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Purpose: This study aimed to develop a biocompatible oximetric electron paramagnetic resonance (EPR) spin probe with reduced self-relaxation, and sensitivity to oxygen for a higher signal-to-noise ratio and longer relaxation times at high oxygen concentration, compared to the reference spin probe OX071. Procedures: SOX71 was synthesized by succinylation of the twelve alcohol groups of OX071 spin probe and characterized by EPR at X-Band (9.5 GHz) and at low field (720 MHz). The biocompatibility of SOX71 was tested in vitro and in vivo in mice. A pharmacokinetic study was performed to determine the best time frame for EPR imaging. Finally, a proof-of-concept EPR oxygen imaging was performed on a mouse model of a fibrosarcoma tumor. Results: SOX71 was synthesized in one step from OX071. SOX71 exhibits a narrow line EPR spectrum with a peak-to-peak linewidth of 66 mG, similar to OX071. SOX71 does not bind to albumin nor show cell toxicity for the concentrations tested up to 5 mM. No toxicity was observed after systemic delivery via intraperitoneal injection in mice at twice the dose required for EPR imaging. After the injection, the probe is readily absorbed into the bloodstream, with a peak blood concentration half an hour, post-injection. Then, the probe is quickly cleared by the kidney with a half-life of ~ 45 min. SOX71 shows long relaxation times under anoxic condition (T1e = 9.5 µs and T2e = 5.1 µs; [SOX71] = 1 mM in PBS at 37 °C, pO2 = 0 mmHg, 720 MHz). Both the relaxation rates R1e and R2e show a decreased sensitivity to pO2, leading to twice longer relaxation times under room air conditions (pO2 = 159 mmHg) compared to OX071. This is ideal for oxygen imaging in samples with a wide range of pO2. Both the relaxation rates R1e and R2e show a decreased sensitivity to self-relaxation compared to OX071, with a negligible effect of the probe concentration on R1e. SOX71 was successfully applied to image oxygen in a tumor. Conclusion: SOX71, a succinylated derivative of OX071 was synthesized, characterized, and applied for in vivo EPR tumor oxygen imaging. SOX71 is highly biocompatible, and shows decreased sensitivity to oxygen and self-relaxation. This first report suggests that SOX71 is superior to OX071 for absolute oxygen mapping under a broad range of pO2 values. [ABSTRACT FROM AUTHOR]

The electronic, spectral and structural properties of a molecular machine composed of a phenylene rotator encased by two trityl stators and two acetylides as axis are investigated theoretically to evaluate the rotational dynamics by DFT method. The changes in these properties and intramolecular rotation barriers caused by substituting F, CN, NO2, and NH2 on the central phenylene were also investigated. The potential energy surface calculations showed that the activation barrier of phenylene rotation is lower than 1 kcal/mol, for all considered systems. The results of the computational method were in good agreement with previously reported experimental results. The dynamical features of the studied molecules suggest that this kind of structure can act as a molecular machine at room temperature in the living organisms. The displacement of phenylene hydrogen atoms with polar groups improves this property and it is expected that these compounds may be helpful in drug delivery.

