The relationship between ion mobility and collision cross section of peptides and proteins: an experimental and theoretical study

离子迁移谱分析技术由Cohen和Karasek在1970年开发，作为早期气相离子化学研究的传感器。它已被用于检测各种分析物，包括非法药物，化学战剂，爆炸物和环境污染物。离子迁移率是一种测量气相离子在电场影响下通过缓冲气体的速度的方法，它取决于两个因素：离子的旋转平均碰撞截面和离子上的电荷。通过测量离子在已知距离内的漂移时间，可以在一定程度上准确地确定其碰撞截面。在漂移场为直流电势的仪器中，离子的碰撞截面和测量的平均漂移时间之间的关系可以很容易地找到。实验碰撞截面可以与从其他结构研究或计算测量获得的坐标预测的截面进行比较，以获得原子详细的构象信息。离子迁移谱仪中离子的漂移时间与它们的气相碰撞截面之间的关系是很好理解的，并且近年来，离子迁移谱与质谱联用（IM-MS）作为用于结构分析的工具，特别是用于揭示生物分子的构象，已经获得了特别重要的意义。在软电离方法的发展之后，生物相关物种的IM-MS研究开始于20世纪90年代中期和后期，采用自制仪器，将这两种众所周知的分析技术结合起来。在这一时期，Bowers、Jarrold、Clemmer和Hill进行了一些最有影响力的工作，他们的研究为其他人铺平了道路，并促进了商业上可用的移动设备的发展，因为这种技术在生物分析中的作用变得显而易见。沃茨质谱技术公司（英国曼彻斯特）最近推出了第一台市售集成IM-MS仪器Synapt HDMS。施加到离子迁移率分离器内的堆叠环形离子导向器中的连续电极的RF提供了势阱，该势阱将离子径向地限制在装置内。为了推动离子通过装置，包括一系列瞬态DC电压的行波叠加在RF电压之上，因此该装置有时被称为行波离子导向器- TWIG。该电压被顺序地施加到成对的环形电极，从而提供可以推动离子通过装置的电势。这些市售的装置已经使用，效果良好。使用基于TWIG的系统，罗宾逊等人已经评估了多聚体蛋白质的构象，以及复合物的分解，观察单体单元的部分解折叠，同时仍然保留复合物的一些完整性。Synapt与自制仪器相比的优势是无可争议的，占空比更短，通过该仪器的传输效率优于大多数自制设备。然而，为了正确合理化在碰撞截面方面在Synapt仪器上获得的实验漂移时间，需要用在线性离子迁移率仪器上获得的数据进行仔细校准，例如Bowers和Clemmer开发的仪器，也存在于Barran的实验室中。其中一个问题是，蛋白质的可用碰撞截面数据有限，而且往往没有得到很好的验证。这意味着，尽管对应用突触来询问复杂的生物结构非常感兴趣，而且初步工作也很漂亮，但结果仍然有些“未经验证”。请参阅下面的研究策略。

The analytical technique of ion mobility spectrometry was developed by Cohen and Karasek in 1970 as a sensor building on earlier gas-phase ion chemistry investigations. It has since been used to detect a wide range of analytes including illegal drugs, chemical warfare agents, explosives and environmental pollutants. Ion mobility is a measure of how quickly a gas phase ion moves through a buffer gas under the influence of an electric field, and this depends on two factors: the rotationally averaged collision cross section of the ion and the charge present on it. By measuring the drift time of an ion through a known distance it is possible to determine its collision cross section with some degree of accuracy. In instruments where the drift field is a dc potential, the relationship between the collision cross section of an ion and the measured average drift time can be easily found. The experimental collision cross section can be compared to cross sections predicted from co-ordinates obtained from other structural investigations, or from computational measurements to obtain atomistically detailed conformational information. The relationship between the drift times of ions in a ion mobility spectrometer and their gas-phase collision cross section, is well understood, and in recent years ion mobility spectrometry coupled with mass spectrometry (IM-MS) has gained particular importance as a tool for structural analysis and particularly for its use to reveal conformation of biological molecules. After developments in soft ionization methods, IM-MS studies of biological relevant species started in the mid and late 1990's on home built instruments which coupled these two well known analytical techniques. Some of the most influential work in this period was performed by Bowers, Jarrold, Clemmer, and Hill and their investigations have paved the way for others and prompted development of commercially available mobility devices, as the power of this technique for biological analysis became apparent. Waters MS Technologies (Manchester, UK) recently introduced the first commercially available integrated IM-MS instrument the Synapt HDMS. The RF applied to consecutive electrodes in the stacked ring ion guide within the ion mobility separator, provides a potential well which keeps the ions radially confined within the device. In order to propel the ions through the device, a travelling wave comprising a series of transient DC voltages is superimposed on top of the RF voltage, and hence this device is sometimes referred to as a Travelling Wave Ion Guide - TWIG. This voltage is applied sequentially to pairs of ring electrodes providing a potential which can push ions through the device. These commercial available devices have already been used to good effect. Using a TWIG based system, Robinson et al. have assessed conformations of multimeric proteins, and also the disassembly of complexes viewing the partial unfolding of monomer units whilst still retaining some the integrity of the complex. The benefits of the Synapt compared to home built instruments are undisputed, the duty cycles are shorter and the transmission efficiency through this instrument is better than with most home made devices. However, to properly rationalize experimental drift times obtained on Synapt instrumentations in terms of collision cross sections, requires careful calibration with data obtained on a linear ion mobility instrument, such as that developed by Bowers and Clemmer and also present in the lab of Barran. One of the issues with this is that the available collision cross section data for proteins is limited, and also often not well verified. This means that despite the extreme interest in the application of the Synapt to interrogate complex biological structures, and beautiful preliminary work, results are still somewhat 'unverified' This studentship will seek to address this in several ways. See the Research Strategy below.