细胞色素bc_1复合物与去脂的细胞色素bc_1复合物拉曼光谱研究

细胞色素ｂｃ１复合物与去脂的细胞色素ｂｃ１复合物拉曼光谱研究朱克莉潘平雪徐建兴（中国科学院生物物理所北京１００１０１）ＳｔｕｄｙｏｎＣｙｔｏｃｈｒｏｍｅｂｃ１ＣｏｍｐｌｅｘａｎｄＬｉｐｉｄ－ＤｅｐｌｅｔｅｄＣｙｔｏｃｈｒｏｍｅｂｃ１Ｃｏｍｐｌｅｘｗｉ...     

细胞色素bc_1复合物结晶的显微共振拉曼光谱

细胞色素ｂｃ１复合物结晶的显微共振拉曼光谱何季平①岳文海①尤乃亭②李晓原②李五湖②陈震华③（①武汉工业大学材料研究与测试中心武汉４３００７０）（②香港科技大学化学系香港九龙清水湾）（③武汉大学化学系武汉４３００７２）ＭｉｃｒｏＲｅｓｏｎａｎｃｅＲａｍ...     

EPR Spectra of Nitrogen in Ultra-Dispersed Diamonds

The analysis of the electron paramagnetic resonance (EPR) line shape of ultra-dispersed diamond (UDD) obtained by conversion of trotyl and hexogen mixture and purified from other phases and metal compounds is carried out. The observed wide line with g = 2.0028 and a line width of 8.7 G is shown to be formed by superposition of three lines with line widths of 15.3, 8.5 and 3 G and with a ratio of integral intensities of 70:30:1. The procedure of decomposition and subtraction of wide lines has revealed the resolved hyperfine structure (HFS) from donor nitrogen with parameters A = 40.8 G and B = 29.2 G. Experimentally obtained dependence of the line width of the exchange line on the concentration of donor nitrogen in synthetic diamonds assumed that variations in line widths of the EPR spectrum components are caused by different local concentration of donor nitrogen due to distribution of nitrogen impurity during crystallization of diamond nanoparticles. EPR spectra of UDD after annealing in vacuum and at high pressures in the range of diamond phase stability are also discussed. At high-pressure annealing above 973 K, the areas with high concentration of defects are graphitized and a narrow Dyson-shape line from conductivity electrons and a resolved HFS from donor nitrogen can be observed without additional treatment of the EPR spectrum.     

Quantitative analysis of paramagnetic ions in powders from integrated fine-structure EPR Spectra

Integration of fine-structure EPR spectra of paramagnetic ions in powders, with the purpose of determination of concentrations, offers several difficulties. The most imoortant of these results from the circumstance that a spectrum recorded as a function of field strength at constant frequency is considerably distorted with respect to the corresponding spectrum as a function of frequency at constant field strength. At constant frequency, increasing zero-field splitting parameters lead to a substantial loss of integrated intensity as compared to the unperturbed spectrum of ions with the same spin quantum number. By making use of simulated spectra a method is designed to overcome this difficulty and is applied to the EPR spectrum of isolated Fe(III) ions in CuGaS₂:Fe.     

Resolving Conformational and Rotameric Exchange in Spin-Labeled Proteins Using Saturation Recovery EPR

The function of many proteins involves equilibria between conformational substates, and to elucidate mechanisms of function it is essential to have experimental tools to detect the presence of conformational substates and to determine the time scale of exchange between them. Site-directed spin labeling (SDSL) has the potential to serve this purpose. In proteins containing a nitroxide side chain (R1), multicomponent electron paramagnetic resonance (EPR) spectra can arise either from equilibria involving different conformational substates or rotamers of R1. To employ SDSL to uniquely identify conformational equilibria, it is thus essential to distinguish between these origins of multicomponent spectra. Here we show that this is possible based on the time scale for exchange of the nitroxide between distinct environments that give rise to multicomponent EPR spectra; rotamer exchange for R1 lies in the ≈0.1–1 μs range, while conformational exchange is at least an order of magnitude slower. The time scales of exchange events are determined by saturation recovery EPR, and in favorable cases, the exchange rate constants between substates with lifetimes of approximately 1–70 μs can be estimated by the approach.     