The structure of N‐triphenylacetyl‐l‐tyrosine (C29H25NO4, l‐TrCOTyr) is characterized by the presence of both donors and acceptors of classical hydrogen bonds. At the same time, the molecule contains a sterically demanding and hydrophobic trityl group capable of participating in π‐electron interactions. Due to its large volume, the trityl group may favour the formation of structural voids in the crystals, which can be filled with guest molecules. In this article, we present the crystal structures of a series of N‐triphenylacetyl‐l‐tyrosine solvates with chloroform, namely, l‐TrCOTyr·CHCl3 (I) and l‐TrCOTyr·1.5CHCl3 (III), and dichloromethane, namely, l‐TrCOTyr·CH2Cl2 (II) and l‐TrCOTyr·0.1CH2Cl2 (IV). To complement the topic, we also decided to use the racemic amide N‐triphenylacetyl‐dl‐tyrosine (rac‐TrCOTyr) and recrystallized it from a mixture of chloroform and dichloromethane. As a result, rac‐TrCOTyr·1.5CHCl3 (V) was obtained. In the crystal structures, the amide molecules interact with each other via O—H...O hydrogen bonds. Noticeably, the amide N—H group does not participate in the formation of intermolecular hydrogen bonds. Channels are formed between the TrCOTyr molecules and these are filled with solvent molecules. Additionally, in the crystals of III and V, there are structural voids that are occupied by chloroform molecules. Structure analysis has shown that solvates I and II are isostructural. Upon loss of solvent, the solvates transform into the solvent‐free form of TrCOTyr, as confirmed by thermogravimetric analysis, differential scanning calorimetry and powder X‐ray diffraction. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Oxygen is essential in physiology and pathophysiology. Electron paramagnetic resonance (EPR) oximetry, using oxygen sensitive paramagnetic materials, could be attractive for measuring oxygen in tissues. The aim of the present study was to assess the properties of lipid nanocapsules (LNCs) loaded with the nitroxide tempo-benzoate (TB) or tetrathiatriarylmethyl (TAM) radicals. LNCs loaded with the EPR probes were successfully prepared by the phase inversion process leading to nanocapsules of about 60 nm. LNCs protected the TB radical against reduction in vitro. The calibration of the EPR line width (LW) as a function of the pO 2 showed a two-fold increase in sensitivity with TAM-LNC compared to hydrophilic trityl radical. The TAM-LNCs were evaluated in vivo. Contrarily to unencapsulated TAM, for which a rapid decrease in EPR signal was observed, the half-life of TAM-LNCs administered in muscles or in tumours exceeded an hour. Carbogen-challenges in mice demonstrated that the TAM-LNCs responded well to changes in oxygen environment. However, the apparent pO 2 values acquired were higher than the expected physiological values. These results warrant further investigation in the formulation of stable nano-objects encapsulating EPR oxygen sensitive probes. [ABSTRACT FROM AUTHOR]

The cascade process of a dynamic chirality transmission from the permanent chirality center to the stereodynamic triphenylmethyl group has been studied for series of optically active trityl derivatives. The structural analysis, carried out with the use of complementary methods, enabled us to determine the mechanism of chirality transfer. The process of chirality transmission involves a set of weak but complementary electrostatic interactions. The induction of helicity in a trityl propeller is revealed by rising non-zero cotton effects in the area of trityl UV-absorption. The presence of an additional stereogenic center in close proximity to the trityl-containing stereogenic center significantly affects the sign and, to a lesser extent, magnitude of the respective cotton effects. Despite the bulkiness of the trityl, in the crystalline phase, the molecules under study strictly fill the space. In the crystal, molecules form aggregates stabilized by OH•••O hydrogen bonds. However, the presence of two trityl groups precludes formation of OH•••O hydrogen bonding. Additionally, the trityl group seems to be responsible for the formation of the solid solutions by e.g., racemates of trans- and cis-2-tritylcyclohexanol. Therefore, the trityl group acts as a supramolecular protective group, which in turn can be used in the crystal engineering.

The versatility of the trityl cation (TrBF4) as a highly efficient Lewis acid organocatalyst is demonstrated in a light induced benzylic brominaion of alkyl‐arenes under mild conditions. The reaction was conducted at ambient temperature under common hood light (55 W fluorescent light) with catalyst loadings down to 2.0 mol% using N‐bromosuccinimide (NBS) as the brominating agent. The protocol is applicable to an extensive number of substrates to give benzyl bromides in good to excellent yields. In contrast to most previously reported strategies, this protocol does not require any radical initiator or extensive heating. For electron‐rich alkyl‐arenes, the trityl ion catalyzed bromination could be easily switched between benzylic sp3 C−H functionalization and arene sp2 C−H functionalization by simply alternating the solvent. This chemoselective switch allows for high substrate control and easy preparation of benzyl bromides and bromoarenes, respectively. The chemoselective switch was also applied in a one‐pot reaction of 1‐methylnaphthalene for direct introduction of both sp3 C−Br and sp2 C−Br functionality. [ABSTRACT FROM AUTHOR]

Superoxide radical represents one of the most biologically relevant reactive oxygen species involved in numerous physiological and pathophysiological processes. Superoxide measurement through the decay of an electron paramagnetic resonance (EPR) signal of a triarylmethyl (TAM) radical possesses the advantage of a high selectivity and relatively high rate constant of TAM reaction with the superoxide. Hereby we report a straightforward synthesis and characterization of a TAM-TAM biradical showing a high reactivity with superoxide (second-order rate constant, (6.7 ± 0.2) × 103 M−1 s−1) enabling the measurement of superoxide radical by following the increase of a sharp EPR signal associated with the formation of a TAM-quinone-methide monoradical product. [ABSTRACT FROM AUTHOR]

