- Fluorescent Dyes with Large Stokes Shifts Based on Benzo[1,2-d:4,5-d']bis([1,3]dithiole) (“S4-DBD Dyes”)
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We report on a further development of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes by replacement of the four oxygen atoms of the heterocyclic core by sulfur atoms. This variation causes striking changes of the photophysical properties. Whereas absorption and emission significantly shifted to longer wavelength, the fluorescence lifetimes and quantum yields are diminished compared to DBD dyes. The latter effect is presumably caused by an enhanced intersystem crossing to the triplet state due to the sulfur atoms. The very large Stokes shifts of the S4-DBD dyes ranging from 3000 cm–1 to 7400 cm–1 (67 nm to 191 nm) should be especially emphasized. By analogy with DBD dyes a broad variation of absorption and emission wavelength is possible by introducing different electron withdrawing substituents. Moreover, some derivatives for coupling with biomolecules were developed.
- Freyse, Daniel,Kelling, Alexandra,Schuster, David,Wessig, Pablo
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- Improved, odorless access to Benzo[1,2-d;4,5-d′]-bis[1,3]dithioles and tert-butyl arylsulfides via C-S cross coupling
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Benzo[1,2-d;4,5-d′]bis[1,3]dithioles are important building blocks within a range of functional materials such as fluorescent dyes, conjugated polymers, and stable trityl radicals. Access to these is usually gained via tert-butyl aryl sulfides, the synthesis of which requires the use of highly malodorous tert-butyl thiol and relies on SNAr-chemistry requiring harsh reaction conditions, while giving low yields. In the present work, S-tert-butyl isothiouronium bromide is successfully applied as an odorless surrogate for tert-butyl thiol. The C-S bond formation is carried out under palladium catalysis with the thiolate formed in situ resulting in high yields of tert-butyl aryl sulfides. The subsequent formation of benzo[1,2-d;4,5-d′]bis[1,3]dithioles is here achieved with scandium(III)triflate, a less harmful reagent than the usually used Lewis acids, e.g., boron trifluoride or tetrafluoroboric acid. This enables a convenient and environmentally more compliant access to high yields of benzo[1,2-d;4,5-d′]bis[1,3]dithioles.
- Fleck, Nico,Kopp, Kevin,Schiemann, Olav
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- Trityl Radicals with a Combination of the Orthogonal Functional Groups Ethyne and Carboxyl: Synthesis without a Statistical Step and EPR Characterization
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Finland trityl radical (FTR) shows very attractive EPR spectroscopic properties for a manifold of applications. For most of its applications only one chemically reactive functional group is needed. The presence of three equally reactive carboxyl groups leads to FTR modifications through reactions which give statistical mixtures of 1-fold-, 2-fold-, and 3-fold-modified and unmodified FTR. To avoid the side effects of such a statistical reaction - limited yields and separation challenges - we took a route to FTR-type trityl radicals with scaffold assembly by addition of an aryllithium with one type of substituent to a diarylketone with another type of substituent. This gave the two FTR-type trityl radicals 1 and 2 which carry a combination of the chemically orthogonal groups, carboxyl and triisopropylsilylethynyl. Standard column chromatography was sufficient for product isolation on all stages, whereby polar tagging helped. The EPR spectroscopic properties of the trityl radicals 1 and 2 in ethanol were determined in X and W bands. Their g anisotropy and T1 and T2 relaxation times make them spin labels as good as the benchmark FTR. This paper discloses also details on the synthesis of building blocks used for FTR preparation and improved access to the bare FTR scaffold.
- Hintz, Henrik,Vanas, Agathe,Klose, Daniel,Jeschke, Gunnar,Godt, Adelheid
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p. 3304 - 3320
(2019/03/11)
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- Tetrathiatriarylmethyl radicals conjugated to an RGD-peptidomimetic
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Tetrathiatriarylmethyl (TAM) radicals are favourite spin labels for electron paramagnetic resonance imaging (EPRI). In this work, we report a straightforward synthesis of new TAM radicals bound to an Arg-Gly-Asp (RGD)-peptido-mimetic known to be a cell-targeting agent. These new radicals are stable in solution, and sensitive to oxygen, and their experimental EPR data is consistent with density functional theory (DFT) calculations.
