劳伦斯伯克利国家实验室的先进光源，进行了实验在化学动力学光束线和科学办公室基础能源科学办公室，美国能源部根据合同号DE-AC02-05CH11231支持，通过化学科学部。

1。样品装载<ol><li>删除后法兰，拆卸3/8"的不锈钢喷嘴管从设备（参见图1和图2），并确保它是干净和100毫米的孔是明确的（这可以通过寻找光源，通过它）。〜1毫升乙醇清洗，填充管，用棉花提示擦洗内。另外，在超声波浴中充满了肥皂和水或乙醇约20分钟，然后将喷嘴干燥的压缩空气。 </li><li>使用一个小的，干净的抹刀，地点约250mg样品在所述喷嘴的前部，靠近该孔，但不阻止它。避免孔被阻塞的一个好方法是将一个小球铝箔或玻璃纤维在前面的小孔，然后加入样品粉末。采用棉花前端推到管中的样品，以确保它是在前面的25毫米的管。这将包括前部的加热区。 </li><li>重新装上喷嘴仔细的装置里面，以避免移动样品粉末。然后附上鸟笼适配器（参见图2），加热块和热电偶（参见图3）。 </li><li>关闭真空室之前，测量从凸缘表面的距离为22.5英寸的喷嘴的前端，这将允许0.5英寸之间的喷嘴和锥孔。 </li><li>当真空室是封闭的，测试的加热器筒和热电偶连接，以确保它们连接到馈通连接器。 </li><li>确保载气入口阀被关闭。 </li><li>关闭排气阀（如果使用）。 </li><li>慢慢开始泵送使用粗加工泵（4阀）的腔室，腔室中的压力时，&lt;1乇，从涡轮分子泵（5台泵）。 </li><li>当腔室中的压力是10 -6乇时，应用的电压的离子光学飞行质谱仪，和微通道板检测器（后者上的电压逐渐应当接通）（参见图1，用于各种电压）的时间。 </li><li>打开的VUV快门，以便在腔室的光子束。 </li><li>打开的载体气体入口阀和背压调节器设置到第460（这是一个真空调节器，因此，当设置到第460行中的压力将调节至300乇，测量在负的范围从0到-760乇） 。 </li><li>在这些条件下的源和质谱仪室的中的压力应为〜1×10 -6乇〜1×10 -6乇，分别。 </li></ol> 2。收购的质谱<ol><li>百兆网卡（型号为P7889，100 PS / BIN）软件在电脑上，让它在后台运行。 </li><li>打开Labview数据采集程序:"一般Interface.vi"（ 图4）。 </li></ol><html> （*此软件和其它的LabVIEW代码在光束线和相应的作者没有成本提供给大家分享） <ol start="3"><li>在LabVIEW软件使用ALS控制"选项卡 ，设置到所需波长的光子能量。 </li><li>在定标器"选项卡上，设置的时间单位数一起被离散化 （一般为32），的范围内 （箱数）和扫描 （质谱数由彼此的顶部上，以形成最终的质谱），然后单击" 接受"，因此，这些值将被存储和使用。 </li><li>接下来，单击"开始数据采集得到的数据 。当收购结束后，质谱会出现在屏幕上。 </li><li>通过点击" 保存 "按钮，保存的质谱。 （在100 ps的单位所获得的频谱的X轴对应于离子的飞行时间） </li></ol>TLE"&gt; 3。收购的光电离效率曲线（PIE） <ol><li>在LabVIEW软件使用"ALS扫描 "选项卡（ 图5），它是有可能获得数据而调整光束线电机。在这种情况下，选择电机的" 单声道T3能源"的调整在不同的光子能量（波荡器内的同步会自动移动到所需的波长相匹配）。光子的能量设置为所需的值（单位:eV）。 </li><li>输入启动和停止的能量（EV）以及步长。 </li><li>不要输入扫描次数 - 这将是自动更新您输入的值在步骤2.4。 </li><li>单击" 阅读，从K486读通过光电二极管的光电流测量。 </li><li>接下来，单击" 开始 "开始扫描。系统将提示您选择一个文件名的数据将被存储在运行结束。 </li><li>第一列中的数据文件都TAIN的bin的数量（豳＃）和需要转换为质量单位13。典型值是:质量= 0.6 + 1xE-3（豳＃）+ 5xE-7（豳＃）^ 2（更精确的质量校准可以通过使用一个已知的混合气体或室内空气即主要是O 2，N 2和H 2 O的混合物，并符合他们的到来，二次多项式） </li><li>保存数据文件转换成质量与第一列。 </li><li>要绘制PIE曲线，一个简单的方法是使用第二个称为的的"ALS能源scan.vi"，其目的是分析扫描数据，并生成PIE的Labview程序。 </li></ol> 4。绘制一个光电离效率曲线（PIE） <ol><li>正如上面的分析可以完成使用"ALS能源scan.vi"程序（参见图6），然而，我们也将在这里描述到的数据进行分析，而它所需的步骤。 </li><li>在启动程序时，系统会提示您选择的文件containin的克的数据。这是文件保存在步骤3.7，并包含在不同的光子能量在下一列中的第一列和离子计数的群众。请注意，在该文件中的第一行和第二行表示光子能量和该列中的数据的光电流，分别。 </li><li>顶部面板中的存在是一个二维的数据曲线;移动红色水平标记选择一个在一个特定的被显示在下部面板的光子能量的质谱。 </li><li>接下来的步骤是集成的特定质量的离子计数中减去背景信号，同时，在每个光子能量。应设置在下部面板的两个垂直的红色标记以集成的质量峰的周围而没有数据可以作为背景值附近的一个区域与周围的两个蓝色标记。该软件将出现在右边的面板中减去背景的综合数据。 </li><li>介绍一个真实的PIE曲线必须纠正的离子数，以不同的光子通量一个吨的每一步。这是自动完成由软件实现。如果您选择跳过此更正，请单击"关闭" 电流校正"按钮的右侧面板的顶部。如果您选择手动做到这一步，每个光子的能量的光电二极管的量子效率，必须考虑到（从光电二极管制造商，并通过相应的作者），见式（1）。否则，这是所有自动完成的软件。 </li></ol><img alt="式（1）" fo:src="/files/ftp_upload/50164/50164eq1highres.jpg" src="/files/ftp_upload/50164/50164eq1.jpg" /><ol start="6"><li>在右下角点击保存频谱保存校正后的PIE曲线。 </li></ol>

