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Long electron spin coherence lifetimes are crucial for high sensitivity and resolution in many pulse electron paramagnetic resonance (EPR) experiments aimed at measuring hyperfine and dipolar couplings, as well as in potential quantum sensing applications of molecular spin qubits. In immobilized systems, methyl groups contribute significantly to electron spin decoherence as a result of methyl torsional quantum tunneling. We examine the electron spin decoherence dynamics of the nitroxide radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) in both a methyl-free solvent and a methyl-containing solvent at cryogenic temperature. We model nitroxide and solvent methyl effects on decoherence using cluster correlation expansion (CCE) simulations extended to include methyl tunneling and compare the calculations to experimental data. We show that by using the methyl tunneling frequency as a fit parameter, experimental Hahn echo decays can be reproduced fairly well, allowing structural properties to be investigated in silico. In addition, we examine the Hahn echo of a hypothetical system with an unpaired electron and a single methyl to determine the effect of geometric configuration on methyl-driven electron spin decoherence. The simulations show that a methyl group contributes the most to electron spin decoherence if it is located between 2.5 and 6–7 Å from the electron spin, with its orientation being of secondary importance. [ABSTRACT FROM AUTHOR]

It is demonstrated that the time evolution of the electron-nuclear polarization transfer process during pulsed dynamic nuclear polarization (DNP) can be reversed on a microsecond timescale, leading to the observation of DNP echoes. The DNP echoes are induced by consecutive application of two pulse trains that produce effective Hamiltonians that differ only in the sign of the effective hyperfine coupling. The experiments have been performed on a frozen solution of trityl radicals in water/glycerol on a homebuilt X-band electron paramagnetic resonance/DNP spectrometer at 80 kelvins. We envisage that DNP echoes will play an important role in future development of pulsed DNP for sensitivity-enhanced nuclear magnetic resonance, hyperfine spectroscopy, and quantum sensing. [ABSTRACT FROM AUTHOR]

4-Nitrobenzaldehyde (C7H5NO3) (4NB) single crystals were obtained by slow evaporation technique. Single crystals were made paramagnetic by irradiation with a 60Co-gamma rays. Electron Paramagnetic Resonance (EPR) Spectroscopy method was used to detect the radiation damage center formed in the single crystals. As a result of temperature scanning of EPR spectra at different temperatures between 120 and 470 K, it was found to be independent of temperature. That's why the EPR study was done only at 300 K. The radiation effect caused the formation of the 4NB anion radical in the 4NB single crystal. All the protons in the structure created hyperfine structure splittings. The principal values of the hyperfine structure constants resulting from the interaction of the unpaired electron with protons, the principal values of the g-tensor and their direction cosines were calculated. [ABSTRACT FROM AUTHOR]

Donor spins in silicon‐28 are among the best performing qubits in the solid state, offering unmatched coherence times, gate fidelities beyond 99% and the ability to fabricate arrays using deterministic ion implantation. Donor placement precision is improved upon, advantageous for qubit readout and coupling, by implanting molecule ions that carry bystander atoms to boost the detection confidence. Here, the suitability of phosphorus difluoride (PF2$\rm{PF}_2$) molecule ions is demonstrated to fabricate 31P$^{31}\rm{P}$ donor qubits. Using secondary ion mass spectrometry, it is confirmed that 19F$^{19}\rm{F}$ (nuclear spin I=1/2$I=1/2$) diffuses away from the implant site while 31P$^{31}\rm{P}$ remains close to its original location during a donor activation anneal. Electron spin resonance measurements are then performed on PF2$\rm{PF}_2$‐implanted qubit devices. A pure dephasing time of T2∗=20.5±0.5μs$T_2^*= 20.5\pm 0.5 \mu\rm{s}$ and a coherence time of T2Hahn=424±5μs$T_2^{\text{Hahn}}=424\pm 5 \mu\rm{s}$ are extracted for the P donor electron‐ values comparable to those found in conventional atomic 31P$^{31}\rm{P}$‐implanted qubit devices. Additionally, the P donor electron is not found to hyperfine couple to any 19F$^{19}\rm{F}$ nuclear spins in its vicinity. Molecule ions therefore show great promise for producing high‐precision deterministically‐implanted arrays of long‐lived donor spin qubits. [ABSTRACT FROM AUTHOR]

Liquid-liquid phase separation is the key process underlying formation of membrane-less compartments in cells. A highly dynamic cellular body with rapid component exchange is Cajal body (CB), which supports the extensive compositional dynamics of the RNA splicing machinery, spliceosome. Here, we select an arginine-glycine (RG)-rich segment of coilin, the major component of CB, establish its RNA-induced phase separation, and through combined use of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) probes, interrogate its dynamics within the crowded interior of formed droplets. Taking advantage of glycine-based singlet-states, we show that glycines retain a large level of sub-nanoseconds dynamics inside the coilin droplets. Furthermore, the continuous-wave (CW) and electron-electron dipolar (PELDOR) and electron-nucleus hyperfine coupling EPR data (HYSCORE) support the RNA-induced formation of dynamic coilin droplets with high coilin peptide concentrations. The combined NMR and EPR data reveal the high dynamics of the RG-rich coilin within droplets and suggest its potential role in the large dynamics of CBs. The authors show the RNA-induced droplet formation by a component of Cajal bodies and reveal the large nanoseconds mobility of glycine residues inside droplets as a molecular factor potentially contributing to the large dynamics of Cajal bodies. [ABSTRACT FROM AUTHOR]

Correlations of electronic and magnetic resonance parameters of spin charge carriers in thiophene oligomers with their polymerization degrees and conformations have been established by comparison of theoretically obtained density functional theory (DFT) and electron paramagnetic resonance (EPR) data with experimental results. [ABSTRACT FROM AUTHOR]

