EPR Characterization of Mononuclear Dinitrosyl Iron Complex with Persulfide as a New Representative of Dinitrosyl Iron Complexes in Biological Systems: an Overview

Some recent data on the presence of mononuclear dinitrosyl iron complexes (M-DNIC) with persulfide (R-S-S^?) ligands with a characteristic electron paramagnetic resonance signal at g _⊥ = 2.35 and g _|| = 2.02 (g _aver. = 2.03) in biological systems (e.g., Escherichia coli cells and isolated iron–sulfur proteins) are reviewed. The generation of M-DNIC is controlled by inorganic sulfur (sulfide, S^2?) whose binding to thiols gives persulfides. It is suggested that enhanced production of inorganic sulfur is a result of destruction of active centers of iron–sulfur proteins in the presence of NO or NO-containing compounds. Dinitrosyl iron complexes with thiol-containing ligands are the most active participants in this process. Inorganic sulfur may appear in biological systems during the synthesis or resynthesis of active centers of iron–sulfur proteins in response to activation of cysteine desulfurase, the key enzyme in sulfide synthesis from cysteine.     

EPR Studies of CuCl2-ethanolate Complexes

The molecular and electronic structure of the CuCl₂-complexes with monoethanolamine (MEA) and triethanolamine (TEA), and their dynamical properties in solid and in DMF solutions were discussed on the basis of EPR measurements. Measurements indicate a dimeric structure of CuCl₂-MEA complexes with very weak Cu-Cu coupling. Intradimer superexchange interaction is temperature dependent and decreases with temperature. In CuCl₂-TEA monomeric complexes exist with a significant vibronic effect which is due to a change of d_Z2 admixture to the d x²-y² ground state when temperature is changed.     

A Multi-Frequency EPR and ENDOR Study of Rh and Ir Complexes in Alkali and Silver Halides

Aliovalent Rh and Ir cations have been frequently used to influence the photographic properties of silver halide emulsions. The doping introduces several types of related defects with distinct trapping and recombination properties. EPR and ENDOR are, in principle, ideally suited for the determination of the microscopic structure of the individual centres but it will be demonstrated that well-chosen, sometimes sophisticated multi-frequency experiments are necessary in order to (partially) reach this goal. Model studies on single crystals of AgCl and NaCl also appeared indispensable for the unravelling of the spectra.

In the review of Rh-centres in NaCl and AgCl special attention is paid to methods that allow to detect cation vacancies near Rh^2? complexes. An alternative explanation for the high temperature behaviour of the [RhCl₆]^4? complexes in AgCl is presented.     

57Fe Mössbauer Spectroscopic Study on the Assembled Iron Complexes

We have measured the lattice distortion around As (acceptor) and Br (donor) in CdTe with fluorescence detected X-ray absorption spectroscopy. We could experimentally verify the lattice relaxation with a bond length reduction of 8% around the As atom as inferred indirectly from ab initio calculations of the electric field gradient performed with the WIEN97 package in comparison with the measured value in a Perturbed Angular Correlation experiment as recently reported. We have complemented our own calculations of relaxation with WIEN97 with calculations using the FHI96md pseudo-potential program, which allows the use of larger super-cell sizes. Encouraged by the good agreement between experiment and model calculation for As in CdTe as well as similarly for the isovalent Se in CdTe, we extended our investigation to Br in CdTe, where the electric field gradient has also been measured, and could not only verify the derived lattice expansion around Br with our EXAFS analysis but additionally observe fractions of Br in the A-center as well as in a DX-center configuration.     