<ol>
	<li>Golan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ionization+of+dimethyluracil+dimers+leads+to+facile+proton+transfer+in+the+absence+of+hydrogen+bonds.">Ionization of dimethyluracil dimers leads to facile proton transfer in the absence of hydrogen bonds.</a> Nat. 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在超音速喷流产生的分子束的膨胀所产生的单体和二聚体。的DNA碱基的少量样品被放置在一个热蒸发源和加热以产生足够的蒸气压。氩气进行蒸气通过100微米口，通过2毫米的分离器，产生冷分子束14。可替换地，一个热情洋溢束源可以使用，其中样本被放置在与质谱仪的推斥极板（离子光学元件）连接到加热的烘箱。 我们使用真空紫外灯（7.4-25 eV）的，轻轻电离分子...

<table border="1"&gt;<tr&gt;<td<strong&gt;试剂/材料的名称</strong</td&gt;<td<strong&gt;公司</strong</td&gt;<td<strong&gt;产品目录号</strong</td&gt;<td<strong&gt;评论</strong</td&gt;</tr&gt;<tr&gt;<td&gt;尿嘧啶</td&gt;<td&gt; SIGMA</td&gt;<td&gt; U0750</td&gt;<td</td&gt;</tr&gt;<tr&gt;<td&gt; 1,3 - 二甲基脲嘧啶</td&gt;<td&gt;爱秩序</td&gt;<td&gt; 349801</td&gt;<td</td&gt;</tr&gt;</table

molecular beam mass spectrometry with tunable vacuum ultraviolet (vuv) synchrotron radiation

