电子顺磁共振法(EPR)对银杏叶提取物及其卷烟捕获自由基能力研究

自由基存在于人体和卷烟烟气中,会引起人体病理反应和氧化损伤,种类和形态多样,如：O-·₂,HO·,R·,RO·,ROO·。电子顺磁共振法(EPR)是检测和定量分析自由基的重要方法之一。银杏叶提取物(EGB)是由黄酮、内酯、原花青素类成分组成的植物药,具有较好清除自由基和抗氧化能力。本文以槲皮素、芦丁、原花青素等化合物为对照,运用EPR法结合自旋捕集技术研究EGB和EGB卷烟对DPPH,HO·,O2-·、烟气气相自由基、烟气粒相自由基的抑制水平。结果表明,EGB能够有效抑制化学/生物系统和卷烟烟气产生的自由基。尽管抑制自由基整体水平比黄酮单体和原花青素弱,但EGB提取方法简单容易得到,可作为天然抗氧化剂和自由基清除剂用于食品和烟草等行业。EPR法灵敏度高,稳定性好,是用于自由基研究的可靠方法。捕集剂DEPMPO捕集O2-·更加高效,PBN捕集烟气气相自由基比DMPO更有优势。该研究讨论了EGB清除自由基的机理,丰富的酚羟基结构是其抗氧化作用的主要原因。     

电子顺磁共振法(EPR)对银杏叶提取物及其卷烟捕获自由基能力研究（英文）

自由基存在于人体和卷烟烟气中,会引起人体病理反应和氧化损伤,种类和形态多样,如:O_2~(-·),HO~·,R~·,RO~·,ROO~·。电子顺磁共振法(EPR)是检测和定量分析自由基的重要方法之一。银杏叶提取物(EGB)是由黄酮、内酯、原花青素类成分组成的植物药,具有较好清除自由基和抗氧化能力。本文以槲皮素、芦丁、原花青素等化合物为对照,运用EPR法结合自旋捕集技术研究EGB和EGB卷烟对DPPH,HO·,O~(2-·)、烟气气相自由基、烟气粒相自由基的抑制水平。结果表明,EGB能够有效抑制化学/生物系统和卷烟烟气产生的自由基。尽管抑制自由基整体水平比黄酮单体和原花青素弱,但EGB提取方法简单容易得到,可作为天然抗氧化剂和自由基清除剂用于食品和烟草等行业。EPR法灵敏度高,稳定性好,是用于自由基研究的可靠方法。捕集剂DEPMPO捕集O~(2-·)更加高效,PBN捕集烟气气相自由基比DMPO更有优势。该研究讨论了EGB清除自由基的机理,丰富的酚羟基结构是其抗氧化作用的主要原因。     

EPR和NMR自旋标记法研究部分折叠蛋白质构象

部分折叠蛋白质的特征是在溶液中有部分二级结构,但是三级结构接触比较松散或者较少,其意义可能是蛋白质折叠过程的中间态,或者有重要的生理功能. 利用EPR和NMR波谱可以表征其构象特征,从而构建其二级结构、三级结构、四级结构以及构象变化的结构模型. 利用分子生物学的点突变技术可以在蛋白质主链上插入1个或2个半胱氨酸残基,然后把顺磁自旋标记物特异地共价结合在半胱氨酸的侧链巯基上来制备自旋标记样品. 位点特异性自旋标记电子顺磁共振（SDSL-EPR）波谱是通过测定2个自旋标记间的偶极相互作用,从而推测2个硝基氧自由基间的距离. 核磁共振（NMR）波谱则是通过测定单个自旋标记中心对周围原子核驰豫效应增强（PRE）的效应,推测出顺磁中心相对于周围原子核的距离. 连续波EPR和NMR自旋标记方法可以测定2.5 nm左右的偶极相互作用距离,属于长程的距离约束,这对于确定部分折叠蛋白质的构象至关重要. 该文将就蛋白质部分折叠态研究的生物学意义,自旋标记方法以及EPR和NMR方法研究其构象特征举例描述.     

竹秆提取物的抑菌及抗氧化活性

采用滤纸片法比较研究了17种竹子竹秆提取物对水稻白叶枯菌、金黄色葡萄球菌、番茄青枯和菌大肠杆菌的抑菌性能;并以IC50值作为评价抗氧化剂清除DPPH·自由基能力的指标评价提取物的抗氧化能力.结果表明:竹秆提取物具有广谱的抑菌活性,不同竹种对于供试细菌抑制活性不同;竹秆提取物具有较好的抗氧化活性,其中乌哺鸡竹提取物清除自由基效果突出,IC50为96.0mg/L,略强于同质量浓度的人工合成抗氧化剂TBHQ.     

