Triphenylmethyl Research Articles

SET processes in Lewis acid-base reactions: the tritylation of N-heterocyclic carbenes.

Reactions between N-heterocyclic carbenes (NHCs) and the trityl cation, [Ph3C]+, give covalent adducts of type [NHC–CPh3]+ and/or [NHC–C6H5–CPh2]+. EPR spectroscopy, UV-Vis analyses, and trapping experiments imply that adduct formation involves carbene radical cations and the trityl radical. The results demonstrate that single electron transfer (SET) processes should be considered for reaction of NHCs with oxidizing Lewis acids.

Intracellular delivery of liposome-encapsulated Finland trityl radicals for EPR oximetry.

Tetrathiatriarylmethyl (TAM, trityl) radicals have found wide applications in electron paramagnetic resonance (EPR) oximetry. However, the biomedical applications of TAM radicals were exclusively limited to an extracellular region owing to their negatively charged nature. The intracellular delivery of TAM radicals still remains a challenge. In the present work, we report a liposome-based method to encapsulate the water-soluble Finland trityl radical CT-03 for its intracellular delivery. Using the thin lipid film hydration method, CT-03-loaded liposomes were prepared from DSPC/cholesterol/DOTAP with a mean size of 167.5 ± 2.4 nm and a zeta potential of 27.8 ± 0.8 mV. EPR results showed that CT-03 was entrapped into the liposomes and still exhibited good oxygen (O2) sensitivity. Moreover, CT-03 was successfully delivered into HepG2 cells and HUVECs using the CT-03-loaded liposomes. Importantly, the combination of the liposome-encapsulated radical CT-03 and the other TAM radical CT02-H enabled simultaneous measurements of the intracellular and extracellular O2 concentrations and O2 consumption rates in HepG2 cells. Our present study provides a new approach for intracellular delivery of TAM radicals and could significantly expand their biomedical applications.

Thiyl Radicals are Co-products of Dinitrosyl Iron Complexes (DNIC) Formation

This work is the first report when multiharmonic analysis (MHA) was applied for electron paramagnetic resonance imaging (EPRI) for in vivo applications. Phantom studies were performed for established methodology, and in vivo imaging was conduct as a proof-of-concept. Phantom studies showed at least six times improvement of the signal – to – noise (S/N) ratio. Application MHA for 3D EPR in vivo imaging provides images of spin probe distribution in mouse head. The EPRI, in combination with nitroxide and trityl spin probe, was performed to obtained 3D EPR in vivo images using MHA. For both used spin probes, MHA provided images with better S/N ratio, especially in the case of nitroxide, where projections obtained using conventional CW did not allow for reconstructing reliable data. Trityl radical exhibited high resolution and quality of obtained images after MHA. The MHA methodology allows the selection of a second modulation amplitude even 40 times higher than the natural EPR linewidth of the spin probe without line shape distortion, which highly improves the sensitivity of the acquired signal and allowing for imaging mice regardless of their size in a routine animal experiment.

Isolation and Study of Ruthenium-Cobalt Oxo Cubanes Bearing a High-Valent, Terminal RuV-Oxo with Significant Oxyl Radical Character.

High-valent RuV-oxo intermediates have long been proposed in catalytic oxidation chemistry, but investigations into their electronic and chemical properties have been limited due to their reactive nature and rarity. The incorporation of Ru into the [Co3O4] subcluster via the single-step assembly reaction of CoII(OAc)2(H2O)4 (OAc = acetate), perruthenate (RuO4-), and pyridine (py) yielded an unprecedented Ru(O)Co3(μ3-O)4(OAc)4(py)3 cubane featuring an isolable, yet reactive, RuV-oxo moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [RuV(S = 1/2)CoIII3(S = 0)O4] configuration and non-negligible covalency in the cubane core. Significant oxyl radical character in the RuV-oxo unit is experimentally demonstrated by radical coupling reactions between the oxo cubane and both 2,4,6-tri-tert-butylphenoxyl and trityl radicals. The oxo cubane oxidizes organic substrates and, notably, reacts with water to form an isolable μ-oxo bis-cubane complex [(py)3(OAc)4Co3(μ3-O)4Ru]-O-[RuCo3(μ3-O)4(OAc)4(py)3]. Redox activity of the RuV-oxo fragment is easily tuned by the electron-donating ability of the distal pyridyl ligand set at the Co sites demonstrating strong electronic communication throughout the entire cubane cluster. Natural bond orbital calculations reveal cooperative orbital interactions of the [Co3O4] unit in supporting the RuV-oxo moiety via a strong π-electron donation.

