Luo Guanghong, Chen Yong, Siuzdak Gary, Vertes Akos
Department of Chemistry, Institute for Proteomics Technology and Applications, George Washington University, Washington, DC 20052, USA.
J Phys Chem B. 2005 Dec 29;109(51):24450-6. doi: 10.1021/jp054311d.
Benzyl-substituted benzylpyridinium (BP) chloride salts were used as a source of thermometer ions to probe the internal energy (IE) transfer in desorption/ionization on porous silicon (DIOS). To modify their wetting properties and the interaction energies with the thermometer ions, the DIOS surfaces were silylated to produce trimethylsilyl- (TMS), amine- (NH2), perfluoroalkyl- (PFA), and perfluorophenyl-derivatized (PFP) surfaces. Two laser sources--a nitrogen laser with pulse length of 4 ns and a mode locked 3 x omega Nd:YAG laser with a pulse length of 22 ps--were utilized to induce desorption/ionization and fragmentation at various laser fluence levels. The corresponding survival yields were determined as indicators of the IE transfer and the IE distributions were extracted. In most cases, with increasing the laser fluence in a broad range (approximately 20 mJ/cm2), no change in IE transfer was observed. For ns excitation, this was in remarkable contrast with MALDI, where increasing the laser fluence resulted in sharply (within approximately 5 mJ/cm2) declining survival yields. Derivatization of the porous silicon surface did not affect the survival yields significantly but had a discernible effect on the threshold fluence for ion production. The IE distributions determined for DIOS and MALDI from alpha-cyano-4-hydroxycinnamic acid reveal that the mean IE value is always lower for the latter. Using the ps laser, the IE distribution is always narrower for DIOS, whereas for ns laser excitation the width depends on surface modification. Most of the differences between MALDI and DIOS described here are compatible with the different dimensionality of the plume expansion and the differences in the activation energy of desorption due to surface modifications.
苄基取代的苄基吡啶鎓（BP）氯化物盐被用作温度计离子源，以探测多孔硅解吸/电离（DIOS）过程中的内能（IE）转移。为了改变其润湿性以及与温度计离子的相互作用能，对DIOS表面进行硅烷化处理，以制备三甲基硅烷基（TMS）、胺基（NH2）、全氟烷基（PFA）和全氟苯基衍生化（PFP）表面。使用两种激光源——脉冲长度为4 ns的氮激光器和脉冲长度为22 ps的锁模三倍频Nd:YAG激光器——在不同激光能量密度水平下诱导解吸/电离和碎片化。测定相应的存活产率作为IE转移的指标，并提取IE分布。在大多数情况下，在较宽范围（约20 mJ/cm2）内增加激光能量密度时，未观察到IE转移发生变化。对于纳秒级激发，这与基质辅助激光解吸电离（MALDI）形成显著对比，在MALDI中增加激光能量密度会导致存活产率急剧下降（在约5 mJ/cm2范围内）。多孔硅表面的衍生化对存活产率没有显著影响，但对离子产生的阈值能量密度有明显影响。由α-氰基-4-羟基肉桂酸测定的DIOS和MALDI的IE分布表明，后者的平均IE值总是较低。使用皮秒激光器时，DIOS的IE分布总是更窄，而对于纳秒激光激发，宽度取决于表面修饰。此处描述的MALDI和DIOS之间的大多数差异与羽流膨胀的不同维度以及由于表面修饰导致的解吸活化能差异相符。