- Driesschaert, Benot,Levque, Philippe,Gallez, Bernard,Marchand-Brynaert, Jacqueline
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supporting information
p. 8077 - 8084
(2015/02/19)
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- TRIARYLMETHYL RADICALS
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New radical compounds, useful in the field of MRI imaging of formula (I). The radical compounds are in particular new triarylmethyl ("trityl") radicals which can be used as polarizing agents for polarizing a molecule in the DNP process.
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Page/Page column 11
(2014/02/15)
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- Organic preparations with molar amounts of volatile malodorous thiols
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Thiols are indispensable for the preparation of many organic sulfur compounds. Their strong smell and use for gas leakage perception render it almost impossible to work with them without arousing public attention. Molar amounts of the very odoriferous thiol 2-methyl-2-propanethiol (t-butylthiol) are needed, for example, for the large-scale synthesis of two useful synthetic building blocks, 1,2,4,5-tetrakis(t-butylthio)benzene and tetramethylbenzo-2,2, 6,6-[1,2-d;4,5-d']bis[1,3]dithiol. We investigated an array of alternatives to circumvent the problem: (1) alternative thiols (primary, long-chain, tertiary thiols of larger molar mass); (2) exhaust cleaning methods (adsorption, oxidation, conversion to a salt); and (3) thermal exhaust treatment. Only combustion of the fumehood exhaust with domestic gas at 900 °C in a regenerative thermal oxidation unit was able to completely prevent the thiol smell from escaping. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications to view the free supplemental file.
- Mueller, Diana,Adelsberger, Klaus,Imming, Peter
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supporting information
p. 1447 - 1454
(2013/05/22)
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- Generation of trityl radicals by nucleophilic quenching of tris(2,3,5,6-tetrathiaaryl)methyl cations and practical and convenient large-scale synthesis of persistent tris(4-carboxy-2,3,5,6-tetrathiaaryl)methyl radical
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Tris(2,3,5,6-tetrathiaaryl)methyl cations, which were generated from the corresponding triarylmethanols in the presence of strong acids, underwent reaction with nucleophiles to give trityl radicals, as the product of a one-electron reduction of the carbocation. Depending on the nature of the nucleophile, the only byproducts were either diamagnetic quinone methides or asymmetrical monosubstituted trityl radicals. Herein, we report a protocol for the large-scale synthesis of the Finland trityl, which has the advantage of high overall yield and reproducibility. Tris(2,3,5,6-tetrathiaaryl)methyl cations, which were generated from the corresponding triarylmethanols and strong acids, underwent reaction with nucleophiles to give trityl radicals. Depending on the nucleophile, the only byproducts were diamagnetic quinone methides or asymmetrical monosubstituted trityl radicals. A protocol for the large-scale synthesis of the Finland trityl is reported. Copyright
- Rogozhnikova, Olga Yu.,Vasiliev, Vladimir G.,Troitskaya, Tatiana I.,Trukhin, Dmitry V.,Mikhalina, Tatiana V.,Halpern, Howard J.,Tormyshev, Victor M.
