Characterization of ancient and modern papers by CW-EPR spectroscopy

Several old (15th to 18th century), new (1900–1950) and recently produced (after 1990) papers have been investigated by X-band continuous-wave electron paramagnetic resonance (EPR) spectroscopy. Signals from Cu(II), Fe(III), Mn(II) and radicals are apparent. A clear-cut distinction is observed between recently produced papers and the other samples: recent papers show just EPR signals from Mn(II) and sometimes small signals from Fe(III) in rhombic site, while the older samples show usually strong signals from Fe(III), Mn(II), Cu(II) and radicals. Furthermore, Mn(II) EPR signals from recent papers are characterized by small zero-field splitting (ZFS) parameters, indicating Mn(II) in high-symmetry sites, while older samples show broader Mn(II) EPR signals, typical for Mn(II) in low-symmetry sites (increased ZFS parameters).     

EPR Studies of DOPA–Melanin Complexes with Fe(III)

Paramagnetic centers in 3,4-dihydroxyphenylalanine–melanin and its complexes with Fe(III) were examined by electron paramagnetic resonance (EPR) spectroscopy. Paramagnetic centers of melanin play an important role in detoxification of environment and they reveal high activity in binding of metal ions. Two different signals were observed in EPR spectra: lines of o-semiquinone free radicals and lines of paramagnetic Fe(III). Amplitudes of EPR lines of both free radicals and iron ions decrease with increasing Fe(III) content in melanin–metal ion complexes. Free radical concentrations in the melanin samples, g-factors, amplitudes and line widths of EPR spectra were determined. It was stated that fast spin–lattice relaxation processes exist in both free radical system and paramagnetic iron ions in melanin complexes.     

肉苁蓉不同生育阶段矿质元素含量

应用ICP -AES技术测定了肉苁蓉不同生育阶段矿质元素含量.结果显示:(1)肉苁蓉药材的最佳采收期(肉质茎生长期),常量矿质元素中K含量高达9.45 mg·g-1,五种常量矿质元素的含量比例为K∶Na∶P∶Ca∶Mg=12∶ 3.4∶1.6∶ 1.4∶1,微量矿质元素中Fe含量最高为97.31 μg· g-1,五种微...     

The Role of Metal Ions in the Study of Ancient Paper by Electron Paramagnetic Resonance

Samples from covers and endleaves of sixteenth to eighteenth century books in good conservation state from the Biblioteca Nazionale Marciana in Venice have been investigated by means of electron paramagnetic resonance (EPR) spectroscopy and optical microscopy to characterize the embedded paramagnetic species and to test differences and similarities of the materials in the two types of book components. We detected the Mn(II), Fe(III), and Cu(II) paramagnetic ions, and analyzed their EPR signals by comparing them with previous results in literature of EPR studies on paper. Interestingly, the Mn(II) EPR spectrum profile appears as a fingerprint for samples coming from the same book, either from cover or endleaf, and it looks different for samples extracted from different books. We discuss the role of EPR as a spectroscopic tool for characterizing the interaction of the ions with the paper components and as possible agents of degradation.     

Excited-configuration metastable level lifetimes of Cl-like Mn IX and Fe X

Forbidden transitions from levels with 3P and 1D cores in excited configurations of Cl-like Mn IX and Fe X have been isolated using interference filters. The fluorescence decay lifetimes of ions orbiting in a Kingdon ion trap were measured. New relativistic configuration interaction calculations of relevant level lifetimes, to aid the analysis, based on B-spline basis sets, are also presented. Line identifications and experimental lifetimes are Mn IX ((4)D(7/2)-(4)F(9/2)):363(-3/+7) nm; tau(Mn IX3p(4)(3P)3d (4)F(9/2)) = 210+/-42 ms; tau(Fe X,3p(4)(3P)3d (4)F(9/2)) = 85.7+/-9.2 ms; tau(Fe X,3p(4)(3P)3d (4)F(7/2)) = 93+/-30 ms; and tau(Fe X, 3p(4)(1D)3d (2)G(9/2)) = 17.8+/-3.1 ms.     