可调的软电离质谱耦合是一个功能强大的方法来研究孤立的分子复合物和集群及其光谱学和动力学1-4。生物分子的光电离过程的基础研究提供这些系统的电子结构有关的信息。此外，电离能和其他的生物分子在气相中的测定是不平凡的，这些实验提供了一个平台，产生这些数据。我们已经开发出一种汽化热技术加上超音速分子束，它提供一种温和的方式输送到气相中的这些物种。明智地的源气体和温度的组合允许用于形成二聚体和较高的DNA碱基簇。这个特定的工作的重点是， 即非共价相互作用，氢键，堆叠，和静电相互作用的影响，上的电离能和个体的生物分子，它们的配合，在微水1，5-9水化的质子转移。 我们已经进行了理论和实验的可视化特性的光电离动力学的气相尿嘧啶和1,3 -二甲基脲嘧啶二聚体，再加上分子束同步辐射化学动态学光束线的先进光源位于10和实验细节这里。这让我们观察1,3 -二甲基脲嘧啶二聚体内的质子传递，系统与π堆叠的几何形状和没有氢键1。分子束提供了一个非常方便和有效的方式来隔离环境扰动的回报可以准确的比较与电子结构计算，11，12样品的兴趣。通过调节光子的能量同步辐射光电离效率（PIE）曲线可以绘制告诉我们的阳离子电子态。然后这些值可以进行比较的理论模型和计算方法，反过来，详细解释了调查的种类1，3，电子结构和动力学。

图7示出了典型的质谱超音速膨胀的（A）的1,3 -二甲基尿嘧啶蒸气和PIE曲线的三个主要功能（在m / z 140的单体，在M / Z = 141的质子化的单体，和1的在M / Z 280）-1,3 - 二甲基脲嘧啶二聚体之间的真空紫外扫描摘录自8 eV和10 EV（B）。连续三次扫描，灰色的阴影是标准差。 <img alt="图1" fo:content-width="5in" fo:src="/files/ftp_upload/50164/50164fig1highres.jpg"...

Watch this Scientific Journal Video about Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation at JoVE.com

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

加上可调谐的真空紫外同步辐射光电离质谱计在分子束提供了一个方便的工具来探索孤立的气相分子和簇的电子结构。 DNA碱基二聚体的质子转移机制，用这种方法鉴定。

可调式真空紫外（VUV）同步辐射分子束质谱分析

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy ...

molecular-beam-mass-spectrometry-with-tunable-vacuum-ultraviolet-vuv

Research

JoVE Journal

Engineering

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation

12.9K 次观看.  Lawrence Berkeley National Laboratory. 加上可调谐的真空紫外同步辐射光电离质谱计在分子束提供了一个方便的工具来探索孤立的气相分子和簇的电子结构。 DNA碱基二聚体的质子转移机制，用这种方法鉴定。

视频: Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (&omega;) and momentum (k) and the probability to find them in a particular state with given &omega; and k is described by the spectral function A(k, &omega;). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample.
In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He3 cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be determined with an unprecedented clarity.

The overall goal of this method is to determine the low-energy electronic structure of solids at ultra-low temperatures using Angle-Resolved Photoemission Spectroscopy with synchrotron radiation.

在极低的温度下角分辨光电子能谱

The physical properties of a material are defined by its  electronic structure. Electrons in solids are characterized by energy (&omega;)  and momentum ...

科研

工程学

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

分子构象器和星团的空间分离

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Analysis of Volatile and Oxidation Sensitive Compounds Using a Cold Inlet System and Electron Impact Mass Spectrometry

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The analysis of volatile and oxidation sensitive compounds by mass spectrometry is not easily achieved, as all state-of-the-art mass spectrometric methods require at least one sample preparation step, e.g., dissolution and dilution of the analyte (electrospray ionization), co-crystallization of the analyte with a matrix compound (matrix-assisted laser desorption/ionization), or transfer of the prepared samples into the ionization source of the mass spectrometer, to be conducted under atmospheric conditions. Here, the use of a sample inlet system is described which enables the analysis of volatile metal organyls, silanes, and phosphanes using a sector field mass spectrometer equipped with an electron impact ionization source. All sample preparation steps and the sample introduction into the ion source of the mass spectrometer take place either under air-free conditions or under vacuum, enabling the analysis of compounds highly susceptible to oxidation. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes, which have to be handled using inert conditions, such as the Schlenk technique. The principle of operation is presented in this video.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes which have to be handled using inert conditions, such as the Schlenk technique.

挥发和氧化敏感的化合物使用冷进气系统和电子轰击质谱分析

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The ...

