Electron Paramagnetic Resonance Spectra Of Mn2 Research Articles

Evidence of ferromagnetic coupling for manganese pairs in a layered van der Waals GaS semiconductor

Using high-frequency electron paramagnetic resonance (EPR), we have observed the ferromagnetic coupling of manganese Mn2+ pairs in a layered van der Waals GaS semiconductor. The EPR spectra of Mn2+ pairs (Mn24+) [replacing covalently bonded Ga24+ pairs oriented along the chain axis (c axis) of two gallium ions and being situated in the center of the layer] were recorded at 94 and 130 GHz. The fine structure parameters for the lower multiplets with spin S = 5 and S = 4 were determined equal to D = −0.040 cm−1 and D ≅ −0.035 cm−1, respectively. Based on the observation of additional EPR lines in the region of intersection of the levels in the magnetic field of the multiplet with S = 5 and S = 4, the energy of the isotropic exchange interaction J was estimated to be ∼−0.5 cm−1. For all transitions, a well-resolved hyperfine structure was observed, due to the interaction with two equivalent 55Mn nuclei, leading to the appearance of 11 lines with a hyperfine interaction constant A = 30(1) × 10−4 cm−1, which is approximately half the hyperfine interaction constant for single Mn2+ ions. In addition, a signal from single manganese ions Mn2+ with spin S = 5/2 and a hyperfine interaction constant A = 60(1) × 10−4 cm−1 was observed, which are characterized by extremely large fine structure splitting of D = −0.15 cm−1. Simultaneously with EPR studies, the crystals were monitored by photoluminescence and micro-Raman scattering measurements using a microscope with confocal optics.

EPR and optical absorption studies on manganese ion doped in mixed alkali cadmium phosphate glasses

Electron paramagnetic resonance (EPR) spectra of Mn(II) ions in cadmium phosphate glasses are presented with mixed alkali variation as xLi2O + (20 - x) Na2O + 20 CdO + 59.5 P2O5 + 0.5 MnO glass system with 5 ≤ x ≤ 15 mol%. The EPR spectra of Mn(II) ions doped samples exhibit a sextet centered at g = 2·0. The optical absorption spectrum at room temperature shows three bands for Mn(II) ions in octahedral symmetry. The crystal field (Dq) and Racah parameters (B and C) are evaluated. From EPR and optical spectral studies reveals the nature of the bonding is dominantly ionic and its site symmetry is octahedral. At equal composition of alkali content, i.e. for x = 10 the glass system shows the mixed alkali effect.

In-depth investigation of EPR spectra ofMn2+ ions in ZnS single crystals with pure cubic structure

The X (9.8 GHz)-band electron paramagnetic resonance (EPR) properties of substitutionalMn2+ ions in high quality cubic ZnS single crystals grown fromPbCl2 flux have been thoroughly investigated. Accurate spin Hamiltonian (SH) parameters:g = 2.002 25 ± 0.000 06;a = (7.987 ± 0.008) × 10−4 cm−1 and A = −(63.88 ± 0.02) × 10−4 cm−1 were obtained by simulation and fitting to the experimentallyallowed transitions recorded for the magnetic field aligned within ± 0.25° along the main crystal axes. The normally forbidden hyperfine , Δm = ± 1 transitions were also observed. Their position was found to be in agreement, within the experimentalaccuracy of ΔH = ± 0.01 mT, with calculations using the same SH parameters. The angular variation of the ratios ofthe intensities of the central forbidden to the allowed transitions could be accounted foronly by including an additional constant contribution. The observed line broadening of the and fine structure transitions and their line width variation in a (110) plane have beenquantitatively described by considering a random distribution of lattice strains at theMn2+ impurityions. The influence of the forbidden transitions and line broadening on the EPR spectra line shape ofthe Mn2+ ions in cubic ZnS crystalline powders is also examined.

Mn 2+ activated MgSrAl 10O 17 green-emitting phosphor—A luminescence and EPR study

This paper reports on the luminescence and electron paramagnetic resonance (EPR) investigations on MgSrAl 10O 17:Mn 2+ green-emitting phosphor. Single-phase MgSrAl 10O 17 was successfully synthesized by the one-step solution combustion route without the need for post-annealing at a higher temperature. Crystallization of the powder was confirmed by X-ray diffraction. The luminescence of Mn 2+- activated MgSrAl 10O 17 shows a strong green-emission peak around 515 nm due to the 4T 1→ 6A 1 transition of Mn 2+ ions under the excitation (453 nm). The EPR spectra of Mn 2+ ions exhibit a sextet hyperfine structure centered at g ≈1.995. The Mn 2+ ion occupies Mg sites which are in tetrahedral symmetry. The magnitude of the hyperfine splitting ( A) indicates that Mn 2+ is in a moderately ionic environment. The number of spins participating in resonance ( N), the paramagnetic susceptibility ( χ) and the zero-field splitting parameter ( D) have been evaluated and discussed.