Masked Radicals: Iron Complexes of Trityl, Benzophenone, and Phenylacetylene.

We report the first Fe─CPh3 complex, and show that the long Fe─C bond can be disrupted by neutral π-acceptor ligands (benzophenone and phenylacetylene) to release the triphenylmethyl radical. The products are formally iron(I) complexes, but X-ray absorption spectroscopy coupled with density functional and multireference ab initio calculations indicates that the best description of all the complexes is iron(II). In the formally iron(I) complexes, this does not imply that the π-acceptor ligand has radical character, because the iron(II) description arises from doubly-occupied frontier molecular orbitals that are shared equitably by the iron and the π-acceptor ligand, and the unpaired electrons lie on the metal. Despite the lack of substantial radical character on the ligands, alkyne and ketone fragments can couple to form a high-spin iron(III) complex with a cyclized metalladihydrofuran core.

Rapid-scan EPR imaging of a phantom comprised of species with different linewidths and relaxation times.

As a demonstration of the application of rapid-scan EPR to imaging at low frequency and magnetic field, a multi-compartment phantom containing six different samples was imaged. The samples were nitroxide radicals, trityl (substituted triarylmethyl) radicals, and the oxygen-sensitive solid lithium phthalocyanine (LiPc), all of which are useful for in vivo imaging. The 2D spectral-spatial image demonstration was performed at 250 MHz, with samples in sealed tubes of various sizes arranged in a 3D-printed plastic holder. Maximum gradients of 10 G/cm gave a spatial resolution of about 0.1 mm for the narrow trityl and LiPc signals and about 1 mm for the nitroxide. The importance of proper selection of resonator bandwidth and scan rate for obtaining accurate linewidth information is demonstrated for a case in which the phantom is composed of species with signal linewidths and relaxation times that differ by more than a factor of 10.

Insertion of a Cardo Structure into a Polyurethane Framework Using a pH Indicator and Its Impact on Tensile and Shape Memory Properties

Perpendicular cardo structural units were inserted into a polyurethane (PU) framework from the pH indicator (phenolphthalein (PP), phenol red (PR), or bromocresol green (BG)) sharing a triphenylmethyl group. The thermal transitions, mechanical properties, pH-sensitive color change, and low temperature flexibility of the PU modified with the cardo structural units were compared with those of the ordinary PU. Slight cross-linking between PU chains was performed because the insertion of the indicator moieties deteriorated the mechanical properties. The breaking tensile stress and shape recovery capability at 0 °C of the BG-PU series surpassed those of the PP-PU and PR-PU series. The inserted pH indicator moieties did not show the color change under different pH conditions because the isomerization under basic conditions was blocked. Among the three series of PUs, the BG-PU demonstrated the best low temperature flexibility compared with that of the PP-PU and PR-PU due to the functional groups on the phenyl rings of BG. Insertion of a cardo structural unit from the pH indicator reduced the molecular interaction between PU chains.

Synthesis of a Hydrophilic Trityl Radical

Synthesis of a Hydrophilic Trityl Radical

Interaction of Graphene with Out-of-Plane Aromatic Hydrocarbons

In the present article, graphene complexes with out-of-plane organic substances such as a triphenylmethyl radical, anion, and cation are studied. Comparison is made with the similar closed-shell mo...

Trityl-Aryl-Nitroxide-Based Genuinely g-Engineered Biradicals, As Studied by Dynamic Nuclear Polarization, Multifrequency ESR/ENDOR, Arbitrary Wave Generator Pulse Microwave Waveform Spectroscopy, and Quantum Chemical Calculations.

