TOWARD UNDERSTANDING MECHANISM OF MALDI PROCESS

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。质谱法是检测、分析和鉴定生物大分子（如蛋白质、糖缀合物和核酸）的最重要技术。在生物和医学领域，电离技术是质谱分析取得成功的关键。基质辅助激光解吸/电离（MALDI）是其中一种方法，但其基本机理尚不清楚。MALDI技术的进一步发展将取决于识别新的基质材料，这些材料的特性在此之前可能尚未得到充分的认识或利用。最初，我们研究了炸药作为新基质的使用，它可以在激光照射时为分析物提供额外的能量，从而提高检测的灵敏度。爆炸时，炸药会释放出大量气体。因此，我们现在正在开发一种新的MALDI理论，将其作为一种热过程，其中CO2通过激光照射羧酸基质释放，从而产生我们称之为“气动辅助”的现象。我们正在开发质量和传热方程，以模拟在337 nm氮激光的典型3ns脉冲期间或之后的任何时间和任何深度的基质组成，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、生长、最终破裂和溅射熔融基体，夹带结晶过程中形成的分析物离子。这些方程依赖于基体及其脱羧产物的宏观性质，并将计算和预测以下的时空模型：-基体吸收激光辐射，荧光损失一些能量。-激光脉冲后加热、熔化、脱羧和随后冷却的影响。-熔融基质过饱和和与CO2脱羧产物。-熔体中气泡的形成、增长和破裂，以及碎片作为水滴羽的飞行。-通过离子对和单离子的重组，在熔体和羽流的飞行微滴中，分析物离子的竞争性损失。-从分析物离子中部分或全部蒸发基质及其脱羧产物。由计算机模型做出的预测正在与MALDI实验数据进行比较。（在协作项目和其他技术研究与开发项目下报告的额外工作和仪器时间。）

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.)