EPR谱图模拟软件EasySpin的图形用户界面设计

EasySpin是一款较为流行的电子顺磁共振（EPR）谱图模拟和拟合软件,LabVIEW是一种图形化编程语言开发环境．本文介绍了一款使用LabVIEW为EasySpin设计的图形用户界面LV-EasySpin．LV-EasySpin提供了一种直观的操作方法来实现连续波EPR多组分波谱的可视化模拟和拟合．本文辅以各种模式下的实例进行说明,阐述了LV-EasySpin的设计思路与实现方案,最终希望具有简洁、易操作界面的LV-EasySpin可以降低用户使用EasySpin分析EPR谱图的难度．     

An Analysis of the Effects of Eddy Currents on L-Band EPR Spectra

Recently, impressive results have been obtained with EPR studies of living animals and perfused organs using low-frequency EPR. In many instances in such studies, however, there are apparent distortions of the spectra. The shapes of these spectra and theoretical considerations indicate that these effects are due to eddy currents in the moderately conductive biological materials. Therefore the effects of eddy currents produced in biological samples under typical conditions being employed for in vivo EPR studies have been systematically studied in order to determine the extent of these effects and to develop methods for compensating for these effects. The presence of eddy currents was found to decrease the Q factor and distort the shapes of the EPR spectra. The distortion of the spectra led to linewidth broadening, changes in peak heights, and shifts of the apparent center of the lines. These effects could be corrected instrumentally, but this was effective only when signals have a high S/N. The use of appropriate computer simulations, based on linear combinations of the expected absorption and dispersion signals, can effectively correct for the effects of eddy currents and provide accurate data on the parameters of EPR spectra that are needed for most or all of the analyses used in biological studies of animals and tissues at low frequencies.     

EPR Spectra of Transition-Metal Proteins: the Benefits of Data Deposition in Standard Formats

Electron paramagnetic resonance (EPR) spectroscopy can provide answers to significant questions about structure and function in biochemistry. Often EPR spectra of proteins containing transition-metal centers and radicals show the influence of electron spin–spin interactions between paramagnets. Analysis of these spectra provides information about distances and molecular orientations. For small proteins, the shape of the EPR spectra is sensitive to freezing effects, and to changes in the solvent environment; intermolecular spin–spin interactions are also observed. For large complex proteins, details of the EPR spectra are often highly conserved in evolution. Reference spectra of paramagnetic proteins are an aid to identification. The sharing of data is becoming a requirement in the public funding of research, and deposition in public databases is already standard for information such as protein structures and gene sequences. This would require the adoption of standard file formats, such as JCAMP-DX (Joint Committee on Atomic and Molecular Physical Data Exchange) or Bruker BES³T (Bruker EPR Standard for Spectrum Storage and Transfer). An archive of EPR spectra of different types of paramagnetic proteins would assist the identification of paramagnetic centers in biological materials. It would increase the profile of research data, allow comparison of different studies, and further interpretation of data in the light of subsequent discoveries.     

CuAlS2∶Ni+晶体光谱和电子顺磁共振谱研究

Ni 离子在三元化合物CuAlS2半导体中替代离子Cu .应用晶体场理论,结合CuAlS2中Cu 位置的结构数据,计算了CuAlS2∶Ni 晶体的光谱和电子顺磁共振谱(g因子和超精细结构常数),计算结果与实验值符合得很好.     

Application of the SCVT Orientation Grid to the Simulation of CW EPR Powder Spectra

The orientation grid obtained using the spherical centroidal Voronoi tessellation (SCVT) method is assessed for the simulation of continuous-wave electron paramagnetic resonance (CW EPR) powder spectra. The SCVT spherical code presents less distorted Voronoi cells associated to the points of the grid compared to the regular Igloo, SOPHE and EasySpin grids and similar distortions of the cells to the irregular Repulsion grid. The degree of distribution of the SCVT cells’ areas is smaller than for SOPHE, but higher than for the Igloo and Repulsion grids. All compared spherical codes have nearly the same electrostatic potential energy. Simulated CW EPR powder spectra for rhombic systems of spin S = 1/2 are similar when using the energy minimization SCVT and Repulsion spherical codes and show less intense ripples than the spectra calculated with the SOPHE and Igloo grids, but more intense than those obtained using the EasySpin grid. The classical projection method and a new modified form involving the spectral intensities at the orientations of the grid have been tested for the attenuation of the simulation noise, for grids of relatively reduced size.     