An EPR study on mollusk shells from loess-paleosol sequences in the Loess Plateau, central China

Electron Paramagnetic Resonance (EPR) analysis was employed to extract paleoclimatic information from mollusk shells taken from the Luochuan section located on the Loess Plateau of central China. The results show that the EPR spectrum of Mn2+ in mollusk shells is complicated and consists of two sets of six hyperfine lines of Mn2+ that arise from two non-equivalent Mn2+ sites in aragonite. There is no obvious inconsistency of EPR spectral intensities among different species of modern mollusks at Luochuan area; the magnitude of EPR spectra intensities of mollusk shells is correlative with the Mn2+ concentration of the environments. The EPR signals from mollusk shells taken from the loess, which is considered to be formed in the cold and dry glacial environment, are stronger than those from the paleosol deposited under the warm and humid interglacial condition suggesting that the Mn2+ available for mollusks in a cold climate is higher than in a warm climate. We propose that during the glacial period, the mollusks lived in a relatively reductive soil environment with more Mn2+ while during the interglacial period its environment was more oxidizing with less Mn2+. This result provides direct evidence that the loess-paleosol interlayers came into being under alternating redox conditions resulting from fluctuating paleoclimate. The analysis of the EPR spectra of mollusk shells serves as a new tool for retrieving climatic information from the mollusk records.

Solution combustion derived nanocrystalline Zn2SiO4:Mn phosphors: A spectroscopic view

Manganese doped nanocrystalline willemite powder phosphors Zn(2-x)Mn(x)SiO(4) (0.1<or=x<or=0.5) have been synthesized by a low-temperature initiated, self-propagating, gas producing solution combustion process. The phosphors have been characterized by using x-ray diffraction (XRD), energy dispersive spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), and photo luminescence (PL) spectroscopic techniques. The lattice parameters calculated from XRD confirm that Zn(2-x)Mn(x)SiO(4) has a rhombohedral space group R3H. The XRD patterns confirm that Zn(2-x)Mn(x)SiO(4) phosphor samples undergo a phase transformation from beta-willemite to alpha-willemite phase at 950 degrees C. The EPR spectra of Mn(2+) ions exhibit resonance signals at g approximately = 3.24 and g approximately = 2.02, with a sextet hyperfine structure centered around g approximately = 2.02. The EPR signals of Mn(2+) give a clear indication of the presence of two different Mn(2+) sites. The magnitude of the hyperfine splitting (A) indicates that the Mn(2+) is in an ionic environment. The number of spins participating in resonance (N), the paramagnetic susceptibility (chi), and the zero-field splitting parameter (D) have been evaluated as function of x. It is interesting to observe that the variation of N with temperature obeys Boltzmann. The paramagnetic susceptibility is calculated from the EPR data at various temperatures and the Curie constant and Curie paramagnetic temperature was evaluated from the 1/chi versus T graph. The luminescence of Mn(2+) ion in Zn(2)SiO(4) shows a strong green emission peak around 520 nm from the synthesized phosphor particles under UV excitation (251 nm). The luminescence is assigned to a transition from the upper (4)T(1)-->(6)A(1) ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied.

Monitoring of ozone pollution and the physiological activity of Pinus halepensis (Mill.) by electron paramagnetic resonance and other parameters

An investigation of selected Aleppo pines in the forests of Mt Hymettus and Mt Parnis near Athens (Greece) was undertaken at three different sites in the period 1999–2003, because a considerable proportion of pine trees showed visible signs of chlorotic mottle. This condition is characteristic of high and prolonged levels of ozone exposure. Needles from Aleppo pine trees (Pinus halepensis Mill.) were analyzed for their manganese content in combination with Electron Paramagnetic Resonance (EPR) spectra of Mn2+, involved in photosystem II. Manganese is considered as an important bioindicator for the vitality of trees. Also, we investigated the EPR spectrum of the needles in the region of g=2.0045 for “healthy” and “diseased” trees. The antioxidant capacity of the needles’ extract was measured from trees by the DPPH method. Finally, seasonal changes in chlorophyll concentration in the needles were measured to evaluate the effects of ozone. Measurements of ozone concentrations at the three sites showed that there were elevated levels during the summer months. Our experimental results suggest that the concentration of manganese in the needles was lower in the area with higher ozone concentrations, supported by EPR measurements. Higher ozone concentrations also affected the antioxidant potential of the needles and their chlorophyll content during summer months. Our findings also confirmed the resilience of Aleppo pines under stressful conditions and recovery in winter months. Despite the experimental problems, EPR spectra of Mn2+ in combination with other methods can be used as a sensitive bioindicator for ozone pollution, and is the result of oxidative stress affecting the growth cycle of the pine trees and their photosynthetic mechanisms.

