Forbidden matrix proton spin flip satellites in trapped electron EPR spectra

Observation of the 35 GHz EPR spectrum of γ-irradiated 10 M NaOH/H₂O and 10 M NaOD/D₂O glassy ices at 77°K has revealed proton spin flip satellites associated with the trapped elctron EPR line. This suggests that forbidden satellite transitions contribute to the lineshape of the trapped electron line in the 9 GHz spectrum which has commonly been studied.     

Transient EPR emission spectra of a free radical trapped in a single crystal of chloranil

The EPR spectrum of a free trapped in single crystals of chloranil changes its phase from absorption to emission when the crystal is illuminated by visible light. The time evolution of the EPR signal is discussed in terms of the interaction between the doublet species and triplet excitons produced by light excitation.     

Absorption spectra of lead, indium and barium atoms trapped in solid rare gas matrices

Vacuum ultraviolet absorption spectra of lead, indium and barium atoms trapped in solid rare gases are shown. These spectra were obtained photoelectrically and the matrix gases used were argon, krypton and xenon. The results are discussed in relation to previous work.     

Forbidden matrix proton spin flip satelites in 70 GHz ESP spectra of solvated electrons. A geometrical model for the solvated electron in Methanol glass

Proton spin flip satellites have been observed for the first time in the ESR spectrum of solvated electrons in methanol glass at 70 GHz and ≈ 1.5 K. Analysis indicates a solvated electron structure characterized by an electron to OH proton distance of 2.28 ± 0.15 A and 4 ± 2 equivalent first solvation shell methanol molecules. A geometrical model for the solvated electron in methanol glass is suggested.     

Satellite lines in the EPR spectra of nitroxide radicals: experimental data and DFT calculations

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Hyperfine structure of13C and15N nuclei in EPR spectra of phosphiniminoxyls

Conclusions The EPR spectra of some chemically and electrochemically generated phosphoniminoxyls were studied. The hyperfine coupling constants on the¹³C and¹⁵N nuclei were determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 696–698, March, 1984.A calculation of the distribution of the spin density in these radicals by the PCILO method will be made later.     

Influence of conformation on the EPR spectrum of 5,5-dimethyl-1-hydroperoxy-1-pyrrolidinyloxyl: a spin trapped adduct of superoxide

Spin trapping, a technique used to characterize short-lived free radicals, consists of using a nitrone or nitroso compound to "trap" an unstable free radical as a long-lived aminoxyl that can be characterized by EPR spectroscopy. The resultant aminoxyl exhibits hyperfine splitting constants that are dependent on the spin trap and the free radical. Such is the case with 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO-OH) and 2,2-dimethyl-5-hydroperoxy-1-pyrrodinyloxyl (DMPO-OOH) whose hyperfine splitting constants, A(N) = A(H) = 14.9 G and A(N) = 14.3 G, A(H)(beta) = 11.7 G, and A(H)(gamma) = 1.25 G, respectively, have been used to demonstrate the generation of HO(*) and O(2)(*)(-). However, to date, the source of the apparent A(H)(gamma) hyperfine splitting in DMPO-OOH is not known. We consider three possible explanations to account for the unique EPR spectrum of DMPO-OOH. The first is that the gamma-splitting arises from one of the hydrogen atoms at either carbon 3 or carbon 4 of DMPO-OOH. The second is that the gamma-splitting originates from the hydrogen atom of DMPO-OOH. The third is that the conformational properties of DMPO-R change upon going from DMPO-OH to DMPO-OOH. Experimental and theoretical chemical approaches as well as EPR spectral modeling were used to investigate which of these hypotheses may explain the asymmetric EPR spectrum of DMPO-OOH. From these studies it is shown that the 12-line EPR spectrum of DMPO-OOH results not from any proximal hydrogen, but from additional conformers of DMPO-OOH. Thus, the 1.25 G hyperfine splitting, which has been assigned as a gamma-splitting, is actually from two individual EPR spectra associated with different conformers of DMPO-OOH.     

SimLabel: a graphical user interface to simulate continuous wave EPR spectra from site‐directed spin labeling experiments

Site‐directed spin labeling (SDSL) combined with continuous wave electron paramagnetic resonance (cw EPR) spectroscopy is a powerful technique to reveal, at the residue level, structural transitions in proteins. SDSL‐EPR is based on the selective grafting of a paramagnetic label on the protein under study, followed by cw EPR analysis. To extract valuable quantitative information from SDSL‐EPR spectra and thus give reliable interpretation on biological system dynamics, numerical simulations of the spectra are required. Such spectral simulations can be carried out by coding in MATLAB using functions from the EasySpin toolbox. For non‐expert users of MATLAB, this could be a complex task or even impede the use of such simulation tool. We developed a graphical user interface called SimLabel dedicated to run cw EPR spectra simulations particularly coming from SDSL‐EPR experiments. Simlabel provides an intuitive way to visualize, simulate, and fit such cw EPR spectra. An example of SDSL‐EPR spectra simulation concerning the study of an intrinsically disordered region undergoing a local induced folding is described and discussed. We believe that this new tool will help the users to rapidly obtain reliable simulated spectra and hence facilitate the interpretation of their results. Copyright © 2017 John Wiley & Sons, Ltd.     