Diffusion in porous materials is under ongoing active investigation due to its major role in practical applications such as catalysis and chromatography. The complexity of these systems limits the use of the Einstein-Stokes diffusion theory, and it must be distinguished between the microscopic scale of diffusion at a molecular level, which is sensitive to the local surroundings of a diffusing molecule, and the macroscopic scale which takes into account diffusion spanning multiple pores, grain boundaries and inhomogeneity within the material. Here, we employ an in situ approach for quantitative measurements of the diffusion on a macroscopic length scale. For the first time, full time-resolved spectral spatial EPR imaging in combination with the simultaneous iterative reconstruction technique (SIRT) allows the simultaneous observation of the diffusion of two different molecular species inside of an aerogel in a single experiment. [ABSTRACT FROM AUTHOR]

Superoxide radical is involved in numerous physiological and pathophysiological processes. Tetrathiatriarylmethyl (TAM) radicals are known to react with superoxide allowing measurement of superoxide production in biological media. We report the synthesis of a Nitro conjugated TAM radical showing a rate constant of 7 × 10 M s which is two order of magnitude higher than other TAMs, allowing high sensitivity measurement of superoxide. [ABSTRACT FROM AUTHOR]

A triphenylmethylamine-functionalized monolithic capillary column was newly designed for reversed-phase capillary electrochromatographic applications. Incorporation of the three phenyl rings-containing selector (also referred to as trityl selector) was achieved through post-polymerization functionalization of a generic monolithic matrix bearing nucleophilic-sensitive hydroxysuccinimide moieties. Such a 3D polymer matrix was obtained through UV-induced in situ free radical copolymerization of N-acryloxysuccinimide and ethylene dimethacrylate. The separation properties of the trityl monolithic capillary column were initially evaluated vis-à-vis polycyclic aromatic hydrocarbons, as model hydrophobic compounds, and compared to the separation ability of a benzylamine-functionalized monolithic capillary column prepared using the same generic monolithic matrix. Electrochromatographic separation of phenols and anilines was also considered, and our preliminary results suggest the occurrence of hydrophobic interactions due to the aromatic and non-polar nature of the surface-grafted trityl selector. The triphenyl monolithic capillary column exhibited relative standard deviation values (% RSD) below 4.1 % for the here-studied chromatographic parameters, namely, retention factor, selectivity, resolution, and efficiency. [ABSTRACT FROM AUTHOR]

The orchestrated interaction of transmembrane proteins with other molecules mediates several crucial biological processes. Detergent solubilization may significantly alter or even abolish such hetero-oligomeric interactions, which makes observing them at high resolution in their native environment technically challenging. Dipolar electron paramagnetic resonance (EPR) techniques such as pulsed electro-electron double resonance (PELDOR) can provide very precise distances within biomolecules. To concurrently determine the inter-subunit interaction and the intra-subunit conformational changes in hetero-oligomeric complexes, a combination of different spin labels is required. Orthogonal spin labeling using a triarylmethyl (TAM) label in combination with a nitroxide label is used to detect protein-ligand interactions in native lipid bilayers. This approach provides a higher sensitivity and total selectivity and will greatly facilitate the investigation of multimeric transmembrane complexes employing different spin labels in the native lipid environment. [ABSTRACT FROM AUTHOR]

A series of tritylated and dimethoxytritylated analogues of selected pyrimidine and purine nucleosides were synthesized and evaluated for their in vitro inhibitory activity against two important members of the genus Flavivirus in the Flaviviridae family, the yellow fever (YFV) and dengue viruses (DENV). Among all compounds tested, the 5′-O-tritylated and the 5′-O-dimethoxytritylated 5-fluorouridine derivatives exerted potency against YFV. Interestingly in the series of purine analogues, the 5′O, N-bis-tritylated fludarabine derivative revealed strong inhibitory activity against DENV at μ m concentrations, however significantly weaker potency against YFV. [ABSTRACT FROM AUTHOR]

The title Schiff base compound, C25H20N2, crystallizes with two independent molecules (A and B) in the asymmetric unit. In both molecules, the imine group is approximately coplanar with the pyridine ring, with N—C—C—N torsion angles of 170.1 (3) and −172.0 (3) Å. In the crystal, A and B dimers are linked by pairs of C—H...π interactions and further C—H...π bonds link the dimers into a three-dimensional network.