Spectroscopic identification of a dinuclear metal centre in manganese(II)-activated aminopeptidase P from Escherichia coli: implications for human prolidase

Electron paramagnetic resonance (EPR) spectra and X-ray absorption (EXAFS and XANES) data have been recorded for the manganese enzyme aminopeptidase P (AMPP, PepP protein) from Escherichia coli. The biological function of the protein, a tetramer of 50-kDa subunits, is the hydrolysis of N-terminal Xaa-Pro peptide bonds. Activity assays confirm that the enzyme is activated by treatment with Mn2+. The EPR spectrum of Mn2+-activated AMPP at liquid-He temperature is characteristic of an exchange-coupled dinuclear Mn(II) site, the Mn-Mn separation calculated from the zero-field splitting D of the quintet state being 3.5 (+/- 0.1) Angstrom. In the X-ray absorption spectrum of Mn2+-activated AMPP at the Mn K edge, the near-edge features are consistent with octahedrally coordinated Mn atoms in oxidation state +2. EXAFS data, limited to k less than or equal to 12 Angstrom(-1) by traces of Fe in the protein, are consistent with a single coordination shell occupied predominantly by O donor atoms at an average Mn-ligand distance of 2.15 Angstrom, but the possibility of a mixture of O and N donor atoms is not excluded. The Mn-Mn interaction at 3.5 Angstrom, is not detected in the EXAFS, probably due to destructive interference from light outer-shell atoms. The biological function, amino acid sequence and metal-ion dependence of E. coli AMPP are closely related to those of human prolidase, an enzyme that specifically cleaves Xaa-Pro dipeptides. Mutations that lead to human prolidase deficiency and clinical symptoms have been identified. Several known inhibitors of prolidase also inhibit AMPP. When these inhibitors are added to Mn2+-activated AMPP, the EPR spectrum and EXAFS remain unchanged. It can be inferred that the inhibitors either do not bind directly to the Mn centres, or substitute for existing Mn ligands without a significant change in donor atoms or coordination geometry. The conclusions from the spectroscopic measurements on AMPP have been verified by, and complement, a recent crystal structure analysis.

EPR of some oxide glasses implanted with Mn+ and Cu+ ions

Abstract Electron paramagnetic resonance (EPR) spectra of Mn2+ and Cu2+ ions in some Mn+- and Cu+-implanted multicomponent silicate (20Na2O10B2O370SiO2, mol%) and phosphate (36P2O544Na2O20Al2O3 and 65P2O510B2O310Al2O315MgO, mol%) glasses are presented. About 10% of the implanted copper is present as Cu2+ ions surrounded by six ligands which form a tetragonally elongated octahedron. The concentration of Mn2+ ions in the implanted layers of some glasses is comparable with that of implanted manganese ions. The EPR spectra of Mn+-implanted high-phosphate glass indicate that Mn2+ ions can exist in the implantation layers in local environments similar to those present in bulk glasses with appropriate composition. In addition, Mn2+ ions are present in the implantation layers as paramagnetic ions coupled by spin-spin interactions or antiferromagnetic MnO crystals.

Investigation of Strain in II-VI Semiconductor Superlattices Using Electron Paramagnetic Resonance of Mn++

We explore the possibility of using electron paramagnetic resonance (EPR) of Mn++ for measuring uniaxial strain in II-VI superlattices. This work is motivated by the fact that the EPR spectrum of Mn++ is very strongly affected by crystalline fields. Changes in a crystalline field which arise from strain are thus automatically expected to have a profound effect on the EPR spectrum. Consistent with this expectation, we have observed giant crystal field splittings of Mn++ EPR lines in ZnTe/MnTe, CdTe/MnTe, and ZnTe/MnSe superlattices. The EPR spectra observed in these systems are ascribed to isolated Mn++ ions diffused into the ZnTe or the CdTe layers from the respective MnTe or MnSe layers. In addition to providing precise information oii the magnitude and the sign of strain produced by lattice mismatch between the superlattice constituents, we show that the EPR spectrum also provides a direct measure of strain fluctuations in the layered medium. PACS numbers: 78.66.-w, 71.55.Gs

