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

离子迁移率光谱分析技术是由Cohen和Karasek在1970年发展起来的，是建立在早期气相离子化学研究基础上的传感器。自那以后，它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。离子迁移率是衡量气相离子在电场影响下通过缓冲气体的速度，这取决于两个因素：离子的旋转平均碰撞截面和离子上存在的电荷。通过测量一个离子经过已知距离的漂移时间，就有可能以一定的精度确定它的碰撞截面。在漂移场为直流势的仪器中，离子的碰撞截面与测量的平均漂移时间之间的关系很容易找到。可以将实验碰撞截面与从其他结构研究获得的坐标预测的截面进行比较，或者从计算测量中预测截面以获得原子学上详细的构象信息。离子迁移率谱中离子的漂移时间与它们的气相碰撞截面之间的关系是众所周知的，近年来，离子迁移率谱与质谱仪(IM-MS)作为一种结构分析工具，特别是用它来揭示生物分子的构象，已经获得了特别重要的地位。经过软电离方法的发展，生物相关物种的IM-MS研究于20世纪90年代中后期开始在国产仪器上进行，将这两种著名的分析技术结合在一起。鲍尔斯、贾罗尔德、克莱默和希尔在这一时期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，并推动了商业可用移动设备的开发，因为这项技术在生物分析方面的力量变得明显。Waters MS Technologies(英国曼彻斯特)最近推出了第一款商业化的集成IM-MS仪器--Synapt HDMS。施加到离子迁移率分离器内的叠环离子导轨中的连续电极的RF提供了使离子保持径向限制在器件内的势垒。为了推动离子通过该装置，包括一系列瞬时直流电压的行波被叠加在射频电压之上，因此该装置有时被称为行波离子导枝。该电压被顺序地施加到成对的环电极上，从而提供可以推动离子通过该装置的电位。这些商用设备已经投入使用，取得了良好的效果。使用基于树枝的系统，Robinson等人。评估了多聚体蛋白质的构象，以及通过观察单体单元的部分展开来观察复合体的拆解，同时仍然保留了复合体的一些完整性。与国产仪器相比，Synapt的好处是毋庸置疑的，占空比更短，通过这种仪器的传输效率比大多数国产设备更好。然而，要使在Synapt仪器上获得的实验漂移时间在碰撞截面方面得到适当的合理化，需要仔细地使用从线性离子迁移率仪器上获得的数据进行校准，例如由Bowers和Clemmer开发的，也存在于Barran实验室的数据。这其中的一个问题是，可用的蛋白质碰撞截面数据是有限的，而且通常也没有得到很好的验证。这意味着，尽管人们对应用Synapt来询问复杂的生物结构非常感兴趣，并且进行了漂亮的前期工作，但结果仍然有一些未经证实的地方。这个学生将寻求通过几种方式来解决这个问题。请参阅下面的研究战略。

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.