EPR Study of Ligand Effects in Spin Triads of Bis(o-Semiquinonato)Copper(II) Complexes

We report the X-band (9 GHz) electron paramagnetic resonance (EPR) study of series of bis(o-semiquinonato)copper(II) complexes with different ligands. It was found previously, that exchange interactions in spin triads of these compounds are very sensitive to the structure of the ligand coordinated to the central copper(II) ion. Ligand moderates the copper–radical and radical–radical exchange interactions and strongly changes the magnetic properties of the compound. Depending on a ligand, ferromagnetic or antiferromagnetic character of exchange dominates in the system. The EPR study of these complexes allowed us to obtain information on zero-field splitting parameters and their distributions in the studied compounds. The EPR results compliment previously obtained spectroscopic data on these compounds and suggest the pronounced plasticity of the clusters manifested in the broad distributions of their rhombicity parameters.     

Paramagnetic Complexes in Zinc Selenide Crystals with Iron Admixture

Paramagnetic resonance of ZnSe: Fe single crystals was studied at 120 K. Parameters of the spin Hamiltonian were determined for the monoclinic dimer complex Fe³⁺–Cu⁺ and a second discovered Fe³⁺ center, which appears due to association of the iron ion with a K⁺ ion in a Zn²⁺ position or with a zinc vacancy. Effect of illumination of the zinc selenide samples by blue, green and red light on the paramagnetic resonance spectrum was investigated.     

Near-IR Luminescent Rare Earth Ion–Sensitizer Complexes

Rare earth ions, with relatively long luminescence lifetimes, have significant advantages for application in fields as varied as diagnostics and optical amplification. In diagnostics the long luminescence lifetimes allow for extremely sensitive time-gated detection, where the difference in temporal behavior of scatter and background fluorescence and the long-lived rare earth luminescence is utilized. In optical amplification the long excited-state lifetime makes it easier to obtain population inversion, a requirement for effective stimulated emission. Unfortunately the absorption cross section of rare earth ion transitions is extremely low. However, via sensitized excitation by means of a suitable organic molecule, efficient excitation is obtained. It is shown that excitation in the visible part of the spectrum can be used to excite rare earth ions which luminesce in the near-IR, such as ytterbium, neodymium, and erbium, via a fluorescein-derivative as sensitizer. The advantages of this approach are manifold. Low-cost light sources are available for the visible part of the spectrum, and interferences from the matrix (scatter, absorption) are minimal. Detection in the near-IR is almost interference-free. For optical amplification the wavelength regions around 1300 and 1550 nm, which can be covered with the neodymium and erbium complexes, respectively, are the most important for applications in optical telecommunication.     

EPR Study of the Single-Ion Magnetic Anisotropy of the Fe3+ Ion in a Diamagnetic PbGaBO4 Crystal

Journal of Experimental and Theoretical Physics - Crystals of a diamagnetic PbGaBO4 analog containing a small amount (about 0.5 at %) of Fe3+ ions are grown. The single-ion EPR spectra of Fe3+ in...     

EPR of Spin Transitions in Complexes of Cu(hfac)2 with tert-Butylpyrazolylnitroxides

Polymer chain complexes [Cu(hfac)₂L^R] _n exhibit thermally and light-induced magnetic anomalies in many aspects similar to a spin crossover. These compounds attracted significant attention in the field of molecular magnetism and have been extensively studied by electron paramagnetic resonance (EPR) during the last several years. All compounds studied so far were based on copper(II) ions bridged by pyrazolyl-substituted nitronylnitroxides. The present work reports the first EPR study of complexes of Cu(hfac)₂ with tert-butylpyrazolylnitroxides—a new type of nitroxide ligand expected to modify exchange interaction pathways and physical properties of the crystals. The Q-band EPR spectra of three representative novel compounds are principally different from those studied previously, supporting the assumption that the magnetic motif of the compound has changed. Dominant intercluster exchange interactions are now found along the structural polymer chains. This complicates the EPR detection of phase transitions to some extent; however, theoretical modeling of the observed spectral changes allows for unambiguous assignment of different spin states and transitions between them. The magnitudes of intercluster exchange interaction were estimated to be ca. 0.1–1.5 cm^?1 for the studied compounds.     