Direct multielement determination of Cd,Pb, Fe,and Mn in ground coffee samples using energy dispersive X‐ray fluorescence spectrometry

An analytical method was proposed for the quantification of Cd, Pb, Mn, and Fe in ground coffee samples using energy dispersive X‐ray fluorescence (EDXRF) spectrometry. External calibration was possible using the coffee matrix itself as standards with samples previously analyzed by inductively coupled plasma optical emission spectrometry (ICP OES). The ground coffee samples were analyzed in the form of pellets, which were placed in the center of the EDXRF measuring cell for the determination of the analytes. The limits of detection were 62, 55, 86, and 76 μg/kg for Cd, Pb, Fe, and Mn, respectively. Good linearities were obtained for the calibration curves with coefficients of correlation (R) of 0.9959 for Cd, 0.9939 for Pb, 0.9929 for Fe, and 0.9909 for Mn. Precision, evaluated as the relative standard deviation (RSD) of 10 independent measurements of different cataloged samples with an approximate concentration of 400 μg/kg for each analyte, was between 6 and 14% (n = 10), demonstrating that the preparation of the samples in form of pellets was sufficient to perform analyses by EDXRF. The proposed method was applied in the determination of Cd, Pb, Fe, and Mn in ground coffee samples collected in Salvador, Bahia, Brazil. In a parallel comparative procedure, coffee samples were also analyzed by ICP OES after sample pretreatment by acid digestion. A paired Student's t test was carried out (confidence level of 95%, n = 5) and no significant difference was observed between the concentrations obtained by the proposed and comparative methods.     

EPR and optical absorption characteristics of sodic plagioclase from granite pegmatite in Kadavur,India

The electron paramagnetic resonance (EPR) spectra of sodic plagioclase from dykes of granitic pegmatite occurring in the Kadavur area, Tamil Nadu, India, were examined at room temperature to identify paramagnetic impurities in a “low plagioclase” using EPR and optical techniques. The EPR spectra showed the presence of Fe(III) and Mn(II) impurities. After heating the plagioclase samples for various durations at 600 °C, it has been observed that the concentration of Mn(II) remained as such in one sample but completely disappeared in another sample, while there was no change in Fe(III) ion concentration after the heat treatment in either sample. Optical absorption spectra also showed Fe(II) and Fe(III) in addition to Ti(III) impurities in sodic plagioclase before heating, while after heating the relative concentration of Fe(II) and Fe(III) changed, accompanied by the disappearance of Ti(III).     

Effect of Zn2+ and Cu2+ on free radical properties of melanin fromCladosporium cladosporioides

Effect of metal ions on free radical properties of natural melanin produced by soil fungiCladosporium cladosporioides was studied. The electron paramagnetic resonance (EPR) spectrum of the studied melanin consists mainly of a single line of eumelanin, and only a very weak signal of pheomelanin was observed. o-Semiquinone free radicals form paramagnetic centers in melanin. Diamagnetic Zn²⁺ ions produce an increase in the free radical concentration in melanin. Quenching of melanin EPR lines was obtained for melanin and paramagnetic Cu²⁺ ion complexes. Slow spin-lattice relaxation processes are characteristic for the free radicals in melanin samples and fast spin-lattice relaxation was observed for Cu²⁺ ions. The EPR lines of copper ions saturate at higher microwave powers than the EPR lines of melanin.     