New NLO active organic molecular glasses were synthesized based on push-pull azobenzene, which was dendronized with 3,5-bis[2-(trityloxy)ethoxy]benzoic acid and pentafluorophenyl groups were added to enchance thermal and NLO properties via Ar-ArF interactions. The configuration, where pentafluorophenyl groups containing dendronizing fragment was attached to donor part of azochromophore, was very promising in our recent research, therefore trityl groups containing dendron was added to acceptor part to rise the glass transition temperature of amorphous compound. Effect of one or two pentafluorophenyl groups was investigated and about three times better NLO parameters were obtained when using one pentafluorophenyl group, as it has greater possibility of NLO properties enchanting Ar-ArF interactions with neighboring molecules. New convergent method was used to synthesize azobenzene core dendrimer fully functionalized with trityl end groups. Thermal, optical, and NLO properties were compared to previously reported results of dendrimer samples containing both hydroxyl and trityl groups. Full set of trityl end groups resulted in decreased NLO parameters and stability of poled order. Glass transition temperatures of all synthesized molecular glasses were 63–83 °C, and thermal destruction temperatures of all synthesized compounds were at least 250 °C. NLO coefficient d 33 values were 14–73 pm⋅V−1. [Display omitted] • Molecular glasses of pure compounds have high polar order of poled films. • C 6 F 5 CH 2 ether to alkyl fragment is synthesized in mild phase transfer catalysis. • Azobenzene with one C 6 F 5 CH 2 group and trityl dendron shows good NLO properties. [ABSTRACT FROM AUTHOR]

Abstract: This article provides an overview of polarizing mechanisms involved in high-frequency dynamic nuclear polarization (DNP) of frozen biological samples at temperatures maintained using liquid nitrogen, compatible with contemporary magic-angle spinning (MAS) nuclear magnetic resonance (NMR). Typical DNP experiments require unpaired electrons that are usually exogenous in samples via paramagnetic doping with polarizing agents. Thus, the resulting nuclear polarization mechanism depends on the electron and nuclear spin interactions induced by the paramagnetic species. The Overhauser Effect (OE) DNP, which relies on time-dependent spin–spin interactions, is excluded from our discussion due the lack of conducting electrons in frozen aqueous solutions containing biological entities. DNP of particular interest to us relies primarily on time-independent, spin-spin interactions for significant electron–nucleus polarization transfer through mechanisms such as the Solid Effect (SE), the Cross Effect (CE) or Thermal Mixing (TM), involving one, two or multiple electron spins, respectively. Derived from monomeric radicals initially used in high-field DNP experiments, bi- or multiple-radical polarizing agents facilitate CE/TM to generate significant NMR signal enhancements in dielectric solids at low temperatures (<100K). For example, large DNP enhancements (∼300 times at 5T) from a biologically compatible biradical, 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL), have enabled high-resolution MAS NMR in sample systems existing in submicron domains or embedded in larger biomolecular complexes. The scope of this review is focused on recently developed DNP polarizing agents for high-field applications and leads up to future developments per the CE DNP mechanism. Because DNP experiments are feasible with a solid-state microwave source when performed at <20K, nuclear polarization using lower microwave power (<100mW) is possible by forcing a high proportion of biradicals to fulfill the frequency matching condition of CE (two EPR frequencies separated by the NMR frequency) using the strategies involving hetero-radical moieties and/or molecular alignment. In addition, the combination of an excited triplet and a stable radical might provide alternative DNP mechanisms without the microwave requirement. [Copyright &y& Elsevier]

Abstract: In rapid scan EPR the magnetic field is scanned through the signal in a time that is short relative to electron spin relaxation times. Previously it was shown that the slow-scan lineshape could be recovered from triangular rapid scans by Fourier deconvolution. In this paper a general Fourier deconvolution method is described and demonstrated to recover the slow-scan lineshape from sinusoidal rapid scans. Since an analytical expression for the Fourier transform of the driving function for a sinusoidal scan was not readily apparent, a numerical method was developed to do the deconvolution. The slow scan EPR lineshapes recovered from rapid triangular and sinusoidal scans are in excellent agreement for lithium phthalocyanine, a trityl radical, and the nitroxyl radical, tempone. The availability of a method to deconvolute sinusoidal rapid scans makes it possible to scan faster than is feasible for triangular scans because of hardware limitations on triangular scans. [ABSTRACT FROM AUTHOR]

