Electron spin echo envelope modulation from trapped electrons in a glassy medium

An amplitude modulation of the electron spin echo envelope has been observed for radiation-produced trapped electrons in 10 M NaOD/D₂O at 77°K but not in 10 M N₂OH/H₂O. The modulation has been simulated theoretically by generalizing the single crystal model of Rowan et al. to disordered systems. The modulation has been interpreted as due to dipolar interactions with deuterons in molecules of the second solvation shell around the trapped electrons.     

Structural transition in nickel-doped zinc fluotitanate observed by electron paramagnetic resonance

The EPR spectrum of Ni²⁺ in single crystals of zinc fluotitanate ZnTiF₆·6H₂O has been studied between 4.2 K and room temperature in the frequency range 14.0–16.5 GHz. A structural transition was observed at (180±2) K between a high-temperature trigonal structure and a low temperature orthorhombic structure. Spin hamiltonian parameters are reported above and below the transition.     

The EPR spectrum of O on magnesium oxide

The EPR spectrum of O⁻ on MgO has been observed following the reaction of N₂O with electrons trapped at the surface. The spectrum of the ion in axial symmetry is characterized by g_⊥ = 2.041 and g_∥ = 2.0016. Upon exposure to H₂, CO, CO₂ or additional N₂O the spectrum is replaced by another having g₁ = 2.0172, g₂ = 2.0100 and g₃ = 2.0014. This spectrum is tentatively assigned to the O₃⁻ ion.     

The Transient Complex of Cytochrome c and Cytochrome c Peroxidase: Insights into the Encounter Complex from Multifrequency EPR and NMR Spectroscopy

We present a novel approach to study transient protein-protein complexes with standard, 9 GHz, and high-field, 95 GHz, electron paramagnetic resonance (EPR) and paramagnetic NMR at ambient temperatures and in solution. We apply it to the complex of yeast mitochondrial iso-1-cytochrome c (Cc) with cytochrome c peroxidase (CcP) with the spin label [1-oxyl-2,2,5,5-tetramethyl-Δ3-pyrroline-3-methyl)-methanethiosulfonate] attached at position 81 of Cc (SL−Cc). A dissociation constant K_D of 20±4×10⁻⁶ M (EPR and NMR) and an equal amount of stereo-specific and encounter complex (NMR) are found. The EPR spectrum of the fully bound complex reveals that the encounter complex has a significant population (60 %) that shares important features, such as the Cc-interaction surface, with the stereo-specific complex.     

Interpretation of EPR and optical spectra of Ni(II) ions in crystalline lattices at ambient temperature

Many biologically important paramagnetic metal ions are characterized by electron paramagnetic resonance (EPR) spectroscopy to use as spin probes to investigate the structure and function of biomolecules. Though nickel(II) ions are an essential trace element and part of many biomolecules, the EPR properties are least understood. Herein, the EPR and optical absorption spectra measured at 300 K for Ni(II) ions diluted in two different diamagnetic hosts are investigated and reported. The EPR spectrum of a polycrystalline Ni/Mg(3-methylpyrazole)₆(ClO₄)₂ [Ni/MMPC] shows two transitions at X-band frequency (~9.5 GHz), suggesting the zero-field splitting parameter (D) is larger than the resonance field of the free electron (H_o). This incomplete and complex spectrum is successfully analyzed to obtain EPR parameters. The EPR spectrum of the polycrystalline Ni/Zn(pyrazole)₆(NO₃)₂ [Ni/ZPN] shows a triplet spectrum indicating D < H_o. A detailed analysis of single-crystal EPR data yielded the spin Hamiltonian parameters. The optical absorption spectra are deconvoluted to understand the symmetry of the coordination environment in the complex.     