The study addresses the question of stabilisation of the azo anion radical state of azobis(benzothiazole) (abbt, L) on a selective ruthenium platform without the involvement of direct intramolecular electron transfer (IET) or solvent oxidation, as has been demonstrated earlier, and its reversible electron-reservoir feature were investigated. Specifically, the ruthenium-hydride metal precursor (RuII(H)(Cl)(CO)(PPh3)3)-mediated stabilisation of the azo anion radical of abbt derivatives in RuII(L˙−)(Cl)(CO)(PPh3)2 (1: L1 = 2,2′-azobis(benzothiazole), 2: L2 = 2,2′-azobis(6-methylbenzothiazole), 3: L3 = 2,2′-azobis(6-chlorobenzothiazole)) without the alteration of the metal oxidation state (RuII). The radical state of L˙− in 1–3 (S = 1/2, μeff/B.M. = 1: 1.83, 2: 1.78, 3: 1.86 in CDCl3 at 298 K, determined by Evans method) displayed free radical electron paramagnetic resonance (EPR) (g ≈ 2.0) with the partial resolution of nitrogen hyperfine splitting. The effective role of the Ru–H metal precursor towards the {L0–RuII–H} → {RuII–L˙− + 1/2 H2} transformation in 1–3 was corroborated by the detection of H2 gas from the reaction mixture as well as by its calculated favourable thermodynamic parameters (ΔG: −76 to −84 kcal mol−1). Moreover, the low oxidation potential of L˙− → L0 in 1–3 (0.14–0.31 V versus SCE) facilitated the isolation of the corresponding oxidised complexes [RuII(L0)(Cl)(CO)(PPh3)2]ClO4 ([1]ClO4, [2]ClO4, [3]ClO4) by using AgClO4 as the chemical oxidant. The structural evaluation of [1]ClO4 to [3]ClO4 revealed: (i) a lengthening of the azo bond (N1–N4 > 1.3 Å) with respect to the corresponding free ligand (L ≈ 1.25 Å) due to dπ(RuII) to π*(azo) back bonding and (ii) the planar/slightly non-planar L2, L1/L3 (torsional angle: 8.09°, 9.07°) introduced two equivalent and inequivalent PPh3 co-ligands in [2]ClO4, [1]ClO4, and [3]ClO4, respectively. The L0 state in 1+–3+ could also be reduced to L˙− in 1–3 by hydrazine hydrate, attributed to its reversible electron-reservoir feature. Also, 1n–3n (n = 1, 0, −1) exhibited mixed metal–ligand-based charge-transfer transitions in the UV-visible region as a function of L and n. [ABSTRACT FROM AUTHOR]

The nature of the photoexcited triplet state of free-base 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4−) has been investigated by advanced Electron Paramagnetic Resonance (EPR) techniques combined with quantum chemical calculations. The zero-field splitting (ZFS) parameters, D and E, the orientation of the transition dipole moment in the ZFS tensor frame, and the proton hyperfine couplings have been determined by magnetophotoselection-EPR and pulse electron-nuclear double resonance spectroscopy. Both time-resolved and pulse experiments exploit the electron spin polarization of the photoexcited triplet state. Comparison of the magnetic observables with computational results, including CASSCF calculations of the ZFS interaction tensor, provides an accurate picture of the triplet-state electronic structure. The theoretical investigation has been integrated with a systematic analysis on the parent free-base porphyrin molecule to assess the effect of the sulfonatophenyl substituents on the magnetic tensors. Additionally, the magnetophotoselection effects are discussed in terms of tautomerization in the excited singlet state of H2TPPS4−. [ABSTRACT FROM AUTHOR]

Methods of controlling spin coherence by molecular design are essential to efforts to develop molecular qubits for quantum information and sensing applications. In this manuscript, we perform the first studies of how arrangements of 35/37Cl nuclear spins in the ligand shell and counterion selection affect the coherent spin dynamics of V(IV) complexes at a high magnetic field. We prepared eight derivatives of the vanadium triscatecholate complex with varying arrangements of 35/37Cl substitution on the catechol backbone and R3NH+ counterions (R = Et, n-Bu, n-Hex) and investigated these species via structural and spectroscopic methods. Hahn-echo pulsed electron paramagnetic resonance (EPR) experiments at high-frequency (120 GHz) and field (ca. 4.4 T) were used to extract the phase-memory relaxation time (Tm) and spin-lattice relaxation (T1) times of the series of complexes. We found Tm values ranging from 4.8 to 1.1 μs in the temperature range of 5 to 40 K, varying by approximately 20% as a function of substitutional pattern. In-depth analysis of the results herein and comparison with related studies of brominated analogues disproves multiple hypothesized mechanisms for Tm control. Ultimately, we propose that more specific properties of the halogen atoms, e.g. the chemical shift, V⋯Cl hyperfine coupling, and quadrupolar coupling, could be contributing to the V(IV) Tm time. [ABSTRACT FROM AUTHOR]

In this contribution, the relative hyperfine couplings are determined for the 1H nuclei of the flavin mononucleotide (FMN) radical in an aqueous environment. In addition, three structural analogs with different methylation patterns are characterized and the influence of the substituents at the isoalloxazine moiety on the electronic structure of the radicals is explored. By exploiting nuclear hyperpolarization generated via the photo-CIDNP (chemically induced dynamic nuclear polarization) effect, it is possible to study the short-lived radical species generated by in situ light excitation. Experimental data are extracted by least-squares fitting and supported by quantum chemical calculations and published values from electron paramagnetic resonance and electron-nuclear double resonance. Furthermore, mechanistic details of the photoreaction of the investigated flavin analogs with l-tryptophan are derived from the photo-CIDNP spectra recorded at different pH values. Thereby, the neutral and anionic radicals of FMN and three structural analogs are, for the first time, characterized in terms of their electronic structure in an aqueous environment. [ABSTRACT FROM AUTHOR]

