INCLUSION OF A MALDI ION-SOURCE IN THE ION CHROMATOGRAPHY TECHNIQUE - CONFORMATIONAL INFORMATION ON POLYMER AND BIOMOLECULAR IONS
INCLUSION OF A MALDI ION-SOURCE IN THE ION CHROMATOGRAPHY TECHNIQUE - CONFORMATIONAL INFORMATION ON POLYMER AND BIOMOLECULAR IONS
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DOI：
10.1016/0168-1176(95)04211-3
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发表时间：
1995-08-31
影响因子：
1.8
通讯作者：
BOWERS, MT
中科院分区：
文献类型：
--
作者：
VON HELDEN, G;WYTTENBACH, T;BOWERS, MT
基质辅助激光解吸电离 (MALDI) 源已与 UCSB 开发的离子色谱仪耦合。信号源对单个样品产生持续数小时的强烈、一致的信号。在本文中，我们报告了该方法在一系列钠阳离子化聚乙二醇（PEG）聚合物中的应用。已获取 Na(+)PEG5 至 Na(+)PEG19 的数据。在 80 至 580 K 范围内测量了 Na(+)PEG9、Na(+)PEG13 和 Na(+)PEG17 氦气中离子淌度（碰撞截面）的温度依赖性。为了提取离子构象以及它们如何随温度变化，我们对这三个系统进行了详细分析。该分析包括与之前使用的方法相比的一些重大变化。分子力学方法既用于获得最低能量 0 K 结构，又用于预测这些结构随着温度升高将如何变化。为了解释观察到的低温结果，引入了 12-6-4 势来代替之前使用的硬球势。对于详细研究的所有三个系统，PEG 单元上的氧原子溶剂化了 Na+ 离子，形成了围绕 Na+ 的五个氧原子以及该环上方和下方的其他几个氧原子的冠醚型环。该分子力学模型也适用于中性PEG13。在这种情况下，当 T 小于或等于 200 K 时，获得了相当紧凑的结构，但在 200 到 300 K 之间发生突然的熔化型转变，并且在 300 K 及以上，混沌运动占主导地位。还报告了有关 C-60(+) 离子迁移率的温度依赖性的数据。预计该离子在此处报告的温度范围内只会稍微改变形状。因此，它提供了一组出色的校准数据，用于评估用于描述碰撞过程的分子内相互作用势。
A matrix-assisted laser desorption ionization (MALDI) source has been coupled to the ion chromatography instrument developed at UCSB. The source produces a strong, consistent signal for several hours on a single sample. In this paper we report the application of this method to a series of poly(ethylene glycol) (PEG) polymers cationized by sodium. Data have been taken for Na(+)PEG5 to Na(+)PEG19. The temperature dependence of the ion mobility (collision cross-section) in He gas for Na(+)PEG9, Na(+)PEG13 and Na(+)PEG17 has been measured from 80 to 580 K. A detailed analysis of these three systems has been accomplished in order to extract the conformations of the ion and how they vary with temperature. This analysis included several significant changes from methods used previously. Molecular mechanics methods were used both to obtain the lowest energy 0 K structures and to predict how these structures would change as temperature increases. In order to account for the observed low temperature results, a 12-6-4 potential was incorporated in place of the hard-sphere potential used previously. For all three systems studied in detail, the oxygen atoms on the PEG units solvated the Na+ ion, forming a crown ether type ring of five oxygens surrounding Na+ and several others above and below this ring. The molecular mechanics model was also applied to neutral PEG13. In this instance a quite compact structure is obtained for T less than or equal to 200 K but a sudden melting type transition occurs between 200 and 300 K and chaotic motion dominates at and above 300 K. Data are also reported on the temperature dependence of the ion mobility of C-60(+). This ion is expected to change shape only slightly over the temperature range reported here. Consequently it provided an excellent set of calibration data for evaluating the intramolecular interaction potentials used to describe the collision process.