Automatic fitting procedures for EPR spectra of disordered systems: matrix diagonalization and perturbation methods applied to fluorocarbon radicals

Two types of automatic fitting procedures for EPR spectra of disordered systems have been developed, one based on matrix diagonalization of a general spin Hamiltonian, the other on 2nd order perturbation theory. The first program is based on a previous Fortran code complemented with a newly written interface in Java to provide user-friendly in and output. The second is intended for the special case of free radicals with several relatively weakly interacting nuclei, in which case the general method becomes slow. A least squares' fitting procedure utilizing analytical or numerical derivatives of the theoretically calculated spectrum with respect to the g- and hyperfine structure (hfs) tensors was used to refine those parameters in both cases. 'Rigid limit' ESR spectra from radicals in organic matrices and in polymers, previously studied experimentally at low temperature, were analyzed by both methods. Fluorocarbon anion radicals could be simulated, quite accurately with the exact method, whereas automatic fitting on, e.g. the c-C(4)F(8)(-) anion radical is only feasible with the 2nd order approximative treatment. Initial values for the (19)F hfs tensors estimated by DFT calculations were quite close to the final. For neutral radicals of the type XCF(2)CF(2)* the refinement of the hfs tensors by the exact method worked better than the approximate. The reasons are discussed. The ability of the fitting procedures to recover the correct magnetic parameters of disordered systems was investigated by fittings to synthetic spectra with known hfs tensors. The exact and the approximate methods are concluded to be complementary, one being general, but limited to relatively small systems, the other being a special treatment, suited for S=1/2 systems with several moderately large hfs.     

A general approach for prediction of motional EPR spectra from Molecular Dynamics (MD) simulations: application to spin labelled protein

A general approach for the prediction of EPR spectra directly and completely from single dynamical trajectories generated from Molecular Dynamics (MD) simulations is described. The approach is applicable to an arbitrary system of electron and nuclear spins described by a general form of the spin-Hamiltonian for the entire motional range. It is shown that for a reliable simulation of motional EPR spectra only a single truncated dynamical trajectory generated until the point when correlation functions of rotational dynamics are completely relaxed is required. The simulation algorithm is based on a combination of the propagation of the spin density matrix in the Liouville space for this initial time interval and the use of well defined parameters calculated entirely from the dynamical trajectory for prediction of the evolution of the spin density matrix at longer times. A new approach is illustrated with the application to a nitroxide spin label MTSL attached to the protein sperm whale myoglobin. It is shown that simulation of the EPR spectrum, which is in excellent agreement with experiment, can be achieved from a single MD trajectory. Calculations reveal the complex nature of the dynamics of a spin label which is a superposition of the fast librational motions within dihedral states, of slow rotameric dynamics among different conformational states of the nitroxide tether and of the slow rotational diffusion of the protein itself. The significance of the slow rotameric dynamics of the nitroxide tether on the overall shape of the EPR spectrum is analysed and discussed.     

An FT-IR demonstration of the occurrence of satellite bands in the spectra of hydrogen bonds in crystals

OH stretching fundamentals in the spectra of hydrogen-bonded crystals are accompanied by satellite bands due to sum and difference transitions involving one quantum of the OH stretching vibration and one or more quanta of the low-frequency vibration of the hydrogen bond. Such satellites were detected in the FT-IR spectra of two hydrogen-bonded crystals, ice and methanol.NRCC No. 29006     

Vibration of “Extra hydrogen” atoms in the Raman spectra of zwitterions containing the dicarba-nido-undecaborate anion

Raman spectra were obtained for two zwitterions containing the dicarba-nido-undecaborate anion: 5(6)-dimethylsulfoxonium 7,8-dicarba-nido-undecaborate and B-N-pyridinium 7,9-dicarba-nido-undecaborate. Vibrations were found for extra hydrogen, which appear in the Raman spectrum as broad weak bands at –2000 cn¹, characteristic for BHB bridges. This assignment was supported by the spectrum of the deutero analog, in which the extra hydrogen is replaced by a deuterium atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2639–2641, November, 1989.     

Nanoscale heterogeneities in ionic liquids: insights from EPR of spin probes

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Effect of fluorine replacement of hydrogen atoms in aromatic compounds on magnetic shielding of nuclei of heavy atoms at a distance from position of substitution

Conclusions From¹³C,¹⁵N,¹⁷O,¹⁹F,²⁹Si,³¹P,⁷³Ge,⁷⁷Se,¹¹⁹Sn, and¹²⁵Te NMR data, it follows that complete replacement of phenyl hydrogen atoms by fluorine in compounds C₆H₅X leads to a systematic increase in shielding of nuclei in the ring carbon atom bonded to the X group and in shielding of the nucleus of the -atom of X, along with deshielding of the nuclei of the - and -atoms of X. The effect evidently has a long-range character and can be described by the extended theory of Dewar and Kelemen.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 829–832, April, 1989.     

Time-resolved EPR spectra of the triplet excited states of diaminoacridine guests in polar potassium hydrogen phthalate single crystals

Mixed crystals of potassium hydrogen phthalate containing 3,6-diaminoacridine were photoexcited with visible light and the resulting triplet excited states were analyzed by time resolved EPR spectroscopy. Spectra from discrete growth sectors were compared with powders and polycrystalline glasses prepared at various pHs. The data yield the predominant protonation state and orientation of the triplets in each of a pair of growth sectors bounding the positive and negative ends of the polar crystal.     

独立组分分析在红外光谱分析中的应用

针对红外光谱的黑色体系分析,提出了一种基于独立组分分析(ICA)的红外光谱定性分析方法.其主要优点在于可从混合光谱中分离出独立组分的光谱,且这种分离是盲源分离,混合物的组分预先是未知的.对ICA在正己醇、丙酮和正丁醇的混合中红外光谱分离中的应用进行了研究,验证了体系的独立性,并对ICA算法做了一定的改进,讨论了各种预处理方法对其分离结果的误差.