The origin of the radiobiological damage in cells stored in cryostatic conditions

The radiation induced free radical damage in Chinese hamster lung fibroblast V-79 cells stored in DMEM culture medium containing 10% DMSO has been investigated by matrix EPR spectroscopy in connection with the H₂O/DMSO binary phase diagram. A major part of the indirect effect is due to radicals from the DMSO·3H₂O phase in the freezing medium, which are released on warming in the temperature range between 130 K and 160 K, that is, far below the eutectic melting temperature (210 K). The radicals trapped in the DMSO·3H₂O phase react with oxygen above 160 K giving reactive oxygen species (ROS) of the type of peroxyl radicals. A lower limit yield of 10–15% was calculated for this conversion. Scavenging experiments with a stable nitroxyl radical (tempol) have demonstrated that part of the DMSO·3H₂O radicals escape by mutual recombination on melting and are therefore available for inducing indirect cell damage. The same experiments performed with pure frozen water have shown that OH radicals are not available for inducing cell damage. The EPR measurements performed on H₂O/DMSO frozen mixtures suggest that the radiation induced radical forming process does not change when passing to the low dose range below 1 Gy, in agreement with the linear model.     

Magnetic and Spectroscopic Studies on the Complexes of 9-Oxo-10-Acridinemetanophosphonic Ion with Cu (II) Co (II)and Ni (II)

Abstract

Three complexes of 9-oxo-10-acridinemetanophosphonlc ion (PMA⁼ see figure) have been synthesised. The meta1:ligand ratio in the complexes is equal 1:1 and their formulas are (CUPMA) ₂,×5H₂O,NiPMA×4H₂O and CoPMA×4H₂O. The structure of the complexes has been investigated by the IR,FIR, Raman spectroscopy, UV-VIS spectroscopy, magnetic measurements and EPR spectroscopy. The physical properties of the complexes obtained are characteristic for inorganic polymers. The lowering of the ν(P-Q) stretching frequency by about cm^?, in the spectra of the complexes as compared to that of the free ligand suggests that the phosphonlc group takes part in coordination. Data from the EPR spectrum indicate that Cu(II)may form the dimeric, water bridged or even more complicated polymeric structures.     

A single crystal EPR study of VO ions doped in Cs2Co(SO4)2.6H2O Tutton salt

EPR spectra of VO²⁺ ions doped in single crystals of Cs₂Co(SO₄)₂.6H₂O single crystals have been studied at various temperatures (390–103 K) on X-band frequency. The detailed EPR analysis shows three vanadyl complexes with differing intensities. The g and A tensors are found to be axially symmetric. The intense vanadyl complexes in the lattice are found to occupy the Co²⁺ substitutional sites, whereas the weak vanadyl complex at the interstitial sites. The optical absorption spectrum at room temperature shows three absorption bands characteristic of VO²⁺ ions in tetragonal symmetry. By correlating the EPR and optical data, the molecular bonding coefficients and the Fermi contact interaction terms have been evaluated and discussed. The line broadening of VO²⁺ spectra on cooling the crystal is explained on the basis of spin-lattice relaxation narrowing. The spin-lattice relaxation time for the host Co²⁺ ions has been estimated at various temperatures.     

A fractional bond order of 1/2 in Pd(2)(5+)--formamidinate species; the value of very high-field EPR spectra

Reaction of Pd(2)(DAniF)(4), 1, (DAniF = di-p-anisylformamidinate) with 1 equiv of AgPF(6) in CH(2)Cl(2) at or below -10 degrees C produces the paramagnetic species [Pd(2)(DAniF)4]PF(6), 1-PF(6), that has been studied by X-ray crystallography, UV-vis spectroscopy, electrochemistry, and multifrequency (9.5, 34.5, 110, and 220 GHz) EPR spectroscopy. Upon oxidation of the precursor, the Pd-Pd distance decreases by 0.052 Angstrom from 2.6486(8) to 2.597(1) Angstrom. The EPR spectra show broad signals with line widths of about 1000 G. The spectra collected at high field show a large spread of g tensor components ( approximately 0.03), but these are masked at lower frequencies (9.5 and 34.5 GHz). A reinvestigation using high-field EPR of the p-tolyl analogue, which is the only other structurally characterized Pd(2)(5+) species (Cotton, F. A.; Matusz, M.; Poli, R.; Feng, X. J. Am. Chem. Soc. 1988, 110, 1144), shows that this species, which had been reported to give an isotropic 9.5 GHz EPR spectrum, also gives anisotropic 110 and 220 GHz EPR spectra with a similarly large spread of g tensor components consistent with the unpaired electron residing in a metal-based MO. The results of these studies and calculations using density functional theory are consistent with the oxidation being metal-based, resulting in an uncommon Pd(2)(5+) species with a Pd-Pd bond order of 1/2.     