The adducts formed between 25Mg+ with 14N2 and 25Mg+ with 15N2 have been trapped in a solid neon matrix and studied with electron spin resonance (ESR) spectroscopy. These radical species were formed through the interaction of laser ablated magnesium and nitrogen gas. The Mg+-N2 radical species was found to have a ground electronic state of 2Σ+ in a linear configuration with discrete coupling to the proximate nitrogen resolved in the spectra. Fitting the ESR spectra allowed magnetic parameters to be determined as follows: g⊥ = 2.0012(5), g∥ = 2.0015(8), A⊥(1-14N) = 32(3) MHz, A∥(1-14N) = 34(5) MHz, A⊥(1-15N) = 45(4) MHz, A∥(1-15N) = 47(6) MHz, A⊥(25Mg) = −581(5) MHz, and A∥(25Mg) = −582(5) MHz, and estimates derived for A⊥(2-14N) = 1(2) MHz, A∥(2-14N) = 2(5) MHz, A⊥(2-15N) = 2(2) MHz, and A∥(2-15N) = 4(6) MHz. Ab initio calculations using the coupled-cluster single double triple methodology showed that the linear form was 59.7 kcal mol−1 more stable than the T-shaped form. The potential energy curve around the equilibrium geometry was explored using the complete active space self-consistent field approach, and Hartree–Fock singles and double configuration interaction and multireference singles and double configuration interaction calculations of the hyperfine coupling constants were undertaken, and reasonable agreement with the experiment was observed. [ABSTRACT FROM AUTHOR]

A test set of N,N,N',N'-tetrasubstituted p-phenylenediamines are experimentally explored using ESR (electron spin resonance) spectroscopy and analysed from a computational standpoint thereafter. This computational study aims to further aid structural characterisation by comparing experimental ESR hyperfine coupling constants (hfccs) with computed values calculated using ESR-optimised "J-style" basis sets (6-31G(d,p)-J, 6-31G(d,p)-J, 6-311++G(d,p)-J, pcJ-1, pcJ-2 and cc-pVTZ-J) and hybrid-DFT functionals (B3LYP, PBE0, TPSSh, ω B97XD) as well as MP2. PBE0/6-31g(d,p)-J with a polarised continuum solvation model (PCM) correlated best with the experiment, giving an R 2 value of 0.8926. A total of 98% of couplings were deemed satisfactory, with five couplings observed as outlier results, thus degrading correlation values significantly. A higher-level electronic structure method, namely MP2, was sought to improve outlier couplings, but only a minority of couples showed improvement, whilst the remaining majority of couplings were negatively degraded. [ABSTRACT FROM AUTHOR]

Photoexcited organic chromophores appended to stable radicals can serve as qubit and/or qudit candidates for quantum information applications. 1,6,7,12‐Tetra‐(4‐tert‐butylphenoxy)‐perylene‐3,4 : 9,10‐bis(dicarboximide) (tpPDI) linked to a partially deuterated α,γ‐bisdiphenylene‐β‐phenylallyl radical (BDPA‐d16) was synthesized and characterized by time‐resolved optical and electron paramagnetic resonance (EPR) spectroscopies. Photoexcitation of tpPDI‐BDPA‐d16 results in ultrafast radical‐enhanced intersystem crossing to produce a quartet state (Q) followed by formation of a spin‐polarized doublet ground state (D0). Pulse‐EPR experiments confirmed the spin multiplicity of Q and yielded coherence times of Tm=2.1±0.1 μs and 2.8±0.2 μs for Q and D0, respectively. BDPA‐d16 eliminates the dominant 1H hyperfine couplings, resulting in a single narrow line for both the Q and D0 states, which enhances the spectral resolution needed for good qubit addressability. [ABSTRACT FROM AUTHOR]

Magnetic molecules have shown great potential in quantum information processing due to the chemical tunablity of their quantum behaviors. Chemical derivatives of endohedral nitrogen fullerenes with long coherence time and rich energy levels were synthesized and studied to demonstrate the ability of multiprocessing in quantum information using electron magnetic resonance. After initialization of the 12‐levelled spin system, subgroups of spin energy levels coursed by the hyperfine couplings can be selectively manipulated. The cooperatively combining of the parallel calculations enabled quantum error correction, increasing the correct rate by up to 17.82 %. Also, different subgroups of transitions divided by hyperfine coupling can be treated as independent qubits, and multi‐task quantum computing were realized by performing Z‐gate and X‐gate simultaneously, which accelerates the overall gating speed. [ABSTRACT FROM AUTHOR]

EPR spectroscopy requires a combination of fixed microwave radiation and resonant external magnetic field. Bigger is not necessarily better in that low-frequency and -field EPR (LFEPR) can provide useful information as well as reduced linewidths that can allow better observation of hyperfine coupling. More importantly, LFEPR allows very low g values to be readily observed, such as often found in low-spin d5 systems. [ABSTRACT FROM AUTHOR]

In order to take advantage of the strong correlation between geometric changes and electronic properties, better understanding of the structure and properties of perovskites doped with paramagnetic transition metal ions is required. Computational characterization of these dopants and calculated hyperfine values provide a guide that can ultimately aid in the interpretation of experimentally obtained electron paramagnetic resonance (EPR) spectra. In this study, we perform ab initio calculation of the hyperfine splitting parameter for Sr-substituted Mn2+ in SrTiO3 in various geometries in order to assign experimentally reported EPR peaks to exact dopant structures. Additionally, we calculate the hyperfine parameters for Mn4+ and Mn2+∕4+ with adjacent oxygen vacancy, which remain to be assigned peaks in experimental EPR spectra. Calculation of Ti-substituted Mn is largely hindered by the highly correlated electronic structure; however, it is shown that reasonable hyperfine values for Ti-site defects can be obtained by tuning functional parameters. Overall, this study demonstrates that calculating the hyperfine splitting for a transition metal dopant in a complex oxide is feasible and can provide a fingerprint for different geometries in equivalently defected systems. [ABSTRACT FROM AUTHOR]

The γ-irradiated 77K samples (RaO)x(SiO2)y with adsorbed water were studied using EPR spectroscopy, and EPR spectrum with g=2.0028 and hyperfine splitting constant A(H)=505.3 G belonging to hydrogen atoms was registered. EPR, presumably attributed to paramagnetic hole (≡Si-O)+, electronic (≡Si-)- centers and products of their interaction with water molecules spectra was registered. It is assumed that the main part of atomic hydrogen was oxidized to the HO2• radical, and some of the H• atoms participate in surface radiative hydrogenation reactions with the formation of hydrogen-containing radicals when irradiated samples were heated from 77 K to room temperature. It is also assumed that •OH radicals are formed on the surface of γ--irradiated at 77K (RaO)x(SiO2)y samples. [ABSTRACT FROM AUTHOR]