Spin Trapping Studies of Amine-Stabilized Trialkylborane Free Radical Initiator Systems: Kinetics and Mechanism

The free radical initiation chemistry of highly reactive trialkylboranes (R₃B, R?=?n-butyl), stabilized by complexation to amines (A?CR₃B), has been investigated using spin trapping methods and electron paramagnetic resonance spectroscopy. Protonation of A?CR₃B leads to release of R₃B and its subsequent autooxidation in the presence of molecular oxygen. This reaction provides highly reactive alkyl and alkoxy radicals for initiation of ???Colefin polymerization. Kinetic traces of the R₃B autooxidation reaction were obtained by monitoring the relative concentrations of trapped radical species as a function of time for several different initial conditions (acid concentrations). Analysis of a representative kinetic run is discussed in terms of several proposed mechanisms from the literature.     

原子吸收法测定中药黄芩中不同化学形态的Cu、Zn、Fe和Mn

研究用原子吸收光谱法(AAS)测定中药黄芩水煎液中Cu,Zn,Fe和Mn化学形态的分析方法.水煎液经0.45 μm滤膜过滤后分为悬浮态和可溶态组分试样;对于可溶态组分试样,采用LSA-10大孔树脂将其分为有机态和无机态组分试样,并采用正辛醇-水分配体系,在模拟人体胃肠环境条件下,将水可溶态中4待测元索分离为醇溶态和水溶态,然后用AAS测定上述各组分试样中待测元素的含量,即可给出比现有的仅测量中药黄芩中上述各待测元素总量为多的信息.该法待测元素Cu,Zn,Mn的检出限(3倍空白标准差)为0.01μg·mL-1,Fe为0.02μg·mL-1,精密度(RSD,n=11)为1.5%～3.6%,对可溶态和无机态组分试样进行加标测定的回收率为96.7%～105.0%.所得结果对黄芩的综合研究有重要的实际意义.     

电感耦合等离子体原子发射光谱法分析不同产地大豆中的矿物元素含量

选取江西、黑龙江、吉林和安徽4产地同一种属大豆经硝酸湿法消解后,采用电感耦合等离子体原子发射光谱法同时测定了其中K, P, Mg, Ca, Fe,Al, Zn, Mn 和Na元素的含量,并采用Ducan多重比较方法对结果进行统计分析。结果表明：大豆中含有丰富的矿物元素,其中K,P,Mg,Ca,Fe元素含量较高,且排序不因产地的变化而改变。Mn, Zn,Al,Na元素的排序则受产地影响较大。K, P, Mg的含量受产地的影响不大,表现出某一品种大豆自身生长对主要矿物质的需求是相对稳定的。不同产地大豆中Al, Ca,Fe, Na, Mn,Zn元素的含量差异显著(P<0.05),说明这几种微量元素的含量受土壤及环境的影响较大,其中安徽大豆中的铁元素(70.93 mg·kg-1)和江西大豆中的锰元素(32.69 mg·kg-1)显著高于其他3个样品。     

Investigation of impurity phase formation for (ZnO)1−x(TMO)x bulk samples formed by ball milling

Structural, compositional, optical and magnetic properties have been studied for polycrystalline (ZnO)_0.90(TMO)_0.10 bulk samples, where TM (transition metal ions) = Mn, Fe, and Co. The quantitative Rietveld analysis showed relatively higher percentage of impurity (spinel and oxide) phases of about 33.76, 52.38 and 55.61% for Mn, Fe and Co doped ZnO samples, respectively. The de-convolution of XPS spectra indicated the presence of different phases. The appearance of shaking satellites in XPS spectra confirmed the presence of different valence states of dopant ions. The red shift in energy band gap, estimated from reflectance UV-vis spectroscopy, was observed for all TM doped bulk samples. For Mn doping, paramagnetic behavior was obtained while for Co and Fe, weak ferromagnetic behavior was observed at room temperature.     