Trityl and nitroxide radicals are connected by π-topologically controlled aryl linkers, generating genuinely g-engineered biradicals. They serve as a typical model for biradicals in which the exchange (J) and hyperfine interactions compete with the g-difference electronic Zeeman interactions. The magnetic properties underlying the biradical spin Hamiltonian for solution, including J's, have been determined by multifrequency CW-ESR and 1H ENDOR spectroscopy and compared with those obtained by quantum chemical calculations. The experimental J values were in good agreement with the quantum chemical calculations. The g-engineered biradicals have been tested as a prototype for AWG (Arbitrary Wave Generator)-based spin manipulation techniques, which enable GRAPE (GRAdient Pulse Engineering) microwave control of spins in molecular magnetic resonance spectroscopy for use in molecular spin quantum computers, demonstrating efficient signal enhancement of specific weakened hyperfine signals. Dynamic nuclear polarization (DNP) effects of the biradicals for 400 MHz nuclear magnetic resonance signal enhancement have been examined, giving efficiency factors of 30 for 1H and 27.8 for 13C nuclei. The marked DNP results show the feasibility of these biradicals for hyperpolarization.

Site Selective and Efficient Spin Labeling of Proteins with a Maleimide-Functionalized Trityl Radical for Pulsed Dipolar EPR Spectroscopy.

Pulsed dipolar electron paramagnetic resonance spectroscopy (PDS) in combination with site-directed spin labeling (SDSL) of proteins and oligonucleotides is a powerful tool in structural biology. Instead of using the commonly employed gem-dimethyl-nitroxide labels, triarylmethyl (trityl) spin labels enable such studies at room temperature, within the cells and with single-frequency electron paramagnetic resonance (EPR) experiments. However, it has been repeatedly reported that labeling of proteins with trityl radicals led to low labeling efficiencies, unspecific labeling and label aggregation. Therefore, this work introduces the synthesis and characterization of a maleimide-functionalized trityl spin label and its corresponding labeling protocol for cysteine residues in proteins. The label is highly cysteine-selective, provides high labeling efficiencies and outperforms the previously employed methanethiosulfonate-functionalized trityl label. Finally, the new label is successfully tested in PDS measurements on a set of doubly labeled Yersinia outer protein O (YopO) mutants.

Abstract 1944: Detection of metabolic change in glioblastoma after radiotherapy using hyperpolarized 13C-MRI: Glycolytic metabolism in cancer stem cell-like cell-derived tumor model

Abstract OBJECTIVES: Since the cancer stem-like cells (CSCs) play an important role in the resistance against radiation therapy due to its different metabolic profile, investigation of the specific metabolic characteristics of CSCs is valuable. Dynamic nuclear polarization (DNP) technique using 13C-labeled substrates enables magnetic resonance imaging (MRI) to monitor specific enzymatic reactions in tumors. In this study, DNP-MRI along with hyperpolarized [1-13C] pyruvate was conducted to evaluate the metabolic change in glycolytic profiles after irradiation between a glioblastoma cell line and a CSC-derived glioma using orthotopic xenograft mouse model. A microarray analysis was also performed to compare to the imaging study. METHODS: DNP-MRI A 3T MRI scanner along with a custom-made head coil was used. To obtain hyperpolarized [1-13C] pyruvate, 30 μL of [1-13C] pyruvic acid containing 15 mM of OX063 (trityl radical compound) and 2.5 mM of the gadolinium chelate were polarized at 3.35 T and 1.4 K in the Hypersense DNP polarizer. The hyperpolarized sample dissolved in a buffered medium was injected via the tail vein followed by an acquisition of 13C-two-dimensional MR-spectroscopy to measure the pyruvate-to-lactate ratios (Lac/Pyr) in the tumor region and the contralateral normal brain separately. Cell lines A human glioblastoma cell line, U251 and a glioma CSC line, NSC11 were cultured for stereotactic intracranial injection. Animal model Orthotopic brain tumor model was developed in athymic nude mice by intracranial implantation. When the tumor volume reached 50 +/- 10 mm3 on T2-weighted MRI, a sequence of DNP-MRI scans was performed 24 hours before and 6, 16 and 24 after 6-Gy whole-brain irradiation (N = 4 each with a non-irradiated control group). Independently, a microarray analysis using the tumor tissue samples excised 6 and 24 hours after irradiation was performed on Affymetrix Human Genome U133 Plus 2.0 array. RESULTS: DNP-MRI showed a decrease in Lac/Pyr 6 and 16 hours after irradiation compared to the control group in U251 whereas no significant change was observed in the NSC11 tumor. The microarray analysis showed a significant down-regulation of lactate dehydrogenase A (LDH-A) expression in U251 6 and 24 hours after irradiation, consistent with the finding of DNP-MRI. In the microarray analysis, SIRT2 and KLF4 expression also changed in the U251 tumor, suggested to regulate the LDH-A activity/expression. CONCLUSION: DNP-MRI demonstrated the difference in radiation response in glycolytic metabolism between the glioblastoma cell line and the CSC-derived glioma. This technique might be a feasible diagnostic method evaluating metabolic profiles of the brain tumors in the clinical settings of pretreatment and post-treatment. Citation Format: Tatsuya Kawai, Murali C. Krishna, Tamalee Kramp, Jeffery R. Brender, Philip Tofilon, Kevin A. Camphausen. Detection of metabolic change in glioblastoma after radiotherapy using hyperpolarized 13C-MRI: Glycolytic metabolism in cancer stem cell-like cell-derived tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1944.

