work. Decrease of diffusion current with time is perhaps due to a disproportionation (the very unstable di-imine has been shown to revert to the radical in aqueous solution). Polarographic waves given by the Wurster salt of diaminodurene suggest that the radical does not exist in aqueous solution. Waves corresponding to the original amine and duroquinone (formed by hydrolysis of the di-imine) are obtained.

Some Higher Members of the Wurster Salts Series

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSome Higher Members of the Wurster Salts SeriesRobert F. MilliganCite this: J. Am. Chem. Soc. 1950, 72, 6, 2775–2776Publication Date (Print):June 1, 1950Publication History Published online1 May 2002Published inissue 1 June 1950https://doi.org/10.1021/ja01162a515RIGHTS & PERMISSIONSArticle Views70Altmetric-Citations5LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (270 KB) Get e-Alerts Get e-Alerts

Calculation of the Absorption Spectrum of Wurster's Salts

The so-called Wurster's salts, radicals which occur in the oxidation of the paraphenylene diamines, show a strong absorption in the visible. The frequency and the intensity were calculated by the method of completely antisymmetrized products of molecular orbitals, with the introduction of but one empirical constant, namely, the difference between the ionization potential of the non-bonding nitrogen electron in ammonia, and the ionization potential of benzene. The results are in good agreement with the observed absorption band. The calculated intensity corresponds to an electron number of about 0.3, the observed one to about 0.1. The shift of the band to longer wave-length, and the intensification upon substitution of C${\mathrm{H}}_{3}$ groups on the nitrogen is explained qualitatively.

The Free Radicals of the Type of Wurster's Salts

The Free Radicals of the Type of Wurster's Salts