Department of Chemistry, Seoul National University, Seoul, Korea.
J Am Soc Mass Spectrom. 2011 Jun;22(6):1070-8. doi: 10.1007/s13361-011-0115-y. Epub 2011 Apr 9.
Time-of-flight (TOF) mass spectra for a peptide (Y(6)) were obtained by utilizing matrix-assisted infrared laser desorption ionization (IR-MALDI) with glycerol as the matrix and by ultraviolet MALDI with α-cyano-4-hydroxycinnamic acid (CHCA), sinapinic acid (SA), and 2,5-dihydroxybenzoic acid (DHB). Collisional activation during ion extraction and exothermicity in the gas-phase proton transfer were found to be unimportant as the driving forces for in-source (ISD) and post-source (PSD) decays, indicating that the thermal energy acquired during photo-ablation is responsible for their occurrence. The temperatures of Y(6) + H in the 'early' and 'late' matrix plumes were estimated by the kinetic analysis of the ISD and PSD yields, respectively. The order of the temperatures was glycerol < DHB ≈ SA < CHCA in the early plume and glycerol < DHB < SA < CHCA in the late plume. For each matrix, the temperature in the late plume was lower than in the early plume by 300-400 K, which was attributed to expansion cooling. The model (thermalization followed by expansion cooling) proposed to explain the occurrence of both rapid ISD and slow PSD is not only in sharp contrast with but also mutually exclusive with the prevailing explanation that the exothermicity in proton transfer and in-plume collisional activation are the driving forces for ion fragmentation in MALDI. The model also explains why MALDI is more successful for mass spectrometry of labile molecules than other desorption techniques that do not utilize a matrix. Factors affecting the plume temperature are also discussed.
利用甘油作为基质的基质辅助红外激光解吸电离（IR-MALDI）和利用α-氰基-4-羟基肉桂酸（CHCA）、3,5-二甲氧基肉桂酸（SA）和2,5-二羟基苯甲酸（DHB）的紫外 MALDI，得到了肽（Y(6)）的飞行时间（TOF）质谱。在离子提取过程中的碰撞激活和气相质子转移中的放热被发现对于源内（ISD）和源后（PSD）衰变不是重要的驱动力，这表明在光烧蚀过程中获得的热能是它们发生的原因。通过 ISD 和 PSD 产率的动力学分析，分别估算了Y(6) + H在“早期”和“晚期”基质羽流中的温度。在早期羽流中，温度的顺序为甘油< DHB≈SA<CHCA，在晚期羽流中，温度的顺序为甘油< DHB<SA<CHCA。对于每种基质，晚期羽流中的温度比早期羽流中的温度低 300-400 K，这归因于膨胀冷却。提出的模型（热化后膨胀冷却）来解释快速的 ISD 和缓慢的 PSD 的发生，不仅与流行的解释（质子转移中的放热和在羽流中的碰撞激活是 MALDI 中离子碎裂的驱动力）形成鲜明对比，而且相互排斥。该模型还解释了为什么 MALDI 比不使用基质的其他解吸技术更成功地用于易失分子的质谱分析。还讨论了影响羽流温度的因素。