化学

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the wavelength of the strong-field ionizing pump pulse from the commonly used 800 nm into the near-infrared (1200-1600 nm), the contribution of adiabatic electron tunneling to the ionization process increases relative to multiphoton absorption. Adiabatic ionization results in predominant population of the ground electronic state of the ion upon electron removal, which effectively prepares a coherent vibrational state (&#34;wave packet&#34;) amenable to subsequent excitation. In our experiments, the coherent vibrational dynamics are probed with a weak-field 800 nm pulse and the time-dependent yields of dissociation products measured in a time-of-flight mass spectrometer. We present the measurements on the molecule dimethyl methylphosphonate (DMMP) to illustrate how using 1500 nm pulses for excitation enhances the amplitude of coherent oscillations in ion yields by a factor of 10 as compared to 800 nm pulses. This protocol may be implemented in existing pump-probe setups through the incorporation of an optical parametric amplifier (OPA) for wavelength conversion.

We present a protocol for probing ultrafast vibrational coherences in polyatomic radical cations that result in molecular dissociation.

强场绝热电离多原子自由基阳离子超快振动相干的测量

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the ...

Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves several steps, include drawing samples, cooling, cutting, transport to the laboratory, and analysis. The whole analysis process requires more than 30 minutes, which hinders on-line process control. Laser-induced breakdown spectroscopy is an excellent on-line analysis method that can satisfy the requirements of vacuum induction melting because it is fast and noncontact and does not require sample preparation. The experimental facility uses a lamp-pumped Q-switched laser to ablate melted liquid steel with an output energy of 80 mJ, a frequency of 5 Hz, a FWHM pulse width of 20 ns, and a working wavelength of 1,064 nm. A multi-channel linear charge coupled device (CCD) spectrometer is used to measure the emission spectrum in real time, with a spectral range from 190 to 600 nm and a resolution of 0.06 nm at a wavelength of 200 nm. The protocol includes several steps: standard alloy sample preparation and an ingredient test, smelting of standard samples and determination of the laser breakdown spectrum, and construction of the elements concentration quantitative analysis curve of each element. To realize the concentration analysis of unknown samples, the spectrum of a sample also needs to be measured and disposed with the same process. The composition of all main elements in the melted alloy can be quantitatively analyzed with an internal standard method. The calibration curve shows that the limit of detection of most metal elements ranges from 20-250 ppm. The concentration of elements, such as Ti, Mo, Nb, V, and Cu, can be lower than 100 ppm, and the concentrations of Cr, Al, Co, Fe, Mn, C, and Si range from 100-200 ppm. The R2 of some calibration curves can exceed 0.94.

During vacuum induction melting, laser-induced breakdown spectroscopy is used to perform real-time quantitative analysis of the main-ingredient elements of a molten alloy.

激光击穿光谱对真空感应熔融的定量分析

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves ...

Sample Preparation and Transfer Protocol for In-Vacuum Long-Wavelength Crystallography on Beamline I23 at Diamond Light Source

Long-wavelength macromolecular crystallography (MX) exploits the anomalous scattering properties of elements, such as sulfur, phosphorus, potassium, chlorine, or calcium, that are often natively present in macromolecules. This enables the direct structure solution of proteins and nucleic acids via experimental phasing without the need of additional labelling. To eliminate the significant air absorption of X-rays in this wavelength regime, these experiments are performed in a vacuum environment. Beamline I23 at Diamond Light Source, UK, is the first synchrotron instrument of its kind, designed and optimized for MX experiments in the long wavelength range towards 5 &#197;. 
To make this possible, a large vacuum vessel encloses all endstation components of the sample environment. The necessity to maintain samples at cryogenic temperatures during storage and data collection in vacuum requires the use of thermally conductive sample holders. This facilitates efficient heat removal to ensure sample cooling to approximately 50 K. The current protocol describes the procedures used for sample preparation and transfer of samples into vacuum on beamline I23. Ensuring uniformity in practices and methods already established within the macromolecular crystallography community, sample cooling to liquid nitrogen temperature can be performed in any laboratory setting equipped with standard MX tools. 
Cryogenic storage and transport of samples only require standard commercially available equipment. Specialized equipment is required for the transfer of cryogenically cooled crystals from liquid nitrogen into the vacuum endstation. Bespoke sample handling tools and a dedicated Cryogenic Transfer System (CTS) have been developed in house. Diffraction data collected on samples prepared using this protocol show excellent merging statistics, indicating that the quality of samples is unaltered during the procedure. This opens unique opportunities for in-vacuum MX in a wavelength range beyond standard synchrotron beamlines.