• The paramagnetic center in 2-nitrobenzoic acid single crystal was examined. • Gamma ray created a resonance structure in the carboxyl group. • The 2-nitrobenzoic acid anion radical was formed. • Paramagnetic structure was analyzed by EPR spectroscopy. 2-nitrobenzoic acid (C 7 H 5 NO 4) (2NBA) single crystals were made paramagnetic using 60Co-gamma rays. An attempt was made to detect the resonance form formed in 2-nitrobenzoic acid single crystal with Electron Paramagnetic Resonance (EPR) Spectroscopy. EPR spectra were taken at 125 K in three different axes of the crystal. As a result of EPR analysis of gamma irradiated 2NBA single crystal, it was understood that 2NBA anion radical was formed. The principal values of the hyperfine structure constants, the principal values of the g-tensor and their direction cosines were calculated. [ABSTRACT FROM AUTHOR]

Graphical depiction of LUMOs of cis and trans isomers of VO(acac) 2 pyr complexes in oxidized state, and corresponding SOMOs of the reduced state. [Display omitted] The use of vanadium complexes for potential applications in medicine largely depends on the structural properties of the complex itself, as well as on the electronic configuration of the metal and its oxidation state. When the vanadium complex binds to biomolecules or by binding solvent molecules to the complex, there is a change in the structure but also a change in the redox properties of the complex. Using theoretical methods, especially Density Functional theory (DFT), it is possible to determine which factors influence changes in the redox properties of the complex. Furthermore, by calculating the Electron Paramagnetic Resonance (EPR) constants of hyperfine coupling, it is possible to obtain not only data on the electronic configuration, but also to predict changes in redox properties upon changes in the structure of the complex. DFT results show that the binding of pyridine or imidazole to the VO(acac) 2 complex leads to a lowering of the redox potential. The largest changes in the redox potential were observed in the case when the incoming ligand binds in a cis position relative to the V O bond. [ABSTRACT FROM AUTHOR]

We report on terahertz (THz) electron paramagnetic resonance generalized spectroscopic ellipsometry (THz-EPR-GSE). Measurements of field and frequency dependencies of magnetic response due to spin transitions associated with nitrogen defects in 4H-SiC are shown as an example. THz-EPR-GSE dispenses with the need of a cavity, permits independently scanning field and frequency parameters, and does not require field or frequency modulation. We investigate spin transitions of hexagonal (h) and cubic (k) coordinated nitrogen including coupling with its nuclear spin (I = 1), and we propose a model approach for the magnetic susceptibility to account for the spin transitions. From the THz-EPR-GSE measurements, we can fully determine polarization properties of the spin transitions, and we can obtain the k coordinated nitrogen g and hyperfine splitting parameters using magnetic field and frequency dependent Lorentzian oscillator line shape functions. Magnetic-field line broadening presently obscures access to h parameters. We show that measurements of THz-EPR-GSE at positive and negative fields differ fundamentally and hence provide additional information. We propose frequency-scanning THz-EPR-GSE as a versatile method to study properties of spins in solid state materials. [ABSTRACT FROM AUTHOR]

High concentration of negatively charged nitrogen-vacancy (NV−) centers was created in diamond single crystals containing approximately 100 ppm nitrogen using electron and neutron irradiation and subsequent thermal annealing in a stepwise manner. Continuous-wave electron paramagnetic resonance (EPR) was used to determine the transformation efficiency from isolated N atoms to NV− centers in each production step and its highest value was as high as 17.5%. Charged vacancies are formed after electron irradiation as shown by EPR spectra, but the thermal annealing restores the sample quality as the defect signal diminishes. We find that about 25% of the vacancies form NVs during the annealing process. The large NV− concentration allows observing orientation dependent spin-relaxation times and also determining the hyperfine and quadrupole coupling constants with high precision using electron spin echo (ESE) and electron-nuclear double resonance (ENDOR). We also observed the EPR signal associated with the so-called W16 centers, whose spectroscopic properties might imply a nitrogen dimer-vacancy center for its origin. [Display omitted] [ABSTRACT FROM AUTHOR]

The objective of spectral analysis is to resolve and extract relevant features from experimental data in an optimal fashion. In continuous-wave (cw) electron spin resonance (ESR) spectroscopy, both g values of a paramagnetic center and hyperfine splitting (A) caused by its interaction with neighboring magnetic nuclei in a molecule provide important structural and electronic information. However, in the presence of g- and/or A-anisotropy and/or large number of resonance lines, spectral analysis becomes highly challenging. Either high-resolution experimental techniques are employed to resolve the spectra in those cases or a range of suitable ESR frequencies are used in combination with simulations to identify the corresponding g and A values. In this work, we present a wavelet transform technique in resolving both simulated and experimental cw-ESR spectra by separating the hyperfine and super-hyperfine components. We exploit the multiresolution property of wavelet transforms that allow the separation of distinct features of a spectrum based on simultaneous analysis of spectrum and its varying frequency. We retain the wavelet components that stored the hyperfine and/or super-hyperfine features, while eliminating the wavelet components representing the remaining spectrum. We tested the method on simulated cases of metal–ligand adducts at L-, S-, and X-band frequencies, and showed that extracted g values, hyperfine and super-hyperfine coupling constants from simulated spectra, were in excellent agreement with the values of those parameters used in the simulations. For the experimental case of a copper(II) complex with distorted octahedral geometry, the method was able to extract g and hyperfine coupling constant values, and revealed features that were buried in the overlapped spectra. [ABSTRACT FROM AUTHOR]

The cationic meso-aryl-substituted porphyrins and their metal complexes were studied as model compounds for photodynamic therapy by electron spin resonance (ESR) techniques. Symmetrical cationic porphyrins with terminal pyridinium groups on short alkyl spacers and their Zn(II) and Cu(II) complexes were synthesized. Zero-field splitting parameters of the photoexcited triplet states were determined by time-resolved ESR. For Cu(II) complexes, the hyperfine coupling between the paramagnetic ligand and the nitrogen atoms of the porphyrin ring was measured. The effect of pyridinium substituents and the ligand on the magnetic-resonance parameters of porphyrins was analyzed on the basis of the obtained results. [ABSTRACT FROM AUTHOR]

