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Ion fragmentation methods for characterizing peptides and hydrated ions in the gas phase.

机译:用于在气相中表征肽和水合离子的离子裂解方法。

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With the introduction of soft ionization techniques, such as electrospray ionization, large labile molecules now can be readily transferred to gas phase, and a new area in gas-phase chemistry of biomolecules was opened. The traditional method of studying ion energetics is to deposit a known amount of energy into an ion by using photons of a given frequency or transferring a specific amount of collisional energy. These approaches, however, are inefficient for large molecules because of the kinetic shift effect resulting from their many degrees of freedom.; The most accurate and versatile method for probing gas-phase energetics for large ions is blackbody infrared radiative dissociation (BIRD). Nevertheless, BIRD cannot be operated in pulsed format making it difficult to couple with other ion characterization techniques. In addition, the temperature range of BIRD is limited based on how hot the magnet bore and vacuum chamber components can be heated. Chemical systems which dissociate quicker than internal energy equilibration or those dissociate too slow at the highest accessible temperature cannot be accurately measured by BIRD.; Several dissociation techniques are developed here for energetic studies. A thermal jacket which encloses the FT-ICR ion cell is built. It can be cooled by liquid nitrogen, therefore extending the range of BIRD to colder temperatures to study fragile ions, such as highly hydrated magnesium and calcium ions. In developing a broadband pulsed dissociation technique, six tungsten filaments which can be resistively heated are attached to an ion cell. Photons emitted from filaments promote dissociation of molecular ions of acetophenone and n-butylbenzene, protonated leucine enkephalin and doubly protonated bradykinin. The visible photons emitted from the heated filaments play an active role in the dissociation process of n-butylbenzene as they promote the formation of m/z 91 ions, an ion not observed using just infrared radiation either generated thermally or with a CO2 laser. SO42-(H 2O)n; n = 3--17, are examined using three dissociation techniques: BIRD, infrared laser, and collisional-induced dissociation. Experimental results indicate that the elimination of water molecule is entropically favorable but energetically unfavorable compared to the charge separation dissociation via proton transfer. Moreover, the BIRD kinetics show unusual stability for the clusters n = 6 and 12, which suggests changes in structural conformation for these clusters. The new techniques described here open up new possibilities for studying chemical systems which are difficult to examine by other methods, and studying chemical reactions using these new techniques shed new light to the reaction mechanism.
机译:随着诸如电喷雾电离之类的软电离技术的引入,大的不稳定分子现在可以很容易地转移到气相中,并且开辟了生物分子气相化学的新领域。研究离子能量学的传统方法是通过使用给定频率的光子或转移特定数量的碰撞能量,将已知数量的能量沉积到离子中。然而,由于大分子的许多自由度引起的动力学位移效应,这些方法对于大分子是无效的。用于探测大离子的气相高能的最准确,最通用的方法是黑体红外辐射解离(BIRD)。然而,BIRD无法以脉冲形式进行操作,因此很难与其他离子表征技术结合使用。此外,BIRD的温度范围受磁铁孔和真空室组件的加热程度所限制。 BIRD无法准确测量比内部能量平衡解离快的化学体系,或在最高可及温度下解离太慢的化学体系。这里开发了几种解离技术用于能量学研究。内置了一个热外套,它包裹了FT-ICR离子电池。它可以通过液氮冷却,因此将BIRD的范围扩展到较低的温度,以研究易碎的离子,例如高度水合的镁和钙离子。在开发宽带脉冲解离技术时,将六个可以电阻加热的钨丝连接到离子电池上。灯丝发出的光子促进了苯乙酮和正丁苯,质子化亮氨酸脑啡肽和双质子化缓激肽的分子离子解离。从加热的灯丝发出的可见光子在正丁基苯的离解过程中起着积极作用,因为它们促进了m / z 91离子的形成,而仅使用热或CO2激光产生的红外辐射无法观察到该离子。 SO42-(H 2O)n; n = 3--17,使用三种解离技术检查:BIRD,红外激光和碰撞诱导解离。实验结果表明,与通过质子转移进行的电荷分离解离相比,消除水分子在熵上有利,但在能量上不利。此外,BIRD动力学对n = 6和12的团簇显示出异常的稳定性,这表明这些团簇的结构构象发生了变化。这里描述的新技术为研究用其他方法难以检查的化学系统开辟了新的可能性,并且使用这些新技术研究化学反应为反应机理提供了新的思路。

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