Here, we present a protocol for cryogenic sample preparation and transfer of crystals into the vacuum endstation on beamline I23 at Diamond Light Source, for long-wavelength macromolecular X-ray crystallography experiments.

金刚石光源下光束线I23真空长波长晶体学的样品制备和转移实验方案

Long-wavelength macromolecular crystallography (MX) exploits the anomalous scattering properties of elements, such as sulfur, phosphorus, potassium, ...

生物化学

Whole-body Mass Spectrometry Imaging by Infrared Matrix-assisted Laser Desorption Electrospray Ionization (IR-MALDESI)

Ambient ionization sources for mass spectrometry (MS) have been the subject of much interest in the past decade. Matrix-assisted laser desorption electrospray ionization (MALDESI) is an example of such methods, where features of matrix-assisted laser desorption/ionization (MALDI) (e.g., pulsed nature of desorption) and electrospray ionization (ESI) (e.g., soft-ionization) are combined. One of the major advantages of MALDESI is its inherent versatility. In MALDESI experiments, an ultraviolet (UV) or infrared (IR) laser can be used to resonantly excite an endogenous or exogenous matrix. The choice of matrix is not analyte dependent, and depends solely on the laser wavelength used for excitation. In IR-MALDESI experiments, a thin layer of ice is deposited on the sample surface as an energy-absorbing matrix. The IR-MALDESI source geometry has been optimized using statistical design of experiments (DOE) for analysis of liquid samples as well as biological tissue specimens. Furthermore, a robust IR-MALDESI imaging source has been developed, where a tunable mid-IR laser is synchronized with a computer controlled XY translational stage and a high resolving power mass spectrometer. A custom graphical user interface (GUI) allows user selection of the repetition rate of the laser, number of shots per voxel, step-size of the sample stage, and the delay between the desorption and scan events for the source. IR-MALDESI has been used in variety of applications such as forensic analysis of fibers and dyes and MSI of biological tissue sections. Distribution of different analytes ranging from endogenous metabolites to exogenous xenobiotics within tissue sections can be measured and quantified using this technique. The protocol presented in this manuscript describes major steps necessary for IR-MALDESI MSI of whole-body tissue sections.

Whole-body Mass Spectrometry Imaging by Infrared Matrix-assisted Laser Desorption Electrospray Ionization IR-MALDESI

A mass spectrometry imaging (MSI) source operated at atmospheric pressure was developed by coupling mid-infrared laser desorption and electrospray post-ionization. Exogenous ice matrix was used as the energy-absorbing matrix to facilitate resonant desorption of tissue-related material. This manuscript provides a step-by-step protocol for performing IR-MALDESI MSI of whole-body neonatal mouse.

全身质谱成像红外基质辅助激光解吸电喷雾电离（IR-MALDESI）

Ambient ionization sources for mass spectrometry (MS) have been the subject of much interest in the past decade. Matrix-assisted laser desorption ...

生物工程

Analyzing Large Protein Complexes by Structural Mass Spectrometry

Living cells control and regulate their biological processes through the coordinated action of a large number of proteins that assemble themselves into an array of dynamic, multi-protein complexes1. To gain a mechanistic understanding of the various cellular processes, it is crucial to determine the structure of such protein complexes, and reveal how their structural organization dictates their function. Many aspects of multi-protein complexes are, however, difficult to characterize, due to their heterogeneous nature, asymmetric structure, and dynamics. Therefore, new approaches are required for the study of the tertiary levels of protein organization.
One of the emerging structural biology tools for analyzing macromolecular complexes is mass spectrometry (MS)2-5. This method yields information on the complex protein composition, subunit stoichiometry, and structural topology. The power of MS derives from its high sensitivity and, as a consequence, low sample requirement, which enables examination of protein complexes expressed at endogenous levels. Another advantage is the speed of analysis, which allows monitoring of reactions in real time. Moreover, the technique can simultaneously measure the characteristics of separate populations co-existing in a mixture. 
Here, we describe a detailed protocol for the application of structural MS to the analysis of large protein assemblies. The procedure begins with the preparation of gold-coated capillaries for nanoflow electrospray ionization (nESI). It then continues with sample preparation, emphasizing the buffer conditions which should be compatible with nESI on the one hand, and enable to maintain complexes intact on the other. We then explain, step-by-step, how to optimize the experimental conditions for high mass measurements and acquire MS and tandem MS spectra. Finally, we chart the data processing and analyses that follow. Rather than attempting to characterize every aspect of protein assemblies, this protocol introduces basic MS procedures, enabling the performance of MS and MS/MS experiments on non-covalent complexes. Overall, our goal is to provide researchers unacquainted with the field of structural MS, with knowledge of the principal experimental tools.