Molecular and supramolecular helicity induction in trityl group-containing compounds: The case of chiral 3,3,3-triphenylpropionic acid derivatives

The process of dynamic chirality transmission from permanent chirality element to stereodynamic triphenylmethyl group placed in the distance of 4 bonds, has been studied for series of optically active 3,3,3-triphenylpropionic acid derivatives. Structural analysis, carried out with the use of complementary methods and supported by theoretical calculations, enabled us to determine the mechanism of chirality transmission. The observed chirality transfer phenomenon, demonstrated unequivocally as raising of non-zero Cotton effects in the region of UV absorption of trityl group, is a cascade process driven by weak intramolecular interactions. Despite the much larger inductor-effector distance, the sensitivity in chirogenesis is comparable to other stereodynamic probes reported so far. In the crystalline phase, the combination of trityl group with amino acid moiety results in the formation of helical superstructures, where individual molecules are held together by hydrogen bonding cascades. The proper combination of functionalities in the molecule skeleton allows, to some extent, the control over the association process and authorizes determination of the trityl group as the supramolecular synthon.

Synthesis and Characterization of Hydrophilic Trityl Radical TFO for Biomedical and Biophysical Applications.

Tetrathiatriarylmethyl (TAM, trityl) radicals have found wide applications as spin probes/labels for EPR spectroscopy and imaging, and as polarizing agents for dynamic nuclear polarization. The high hydrophilicity of TAM radicals is essential for their biomedical applications. However, the synthesis of hydrophilic TAM radicals (e.g., OX063) is extremely challenging and has only been reported in the patent literature, to date. Herein, an efficient synthesis of a highly water-soluble TAM radical bis(8-carboxyl-2,2,6,6-tetramethylbenzo[1,2-d:4,5-d']bis([1,3]dithiol-4-yl)-mono-(8-carboxyl-2,2,6,6-tetrakis(2-hydroxyethyl)benzo[1,2-d:4,5-d']bis([1,3]dithiol-4-yl)methyl (TFO), which contains four additional hydroxylethyl groups, relative to the Finland trityl radical CT-03, is reported. Similar to OX063, TFO exhibits excellent properties, including high water solubility in phosphate buffer, low log P, low pKa , long relaxation times, and negligible binding with bovine serum albumin. On the other hand, TFO has a sharper EPR line and higher O2 sensitivity than those of OX063. Therefore, in combination with its facile synthesis, TFO should find wide applications in magnetic resonance related fields and this synthetic approach would shed new light on the synthesis of other hydrophilic TAM radicals.

Dextran-conjugated tetrathiatriarylmethyl radicals as biocompatible spin probes for EPR spectroscopy and imaging.

Tetrathiatriarylmethyl (TAM) radicals represent soluble paramagnetic probes for biomedical electron paramagnetic resonance (EPR)-based spectroscopy and imaging. There is an increasing demand in the development of multifunctional, biocompatible and targeted trityl probes hampered by the difficulties in derivatization of the TAM structure. We proposed a new straightforward synthetic strategy using click chemistry for the covalent conjugation of the TAM radical with a water-soluble biocompatible carrier exemplified here by dextran. A set of dextran-grafted probes varied in the degrees of Finland trityl radical loading and dextran modification by polyethelene glycol has been synthesized. The EPR spectrum of the optimized macromolecular probe exhibits a single narrow line with high sensitivity to oxygen and has advantages over the unbound Finland trityl of being insensitive to interactions with albumin. In vivo EPR imaging of tissue oxygenation performed in breast tumor-bearing mouse using dextran-grafted probe demonstrates its utility for preclinical oximetric applications.