Isotopic Study of Rotational Spectra of the Ar-Acetylene Complex

Rotational spectra of the weakly bound complex Ar-acetylene were measured using a Fourier transform microwave spectrometer. Eight additional transitions of the normal isotopomer were detected, following the earlier radiofrequency and microwave investigations [R. L. DeLeon and J. S. Muenter, J. Chem. Phys. 72, 6020-6023 (1980); Y. Ohshima, M. Iida, and Y. Endo, Chem. Phys. Lett. 161, 202-206 (1989)]. Spectra of four minor isotopomers, namely Ar-DCCD, Ar-H(13)C(13)CH, Ar-DCCH, and Ar-H(13)C(12)CH, were newly assigned and analyzed. A semirigid rotor model was employed to obtain the rotational and centrifugal distortion constants, which were in turn used to extract structural information about the complex. The unusually large standard deviations of the spectroscopic fits are indicators of large-amplitude internal motions of the acetylene subunit. Separate fits of the individual K-stacks yielded lower standard deviations, and their results were used to interpret some of the unusual spectroscopic observations. Copyright 2001 Academic Press.     

城市空气质量监测系统(DOAS)谱线漂移问题及解决方法

城市空气质量监测系统中差分光学吸收光谱法的光学部分受到外界影响(温度、光纤位置等),或是氙灯自身的变化,都会引起测量谱线的漂移。如果灯信号谱与大气测量信号谱谱线漂移不一致而产生谱线相对偏移,将直接影响测量结果的准确性。因此,在运用DOAS方法进行大气痕量气体污染物浓度反演时,必须对大气测量信号谱和灯信号谱进行波长匹配。文章通过对氙灯自身发射光谱特殊结构的研究,提出了利用氙灯特征发射峰,通过对两个信号光谱进行最小二乘拟合,达到谱线校正的方法。实验结果证明,这种方法可以有效地减小谱线相对偏移对大气痕量气体污染物浓度反演结果的影响。     

Maximum-Likelihood Common-Factor Analysis as a Powerful Tool in Decomposing Multicomponent EPR Powder Spectra

An advanced multivariate statistical technique, maximum-likelihood common-factor analysis (MLCFA), is used to decompose a set of multicomponent EPR powder spectra. Once the correct number of constituents is detected by MLCFA, the resulting abstract-factor spectra are transformed into real EPR powder spectra by means of a minimization procedure or a target transformation. The technique is applied to both simulated and experimental EPR powder spectra. The results indicate that the technique MLCFA is potentially of great value in the field of EPR of polycrystalline materials.     

Distribution and regulation of stochasticity and plasticity in Saccharomyces cerevisiae

Stochasticity is an inherent feature of complex systems with nanoscale structure. In such systems information is represented by small collections of elements (e.g., a few electrons on a quantum dot), and small variations in the populations of these elements may lead to big uncertainties in the information. Unfortunately, little is known about how to work within this inherently noisy environment to design robust functionality into complex nanoscale systems. Here, we look to the biological cell as an intriguing model system where evolution has mediated the trade-offs between fluctuations and function, and in particular we look at the relationships and trade-offs between stochastic and deterministic responses in the gene expression of budding yeast (Saccharomyces cerevisiae). We find gene regulatory arrangements that control the stochastic and deterministic components of expression, and show that genes that have evolved to respond to stimuli (stress) in the most strongly deterministic way exhibit the most noise in the absence of the stimuli. We show that this relationship is consistent with a bursty two-state model of gene expression, and demonstrate that this regulatory motif generates the most uncertainty in gene expression when there is the greatest uncertainty in the optimal level of gene expression.     

Simulation of EPR Spectra as a Tool for Interpreting the Degradation Pathway of Hyaluronan

Electron paramagnetic resonance (EPR) spin trapping is one of the choice techniques for identifying free radicals and is often used in the study of biological systems. However, its sensitivity can result in a typical complicated EPR spectrum. The accurate simulation of these systems is essential for correct identification of the radical species, whenever more than one species contributes to the spectrum. Programs implementing the linear combination of single simulations allow the interpretation of EPR spectra without modifying experimental conditions. In this study, this approach was used to investigate the influence of the ferrous ion and the role of oxygen, as well on the formation of transient radical species, in the whole mechanism of hyaluronan degradation. Degradation was carried out under different environmental conditions (air, O₂, Ar, N₂, N₂ + CO₂) and EPR spin trapping studies were performed. The advantages of the simulation of multiple species EPR spectra were applied to the obtained results and some aspects of hyaluronan degradation mechanism were elucidated. The depolymerization reaction pathway has been defined according to two possible subsequent steps: the first is consistent with formation of an amidyl radical that induces a series of strand scissions, which stabilize at two different levels of molecular weight. The second step occurs when the molecular weight is lower than before and two different adducts are generated.