一种从EPR粉末谱精确提取自旋哈密顿及线型参数的拟合方法

本文提出一种从EPR粉末谱精确提取自旋哈密顿和线型参数的拟合方法,适用于不同单晶线型和哈密顿。该方法不但可用于共振磁场能解析表示的情形,而且也可用于共振磁场只能通过对角化哈密顿数值解出的情形。     

三角对称晶场中4A2(3d3)态离子EPR参量的SS和SOO机制

考虑了在以前工作中被忽略的自旋与自旋 (Spin spin(SS) )磁相互作用以及一个电子自旋与另外电子轨道 (Spin other orbit (SOO) )之间的磁相互作用 ,用VisualBasic6.0设计了新的CDM/EPR计算程序 .该程序不仅能计算 4 A2 (3d3)态离子在晶体中的EPR参量 ,而且能计算体系的光谱精细结构 .利用该程序研究了红宝石晶体与绿宝石晶体的EPR参量与光谱精细结构 ,理论与实验符合甚好 .在此基础上 ,研究了SS与SOO磁相互作用对EPR参量及其光谱的贡献 .发现在磁相互作用的三个部分中 ,EPR参量的主要来源是旋 轨 (Spin orbit (SO) )耦合相互作用 ;SS磁相互作用对零场分裂 (Zero fieldsplitting(ZFS) )参量D具有重要贡献 ,在研究中不能被忽略 ,而SOO磁相互作用对ZFS参量D的贡献较小 ;SS与SOO磁相互作用对Zeemang因子以及光谱的贡献甚微     

一种基于近红外光谱的天然产物抗氧化活性预测评价方法

提出了一种基于近红外(NIR)光谱的黄酮类提取物抗氧化活性计算预测新方法。采用1,1-二苯-2-苦肼基(DPPH)法测定28种黄酮类中药材提取物的抗氧化活性,并在4 000～10 000 cm-1范围扫描样品的红外光谱,采用偏最小二乘(PLS)算法建立了黄酮类组分近红外光谱与抗氧化活性之间的校正模型。建模过程中,以交叉验证相关系数(R2),交叉验证误差均方根(RMSECV)为指标,确定了用于建模的最优近红外波段和光谱预处理方法。校正模型的RSECV为9.50%,R2为 0.901 7,预测误差均方根(RMSEP)为14.8%。该方法快速无损、操作简便,可用于中药及天然产物提取物抗氧化活性的快速评价。     

对<再论“EPR”问题的双波解答>的评论

论文“再论‘EPR问题的双波解答”是错误的.由该文给出的自旋状态的双波描述可以推算出自旋为h/2的粒子有不是±h/2的自旋观测值(例如0值),这显然与实验不符,因此该文不能够对EPR问题(自旋提法)作出正确解答.     

几种新疆特色干果清除自由基活性

为了寻找天然高效强抗氧化剂,并为综合利用提供依据,实验采用DPPH·法研究了6种新疆特色干果不同溶剂提取液及醇提液中不同溶剂萃取相的抗氧化活性,测定了它们的提取液对DPPH·的清除能力.实验结果表明:这几种干果的抗氧化活性成分主要存在于醇溶液中而非水溶液中；在醇提液的各萃取相中,各萃取相均具有不同程度抗氧化活性,其中抗氧化成分在乙酸乙酯萃取相中含量最高,正丁醇萃取相次之,石油醚萃取相最低.杏仁、核桃、黑加仑、无花果、巴旦木、红枣在乙酸乙酯萃取相中黄酮类化合物的IC50值分别为8.15、10.25、4.08、4.44、7.g4、5.44μg/mL.     

Ni2+掺杂到氟化物钙钛矿中的局域结构畸变和基态分裂的理论研究

基于双自旋轨道耦合系数模型并结合完全能量矩阵的方法,研究了AMF₃(A=K, Rb; M=Zn, Cd, Ca):Ni²⁺和K₂ZnF₄:Ni²⁺体系中Ni²⁺的基态分裂和局域结构． 通过模拟光谱和电子顺磁共振(EPR)谱,结果显示在研究氟化物络合分子的能级精细结构和局域结构畸变时,配体F^-对体系的自旋轨道耦合机理的影响不可忽略,同时讨论了EPR参量随夹角、自选轨道耦合、平均参量以及偏离参量的变化规律.     

