Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Nankang District, Taipei 115, Taiwan, ROC.
J Phys Chem B. 2010 Aug 26;114(33):10853-9. doi: 10.1021/jp104178m.
The initial ionization reaction in matrix-assisted laser desorption/ionization (MALDI) was examined on the basis of the appearance of photoelectrons. The threshold laser fluence for the ejection of photoelectrons from 2,5-dihydroxybenzoic acid (DHB), sinapinic acid (SA), and trihydroxyacetopheone (THAP) on stainless steel (SS) substrates was 0.05, 0.41, and 8.39 mJ/cm(2), respectively. These values are considerably lower than those for MALDI ions, indicating that the electron detachment likely precedes other ionization reactions. The SS substrate played an insignificant role in the production of photoelectrons because suspended DHB produced a photoelectron signal similar to DHB on the SS surface, and decreasing the DHB thickness on the SS reduced the photoelectron intensity. For crystalline DHB and SA, the photoelectron intensity increased with the laser (337 nm) fluence in a relationship of less than second order, suggesting considerable reductions of ionization potentials in comparison with free molecules. According to ab initio calculations, the ionization potential of DHB clusters reduces as the cluster size increases from monomer to octamer. The impact of these abundant electrons on the ion production in MALDI is discussed.
基于光电子的出现，研究了基质辅助激光解吸/电离（MALDI）中的初始电离反应。从不锈钢（SS）衬底上 2,5-二羟基苯甲酸（DHB）、芥子酸（SA）和三羟基苯乙酮（THAP）中逐出光电子的阈值激光通量分别为 0.05、0.41 和 8.39 mJ/cm²。这些值明显低于 MALDI 离子的值，表明电子脱离可能先于其他电离反应。SS 衬底在光电子的产生中作用不大，因为悬浮的 DHB 产生的光电子信号与 SS 表面上的 DHB 相似，并且降低 SS 上的 DHB 厚度会降低光电子强度。对于结晶的 DHB 和 SA，光电子强度随激光（337nm）通量的增加呈小于二级的关系增加，这表明与游离分子相比，电离势有相当大的降低。根据从头算计算，DHB 团簇的电离势随着从单体到八聚体的团簇尺寸的增加而降低。讨论了这些丰富电子对 MALDI 中离子产生的影响。