Chiral open-shell molecules possessing permanent electric dipole moments have an EPR signal at the difference frequency of the electron and nuclear resonances, allowing direct enantiomeric discrimination by signal phase. The effect depends on the vector antisymmetry of the hyperfine coupling. Quantum chemistry suggests chiral bisfluorene methyl radical derivatives as promising for experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Doubly charged peroxylamine disulfonate (Frémy's salt) resides in the polar nanodomains of room-temperature ionic liquids. • Neutral di- tert -butyl nitroxide (DTBN) resides in the nonpolar nanodomains of room-temperature ionic liquids. • Rotational anisotropy of Frémy's salt increases with increasing cation alkyl chain length. • The activation energy of the rotation of Frémy's salt and di- tert -butyl nitroxide is the same as that of the viscous flow. • Long-range collective motion governs the activation energy of Frémy's salt and di- tert -butyl nitroxide rotation. We have studied the rotational diffusion of two prolate nitroxide probes, the doubly negatively charged peroxylamine disulfonate (Frémy's salt − FS) and neutral di- tert -butyl nitroxide (DTBN), in a series of 1-alkyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquids (RTILs) having alkyl chain lengths from two to eight carbons using electron paramagnetic resonance (EPR) spectroscopy. Though the size and shape of the probes are reasonably similar, they behave differently due to the charge difference. The rotation of FS is anisotropic, and the rotational anisotropy increases with the alkyl chain length of the cation, while the rotation of DTBN is isotropic. The hyperfine coupling constant of DTBN decreases as a function of the alkyl chain length and is proportional to the relative permittivity of ionic liquids. On the other hand, the hyperfine coupling constant of FS increases with increasing chain length. These behaviors indicate the location of each probe in RTILs. FS is likely located in the polar region near the network of charged imidazolium ions. DTBN molecules are predominately distributed in the nonpolar domains. [ABSTRACT FROM AUTHOR]

A facile synthesis method is introduced how to prepare magnetically active ultraviolet emitting manganese ions incorporated into ZnSxSe1−x colloidal quantum dot (nanoalloy) at 110 °C in aqueous solutions. The reaction time is the main factor to control the hydrodynamic size from 3 to 10 nm and the precursor ratio is significant to tune the alloy composition. ZnS shell layer on the ZnSxSe1−x core was grown to passivate environmental effects. The nanoalloy has ultraviolet emission at 380 nm having a lifetime of 80 ns and 7% quantum yield. The incorporation of Mn2+ ions into the nanoalloys induced magnetic activity but did not modify the structure and photophysical properties of the nanoalloys. Colloidal and powdery samples were prepared and analyzed by electron paramagnetic resonance (EPR) spectroscopy. In the colloidal dispersions, EPR spectra showed hyperfine line splitting regardless of the Mn2+ ion fractions, up to 6%, indicating that Mn2+ ions incorporated into the nanoalloys were isolated. EPR signals of the powdery samples were broadened when the fraction of Mn2+ ions was higher than 0.1%. The EPR spectra were simulated to reveal the locations and interactions of Mn2+ ions. The simulations suggest that the Mn2+ ions are located on the nanoalloy surfaces. These findings infer that the magnetic dipolar interactions are regulated by the initial mole ratio of Mn/Zn and the physical state of the nanoalloys adjusted by preparation methods. [ABSTRACT FROM AUTHOR]

Silicon nanoelectronic devices can host single-qubit quantum logic operations with fidelity better than 99.9%. For the spins of an electron bound to a single-donor atom, introduced in the silicon by ion implantation, the quantum information can be stored for nearly 1 second. However, manufacturing a scalable quantum processor with this method is considered challenging, because of the exponential sensitivity of the exchange interaction that mediates the coupling between the qubits. Here we demonstrate the conditional, coherent control of an electron spin qubit in an exchange-coupled pair of 31P donors implanted in silicon. The coupling strength, J = 32.06 ± 0.06 MHz, is measured spectroscopically with high precision. Since the coupling is weaker than the electron-nuclear hyperfine coupling A ≈ 90 MHz which detunes the two electrons, a native two-qubit controlled-rotation gate can be obtained via a simple electron spin resonance pulse. This scheme is insensitive to the precise value of J, which makes it suitable for the scale-up of donor-based quantum computers in silicon that exploit the metal-oxide-semiconductor fabrication protocols commonly used in the classical electronics industry. Operating donor-based quantum computers in silicon is hindered by the dependence of inter-qubit coupling on the precise donor position. Here, the authors show controlled rotation operation on exchange-coupled electron spins in the weak-exchange regime, loosening the requirements on positioning precision. [ABSTRACT FROM AUTHOR]

Growing high-purity diamond containing dense negatively charged nitrogen-vacancy (NV−) centre ensembles is desirable for the development of sensitive quantum sensors that explore the coherent manipulation of the spin states of this atomic-scale defect. By using N 2 O as a dopant, we demonstrate that millimetre-thick single crystals can be grown by Chemical Vapour Deposition (CVD) with substitutional nitrogen concentrations as high as 26 ppm. With a high-energy electron irradiation treatment and in-situ annealing, up to 20% of this nitrogen can be successfully converted into NV− centres leading to densities of almost 5 ppm and to a crystal displaying pink colouration and appealing optical properties. The longitudinal relaxation T 1 time in such a highly doped diamond is measured to be around 3.5 ms at 300 K while inhomogeneous dephasing time T 2 ∗ is estimated to 600 ns. Despite the high NV density, Electron Spin Resonance lines are resolved with clear hyperfine splitting induced by the nuclear spin of nitrogen. The dependence of T 1 on the orientation of the magnetic field suggests that relaxation is dominated by NV-NV dipole interactions when no magnetic field is applied. Such engineered crystals constitute a promising platform for developing future quantum sensing applications. Image 1 • Millimetre thick diamond single crystals with addition of 500 ppm of N 2 O. • Substitutional nitrogen conversion into NV centres by electron irradiation and in situ annealing with 20% efficiency. • High total NV density of 7 ppm (NV− of 4.6 ppm) leading to pink colouration. • Long T 2 ∗ coherence time of 600 ns in irradiated samples. • High [NV−] × T 2 ∗ products of 3 μs ppm. [ABSTRACT FROM AUTHOR]