Antioxidant Activities of Some New Chromonyl-2,4-Thiazolidinediones and Chromonyl-2,4-Imidazolidinediones Having Chromone Cores

The antioxidant properties of 11 new synthesized chromonyl-2,4-thiazolidinediones and chromonyl-2,4-imidazolidinediones (CBs) were investigated. The antioxidant activities and mechanisms of the CBs interaction with reactive oxygen species (ROS) were clarified using various in vitro antioxidant assay methods including superoxide anion radical ( $ \mathrm{O}\overline{{}_2^{\bullet }} $ ), hydroxyl radical (HO^?), 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH^?) scavenging activity and the iron (II)-ferrozine complex formation. The potassium superoxide/18-crown-6 ether dissolved in dimethylsulfoxide (DMSO) was applied as a source of superoxide anion radical. Hydroxyl radicals were produced in the Fenton-like reaction Fe(II)+H₂O₂. Chemiluminescence, spectrophotometry, and electron paramagnetic resonance (EPR) spectroscopy using 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) as spin trap were applied as the measurement techniques. The CBs examined that exhibited good free radical scavenging activity also showed strong total antioxidant power capacity. Possible mechanisms of antioxidation are proposed to explain the differences in the experimental results between the chromone derivatives with imidazolidine-2,4-dione ring and those with thiazolidine-2,4-dione ring. In conclusion, some of the new CBs are promising to be applied as inhibitors of free radicals.     

Potential of electron paramagnetic resonance to study Einstein-Podolsky-Rosen-Bohm pairs

The potential of electron paramagnetic resonance (EPR) methods to study the correlation of the states of two noninteracting spins prepared in the singlet state (Einstein-Podolsky-Rosen-Bohm [EPRB] pairs) is discussed. EPR methods with a selective excitation of spins in the EPRB pairs allow one, in principle, to reveal this correlation of spin states if single-spin measurements are performed. However, it is illustrated that the conventional ensemble EPR experiments, when the average values of projections of the spin moments are observables, fail in studying the correlation of spins in EPRB pairs. An exploitation of the EPR phenomenon to study the correlation of spins for ensembles of EPRB pairs needs some modifications of the experimental approach: either the indirect detection of EPR signals (new observables) should be used or the EPRB pairs should be transferred to another state when the spin-spin interaction becomes essential, while EPR observables manifest the spin correlation in the precursor EPRB pair state. In this respect it appears that in spin chemistry many results were already obtained which demonstrate that it is a reality that two spins might occupy the “entangled” (correlated) state, when there is no interaction between them. The results obtained in spin chemistry confirm the quantum mechanical predictions for spin-correlated pairs of spins which can be considered as a realization of EPRB pairs.     

EPR and NMR study of molecular components mobility and organization in goat milk under ultrasound treatment

The effect of ultrasound treatment on molecular mobility and organization of the main components in raw goat milk was studied by EPR and NMR spectroscopies. NMR relaxation studies showed an increase in the spin–lattice T₁ and spin–spin T₂ relaxation times in goat milk products (cream, anhydrous fat) and change in the diffusion of proton-containing molecules during ultrasound treatment. The diffusion became more uniform and could be rather accurately approximated by one effective diffusion coefficient D_eff, which indicates homogenization of goat milk components, dispersion of globular and supermicellar formations under sonication. EPR studies have shown that molecular mobility and organization of hydrophobic regions in goat milk are similar to those observed in micellar formations of surfactants with a hydrocarbon chain length C12–C16. Ultrasound treatment did not affect submicellar and protein globule organization. Free radicals arising under ultrasound impact of milk reacted quickly with components of goat milk (triglycerides, proteins, fatty acids) and were not observed by spin trapping method.     

Probing How Counterion Structure and Dynamics Determine Polyelectrolyte Solutions Using EPR Spectroscopy

In this review article, we describe how methods of electron paramagnetic resonance (EPR) spectroscopy were used to investigate polyion–counterion interactions in polyelectrolyte solutions. This subject is usually treated experimentally by light, X-ray, or neutron scattering techniques. It is shown that a large arsenal of EPR spectroscopic methods–from various sophisticated methods of line shape analysis of continuous-wave EPR, via electron spin echo envelope modulation, nanoscale distance measurements through double electron–electron resonance to high-field pulse EPR–can be used to characterize the intrinsically complicated structures formed in polyelectrolyte solutions. We show that even polymer physical models such as scaling relations can be tested in this way. The distinguishing feature with respect to the numerous scattering studies in this area is that EPR techniques are local methods, and by employing spin-carrying (i.e., EPR-active) probe ions, it is possible to examine polyelectrolytes from the counterions’ point of view.     