Novel VO (IV) complexes derived from a macrochelates: Synthesis,characterization, molecular modeling and in vivo insulin-mimic activity studies

For the development of extensive investigations into a potential medicinal application of vanadium coordination compounds for the oral treatment of diabetes, new mono and bimetallic VO (IV) complexes with N,N′-(2,2′-(9,10-dihydro-9,10-ethanoanthracene-11,12-dicarbonyl) bis (hydrazine-1-carbonothioyl)) dibenzamide (H₆EBT) and 2,2′-((9S,10S,11R,12R)-9,10-dihydro-9,10-ethanoanthracene-11, 12-dicarbonyl) bis (N-phenylhydrazine-1-carboxamide) (H₆EPH) have been isolated and characterized. The FTIR and NMR spectral data revealed that H₆EBT acts as neutral tridentate and dibasic hexadentate while H₆EPH as dibasic tridentate and tetrabasic hexadentate. The electronic and ESR spectra indicated that complexes has octahedral geometry. ESR spectrum of [(VO)(H₆EBT)(SO₄)].5H₂O gives a well resolved hyperfine eight-line pattern typical spectrum for mononuclear vanadyl complexes with g˃ g_⊥ = 1.9 suggesting that the ligand donor atoms ONS are coplanar with the two chelate rings forming octahedral geometry. Also, the high parallel hyperfine splitting value, A = 0.0108, than perpendicular one (A_⊥ = 0.0087) indicated that the single d- electron is in a σ-nonbonding orbital and aiming away from the equatorial ligands. On the other hand, the EPR spectra of the binuclear [(VO)₂(H₄EBT)(SO₄)]3H₂O and [(VO)₂(H₂EPH)(H₂O)₂].10H₂O complexes gave a single broad line centered at g = 2.05 and 2.07, respectively, without resolved hyperfine structure paramagnetic triplet (S = 1) is consistent with the anomalous value of the magnetic moment value (μ_eff = 1.100 and 0.99 B.M.) supporting a binuclear nature. The TG analyses confirmed the existence of solvent molecules inside and/or outside the coordination sphere. The DFT molecular modeling of ligands and its VO (IV) complexes supported the suggested geometries. Also, all compounds were screened for in vivo insulin-mimetic activity.     

Electron paramagnetic resonance of Mn(II) in [M(H2O)6]PtCl6 (M=Zn,Mg, Cd) single crystals

EPR studies have been carried out on Mn(II)-doped single crystals of [Zn(H₂O)₆]PtCl₆, [Mg(H₂O)₆]PtCl₆ and [Cd(H₂O)₆]PtCl₆ from room temperature to 77 K at X-band frequencies (⋍9.5 GHz). MN(II) ions substituting the divalent metals exhibit a unique magnetic behavior with the z-axes directed along the c-axes of the crystals. A non-linear iterative least-squares fitting procedure for the analysis of EPR spectra is presented. In this method calculation of the spin-Hamiltonian parameters can be carried out for any orientation of the external magnetic field with respect to the crystal symmetry axis.     

Investigation of structure of Fe3+ magnetic center in polyparaphenylene

In the temperature range between 4.2 and 300 K, the EPR spectrum of the impurity Fe³⁺ ion in the organic polyparaphenylene has been investigated. An effect developed as an unusual temperature change of Fe³⁺ EPR spectrum has been revealed. The EPR spectrum of powder sample consists of two resonance lines. Line 1 with the effective g‐value equal to g₁ = 4.21 ± 0.05 is of the maximum intensity at T = 4.2 K. With temperature increase, the intensity of line 1 decreases until vanishing. Line 2 is observed over the whole temperature range. For T = 300 K, the g‐value of line 2 is g₂ = 2.00 ± 0.09. To study the structure of magnetic ion molecular environment and define nonequivalent positions of the magnetic ion in polyparaphenylene, a calculation was done of the energy of Fe³⁺ magnetic ion for various possible molecular environments. It is shown that in polyparaphenylene for the Fe³⁺ magnetic ion there are two different stationary molecular environments. The obtained model of magnetic ion molecular environment was used to explain the temperature dependence of the EPR spectrum. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