The electronic structure and the equilibrium geometry of the VN 3 defect in diamond are computed by using a quantum mechanical approach, the main ingredients being an all electron gaussian type basis set, a global hybrid functional, the supercell scheme (216 atoms) and the CRYSTAL code. For the first time the Fermi contact and the hyperfine coupling tensor B of the open shell structure (S z = 1/2) are evaluated and compared with available experimental EPR (electron paramagnetic resonance) data. The agreement is excellent. The infrared (IR) spectrum is also computed. It results to be very close to the one of the so called B defect (VN 4), and with similarities to the one of the other members of the VN x (x = 0, 1, 2) family, so that the attribution of specific experimental peaks to one of the five mentioned compounds is difficult and questionable. The peaks measured by Sutherland (Nature, 174 , 901, 1954) and attributed to the B center might, at least in part, come from both VN 3 and VN 4. Being the ground state of the latter a closed shell, and then EPR inactive, a combined use of the two spectroscopies (IR and EPR) is mandatory for the identification of the relative weight of the two defects. Image 1 [ABSTRACT FROM AUTHOR]

Local approximations of high-level ab initio methods make superior accuracy in the computation of molecular properties accessible by drastically decreasing computational times. As a consequence, these methods become applicable not only for large systems but also in schemes for which large numbers of calculations are necessary. In this work, we apply a recently developed open-shell implementation of the domain-based pair natural orbital coupled cluster singles doubles (DLPNO-CCSD) approach for the computation of vibrational corrections to the isotropic values of electron paramagnetic resonance (EPR) hyperfine coupling constants. We assess density functional theory (DFT) and DLPNO-CCSD approaches using two common but very different schemes: (1) vibrational perturbation theory based on equilibrium geometries, and (2) explicit canonical ensemble averages using configuration snapshots sampled from revPBE0-D3(0) ab initio molecular dynamics simulations. Both approaches are found to yield very similar results for the spin probe 2,2,3,4,5,5-hexamethylperhydroimidazol-1-oxyl (HMI) and are both feasible for systems of around 30 atoms. However, the numerical stability required for higher derivatives can become a limitation for local correlation methods in the case of vibrational perturbation theory. [ABSTRACT FROM AUTHOR]

A stable triarylmethyl spin probe whose electron paramagnetic resonance (EPR) spectrum is highly sensitive to molecular tumbling is reported. The strong anisotropy of the hyperfine coupling tensor with the central carbon of a 13C1‐labeled triarylmethyl radical enables the measurement of the probe rotational correlation time with applications to measure microviscosity and molecular dynamics. [ABSTRACT FROM AUTHOR]

A set of glass samples with composition based on ternary 50P2O5–30Na2O–20ZnO (PNZ) matrix doped with different MnO contents was prepared via melt-quenching technique. Thermal, structural and spectroscopic properties were investigated by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), Raman spectroscopy, UV–visible absorption, photoluminescence (PL) and by electron paramagnetic resonance (EPR) using Mn2+ as probe. Glass compositions (100-x)PNZ:xMn (0.01 ≤ x ≤ 1.0 in mol% of MnO) were characterized as glasses after careful analysis of the thermal and structural data. While DSC curves show the presence of the glass transition phenomenon (Tg), XRD analysis identified the non-crystalline arrangement, compatible with glass structure. Raman spectra of PNZ:xMn samples showed that the successive increase in Mn2+ content leads to rise of vibrational modes assigned to phosphate Q1 units, suggesting the breakdown of phosphate glass network chains. UV–Vis absorption spectra of glasses presented absorption bands centered at 250, 318, 341, 358 and 408 nm attributed to the Mn2+ electronic transitions. Glass samples containing above 0.06 mol% of MnO presented a broadband absorption centered at 511 nm assigned to the presence of traces of Mn3+. Additionally, UV–Vis, PL and EPR data showed that Mn2+ ions are occupying octahedral arrangements. Besides, EPR results suggest that the increase in MnO concentration influences on the EPR signal and hyperfine splitting constant suggests the presence of a moderately ionic bond between Mn2+ and PNZ glass network. [ABSTRACT FROM AUTHOR]

Alanine is used as a transfer standard dosimeter for gamma ray and electron beam calibration. An important factor affecting its dosimetric response is humidity which can lead to errors in absorbed dose calculations. Ab initio molecular dynamics calculations were performed to determine the environmental effects on the electron paramagnetic resonance (EPR) parameters of L‐α‐alanine radicals in acidic and alkaline solutions. A new result, not dissimilar to the closed‐shell amino acid molecule alanine, is that the non‐zwitterionic form of the alanine radical is the stable form in the gas phase while the zwitterionic neutral alanine radical is not a stable structure in the gas phase. Geometric and EPR parameters of radicals in both gas and solution phases are found to be dependent on hydrogen bonding of water molecules with the polar groups and on dynamic solvation. Calculations on the optimized free radicals in the gas phase revealed that for the neutral radical, hydrogen bonding to water molecules drives a decrease in the magnitudes of g‐tensor components gxx and gyy without affecting neither gzz component nor the hyperfine coupling constants (HFCCs). The transfer from the gas to solution phase of the alanine radical anion is accompanied with an increase in the spin density on the carboxylic group's oxygen atoms. However, for the neutral radical, this transfer from gas to solution phase is accompanied with the decrease in the spin density on oxygen atoms. Calculated isotropic HFCCs and g‐tensor of all radicals are in good agreement with experiment in both acidic and alkaline solutions. [ABSTRACT FROM AUTHOR]