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.     

Manifestations in the EPR spectrum shape of memory effects in the electron spin polarization in the case of two consecutive radical pairs

Electron paramagnetic resonance (EPR) spectra of two consecutive radical pairs (RPs) diffusing inside micelles are numerically calculated. Calculations are carried out for various values of the micelle radius, exchange integral, and mutual diffusion coefficient. In the simple case when the hyperfine interaction with magnetic nuclei can be neglected, it is demonstrated that the spin dynamics in the primary radical pair (RP1) manifests itself in the EPR spectrum of the secondary radical pair (RP2) in a characteristic way: the oddness of the EPR spectrum with respect to its center is violated, and the EPR line intensities and widths for the two partners in the RP2 differ. These features of the RP2 EPR spectrum shape are interpreted as follows: the spin dynamics in the RP1 produces a longitudinal spin polarization and a transverse spin polarization (i.e., spin coherence). Both polarizations are transferred from RP1 to RP2. This spin polarization transfer causes the above features of the RP2 EPR spectrum shape. It is shown that the RP2 EPR spectrum in a sequence of RPs cannot be simulated as a spectrum of a single RP. The features of the RP2 EPR spectrum shape may be, in principle, exploited to reveal the existence of the short-lived RP1.     

A novel approach to the simulation of nitroxide spin label EPR spectra from a single truncated dynamical trajectory

A simple effective method for calculation of EPR spectra from a single truncated dynamical trajectory of spin probe orientations is reported. It is shown that an accurate simulation can be achieved from the small initial fraction of a dynamical trajectory until the point when the autocorrelation function of re-orientational motion of spin label has relaxed. This substantially reduces the amount of time for spectra simulation compared to previous approaches, which require multiple full length trajectories (normally of several microseconds) to achieve the desired resolution of EPR spectra. Our method is applicable to trajectories generated from both Brownian dynamics and molecular dynamics (MD) calculations. Simulations of EPR spectra from Brownian dynamical trajectories under a variety of motional conditions including bi-modal dynamics with different hopping rates between the modes are compared to those performed by conventional method. Since the relatively short timescales of spin label motions are realistically accessible by modern MD computational methods, our approach, for the first time, opens the prospect of the simulation of EPR spectra entirely from MD trajectories of real proteins structures.     

Current status of the proposals for unification of notations and guidelines for data presentation in the EMR Area: Blueprint for future actions

The tremendous development of the electron magnetic resonance (EMR), i.e., electron paramagnetic resonance (EPR), electron spin resonance (ESR), and related spectroscopic techniques, and their applications in a number of fields is accompanied by a rather messy situation in the underlying theoretical framework. This is especially true concerning the EPR of transition ions in crystals, where an abundance of notations and lack of widely accepted clear definitions of the basic theoretical concepts characterize the current situation. As a consequence, proliferation of a number of terminological misconceptions and incorrect relations for the zero-field splitting parameters has taken place. Major problems detrimental for the future of EMR as well as the efforts aimed at alleviating these problems are reviewed. Rationales for coordinated activities in three major directions are outlined. This includes unification of spin Hamiltonian notations, unification of EMR nomenclature, and making better use of the various categories of data generated during EMR studies.     

Importance of volume limitation for tissue redox status measurements using nitroxyl contrast agents: a comparison of X-band EPR bile flow monitoring (BFM) method and 300 MHz in vivo EPR measurement

Methods proposed for in vivo redox status estimation, X-band (9.4 GHz) electron paramagnetic resonance (EPR) bile flow monitoring (BFM) and 300 MHz in vivo EPR measurement, were compared. The spin probe 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl-PROXYL) was utilized for both methods, due to its suitable lipophilicity. EPR signal decay of a nitroxyl spin probe in the bile flow and in the liver region (upper abdomen) of several rat groups with different selenium status were measured by both the BFM and the in vivo EPR method, respectively. The nitroxyl radical clearance measured with in vivo EPR method may be affected not only by the redox status in the liver but also by information from other tissues in the measured region of the rat. On the other hand, the time course of nitroxyl radical level in the bile flow of rats was found to be a reliable index of redox status. Measurement site and/or volume limitation, which was achieved by the BFM method in this paper, is quite important in estimating reasonable EPR signal decay information as an index of tissue/organ redox status.