EPR of Mn2+ in single crystals of calcium hexachlorostannate hexahydrate

An EPR study has been carried out on Mn²⁺-doped single crystals of calcium hexachlorostannate hexahydrate [Ca(H₂O)6] SnCl₆ in the temperature range 77–378 K at X-band frequencies (9.3 GHz). Mn²⁺ ions substituting the divalent metal exhibit a unique magnetic complex with the z-axis directed along the c-axis of the crystal. The temperature dependence of the zero-field splitting parameter is discussed.     

Photolysis of poly(ethylene terephthalate)

The photolysis of poly(ethylene terephthalate) films was studied in vacuo with light of wavelengths 2537 and 3130 A. A very stable filter system which cuts out the 3025 A. line was developed to isolate 3130 A. from a mercury spectrum. Despite the fact that the penetration of 2537 A. light was limited to a depth of a ca. 10³ A. whereas 3130 A. light was more uniformly absorbed it was possible to demonstrate that the quantum yields for CO and CO₂ formation were in agreement for the two wavelengths. Quantum yields for fractures and crosslinks were estimated by sol-gel analysis. An absorption maximum which develops near 13 μ after exposure of poly(ethylene terephthalate) to light or γ-rays was attributed to the formation of groups formed by elimination of CO and CO₂. ESR spectra for trapped radicals were tentatively assigned to the components p-C₆H₃· and ·O? CH₂? CH₂? . It is suggested that the former radicals combine to form crosslinks. Quantum yields (× 10⁴) with 3130 A. light are: CO, 6; CO₂, 2; crosslinks, 5.5; trapped radicals, 1.5; With 2537 A. light, quantum yields are: CO, 6–9; CO₂, 2–3; the network formed was not characterized as to crosslinks and fractures; trapped radicals were observed to exist but not determined.     

Zur Kenntnis der polymeren Achtringstruktur des Kupfer(II)-dichlorophosphats

Note on the polymeric 8-ring structure of copper(II) dichlorophosphate According to the vibrational spectrum, the Cu atoms in Cu(O₂PCl₂)₂ are linked to a polymeric 8-ring structure by O? P? O bridges resulting in a square planar coordination of Cu²⁺. From the EPR spectrum a canting angle 2γ? 104° between adjacent CuO₄ planes can be deduced as an additional information. The EPR powder data are discussed with respect to an alternative structural model: 2γ may be located either within each polymeric Cu(II) complex resulting in a strongly corrugated chain structure, or all CuO₄ planes of a chain may run parallel; 2γ then ought to be the angle between the CuO₄ planes of different chains.     

Paramagnetic resonance and non-resonant microwave absorption in iron niobate

An electron paramagnetic resonance (EPR) study of FeNbO₄ powder samples in monoclinic phase (wolframite-type) at X-band (8.8–9.8 GHz), in the 90–300 K temperature range, is presented. For all the temperatures, the EPR spectrum shows a single line associated with Fe³⁺ ions. Changes in the lineshape of the EPR spectrum, which can be attributed to Fe²⁺ ions, are detected at low temperatures. This behavior can be ascribed to a strong magnetic dipolar interaction between Fe²⁺ and Fe³⁺ ions. The non-resonant microwave absorption techniques: magnetically-modulated microwave absorption spectroscopy (MAMMAS) and low-field microwave absorption spectroscopy (LFMAS), were used for a further knowledge on this material. MAMMAS response suggests also the presence of Fe²⁺ ions, that originates a change in microwave absorption regime for T < T_p (=140 K), associated with the presence of short-range magnetic correlations. LFMAS spectra showed a linear behavior with positive slope and non-hysteretic traces. The profiles obtained by plotting the slope vs. temperature of the LFMAS line are similar to those detected by the MAMMAS technique, confirming that both types of measurement show the same processes of absorption.     