A new series of transition‐metal complexes of Schiff base ligand containing the amino mercapto triazole moiety (HL) was prepared. The Schiff base and its metal complexes were elucidated by different spectroscopic techniques (infrared [IR], 1H nuclear magnetic resonance, UV–Visible, mass, and electron spin resonance [ESR]), and magnetic moment and thermal studies. Quantum chemical calculations have been carried out to study the structure of the ligand and some of its complexes. The IR spectra showed that the ligand is chelated with the metal ion in a neutral, tridentate, and bidentate manner using NOS and NO donors in complexes 1–6, 10–12, and 7 and 8, respectively, whereas it behaves in a monobasic tridentate fashion using NOS donor sites in copper(II) nitrate complex (9). The magnetic moment and electronic spectra data revealed octahedral and square pyramidal geometries for complexes 2, 11, 12, and 5–8 and 10, respectively. However, the other complexes were found to have tetrahedral (4), trigonal bipyramidal (1 and 3), and square planar (9) structures. Thermal studies revealed that the chelates with different crystallized solvents undergo different types of interactions and the decomposition pathway ended with the formation of metal oxygen (MO) and metal sulfur (MS) as final products. The ESR spectrum of copper(II) complex 10 is axial in nature with hyperfine splitting with 2B1g as a ground state. By contrast, complexes 7 and 8 undergo distortion around the Cu(II) center, affording rhombic ESR spectra. The HL ligand and some of its complexes were screened against two bacterial species. Data showed that complex 12 demonstrated a better antibacterial activity than HL ligand and other chelates. [ABSTRACT FROM AUTHOR]

The classical model of an ideal crystal, parametrized according to non-empirical calculations, is used to determine the structure and geometry of the atomic lithium trapping sites in solid inert gases RG = Ar, Kr, and Xe, and to define their thermodynamic stability. The diversity of the observed stable sites reduces to four highly symmetric structures corresponding to the interstitial introduction of an Li atom, its substitution of an inert gas atom, or its incorporation into tetrahedral and octahedral vacancies formed by the removal of four and six inert gas atoms from the crystal lattice. The non-empirically calculated dependences of the isotropic hyperfine coupling constant tensor on the distance in the diatomic Li@RG complex are used to estimate the shifts of the electron paramagnetic resonance signals in the predicted thermodynamically stable sites. A comparison with published data does not contradict the assignment of the observed multiple signals to certain types of stable sites, taking into account the spectral features of samples that were prepared by thermal deposition and laser ablation in three different inert gases. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) spectroscopy has been proven to be an important technique for studying paramagnetic systems. Probably, the most accessible EPR parameter and the one that provides a significant amount of information about molecular structure and spin density is the hyperfine coupling constant (HFCC). Hence, accurate quantum-chemical modeling of HFCCs is frequently essential to the adequate interpretation of EPR spectra. It requires the precise spin density, which is the difference between the densities of α- and β-electrons, and thus, its quality is expected to reflect the quality of the total electron density. The question of which approximate exchange-correlation density functional yields sufficiently accurate HFCCs, and thus, the spin density remains open. To assess the performance of well-established density functionals for calculating HFCCs, we used a series of 26 small paramagnetic species and compared the obtained results to the CCSD reference values. The performance of DFT was also tested on EPR-studied o-semiquinone radical interacting with water molecules and Mg2+ cation. The HFCCs were additionally calculated by the DLPNO-CCSD method, and this wave function-based technique was found superior to all functionals we tested. Although some functionals were found, on average, to be fairly efficient, we found that the most accurate functional is system-dependent, and therefore, the DLPNO-CCSD method should be preferred for theoretical investigations of the HFCCs and spin density. [ABSTRACT FROM AUTHOR]

Gamma irradiated trans-chalcone (C15H12O) single crystals are investigated at 120 K using electron paramagnetic resonance technique. Trans-chalcone single crystals are irradiated with 60Co-γ rays, at room temperature. The EPR spectra of gamma irradiated trans-chalcone single crystals are studied for different orientations of crystals in a magnetic field. The spectra are found to be temperature independent. The structure of the radical produced by γ-irradiation of a single crystal of trans-chalcone is discussed. The investigation of EPR spectra of gamma-irradiated single crystals of trans-chalcone shows the presence of two trans-chalcone anion radicals. The two trans-chalcone anion radicals are created by the scission of the carbon-oxygen double bond. The reduction of trans-chalcone is identified which is formed by the addition of an electron to oxygen of the formed C-O bond. The principal values of the hyperfine coupling tensors of the unpaired electron and the principal values of the g-tensors and direction cosines of the radiation damage centers are determined. The results are found to be in good agreement with the existing literature. [ABSTRACT FROM AUTHOR]

• 2D correlated hyperfine spectroscopy confirms binding of TC via Mn2+ to its aptamer. • THYCOS and 2D EDNMR were used to correlate 31P (RNA) and 13C (TC) nuclei to Mn2+. • THYCOS was able to determine the sign of the 13C hyperfine coupling. • 2D EDNMR is 20 times more sensitive that THYCOS. The tetracycline-binding RNA aptamer (TC-aptamer) binds its cognate ligand the antibiotic tetracycline (TC) via a Mg2+ or Mn2+ ion with high affinity at high divalent metal ion concentrations ( K D = 800 pM , ⩾ 10 mM). These concentrations lie above the physiological divalent metal ion concentration of ca. 1 mM and it is known from literature, that the binding affinity decreases upon decreasing the divalent metal ion concentration. This work uses a Mn2+ concentration of 1 mM and 1D-hyperfine experiments reveal two pronounced 31P couplings from the RNA besides the 13C signal of 13C-labeled TC. From these 1D-hyperfine data alone, however, no conclusions can be drawn on the binding of TC. Either TC may bind via Mn2+ to the aptamer or TC may form a free Mn-TC complex and some Mn2+ also binds to the aptamer. In this work, we show using 2D-correlated hyperfine spectroscopy at Q-band frequencies (34 GHz), that the 13C and 31P signals can be correlated; thus arising from a single species. We use THYCOS (triple hyperfine correlation spectroscopy) and 2D ELDOR-detected NMR (2D electron electron double resonance detected NMR) for this purpose showing that they are suitable techniques to correlate two different nuclear spin species (13C and 31P) on two different molecules (RNA and TC) to the same electron spin (Mn2+). Out of the two observed 31P-hyperfine couplings, only one shows a clear correlation to 13C. Although THYCOS and 2D EDNMR yield identical results, 2D EDNMR is far more sensitive. THYCOS spectra needed a time factor of × 20 in comparison to 2D EDNMR to achieve a comparable signal-to-noise. [ABSTRACT FROM AUTHOR]