对苯二甲酸根桥联的双铁(Ⅲ)配合物的穆斯堡尔研究

本文以对苯二甲酸根（ＴＰＨＡ）为桥合成了三个双核铁（Ⅲ）的配合物。经元素分析、红外光谱、穆斯堡尔谱等方法推定配合物具对苯二甲酸根桥联结构，Ｆｅ（Ⅲ）的配位环境粉入面体构型。配合物的低温（７８Ｋ）穆斯堡尔谱显示两组不同的双峰，说明Ｆｅ（Ⅲ（具有自旋交叉现象。     

Systematic Atomic Number Effects in Complexes Exhibiting Ligand Luminescence. III. Ion Pair Complexes of Rhodamine B1

Excited state rate constants have been obtained for complexes of rhodamine B and tetrachloroanions of the group IIIA metals. The results were analyzed by comparison with a heavy atom effect model. Other interaction mechanisms were discussed as well as the suitability of this system for time resolved fluorescence analysis.     

Interaction of the Iron(II) Cage Complexes With Proteins: Protein Fluorescence Quenching Study

Interaction of the iron(II) mono- and bis-clathrochelates with bovine serum albumin (BSA), β-lactoglobulin, lysozyme and insulin was studied by the steady-state and time-resolved fluorescent spectroscopies. These cage complexes do not make significant impact on fluorescent properties of β-lactoglobulin, lysozyme and insulin. At the same time, the monoclathrochelates strongly quench a fluorescence intensity of BSA and substantially decrease its excited state lifetime due to their binding to this protein. This occurs due to the excitation energy transfer from a tryptophan residue to a cage molecule or/and to the change of the tryptophan nearest environment caused by either clathrochelate binding or an alteration of the BSA conformation. The effect of the iron(II) bis-clathrochelate on BSA fluorescence is much weaker as compared to its monomacrobicyclic analogs as a result of an increase in its size.     

取代铁卟啉的拉曼及红外光谱分析

合成了系列取代铁卟啉化合物,研究了拉曼光谱及红外光谱.对二价铁卟啉RTPPFe(Ⅱ)和三价铁卟啉RTPPFeCl(Ⅲ)的红外光谱和拉曼光谱进行了对比分析,结果表明,二价铁卟啉在常温下是不稳定的,通常在其轴向位置上吸附氧分子而形成铁卟啉的超氧化物RTPPFe-O2,其稳定的立体构型为end-on式结构.采用量化软件对化合物的分子结构进行了模拟,得出了其分子结构参数,并结合化合物的红外及拉曼光谱,研究了分子结构对波谱位移的影响.不同结构的二价铁卟啉RTPPFe-O2拉曼及红外吸收峰的位置发生了不同程度的位移,其位移情况与分子的扭曲程度有关.即RTPPFe-O2的Fe-O2特征拉曼吸收峰以及红外特征吸收峰(Fe-O)的位置随着Fe-O-O角的增大而向高波数移动.     

EPR Study of Accumulation and Toxic Effect of Iron and Copper During the Development of Solanum tuberosum L. in vitro

Journal of Applied Spectroscopy - The migration and accumulation of iron and copper ions during the growth of Solanum tuberosum L. vial potatoes were studied. The speciation and content of the...     

Spin States of Iron(III) in Highly Saddled Dodecaphenylporphyrin Complexes

The alignment correlation term in the β-decay angular distribution from purely nuclear spin aligned ²⁰Na has been measured for the first time. The final objective is to test the G parity symmetry, one of the fundamental symmetry in the weak nucleon current. For artificial creation of the alignment, the knowledge of the hyperfine interaction of ²⁰Na implanted in a single-crystal ZnO was utilized. *Research Abroad, Japan Society for the Promotion of Science     

橙皮苷-镧配合物的合成

采用碱提酸沉法从桔子皮中提取橙皮苷,并以橙皮苷化合物为配体与镧离子配位,合成出橙皮苷-镧配合物。利用傅里叶红外光谱仪(KBr压片),对橙皮苷及其配合物进行了结构表征。