弱场搜寻态分子静电导引的理论与实验研究

我们知道当极性冷分子与非均匀静电场的相互作用势大于零时，弱场搜寻态分子将被排斥到低电场区域，从而实现冷分子的静电导引。本文提出了一种采用平行载荷导线和接地平板来实现冷分子静电导引的新方案，并详细计算了平行载荷导线在空间产生的静电场分布及其与载荷导线参数的关系，发现在电场阱中心附近的电场梯度越大，相应的Stark势能越大，分子感受到的偶极梯度力也越大。实验结果表明，这种方案可以实现弱场搜寻态溴甲烷超声分子束平动温度为几K的静电导引，通过改变导线和平板的空间位置及其电压，可以获得较高的导引效率。研究表明该方案不仅可用于弱场搜寻态冷分子的静电导引，     

静电六极装置电场分布的数值计算方法及在N2O分子转动态选择、取向中的应用

阐述求解极性分子转动态选择及取向静电六极装置中势能分布、电场分布的数值计算方法.为了获得电场分布公式,需通过数值迭代求解势能满足的Laplace方程,获取数值分布点,通过数值分布点,由待定系数的多级展开势能解析表达式进行最小二乘拟合获得势能分布公式,由势能对空间向量的微分获得电场分布.分子在六极电场中的运行轨迹采用经典Newton方程描述,并通过四阶龙格-库塔方法(Four Order Runge-Kutta Method)实现数值求解,其中能量处理采用量子力学方法.应用此方法给出静电六极装置的电场分布公式,运用获得的电场分布公式计算和讨论电场对极性分子N₂O的静电六极转动态选择、取向所带来的影响.     

一种光学通道开放且适合构建晶格的静电阱

提出了一种用三个带电球电极形成一个光学通道开放、针对弱场搜寻态冷极性分子的静电囚禁方案。给出了方案图,用镜像法推导了空间电场分布的解析解,并利用有限元软件得到了电场分布的数值解。采用经典蒙特卡罗法模拟了冷极性分子被装载和囚禁于静电阱的动力学过程。研究了入射分子束速度和装载时刻对装载效率的影响,给出了被囚禁的冷分子的温度。讨论了所提方案在芯片表面囚禁,尤其是在静电晶格方面的潜在应用。结果表明,装载效率可以达到47.4%,阱中冷分子的温度为25.4mK。     

外电场作用下苯乙烯分子结构和电子光谱

采用密度泛函B3P86方法在6-311G基组水平上优化得到了在不同外电场(0—0.05a.u.)作用下,苯乙烯分子的基态电子状态、几何结构、电偶极矩和分子总能量.在优化构型下利用杂化CIS-DFT方法(CIS-B3P86)研究了同样外电场条件下对苯乙烯的激发能和振子强度的影响.计算结果表明,分子几何构型与电场大小呈现强烈的依赖关系,分子偶极矩随电场的增加而增大.分子总能量随着电场增加而降低.激发能随电场增加快速减小,表明在电场作用下,分子易于激发和解离. 关键词： 苯乙烯 电场 激发态 杂化CIS-DFT     

外电场作用下乙酸乙烯酯的分子结构和激发态

采用密度泛函B3LYP方法在6-31G(d)基组水平上,计算了乙酸乙烯酯分子在不同外电场(0.000 a.u.~0.030 a.u.)作用下的基态几何结构、电偶极距、电荷分布及分子总能量,然后利用杂化CIS-DFT方法在相同基组下研究了外电场对乙酸乙烯酯分子前8个激发态的激发能、波长和振子强度的影响.结果表明,分子的几何结构、电荷分布与外电场的大小呈现强烈的依赖关系.随着外电场的不断增加,分子的总能量逐渐减小,偶极距逐渐增大,激发能随电场的增加总体上呈减小的趋势,表明在外电场作用下,乙酸乙烯酯分子易于激发,激发态波长随电场的增加总体上呈增大的趋势,且电子跃迁光谱都集中在紫外区.     