Abstract: An asymmetric derivative of the triarylmethyl radical, TAM-H, containing one aldehyde and two carboxyl groups, was synthesized. The electron paramagnetic resonance (EPR) spectrum of TAM-H is characterized by a doublet of narrow lines with a linewidth of 105 mG under anoxic conditions and hyperfine interaction constant of 245 mG. The partial overlap of the components of the doublet results in enhanced sensitivity of the spectral amplitudes ratio to oxygen compared with oxygen-induced linewidth broadening of a single line. Application of the TAM-H probe allows for EPR measurements in an extended range of oxygen pressures from atmospheric to 1 mm Hg, whereas the EPR spectrum linewidth of the popular TAM-based oxygen sensor Oxo63 is practically insensitive to oxygen partial pressures below 20 mm Hg. Enhanced sensitivity of the TAM-H probe relative to Oxo63 was demonstrated in the detection of oxygen consumption by Met-1 cancer cells. The TAM-H probe allowed prolonged measurements of oxygen depletion during the hypoxia stage and down to true anoxia (≤1.5 mm Hg). [Copyright &y& Elsevier]

Abstract: A rapid, mild and highly efficient procedure for the chemoselective deprotection of triphenylmethyl (trityl, Tr), p-anisyldiphenylmethyl (monomethoxytrityl, MMT) and di-(p-anisyl)phenylmethyl (dimethoxytrityl, DMT) groups from nucleoside trityl ethers has been established. The deprotection was achieved at room temperature, using a catalytic amount of silica sulfuric acid (SSA) in acetonitrile. The trityl nucleosides were deprotected in 2–17min without any depurination. These conditions are compatible with other acid sensitive hydroxyl protecting groups such as p-methoxybenzyl (PMB), isopropylidene, cyclohexylidene, di-(p-anisyl)methylidene, triisopropylsilyl (TIPS) and t-butyldimethylsilyl (TBDMS). [Copyright &y& Elsevier]

Abstract: Electron paramagnetic resonance imaging (EPRI) provides direct detection and mapping of free radicals. The continuous wave (CW) EPRI technique, in particular, has been widely used in a variety of applications in the fields of biology and medicine due to its high sensitivity and applicability to a wide range of free radicals and paramagnetic species. However, the technique requires long image acquisition periods, and this limits its use for many in vivo applications where relatively rapid changes occur in the magnitude and distribution of spins. Therefore, there has been a great need to develop fast EPRI techniques. We report the development of a fast 3D CW EPRI technique using spiral magnetic field gradient. By spiraling the magnetic field gradient and stepping the main magnetic field, this approach acquires a 3D image in one sweep of the main magnetic field, enabling significant reduction of the imaging time. A direct one-stage 3D image reconstruction algorithm, modified for reconstruction of the EPR images from the projections acquired with the spiral magnetic field gradient, was used. We demonstrated using a home-built L-band EPR system that the spiral magnetic field gradient technique enabled a 4–7-fold accelerated acquisition of projections. This technique has great potential for in vivo studies of free radicals and their metabolism. [Copyright &y& Elsevier]

Abstract: Triphenylmethyl chloride (“trityl chloride”, Ph3CCl) will transfer chloride ions to aluminium alkyls and methylaluminoxane and it is thereby converted into 1,1,1-triphenylethane (“trityl methyl” Ph3CMe) and the triphenylcarbonium ion (“trityl ion”, Ph3C+). IR spectra of these trityl species have been recorded. Assignments are supported by quantum chemical calculations, leading to significant revisions for some of the modes that are most influenced by reactions. A bright yellow colour shown to be due to the trityl cation, makes trityl chloride a useful indicator for ion pair formation. Trimethyl aluminium (TMA) is chlorinated by trityl chloride and forms dimethyl aluminium chloride (DMAC). DMAC will form a stable ion pair with trityl chloride, probably by forming the anion Al2Cl3Me4 −. Large excess of trityl chloride causes the formation of AlCl4 −, and probably AlCl3Me− and AlCl2Me2 − anions. It appears that methyl aluminium chloride anions are formed if, and only if, the anions have at least three chlorine atoms, possibly because of the need to dissipate the negative charge enough to keep the anion dissolved in the hydrocarbon solvent. Methylaluminoxane (MAO) also forms ion pair with trityl chloride, although to lesser extent and less persistent. [Copyright &y& Elsevier]