Electron paramagnetic resonance study of VO2+, Mn2+ and Cu2+ in oxyfluoroborate glasses

Abstract Electron paramagnetic resonance (EPR) studies have been performed on 20mol.%Li2O-10mol.%Li2F2-70mol.%B2O3 glass doped with vanadium, manganese and copper. In the presence of vanadium, a VO2+ group is observed with an anisotropic hyperfine structure. The EPR spectrum of Mn2+ exhibits resonances at g=1.956 and 4.468 and a shoulder at around 2.968. Cu2+ is located in a tetragonally elongated octahedral coordination. Its Jahn-Teller character gives rise also to an anisotropic hyperfine structure. The spin Hamiltonian parameters are evaluated. The effect of addition of fluorine on the spin Hamiltonian parameters is discussed.

EPR spectra of Mn 2+ doped CdX 2PbY 2KI (X, Y = Cl, Br) glasses

Electron paramagnetic resonance (EPR) spectra of glasses of five compositions: 1. I, (CdCl 2) 0.3(PnCl 2) 0.6(KI) 0.1; 2. II, (CdCl 2) 0.3(PbCl 2) 0.5(KI) 0.2; 3. III, (CdCl 2) 0.3(PbBr 2) 0.5(KI) 0.2; 4. IV, (CdCl 2) 0.2(PbBr 2) 0.6(KI) 0.2; and 5. V, (CdBr 2) 0.2(PbBr 2) 0.6(KI) 0.2 doped with MnCl 2 and MnBr 2 at concentrations from 0.1 to 3.0 mol% were investigated. An intense g eff ≊ 2.0 resonance was found in all glasses studied; the other resonances, g eff ≊ 4.3 and g eff = 3.3, changed their intensities in relation to the g eff ≊ 2.0 resonance in dependence on the composition of the host glasses. Most of the magnetically active centres of impurity Mn 2+ ions with the g eff ≊ 4.3 were assumed to be tetragonally distorted octahedrons that could be described by fourth order spin Hamiltonian. The assumption was supported by temperature behavior of intensities of the g eff ≊ 4.3 resonance. The local structure of most of the magnetically active Mn 2+ centres in glasses with a higher amount of bromide atoms was supposed to be of lower symmetry than the local structure of centres with chloride atoms. The assumption was supported by decrease of intensity of the g eff ≊ 2.0 resonance in relation to the intensity of the other resonances, the g eff ≊ 3.3 and the g eff ≊ 4.3 , in series from chloride through mixed to bromide glasses. The optical spectra of pure and Mn 2+ doped glasses were measured from visible to far infrared region and both kinds of spectra were indistinguishable.

Mn–Mn interaction in adenylylated and unadenylylated glutamine synthetase

The distance between the two catalytically important metal ions of glutamine synthetase was determined by electron paramagnetic resonance (EPR). Mn(II) binds more tightly to the n1 site of this enzyme in the presence of methionine sulfoximine and the influence of Mn(II) bound at the n2 site on the EPR spectrum of Mn(II) at n1 was studied. A monotonic increase in the EPR spectrum of Mn(II) was observed at Mn:E (subunit) ratios of 0 to 0.8. After this point as Mn(II) was added to about 1.8 Mn:E, a decrease in the EPR signal was observed. This phenomenon was found for both adenylylated and unadenylylated forms of glutamine synthetase. The data were analyzed using a theory for dipolar electron-electron relaxation and a distance of 10-12 A was computed for the Mn(II)-Mn(II) separation. These data demonstrate that both modified and unmodified forms of glutamine synthetase which have different catalytic activities have a similar spatial relationship between the two catalytic metal ion sites.

Host spin–lattice relaxation narrowing in the EPR of Mn2+ in CoSO4⋅7H2O single crystals

Electron paramagnetic resonance (EPR) of Mn2+ doped in CoSO4⋅7H2O single crystals has been studied from 300 to 77 K and at ∼9.3 GHz. Two different types of crystals of CoSO4⋅7H2O have been obtained, which grow in two different temperature ranges about 298 K. The two forms exhibit different types of spectra: one form [to be referred to as CoSH(I)] shows two 30 line Mn2+ spectra with D=459×10−4 cm−1, ‖E‖=134×10−4 cm−1 and the other form [to be referred to as CoSH(II)] shows only a single 30 line spectrum with D=234×10−4 cm−1, ‖E‖=19 ×10−4 cm−1. The observation of resolved Mn2+ spectra at 300 K and its broadening on lowering the temperature in CoSO4⋅7H2O:Mn2+ crystals has been discussed in terms of ’’host spin–lattice relaxation narrowing.’’ The observed shift in the Mn2+ gz value from that in diamagnetic hosts is probably due to the Co2+ ions, which produce a local static magnetic field at the site of Mn2+ ions. From the observed linewidth in the EPR spectrum of Mn2+ in single crystals of CoSO4⋅7H2O the T1 of Co2+ in CoSO4⋅7H2O has been estimated to be ∼1.1×10−11 s.

