Triarylmethyl and Related Radicals

Tidwell, Thomas T.

doi:10.1002/9780470666975.ch1

Cited by 15 publications

(15 citation statements)

References 47 publications

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“…Techniques like magnetic resonance imaging (MRI), − dynamic nuclear polarization (DNP), , and spin labeling electron paramagnetic resonance (EPR) spectroscopy − have been established as powerful tools in the life sciences, which all depend on the availability of such persistent radicals. Even though nitroxides have been the reliable flagship radicals for these techniques for decades, trityl radicals have emerged as promising alternatives for the following reasons: (1) Trityl radicals derived from the Finland trityl 1 • (Figure ) are considerably more persistent than the Gomberg radical . For example, trityl derivatives such as the commercially available Oxo63 are used to map local oxygen distributions in vivo with MRI .…”

Section: Introductionmentioning

confidence: 99%

C–C Cross-Coupling Reactions of Trityl Radicals: Spin Density Delocalization, Exchange Coupling, and a Spin Label

et al. 2019

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Organic radicals are usually highly reactive and short-lived species. In contrast, tetrathiatriarylmethyl radicals, the so-called trityl- or TAM-radicals, are stable and do survive over longer times even under in-cell conditions. In addition, they show strong EPR signals, have long phase memory times at room temperature, and are reporters on local oxygen and proton concentrations. These properties facilitated their use for magnetic resonance imaging, dynamic nuclear polarization, and spin-labeling EPR under in-cell conditions. Thus, synthetic approaches are required for functionalization of TAM radicals tailored to the desired application. However, most TAM derivatives reported in the literature are based on esterification of the Finland trityl, which is prone to hydrolysis. Here, we report on an approach in which TAM is site-selective iodinated and subsequently C–C cross-coupled to various building blocks in a modular approach. This yields conjugated trityl compounds such as a trityl attached to a porphyrin, an alkinyl functionalized trityl radical, and a strongly exchange-coupled trityl biradical. This synthesis approach thus has implications not only for magnetic resonance spectroscopy but also for the design of molecular magnets or quantum computing devices.

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Section: Introductionmentioning

confidence: 99%

C–C Cross-Coupling Reactions of Trityl Radicals: Spin Density Delocalization, Exchange Coupling, and a Spin Label

et al. 2019

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“…Figure a exhibits EPR spectra obtained for irradiated ionic compounds of Ph 2 CHPyMe + , cation 4 in Scheme . The deprotonation of oxidized cation is expected to yield a stable Ph 2 C • PyMe + radical that is analogous to the well-known trityl radicals . Indeed, in all of these systems, a singlet Gaussian line with Δ B pp ∼ 18 G was observed that persisted to 300 K (Figure 12S, Supporting Information).…”

Section: Resultsmentioning

confidence: 90%

“…For example, crowded aryloxy (−ArO • ) radicals can be very stable, and many antioxidants and “antirads” (sacrificial agents that are used to reduce radiolytic or oxidative damage) involve −ArOH groups . Conversely, when a substituted Ar 2 CH– group (as in structure 4 in Scheme ) is used as the deprotonation site, the resulting trityl radical is generated as another sterically hindered, persistent radical …”

Section: Introductionmentioning

confidence: 99%

Radiation Stability of Cations in Ionic Liquids. 4. Task-Specific Antioxidant Cations for Nuclear Separations and Photolithography

Shkrob

Marin

2013

J. Phys. Chem. B

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Three families of "task-specific" antioxidant organic cations that include designated sites to facilitate deprotonation following electronic excitation and ionization have been introduced. The deprotonation from the excited state is reversible, leading to minimal damage of the cation, whereas the deprotonation from the oxidized cation yields persistent aroxyl and trityl radicals. This protection improves radiation stability of ionic compounds in 2.5 MeV electron beam radiolysis. Apart from the use of such cations as structural components of room temperature ionic liquid (IL) diluents for nuclear separations, their ionic compounds involving bases of superacids are well suited for use as chemically amplified acid generator resists in electron beam lithography and extreme ultraviolet photolithography.