Electron nuclear quadruple resonance for assignment of overlapping spectra

Multiple resonance methods are important tools in EPR for revealing the network of hyperfine levels of free radicals and paramagnetic centers. The variations of electron nuclear double resonance (ENDOR) or electron spin-echo envelope modulation (ESEEM) techniques help to correlate nuclear frequencies with each other. These methods have limited utility when there is extensive overlap or suspected overlap in the EPR spectrum between different species or different orientations. In the ENDOR spectrum, overlap and second-order shifts of lines also leads to ambiguity in assignment and interpretation. A new electron nuclear multiple resonance method is presented here that is based on population transfer ENDOR. It is a quadruple resonance method that correlates ENDOR lines and reveals the network of hyperfine levels in samples with unoriented paramagnetic species and in samples with overlapping EPR or ENDOR lines.     

M?ssbauer study of contaminated soils by industrial activity in Paramonga city, Region Lima Provinces, Peru

In this work we characterize soils from the Paramonga city, Region Lima Provinces in Peru, which are contaminated by residual chemicals (Br, As and Sr) from sugar and paper industry in the city. Four samples were collected, labelled as S1, S2, S3 and S4 and analized by X-ray diffraction (XRD), energy-dispersive X-ray fluorescence (EDXRF) and M?ssbauer spectroscopy. For all the samples, the chemical analysis by EDXRF revealed the presence of Fe, Mn, Cu, Zn, K, Br, Sr. The XRD detected the presence of quartz as principal phase and copper sulfide and potassium magnesium as secondary phases. The M?ssbauer spectra at room temperature (RT) for all the samples exhibit sextets which reveal the presence of an iron oxide or hydroxide. The fitting M?ssbauer for both samples S1 and S4 have three doublets corresponding to iron in paramagnetic phases and a magnetic component of around 35.50?T corresponding to goethite, α-FeOOH. Sample S2 have two magnetic phases with internal fields of 37?T and 34.6?T which correspond to the goethite and other incorporated element in the structure. The sample S3 have three magnetic fields of H1?=?36.8?T, H2?=?33.6?T and H3?=?34.8?T which correspond to hydroxide iron, pyrrhotite and goethite respectively.     

Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing

Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H_2/Ar atmosphere with different H_2/Ar ratios.It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO.Mn ions initially enter into interstitial sites and a Mn~(3+)O_6 octahedral coordination is produced in the prepared Mn-doped ZnO sample,in which the nearest neighbor Mn~(3+) and O~2 ions could form a Mn~(3+)-O~(2-)-Mn~(3+) complex.After H_2 annealing,interstitial Mn ions can substitute for Zn to generate the Mn~(2+)O_4tetrahedral coordination in the nanocrystals,in which neighboring Mn~(2+) ions and H atoms could form a Mn~(2+)-O~(2-)-Mn~(2+)complex and Mn-H-Mn bridge structure.The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn~(3+)-O~(2-)-Mn~(3+) complex,while the annealed samples exhibit their ferromagnetism,which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn~(2+)-O~(2-)-Mn~(2+)complex.     

Mechanism of relaxation enhancement of spin labels in membranes by paramagnetic ion salts: dependence on 3d and 4f ions and on the anions

Progressive saturation EPR measurements and EPR linewidth determinations have been performed on spin-labeled lipids in fluid phospholipid bilayer membranes to elucidate the mechanisms of relaxation enhancement by different paramagnetic ion salts. Such paramagnetic relaxation agents are widely used for structural EPR studies in biological systems, particularly with membranes. Metal ions of the 3d and 4f series were used as their chloride, sulfate, and perchlorate salts. For a given anion, the efficiency of relaxation enhancement is in the order Mn(2+) > or = Cu(2+) > Ni(2+) > Co(2+) approximately Dy(3+). A pronounced dependence of the paramagnetic relaxation enhancement on the anion is found in the order ClO(-)(4) > Cl(-) > SO(2-)(4). This is in the order of the octanol partition coefficients multiplied by spin exchange rate constants that were determined for the different paramagnetic salts in methanol. Detailed studies coupled with theoretical estimates reveal that, for the chlorides and perchlorates of Ni(2+) (and Co(2+)), the relaxation enhancements are dominated by Heisenberg spin exchange interactions with paramagnetic ions dissolved in fluid membranes. The dependence on membrane composition of the relaxation enhancement by intramembrane Heisenberg exchange indicates that the diffusion of the ions within the membrane takes place via water-filled defects. For the corresponding Cu(2+) salts, additional relaxation enhancements arise from dipolar interactions with ions within the membrane. For the case of Mn(2+) salts, static dipolar interactions with paramagnetic ions in the aqueous phase also make a further appreciable contribution to the spin-label relaxation enhancement. On this basis, different paramagnetic agents may be chosen to optimize sensitivity to different structurally correlated interactions. These results therefore will aid further spin-label EPR studies in structural biology.     