电场作用对4,4’-二吡啶杂环分子电输运特性影响的研究

用从头算理论和弹性散射格利用林函数的方法,计算了电场作用下的4,4’-二吡啶杂环分子体系的电子结构及其电导和电流.计算结果表明,电场作用使得体系在分子和电极间存在电荷转移和重新分布的过程,使分子与电极接触面附近出现电子积聚区和电子耗散区,从而产生附加电偶极子,对分子的电导和电流产生抑制的影响.此外,在分子轨道能级和分子与电极的耦合系数上,电场的影响也比较明显,从而导致了分子的伏-安特性在考虑电场作用前后有较大的差异.考虑电场作用后的伏-安非线性特征与实验结果符合较好.     

强外电场作用下BF分子结构和激发特性

采用密度泛函(DFT)方法LSDA在6-311++G(d,p)基组水平上优化得到了分子轴方向不同电场(-0.03～0.05a.u.)作用下,BF分子的基态结构参数、电偶极矩μ、电荷分布、HOMO能级、LUMO能级等。在优化构型下,用同样的基组采用杂化CIS-DFT方法(CIS-LSDA)研究了同样外电场条件下对BF分子的激发能和振子强度的影响。结果表明:随着电场的增加,分子结构与外电场有着强烈的依赖关系,且对电场方向的依赖呈现非对称性。分子总能量先增大后减小,电偶极矩μ先增大,后减小,最后不断增大。电场对振子强度的影响比较复杂,有的增大有的减小,表明电子跃迁光谱强度受外场影响。     

拉曼光谱法研究不同环境温度下脉冲电场对胰岛素二级结构影响及理论模型分析

近年来,弱电磁辐射生物效应已受到人们的普遍关注.前期研究发现脉冲电场与环境温度对胰岛素分子的构象产生协同效应.因此,文章首先应用拉曼光谱法研究了不同环境温度下脉冲电场对胰岛素分子二级结构的影响,得到胰岛素分子α螺旋结构含量的变化;并运用蛋白质螺旋-线团结构转变模型对实验结果进行定量分析,得到的理论模型可以较好地刻画不同环境温度下,脉冲电场对胰岛素分子α螺旋结构含量的影响.脉冲电场的作用及热力学环境的改变,使蛋白质螺旋结构向无规线团结构发生转变,可以解释脉冲电场作用下,胰岛素分子α螺旋结构含量随环境温度升高而下降的原因.研究结果为进一步研究弱电磁辐射对生物大分子二级结构的非热效应机理提供了一定的实验依据及理论参考.     

外电场作用下N2O分子的结构与光谱特性

采用密度泛函B3LYP方法,在6-311+g(d)基组水平上研究了不同外电场对直线型分子N₂O的基态结构、偶极矩、轨道能级、红外和拉曼光谱特性的影响,并采用杂化CIS方法研究了N₂O分子在外电场作用下前9个激发态的激发特性.结果表明:外电场导致分子键长变化,但并没有改变分子的直线特征,偶极矩和分子总能量随外电场的增加先减小后增大,而能隙随外电场的增加先增大后减小,外电场的增加使LUMO(lowest unoccupied molecular orbital)组成由π~*轨道变为σ~*轨道,外电场使红外光谱发生移动,峰的强度增强或减弱.外电场的增加显著影响了N₂O分子的激发特性.激发能、激发波长受外电场影响发生了变化,同时,振子强度受外电场影响明显,禁阻跃迁变为可允许的跃迁,允许的跃迁在电场作用下变为禁阻跃迁或者跃迁变弱.紫外光谱在电场的作用下吸收峰发生了明显的移动,而且有新的吸收峰产生.     

几种硝基苯类炸药在外电场作用下的分子特性

采用密度泛函理论中的B3LYP方法,在6-31G*水平上研究了外电场对一些硝基苯类炸药分子的总能量、偶极矩、分子轨道能级和前线轨道能量差等分子特性的影响;考察了在外电场作用下分子前线轨道能量差与炸药的电火花感度之间的关系.结果表明,在外电场作用下分子总能量降低,偶极矩增大、前线轨道能量差减小;分子前线轨道能量差与炸药的电火花感度之间几乎线性相关,且外电场对这种线性相关性无明显影响.     