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p. 3347 - 3355
(2013/07/11)
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- Conjugated polymers that respond to oxidation with increased emission
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Thioether-containing poly(para-phenylene-ethynylene) (PPE) copolymers show a strong fluorescence turn-on response when exposed to oxidants in solution as a result of the selective conversion of thioether substituents into sulfoxides and sulfones. We propose that the increase in fluorescence quantum yield (κF) upon oxidation is the result of both an increase in the rate of fluorescence (kF), as a result of greater spatial overlap of the frontier molecular orbitals in the oxidized materials, and an increase in the fluorescence lifetime (τF), due to a decrease in the rate of nonradiative decay. Contrary to established literature, the reported sulfoxides do not always act as fluorescence quenchers. The oxidation is accompanied by spectral changes in the absorption and emission of the polymers, which are dramatic when oxidation causes the copolymer to acquire a donor-acceptor interaction. The oxidized polymers have high fluorescence quantum yields in the solid state, with some having increased photostability. A turn-on fluorescence response to hydrogen peroxide in organic solvents in the presence of an oxidation catalyst indicates the potential of thioether-containing materials for oxidant sensing. The reported polymers show promise as new materials in applications where photostability is important, where tunability of emission across the visible spectrum is desired, and where efficient emission is an advantage.
- Dane, Eric L.,King, Sarah B.,Swager, Timothy M.
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scheme or table
p. 7758 - 7768
(2010/08/06)
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- Large-scale synthesis of a persistent trityl radical for use in biomedical EPR applications and imaging
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Tetrathiatriarylmethyl radicals are ideal spin probes for biological electron paramagnetic resonance (EPR) spectroscopy and imaging. The wide application of trityl radicals as biosensors of oxygen or other biological radicals was hampered by the lack of affordable large-scale syntheses. We report the large-scale synthesis of the Finland trityl radical using an improved addition protocol of the aryl lithium monomer to methylchloroformate. A new reaction for the formal one-electron reduction of trityl alcohols to trityl radicals using neat trifluoroacetic acid is reported as well. Initial applications show that the compound is very sensitive to molecular oxygen. It has already provided high-resolution EPR images on large aqueous samples and should be suitable for a broad range of in vivo applications.
- Dhimitruka, Ilirian,Velayutham, Murugesan,Bobko, Andrey A.,Khramtsov, Valery V.,Villamena, Frederick A.,Hadad, Christopher M.,Zweier, Jay L.
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p. 6801 - 6805
(2008/03/14)
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- Reactivity of molecular oxygen with ethoxycarbonyl derivatives of tetrathiatriarylmethyl radicals
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Tetrathiatriarylmethyl (TAM) radicals are commonly used as oximetry probes for electron paramagnetic resonance imaging applications. In this study, the electronic properties and the thermodynamic preferences for O2 addition to various TAM-type triarylmethyl (trityl) radicals were theoretically investigated. The radicals' stability in the presence of O2 and biological milieu was also experimentally assessed using EPR spectroscopy. Results show that H substitution on the aromatic ring affects the trityl radical's stability (tricarboxylate salt 1-CO2Na > triester 1-CO2Et > diester 2-CO2Et > monoester 3-CO 2Et) and may lead to substitution reactions in cellular systems. We propose that this degradation process involves an arylperoxyl radical that can further decompose to alcohol or quinone products. This study demonstrates how computational chemistry can be used as a tool to rationalize radical stability in the redox environment of biological systems and aid in the future design of more biostable trityl radicals.
- Xia, Shijing,Villamena, Frederick A.,Hadad, Christopher M.,Kuppusamy, Periannan,Li, Yunbo,Zhu, Hong,Zweier, Jay L.
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p. 7268 - 7279
(2007/10/03)
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- General synthesis of persistent trityl radicals for EPR imaging of biological systems.
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In this paper we describe the syntheses of the tetraoxygenated triarylmethyl (trityl) radical 14 and the tetrathiatriarylmethyl (trityl) radicals 15 and 16. The syntheses include new and improved preparations of the key intermediate compounds 1 and 2. The new route to compound 2 is noteworthy for its efficiency and its avoidance of the highly toxic compound phosgene as well as the isolation of the air-sensitive 1,2,4,5-benzenetetrathiol.
- Reddy, T Jagadeeswar,Iwama, Tetsuo,Halpern, Howard J,Rawal, Viresh H
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p. 4635 - 4639
(2007/10/03)
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