TOWARD UNDERSTANDING MECHANISM OF MALDI PROCESS

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。质谱学是检测、分析和鉴定蛋白质、糖结合物和核酸等生物大分子的重要技术。非挥发性物质的电离技术是质谱学在生物和医学领域取得成功的关键。基质辅助激光解吸/电离(MALDI)就是这样一种方法，但这种方法的基本机理还知之甚少。MALDI技术的进一步发展将取决于新的基质材料的鉴定，这些材料具有以前可能没有被充分认识或开发的特性。最初，我们研究了使用炸药作为新的基质，在激光照射下向分析物提供额外的能量，从而提高了检测的灵敏度。炸药爆炸时会释放大量气体。因此，我们现在正在发展一种新的MALDI理论，这是一种通过激光照射羧酸基质释放二氧化碳的热过程，导致了我们所描述的“气动辅助”现象。我们正在开发质量和热传递方程，以模拟在337 nm的氮气激光典型的3 ns脉冲期间或之后的任何时间和任何深度熔体的组成、熔化和热解程度以及熔体中的气体量。气体扩散将导致气泡的形成、长大，最终导致熔融基质的破裂和溅射，携带在结晶过程中形成的分析离子。这些方程依赖于基质及其脱羧基产物的宏观性质，并将计算和预测以下时间和空间模型：-基质对激光辐射的吸收，以及荧光对能量的损失。-激光脉冲后加热、熔化、脱羧化和随后冷却的影响。-熔融基质和脱酸产物与二氧化碳的过饱和。-熔体中气泡的产生、生长和破裂，以及碎片作为液滴羽流的飞行。-在熔体和羽流中飞行的微滴中，通过离子对和单一离子的重新组合，分析离子的竞争损失。-从分析物离子部分或全部蒸发基质及其脱羧基产物。计算机模型所作的预测正在与MALDI实验数据进行比较。(在协作项目和其他技术研究和开发项目下报告的额外工作量和仪器时间。)

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Mass spectrometry is the paramount technique for the detection, analysis and identification of biological macromolecules such as proteins, glycoconjugates and nucleic acids. Ionization techniques for involatile materials are key to the success of mass spectrometry in biology and medicine. Matrix assisted laser desorption/ionization (MALDI) is one such method but the fundamental mechanism of this method is only poorly understood. Further development of the MALDI technique will be dependent upon the identification of new matrix materials with properties that may not have been fully appreciated or exploited before now. Initially we investigated the use of explosives as new matrices that would impart additional energy to the analyte upon laser irradiation, thereby increasing the sensitivity of detection. Upon detonation, explosives release large amounts of gas. Consequently we are now developing a new theory of MALDI as a thermal process in which CO2 is released by laser irradiation of carboxylic acid matrices, resulting in a phenomenon we describe as "pneumatic assistance". We are developing mass and heat transfer equations that model the matrix composition, the degree of melting and pyrolysis, and the amount of gas in the melt at any time and at any depth during or after the typical 3 ns pulse from a nitrogen laser at 337 nm. Gas diffusion will result in bubble formation, growth, eventual bursting and sputtering of molten matrix entraining analyte ions formed during crystallization. The equations rely on macroscopic properties of the matrix and its decarboxylation product, and will calculate and predict a temporal and spatial model of the following: -Absorption of laser radiation by the matrix, with some loss of energy by fluorescence. - The effects of heating, melting, decarboxylation and subsequent cooling after the laser pulse. - Super-saturation of molten matrix and the decarboxylation product with CO2. - Genesis, growth and bursting of bubbles in the melt, and the flight of fragments as a plume of droplets. - Competing loss of analyte ions by recombination of ion pairs and single ions, both in the body of the melt and in flying microdroplets of the plume. - Partial or total evaporation of the matrix and its decarboxylation product from the analyte ions. Predictions made by the computer model are being compared with experimental MALDI data. (Additional effort and instrument time reported under Collaborative projects and other Technical Research and Development projects.)