Bioelectrostatics: Review of widespread importance in biochemistry

The literature reveals an extensive involvement of electrostatics in biological systems. In our prior articles, supporting evidence was cited from sulfates, volatile anesthetics, electron transport in photosynthesis and molecular electrostatic potential studies with DNA. A recent review addresses the involvement of electrochemistry in cell signaling. According to the theoretical framework, electrostatics is believed to be importantly involved in phosphate action in receptors and cell signaling. The main focus is on energetics associated with bioelectrostatics. Examples include action of enzymes, such as, xylose isomerase, SOD and cytochrome c oxidase. In the membrane area, reports deal with the phospholipase-membrane and the nuclear membrane. Other categories are chromosomes, oxidation by hydroxyl radicals, receptors, Hofmeister effect, and histamine. In addition, electrostatic effects have been examined in the plant kingdom.     

Fluorescence Techniques for Determination of the Membrane Potentials in High Throughput Screening

The characterization of small molecules requires identification and evaluation of several predictive parameters, when selecting compounds for pharmacological applications and/or determining their toxicity. A number of them are correlated with the compound interaction with biological membranes and/or capacity to cross them. The knowledge of the extent of adsorption, partition coefficient and permeability along with the compound ability to alter membrane properties are critical for such studies. Lipid bilayers are frequently used as the adequate experimental models of a biological membrane despite their simple structure and a limited number of components. A significant number of the biologically relevant lipid bilayer properties are related to its electrostatics. Three electrostatic potentials were defined for the lipid bilayer; the intrinsic or induced surface electrostatic potential, the dipole potential and the membrane potential. Each of them was measured with dedicated methodologies. The complex measurement protocols and technically demanding instrumentation made the development of efficient HTS approaches for complete characterization of membrane electrostatics practically impossible. However, the rapid development of fluorescence techniques accompanied by rapid growth in diversity and number of dedicated fluorescent probes enabled characterization of lipid bilayer electrostatics in a moderately simple manner. Technically advanced, compact and automated workstations, capable of measuring practically all fluorescence parameters, are now available. Therefore, the proper selection of fluorescent probes with measuring procedures can be designed to evaluate drug candidates in context of their ability to alter membrane electrostatics. In the paper we present a critical review of available fluorescence methods, useful for the membrane electrostatics evaluation and discuss the feasibility of their adaptation to HTS procedures. The significance of the presented methodology is even greater considering the rapid growth of advanced drug formulations, where electrostatics is an important parameter for production processes and pharmacokinetics of the product. Finally, the potential of the membrane electrostatics to emerge as a viable pharmacological target is indicated and fluorescence techniques capable to evaluate this potential are presented.     

Accurate treatments of electrostatics for computer simulations of biological systems: A brief survey of developments and existing problems

Modern computer simulations of biological systems often involve an explicit treatment of the complex interactions among a large number of molecules. While it is straightforward to compute the short-ranged Van der Waals interaction in classical molecular dynamics simulations, it has been a long-lasting issue to develop accurate methods for the longranged Coulomb interaction. In this short review, we discuss three types of methodologies for the accurate treatment of electrostatics in simulations of explicit molecules: truncation-type methods, Ewald-type methods, and mean-field-type methods. Throughout the discussion, we brief the formulations and developments of these methods, emphasize the intrinsic connections among the three types of methods, and focus on the existing problems which are often associated with the boundary conditions of electrostatics. This brief survey is summarized with a short perspective on future trends along the method developments and applications in the field of biological simulations.     

平面静电场拉普拉斯方程的简捷解及其应用

介绍用复杂函数法求解平面静电场的一种简捷方式的几个简单且实用的例子。     

Note on the History of Contact Mechanics and Friction: Interplay of Electrostatics,Theory of Gravitation and Elasticity from Coulomb to Johnson-Kendall-Roberts Theory of Adhesion

Great discoveries are often perceived by subsequent generations as sudden insights of genius scientists. Historical studies show, however, that the real mechanism of creation of new theories and paradigms is often a transfer of knowledge from one subject area to the other. Such transfers made the military engineer Coulomb the founder of the theory of electricity, they made the professor for celestial mechanics Poisson the founder of the electrostatics, and the pioneer in electrodynamics Hertz also became the founder of contact mechanics. Transfer of knowledge can be traced as a very effective way of development of science in many other cases. It often leads to breakthrough and rapid development of the whole branches of science. In the present paper we trace such transfers of knowledge in the history of elasticity and contact mechanics on one side and electrostatics on the other side. The participants of this historical process are Coulomb, Poisson, Hertz, Inglis, Griffith and finally the authors of the theory of adhesive contacts Johnson, Kendall and Roberts. Interestingly, the same principle of "exaptation" (use of a property for a function for which it was not originally created) is currently accepted theory of how major innovations happen also in biological evolution.     