Electron paramagnetic resonance and FT-IR spectroscopic studies of DL-2-aminoadipic acid and ammonium acetate powders

Exposure of powder forms of DL-2-aminoadipic acid and ammonium acetate to gamma radiation results in the formation of free radicals detected by the electron paramagnetic resonance spectroscopy at room temperature. In these compounds, the observed paramagnetic species were attributed to the HOOCCH₂CH₂CH₂CHCOOH and CH₂COONH₄ radicals, respectively. The g values and the hyperfine coupling constants of the unpaired electron with the environmental protons were determined for these two radicals. In work, the observed paramagnetic species were found to be stable at room temperature for more than two months. Also, these compounds were characterised by FT-IR and UV–VIS. Their thermal stabilities were determined by TGA and DTA measurements. Thermal analyses were shown to be unstable of the HOOCCH₂CH₂CH₂CH(NH₂)COOH and CH₃COONH₄ against thermo-oxidative decomposition.     

EPR Technology Spectroscopic Investigation of Generation of Reactive Oxygen Species Free Radicals in Laccase-Activated Jute Fiber

Lignins in jute fibers can be activated by laccase to generate reactive oxygen species (ROS) free radicals for subsequent use in radical graft polymerization. The effect of incubation conditions on the generation of ROS free radicals when jute powders were incubated with laccase was investigated through spin-trapping technique to detect the spin adduct of N-tert-butyl-α-phenylnitrone and ROS free radical using electron paramagnetic resonance spectroscopy. Results revealed that the highest concentrations of ROS free radicals were generated when jute was incubated with laccase (0.54 U/mL) and copper ions (10 mM) in solution at pH 3.5 and a temperature of 60 °C for 1 h.     

金刚石材料的ESR研究

用ESR方法对照研究了中国出产的五颗天然金刚石单晶,四颗人造金刚石单晶和两个化学沉积金刚石膜(CVD)等固体材料.发现I_b型天然金刚石中有四种a_N各向异性的N-中心自由基和一种C-中心自由基;而I_aB3型的未配对电子定域在N3型杂质中心的π^*反键轨道上;I_b型人造金刚石含有少量Ni,Fe等顺磁元素造成ESR线增宽,仅可观察到二重或三重裂分;在不同金刚石膜中.c-中心自由基的浓度可以相差很大.而低浓度的N-中心自由基的浓度相对变化较小;所观察到的C-中心自由基的两个卫星峰(a_H=7.2×10^-4T)是金刚石膜中¹H存在的直接证据.结果表明ESR方法是金刚石及类金刚石材料的一种快捷而有效的表征方法.     

FAAS测定昙花中的7种金属元素

采用火焰原子吸收光谱法对昙花花和茎中K、Mg、Ca、Fe、Zn、Mn、Cu 7种金属元素的含量进行分析测定。结果显示昙花含有丰富的Fe、Zn、Mn、Cu微量元素。花中钾含量高达69763.61μg.g-1,约为茎的两倍。花中Mg、Fe、Zn、Cu的含量也高于茎,而花的Ca、Mn含量明显低于茎。昙花样品的加标回收率为93.8%—104.3%,相对标准偏差RSD≤3.67%,实验结果令人满意。