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“…Since the discovery of the first organic stable radical by Gomberg in 1900 [1], radical chemistry has dramatically expanded with initial intense focus on mastering the structures [2] and the life times [3] of transient species before using transient or stable free radicals in applications ranging from living polymerization [4], to batteries [5], or more recently, for dynamic nuclear polarization (DNP) [6,7]. Free radicals are intimately related to EPR spectroscopy since this technique is specially focused on investigating the single electron(s) carried by several types of compounds.…”

Section: Introductionmentioning

confidence: 99%

EPR Spectroscopy: A Powerful Tool to Analyze Supramolecular Host•Guest Complexes of Stable Radicals with Cucurbiturils

et al. 2020

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Stable organic free radicals are increasingly studied compounds due to the multiple and unusual properties imparted by the single electron(s). However, being paramagnetic, classical methods such as NMR spectroscopy can hardly be used due to relaxation and line broadening effects. EPR spectroscopy is thus better suited to get information about the immediate surroundings of the single electrons. EPR has enabled obtaining useful data in the context of host•guest chemistry, and a classical example is reported here for the stable (2,2,6,6-tetramethyl-4-oxo-piperidin-1-yl)oxyl or 4-oxo-TEMPO nitroxide (TEMPONE) inside the macrocycle host cucurbit [7]uril (CB[7]). Generally and also observed here, a contraction of the spectrum is observed as a result of the reduced nitrogen coupling constant due to inclusion complexation in the hydrophobic cavity of the host. Simulations of EPR spectra allowed determining the corresponding binding constant pointing to a weaker affinity for CB [7], compared to TEMPO with CB [7]. We complement this work by the results of EPR spectroscopy of a biradical: bis-TEMPO-bis-ketal (bTbk) with cucurbit[8]uril (CB[8]). Initial investigations pointed to very weak effects on the spectrum of the guest and incorrectly led us to conclude an absence of binding. However, simulations of EPR spectra combined with NMR data of reduced bTbk allowed showing inclusion complexation. EPR titrations were performed, and the corresponding binding constant was determined. 1 H NMR spectra with reduced bTbk suggested a shuttle mechanism, at nearly one equivalent of CB[8], for which the host moves rapidly between two stations.Molecules 2020, 25, 776 2 of 10 wealth of information, which, correctly extracted, can give users access to crucial information such as stability, structure, or dynamics, in various liquid or solid environments [8]. Supramolecular chemistry principally features diamagnetic compounds, but paramagnetic ones are expected to enable access to new types of applications including molecular magnetic switches [9], dynamic covalent systems [10], or tracers for imaging by stabilizing free radicals in reducing conditions. In the context of host•guest chemistry, the guests are almost exclusively [11] the radicals, and they are included in macrocyclic hosts. Several reviews [12][13][14] have already documented host•guest complexes featuring free radicals and several families of hosts including calixarenes, cyclodextrins, and cucurbiturils. This latter family of pumpkin-shape macrocycles [15][16][17][18][19] possess unique properties, in a broader context, such as ultrahigh binding [20,21], gas adsorption [22], or drug encapsulation and release [23,24]. With cucurbit[n]urils (CB[n]), the main radicals studied are nitroxides [25], in the majority of cases stable ones. In a seminal work, Lucarini and coworkers studied the cucurbit [7]uril (CB[7]) cavity by EPR spectroscopy using several nitroxides [26]. Later, Kaifer and coworkers showed how CB[n] could modulate the extent of spin exchange between covalently linked ...

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Triarylmethyl and Related Radicals

Cited by 15 publications

References 47 publications

C–C Cross-Coupling Reactions of Trityl Radicals: Spin Density Delocalization, Exchange Coupling, and a Spin Label

C–C Cross-Coupling Reactions of Trityl Radicals: Spin Density Delocalization, Exchange Coupling, and a Spin Label

Radiation Stability of Cations in Ionic Liquids. 4. Task-Specific Antioxidant Cations for Nuclear Separations and Photolithography

EPR Spectroscopy: A Powerful Tool to Analyze Supramolecular Host•Guest Complexes of Stable Radicals with Cucurbiturils

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