Effect of the high pressure on the structure and intercalation properties of lithium-nickel-manganese oxides

Lithium-nickel-manganese oxides (Li_1+x(Ni_1/2Mn_1/2)_1−xO₂, x=0 and 0.2), having different cationic distributions and an oxidation state of Ni varying from 2+ to 3+, were formed under a high-pressure (3 GPa). The structure and cationic distribution in these oxides were examined by powder X-ray diffraction, infrared (IR) and electron paramagnetic resonance (EPR) in X-band (9.23 GHz) and at higher frequencies (95 and 285 GHz). Under a high pressure, a solid-state reaction between NiMnO₃ and Li₂O yields LiNi_0.5Mn_0.5O₂ with a disordered rock-salt type structure. The paramagnetic ions stabilized in this oxide are mainly Ni²⁺ and Mn⁴⁺ together with Mn³⁺ (about 10%). The replacement of Li₂O by Li₂O₂ permits increasing the oxidation state of Ni ions in lithium-nickel-manganese oxides. The higher oxidation state of Ni ions favours the stabilization of the layered modification, where the Ni-to-Mn ratio is preserved: Li(Li_0.2Ni_0.4Mn_0.4)O₂. The paramagnetic ions stabilized in the layered oxide are mainly Ni³⁺ and Mn⁴⁺ ions. The disordered and ordered phases display different intercalation properties in respect of lithium. The changes in local Ni,Mn-environment during the electrochemical reaction are discussed on the basis of EPR and IR spectroscopy.     

Darstellung und einige Eigenschaften von Kupfer(I)-Kupfer(II)-Selenocyanaten

Preparation and Some Characteristics of Copper(I)-Copper(II) Selenocyanates From the system Cu²⁺-H₂O-en-SeCN-in dependence on the conditions two new complexes have been prepared: Cu₃en₂(SeCN)(CN)₃· H₂O(I) and Cu₃en₂(SeCN)₂(CN)₂· H₂O(II). They were studied by the methods of infra-red and EPR spectra as well as by those of X-ray diffraction. It has been found that Cu₂₊ is coordinated in these complexes with two molecules of ethylene diamine and one molecule water. The anion ligands have a bridging function and coordinate the copper(I). The EPR spectra show that the two complexes exhibit around the atom Cu²⁺ have different ligand field symmetry. For complex (I) it is a typically axial spectrum with two values of the gfactor g⊥? 2.18 and g⊥? 2.05 while complex (II) has an asymmetrical isotropic spectrum with one g-factor value only g⊥? 2.07.     

Spectral, magnetic and thermal characterisation of new Co(II), Ni(II) and Cu(II) complexes with Schiff base 5-bromo-N,N′-bis-(salicylidene)-o-tolidine

Starting from 5-bromo-N,N′-bis-(salicylidene)-o-tolidine (H₂L) new complexes with Co(II), Ni(II) and Cu(II) were synthesised and characterised. The features of complexes have been assigned from microanalytical, IR, UV–Vis–NIR and EPR spectra, magnetic data at room temperature as well as thermal analysis. IR data are in accordance with bischelate nature of the deprotonated ligand that coordinates through azomethinic nitrogen and phenolic oxygen. The electronic spectra display the characteristic pattern of tetrahedral stereochemistry for [CoL]·H₂O complex and octahedral one for [NiL(OH₂)₂]·H₂O complex. The electronic spectra correlated with magnetic susceptibility measurements indicate a square-planar surrounding for [ML] (M:Ni, Cu) species, while the EPR spectrum of copper complex sustains the proposed stereochemistry. The thermal analysis evidenced that thermal transformations are complex processes according to TG, DTA and DTG curves including (crystallization or coordination) water elimination, thermolyses and oxidative degradation of Schiff base. All these processes lead to the most stable metallic oxides as final product.     

EPR evidence for 17O− on molybdenum oxide supported by silica-gel

The EPR spectrum of ¹⁷O^? on partially reduced molybdenum oxide supported on silica-gel has been observed following adsorption of N₂O at room temperature. The spectrum is chracterized by g_⊥=2.019 and g_|=2.002 with a_|¹⁷O^?=96±1 G and a_|⁹⁵MO,⁹⁷MO=7.5±0.5 G. The O ^?ion appears to undergo exchange with oxide ions at the surface.