A convenient method has been developed for a facile and high-yield conversion of 6-O-tert-butyldimethylsilyl and 6-O-trityl protected monosaccharides to their formate esters, which may serve as useful intermediates for the replacement of the primary hydroxyl group of sugars by other functional groups. [ABSTRACT FROM AUTHOR]

Triphenylmethanesulfenyl chloride TrSCl (6) and triphenylmethanethiosulfenyl chloride TrSSCl (7) react with various thiols RSH to give the corresponding unsymmetrical polysulfides TrSSR 9 and TrSSSR 10, respectively. Compounds 9 and 10 were obtained in excellent yield and identified by 1 H- and 13 C-NMR as well as by elemental analysis. p -Methoxybenzyl trityl trisulfide 10c was characterized by X-ray crystallography. Preliminary experiments showed an interesting reactivity of trisulfides TrSSSR 10 with electrophiles to give polysulfides RS X R; the use of elemental iodine results in the formation of the corresponding hexasulfides RS 6 R, 15 in high yield and with higher than 90% selectivity. [ABSTRACT FROM AUTHOR]

Abstract: Several novel antioxidant-iron chelators bearing 8-hydroxyoxyquinoline moiety were synthesized, and various properties related to their iron chelation, and neuroprotective action were investigated. All the chelators exhibited strong iron(III) chelating and high antioxidant properties. Chelator 9 (HLA20), having good permeability into K562 cells and moderate selective MAO-B inhibitory activity (IC50 110μM), displayed the hightest protective effects against differentiated P19 cell death induced by 6-hydroxydopamine. EPR studies suggested that Chelator 9 also act as radical scavenger to directly scavenge hydroxyl radical. [Copyright &y& Elsevier]

EPR spectra at 250 MHz for a single crystal of lithium phthalocyanine (LiPc) in the absence of oxygen and for a deoxygenated aqueous solution of a Nycomed triarylmethyl (trityl-CD3) radical were obtained at scan rates between 1.3 × 103 and 3.4 × 105 G/s. These scan rates are rapid relative to the reciprocals of the electron spin relaxation times (LiPc: T1=3.5 μs and T2=2.5 μs; trityl: T1=12 μs and T2=11.5 μs) and cause characteristic oscillations in the direct-detected absorption spectra. For a given scan rate, shorter values of T2 and increased inhomogeneous broadening cause less deep oscillations that damp out more quickly than for longer T2. There is excellent agreement between experimental and calculated lineshapes and signal amplitudes as a function of radiofrequency magnetic field (B1) and scan rate. When B1 is adjusted for maximum signal amplitude as a function of scan rate, signal intensity for constant number of scans is enhanced by up to a factor of three relative to slow scans. The number of scans that can be averaged in a defined period of time is proportional to the scan rate, which further enhances signal amplitude per unit time. Longer relaxation times cause the maximum signal intensity to occur at slower scan rates. These experiments provide the first systematic characterization of direct-detected rapid-scan EPR signals. [Copyright &y& Elsevier]

Electron paramagnetic resonance imaging (EPRI) technology has rapidly progressed in the last decade enabling many important applications in the fields of biology and medicine. At frequencies of 300–1200 MHz a range of in vivo applications have been performed. However, the requisite imaging time duration to acquire a given number of projections, limits the use of this technique in many in vivo applications where relatively rapid kinetics occur. Therefore, there has been a great need to develop approaches to accelerate EPRI data acquisition. We report the development of a fast low-frequency EPRI technique using spinning magnetic field gradients (SMFG). Utilizing a 300 MHz CW (continuous wave) EPRI system, SMFG enabled over 10-fold accelerated acquisition of image projections. 2D images with over 200 projections could be acquired in less than 3 s and with 20 s acquisitions good image quality was obtained on large aqueous free radical samples. This technique should be particularly useful for in vivo studies of free radicals and their metabolism. [Copyright &y& Elsevier]

We report an efficient trityl-directed regiospecific synthesis of 2,3-disubstituted-l-histdines and 2,3-disubstituted histamines starting from α-N-trifluoroacetyl-l-histidine methyl ester and α-N-trifluoroacetylhistamine respectively in five steps. # NIPER Communication no. 162. [ABSTRACT FROM AUTHOR]