The first two persistent silenyl radicals (R2C=Si.−R), with a half‐life (t1/2) of about 30 min, were generated and characterized by electron paramagnetic resonance (EPR) spectroscopy. The large hyperfine coupling constants (hfccs) (a(29Siα)=137.5–148.0 G) indicate that the unpaired electron has substantial s character. DFT calculations, which are in good agreement with the experimentally observed hfccs, predict a strongly bent structure (∡C=Si−R=134.7–140.7°). In contrast, the analogous vinyl radical, R2C=C.−R (t1/2≈3 h), exhibits a small hfcc (a(13Cα)=26.6 G) and has a nearly linear geometry (∡C=C−R=168.7°). [ABSTRACT FROM AUTHOR]

Copper ions can catalyze the production of free oxygen radicals (•OH and •OOH) similar to iron ions. The capacity to initiate oxidative damage is most commonly attributed to Cu-induced toxicity in copper-related diseases where there is an increase in copper levels and also when Cu homeostasis and regulation are disrupted. An antioxidant/chelator inhibiting Cu-induced oxidative damage could play a significant role in the treatment of such Cu-related diseases. Deferiprone has high affinity for copper binding and can be considered for the potential treatment of copper toxicity and overloading conditions, such as Wilson's disease. In the present study, the ability of deferiprone to inhibit the production of hydroxyl radicals catalyzed by copper ions was elucidated using an Electron Paramagnetic Resonance (EPR) spin trapping technique. The values of g-factors and hyperfine splitting constants were calculated for Cu(II)-deferiprone 1:1 complex: (a = 58.5 G, g = 2.1667) and 1:2 complex: (a = 73.0 G, g = 2.1378). The TMIO spin trap (2,2,4-trimethyl-2H-imidazole-1-oxide) was used for the detection of free radicals formed in Fenton-like copper-catalyzed reactions. It was demonstrated that the interaction of deferiprone with Cu2+ ions completely inhibited hydroxyl radical (•OH) production in the presence of hydrogen peroxide. It was found also that deferiprone inhibits Cu-induced oxidation of linoleic acid in micellar solution. In addition to existing data for water solutions, the affinity of deferiprone for copper binding in non-aqueous environment has been elucidated. [ABSTRACT FROM AUTHOR]

One of the functions of Human Serum Albumin (HSA) is binding and transport of fatty acids. This ability could be altered by the presence of several blood components such as toxins or peptides – which in turn alters the functionality of the protein. We aim at characterizing HSA and its fatty acid binding in native serum environment. Native ligand binding and deviations from normal function can be monitored by electron paramagnetic resonance (EPR) spectroscopy using spin labeled fatty acids (FAs). Blood serum from healthy individuals is used to examine healthy HSA in its natural physiological conditions at different loading ratios of protein to FAs. Among the EPR spectroscopic parameters (like hyperfine coupling, line shape, rotational correlation time and population of different binding sites) the rotational correlation time is found to differ significantly between binding sites of the protein, especially at loading ratios of four FAs per HSA. Although differences are observed between individual samples, a general trend regarding the dynamics of healthy HSA at different loading ratios could be obtained and compared to a reference of purified commercially available HSA in buffer. [ABSTRACT FROM AUTHOR]

Abstract Al-doped anatase titanium dioxide single crystals and highly Al-doped powders were prepared by chemical vapor transport and by sol-gel process, respectively. Electron paramagnetic resonance (EPR) measurement on the single crystals and powders revealed the characteristic behavior of the UV-induced carriers. The UV-induced EPR sextuplet signals originating from photogenerated holes interacting with Al were observed in both the single crystals and powders. Simulation of the powder pattern of the sextuplet signals observed in EPR measurement indicates that the local structure around the trapped hole in the powder is identical to that of the single crystals. The signal intensity under the UV irradiation and the lifetime of the sextuplets after the UV irradiation decreased with increasing Al content. Rietveld analysis of the X-ray diffraction patterns of the powders revealed that the doped Al substitutes Ti, and that the lattice volume decreases with increasing Al content. The Raman bands of the powders shifted to a higher frequency with increasing Al content. On the basis of these experimental results, the mechanism and the stability of the photogenerated hole are discussed in terms of the dependence of the local structural changes around the doped Al on the Al content. Highlights • The UV-generated hole is trapped at around Al in doped anatase TiO 2. • Localization scheme for the hole trapping is independent of the Al content. • Localization of the hole in Al- short O bond results in elongation of Al- short O bond. • The trapped hole destabilizes with increasing Al content due to chemical pressure. [ABSTRACT FROM AUTHOR]

Graphical depiction of a iso values as a function of H-B-Ti-P torsion angle, and depiction of H-B-Ti-P torsion angle and SOMO of complex 1 for H-B-Ti-P torsion angle of 0°. [Display omitted] Metal complexes with BH 4 - ligands show extravagant structural and dynamic properties, and possess many important and applicable qualities (potent reducing agents and catalysts, materials for hydrogen storage). Electron paramagnetic resonance (EPR) is very important for the characterization of complex compounds, the determination of their electronic configuration and geometry. Also, Density Functional Theory (DFT) can predict EPR parameters and explain them more profoundly. Hence, in this paper hyperfine coupling constants of d and f metal complexes with BH 4 - ligands have been determined by DFT calculations, and analyzed in detail. Of particular importance is the analysis and prediction of hyperfine coupling constants for lanthanide complexes with BH 4 - ligands, given that there is not much data in the literature. Calculations predicted that proton hyperfine coupling constants are very small in the case of complexes of f elements, and are present only due to weak polarization. The increase of covalence and the number of unpaired electrons does not significantly affect the change of constants of BH 4 - ligands, but only of protons that are bound by σ bonds. [ABSTRACT FROM AUTHOR]