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.)
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