Manganese in photosynthetic oxygen evolution. I. Electron paramagnetic resonance study of the environment of manganese in Tris-washed chloroplasts

A manganese electron paramagnetic resonance (EPR) signal not present in untreated chloroplasts is observed in chloroplasts treated by washing in Tris buffer (0.8 M, pH 8.0) for 15 min. Centrifugation indicates that the Mn responsible for the EPR signal is localized in the chloroplasts, not free in the supernatant liquid. Atomic absorption analysis demonstrates that less than 10% of total chloroplast Mn is lost upon Tris treatment. Tris treatment converts 60% of the total chloroplast Mn pool to an EPR-detectable state. Sonication causes the Mn EPR signal to be divided proportionately between the chloroplast pellet and the supernatant liquid. The EPR spectrum of Mn in Tris-washed chloroplasts is identical with that of a divalent aqueous Mn spectrum in g factor, hyperfine splitting, and linewidth temperature dependence. It is concluded that upon Tris treatment, Mn is released into the interior space of the thylakoid membrane. Transport of Mn and anionic chelating agents across the thylakoid membrane was investigated using EPR. The rate of Mn diffusion through the thylakoid membrane is slow, with a t 1 2 of 2.5 h. The rate of transfer of chelating agents such as EDTA is much faster, with t 1 2 of 750 ms. Tris washing also destroys a weak Mn-binding site on the exterior of the thylakoid membrane.

Structural Changes Induced by Substrates and Anions at the Active Site of Creatine Kinase: ELECTRON PARAMAGNETIC RESONANCE AND NUCLEAR MAGNETIC RELAXATION RATE STUDIES OF THE MANGANOUS COMPLEXES

Abstract Structural changes at the active site of creatine kinase which occur upon binding of substrates and inhibitory anions have been examined by electron paramagnetic resonance (EPR) spectroscopy and proton relaxation rate (PRR) studies of manganous complexes with the enzyme. EPR spectra for solutions of ternary complexes involving enzyme and Mn(II)-nucleotides are quite similar to those for the binary Mn(II)-nucleotide complexes in solution and in the solid state. However, there are significant changes in the EPR spectra upon addition of creatine to solutions of E-MnADP or to E-MnATP. The changes show that the binding of creatine induces a rearrangement at the active site which results in a more asymmetrical electronic environment for the Mn(II). Substitutions of ligand groups from the protein into the Mn(II) coordination sphere are suggested as a possible source of the spectral changes. Anions such as nitrate and chloride produce further changes in the EPR spectrum of E-Mn-ADP-creatine and decrease the PRR of water for this complex. The anions apparently bind at the vacant phosphoryl site in the abortive quaternary complex, and their binding induces additional structural changes. Considerable specificity is observed in the effectiveness of various anions on the EPR spectrum or on the PRR of water, nitrate inducing the maximal effect. Experiments with modified substrates show that even minor differences e.g. dADP versus ADP in the molecular structure of the substrates bound to the enzyme are reflected in the EPR spectrum of Mn(II) at the active site. Creatine kinase modified at the essential sulfhydryl groups by reaction with iodoacetamide does not undergo a conformational response upon addition of either creatine or creatine and anions to solutions of its ternary complex with MnADP.

Properties of CaSO4(Mn) Powder for Thermoluminescence Dosimeter

Thermoluminescence and electron paramagnetic resonance (EPR) of CaSO4(Mn) powder have been studied. The intensities of the hyperfine lines in the EPR spectra of Mn++ and the heights of the thermoluminescence glow peak are found to change in parallel, upon varying the conditions of heat treatment and the concentration of Mn++. It is also found that Mn++ present in aggregate state, which gives a broad EPR spectrum, is not an effective activator for thermoluminescence; heat treatment at high temperatures serves to disperse this aggregated Mn++, which increases the thermoluminescence sensitivity. The relation between the thermoluminescence intensity and the radiation dose is linear, so long as the duration of irradiation is within certain limits; the deviation from the linear relation is explained in terms of fading of thermoluminescence at the temperature of irradiation.