[Display omitted] • CW spectra of trityl-nitroxides were analyzed as superimposed AB splitting patterns. • Nitroxide and trityl transitions overlap extensively at X-band. • The spin–spin exchange interaction is attributed to through-bond exchange. • X-band values of 1/T 1 for trityl-nitroxides at 80 to 120 K are similar to mono-nitroxides. Trityl-nitroxides show substantial promise as polarizing agents in solid state dynamic nuclear polarization. To optimize performance it is important to understand the impact of spin–spin interactions on relaxation times of the diradicals. CW spectra and electron spin relaxation were measured for two trityl-nitroxides that differ in the substituents on the amide linker and have different strengths of the exchange interaction J. Analysis of the EPR spectra in terms of overlapping AB spin–spin splitting patterns explains the impact of J on various regions of the spectra. Even modest values of J are large relative to the separation between trityl and nitroxide resonances for some nitrogen nuclear spin state. Two conformations for each diradical were observed in CW spectra in fluid solution at X-band and Q-band. For one diradical J = 15 G (83%) and 5 G (17%) at 293 K, and J = 27 G (67%) and 3 G (33%) with interspin distances of 16 Å and 12 Å, respectively, at 80 K. For the second diradical the exchange interaction is stronger: the two conformations in fluid solution at 293 K had J = 113 G (67%) and 59 G (33%) and at 80 K the value of J was 43 G and there were two conformations with interspin distances of 13 and 11.5 Å. The observation of two conformations for each diradical, with different values of J, demonstrates the dependence of their exchange interactions on through-bond orbital interactions. X-band values of spin relaxation rates 1/T 1 and 1/T m at 80 to 120 K for the trityl-nitroxides are similar to values for nitroxide mono-radicals, and faster than for trityl radicals. These observations show that even for a relatively small value of J, the nitroxide is very effective in enhancing the relaxation of the more slowly relaxing trityl. [ABSTRACT FROM AUTHOR]

Different types of spin labels are currently available for structural studies of biomolecules both in vitro and in cells using Electron Paramagnetic Resonance (EPR) and pulse dipolar spectroscopy (PDS). Each type of label has its own advantages and disadvantages, that will be addressed in this chapter. The spectroscopically distinct properties of the labels have fostered new applications of PDS aimed to simultaneously extract multiple inter-label distances on the same sample. In fact, combining different labels and choosing the optimal strategy to address their inter-label distances can increase the information content per sample, and this is pivotal to better characterize complex multi-component biomolecular systems. In this review, we provide a brief background of the spectroscopic properties of the four most common orthogonal spin labels for PDS measurements and focus on the various methods at disposal to extract homo- and hetero-label distances in proteins. We also devote a section to possible artifacts arising from channel crosstalk and provide few examples of applications in structural biology., (Copyright © 2022 Elsevier Inc. All rights reserved.)

A strategy for high-throughput evaluation of combinatorial compound libraries is reported, which circumvents the necessity to test complex mixtures. The method is based on a new combination of protecting groups, solid-phase linker and tags. The bulk of the library first undergoes a binding assay with the components grafted on beads. A selection of beads carrying strong ligands is stripped from the labelled target and distributed into microvessels. The ligands are cleaved and rinsed into microeluates. Subsequently, a more detailed characterization with a functional assay in solution determines the best performers, which are identified through the peptidic tag left behind on the corresponding mother bead. [ABSTRACT FROM AUTHOR]

Abstract: A new method for the deprotection of trityl thioethers using CuCl as the catalyst under ultrasonic conditions is described. [Copyright &y& Elsevier]

The cascade process of a dynamic chirality transmission from the permanent chirality center to the stereodynamic triphenylmethyl group has been studied for series of optically active trityl derivatives. The structural analysis, carried out with the use of complementary methods, enabled us to determine the mechanism of chirality transfer. The process of chirality transmission involves a set of weak but complementary electrostatic interactions. The induction of helicity in a trityl propeller is revealed by rising non-zero cotton effects in the area of trityl UV-absorption. The presence of an additional stereogenic center in close proximity to the trityl-containing stereogenic center significantly affects the sign and, to a lesser extent, magnitude of the respective cotton effects. Despite the bulkiness of the trityl, in the crystalline phase, the molecules under study strictly fill the space. In the crystal, molecules form aggregates stabilized by OH•••O hydrogen bonds. However, the presence of two trityl groups precludes formation of OH•••O hydrogen bonding. Additionally, the trityl group seems to be responsible for the formation of the solid solutions by e.g., racemates of trans- and cis-2-tritylcyclohexanol. Therefore, the trityl group acts as a supramolecular protective group, which in turn can be used in the crystal engineering. [ABSTRACT FROM AUTHOR]