Decolorization and detoxification of Direct Blue 2B by indigenous bacterial consortium

Azo dyes are widely used in the textile industry despite being poorly biodegradable and highly toxic. Hence, azo dyes need to be removed from effluent prior to environmental discharge. Microbial communities are efficient for the degradation and mineralization of azo dyes. However, little is known about the functional microbial communities responsible for the degradation process. In this study, a novel indigenous bacteria consortium was developed for characterizing the functional microbial communities involved in the degradation of a sulfonated azo dye, Direct Blue 2B (DB2) in a simple batch reactor. The optimal temperature, pH, and salinity for the decolorization process were 38.70 °C, pH 7.57, and 20.10 g L−1 NaCl, respectively. The effect of the operating conditions on microbial community structure were determined using high-throughput Illumina HiSeq sequencing. Gammaproteobacteria, Betaproteobacteria, and Bacilli were dominant under most of the operating conditions. At pH above 8 and NaCl concentration above 30 g L−1, Firmicutes relative abundance did not significantly change suggesting tolerance towards alkaline and hypersaline environments. Tritium aestivum and Glycine max seed germination following exposure to YHK treated DB2 solution was above 80% compared to 50% in untreated DB2 solution. The YHK consortium decolorized dyes structurally different from DB2 such as trimethyl phenyl and direct dyes. The results of this study offer valuable data on improving optimization of dye biodegradation processes and the capability of YHK in in situ bioremediation.

Synthesis of graft copolymers by combination of radical photopolymerization and iniferter process

ABSTRACTVarious PS‐based graft copolymers including polystyrene‐graft‐poly(methyl methacrylate) and poly(styrene‐graft‐poly(ethylene glycol) methacrylate) are prepared via subsequent visible light radical photopolymerization and iniferter processes. Thus, poly(styrene‐co‐4‐chloromethylstyrene) P(S‐co‐VBC) is synthesized by light induced free‐radical polymerization. Then, chloride moieties are substituted with triphenylmethyl (trityl) groups to give trityl‐substituted PS (PS‐trityl) under visible light irradiation using dimanganese decacarbonyl (Mn2(CO)10) photochemistry. Side chains are then grafted from PS‐trityl backbone via iniferter process to give desired graft copolymers in a controlled manner. The precursor intermediates and the final graft copolymers are analyzed by 1H NMR, FT‐IR, and GPC measurements. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1344–1348

Highly sensitive electron paramagnetic resonance nanoradicals for quantitative intracellular tumor oxymetric images.

Purpose: Tumor oxygenation is a critical parameter influencing the efficacy of cancer therapy. Low levels of oxygen in solid tumor have been recognized as an indicator of malignant progression and metastasis, as well as poor response to chemo- and radiation therapy. Being able to measure oxygenation for an individual’s tumor would provide doctors with a valuable way of identifying optimal treatments for patients.Methods: Electron paramagnetic resonance imaging (EPRI) in combination with an oxygen-measuring paramagnetic probe was performed to measure tumor oxygenation in vivo. Triarylmethyl (trityl) radical exhibits high specificity, sensitivity, and resolution for quantitative measurement of O2 concentration. However, its in vivo applications in previous studies have been limited by the required high dosage, its short half-life, and poor intracellular permeability. To address these limitations, we developed high-capacity nanoformulated radicals that employed fluorescein isothiocyanate-labeled mesoporous silica nanoparticles (FMSNs) as trityl radical carriers. The high surface area nanostructure and easy surface modification of physiochemical properties of FMSNs enable efficient targeted delivery of highly concentrated, nonself-quenched trityl radicals, protected from environmental degradation and dilution.Results: We successfully designed and synthesized a tumor-targeted nanoplatform as a carrier for trityl. In addition, the nanoformulated trityl does not affect oxygen-sensing capacity by a self-relaxation or broadening effect. The FMSN-trityl exhibited high sensitivity/response to oxygen in the partial oxygen pressure range from 0 to 155 mmHg. Furthermore, MSN-trityl displayed outstanding intracellular oxygen mapping in both in vitro and in vivo animal studies.Conclusion: The highly sensitive nanoformulated trityl spin probe can profile intracellular oxygen distributions of tumor in a real-time and quantitative manner using in vivo EPRI.

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

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.

Trityl Radicals with a Combination of the Orthogonal Functional Groups Ethyne and Carboxyl: Synthesis without a Statistical Step and EPR Characterization.

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.