Mathematical simulation of complex formation of protein molecules allowing for their domain structure

A physical model of the interactions between protein molecules has been presented and an analysis of their propensity to form complex biological complexes has been performed. The reactivities of proteins have been studied using electrostatics methods based on the example of the histone chaperone Nap1 and histones H2A and H2B. The capability of proteins to form stable biological complexes that allow for different segments of amino acid sequences has been analyzed. The ability of protein molecules to form compounds has been considered by calculating matrices of electrostatic potential energy of amino acid residues constituting the polypeptide chain. The method of block matrices has been used in the analysis of the ability of protein molecules to form complex biological compounds.     

核磁共振技术在生物组织中的应用

在生物组织内部存在大量的生化、生理反应以及分子的扩散运动,它们相互独立, 又相互关联,共同构成一个生化反应网络. 在病理条件下,某些生化反应过程会发生改变,代谢中间体可能会出现质和量的变化. 核磁共振 (NMR)可以对这些过程的研究提供非常有用的信息. 目前,有3种核磁共振波谱技术可以用于生物组织的研究：① 活体组织定域波谱技术;② 生物组织提取物的液体高分辨核磁共振技术;③ 离体组织的高分辨魔角旋转技术. 这些方法各有优劣,互为补充. 介绍了在生物组织的NMR研究方面的最新进展.     

Electrostatic charging of single granules by repeated sliding along inclined metal plates

In this work, repeated sliding tests for single granules were investigated for their electrostatics generation. Several factors were considered including granule length-ratio, sliding face shape, sliding times, sliding area, sliding velocity, front-facing edge, plate inclined angle and humidity. Generally, it is found that electrostatics increases with granule length-ratio. Two kinds of granular sliding face shapes were used in this work, half circle and rectangle. Under the same working conditions, a granule with the sliding face shape of half-circle tends to produce more electrostatics than that of rectangle. In addition, the efficiency of granule charge generation increases with sliding times although the amount of impact charge is decreased by the initial charge. Electrostatics increases with sliding area, which is independent of granule sliding-face shape and sliding times. Electrostatics also increases with granule sliding velocity. Front-facing sliding with a short edge tends to generate more electrostatics than that with a long edge. In this work, three sliding-plate angles were chosen as 30°,54°,70°, where granules sliding along the inclined plate at 54° acquired the highest electrostatics in comparison with other two angles. Humidity has significant effect on electrostatics as that electrostatics decreases with humidity. At lower relative humidity, the granule length-ratio is found to have more effect on electrostatics.     

Mathematical modeling the formation of a histone octamer

A physical model of the interaction of protein molecules and their ability to form complex biological systems for the in vitro case in a solution of monovalent salt has been developed. Their reactive abilities using the methods of electrostatics based on the example of the step-by-step formation of the histone octamer from the H2A, H2B, H3, and H4 proteins have been studied. To analyze the ability of protein molecules to form compounds the matrix of potential energy of interactions between protein molecules in solutions with different concentrations of monovalent salt has been examined.     

Interleukin-3 prevents neuronal death induced by amyloid peptide

Background  

Interleukin-3 (IL-3) is an important glycoprotein involved in regulating biological responses such as cell proliferation, survival and differentiation. Its effects are mediated via interaction with cell surface receptors. Several studies have demonstrated the expression of IL-3 in neurons and astrocytes of the hippocampus and cortices in normal mouse brain, suggesting a physiological role of IL-3 in the central nervous system. Although there is evidence indicating that IL-3 is expressed in some neuronal populations, its physiological role in these cells is poorly known.