Mass spectrometry has proven to be a valuable tool for analyzing large protein complexes. This method enables insights into the composition, stoichiometry and overall architecture of multi-subunit assemblies. Here, we describe, step-by-step, how to perform a structural mass spectrometry analysis, and characterize macromolecular structures.

大蛋白复合物结构质谱分析

Living cells control and regulate their biological processes through the coordinated action of a large number of proteins that assemble themselves into an ...

生物学

Atmospheric-pressure Molecular Imaging of Biological Tissues and Biofilms by LAESI Mass Spectrometry

Ambient ionization methods in mass spectrometry allow analytical investigations to be performed directly on a tissue or biofilm under native-like experimental conditions. Laser ablation electrospray ionization (LAESI) is one such development and is particularly well-suited for the investigation of water-containing specimens. LAESI utilizes a mid-infrared laser beam (2.94 &mu;m wavelength) to excite the water molecules of the sample. When the ablation fluence threshold is exceeded, the sample material is expelled in the form of particulate matter and these projectiles travel to tens of millimeters above the sample surface. In LAESI, this ablation plume is intercepted by highly charged droplets to capture a fraction of the ejected sample material and convert its chemical constituents into gas-phase ions. A mass spectrometer equipped with an atmospheric-pressure ion source interface is employed to analyze and record the composition of the released ions originating from the probed area (pixel) of the sample. A systematic interrogation over an array of pixels opens a way for molecular imaging in the microprobe analysis mode. A unique aspect of LAESI mass spectrometric imaging is depth profiling that, in combination with lateral imaging, enables three-dimensional (3D) molecular imaging. With current lateral and depth resolutions of ~100 &mu;m and ~40 &mu;m, respectively, LAESI mass spectrometric imaging helps to explore the molecular structure of biological tissues. Herein, we review the major elements of a LAESI system and provide guidelines for a successful imaging experiment.

Laser ablation electrospray ionization (LAESI) is an atmospheric-pressure ion source for mass spectrometry. In the imaging mode, a mid-infrared laser probes the distributions of molecules across a tissue section or a biofilm. This technique presents a new approach for diverse bioanalytical studies carried out under native experimental conditions.

常压LAESI质谱生物组织和生物膜的分子成像

Ambient ionization methods in mass spectrometry allow analytical investigations to be performed directly on a tissue or biofilm under native-like ...

Introduction to Mass Spectrometry

Source: Laboratory of Dr. Khuloud Al-Jamal - King&#39;s College London

Mass spectrometry is an analytical chemistry technique that enables the identification of unknown compounds within a sample, the quantification of known materials, the determination of the structure, and chemical properties of different molecules.
A mass spectrometer is composed of an ionization source, an analyzer,&#160;and a detector. The process involves the ionization of chemical compounds to generate ions. When using inductively coupled plasma (ICP), samples containing elements of interest are introduced into argon plasma as aerosol droplets. The plasma dries the aerosol, dissociates the molecules, and then removes an electron from the components to be detected by the mass spectrometer. Other ionization methods such as electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) are used to analyze biological samples. Following the ionization procedure, ions are separated in the mass spectrometer according to their mass-to-charge ratio (m/z), and the relative abundance of each ion type is measured. Finally, the detector commonly consists in an electron multiplier where the collision of ions with a charged anode leads to a cascade of increasing number of electrons, which can be detected by an electrical circuit connected to a computer.
In this video, the procedure of ICP-MS analysis will be described by the detection of 56Fe as an example.