LASER DESORPTION MASS SPECTROMETRY OF LARGE SYNTHETIC PORPHYRIN ARRAYS

Rockefeller University, New York NY

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Abstract

In this work we analyzed by matrix-assisted laser desorption mass spectrometry (MALDIMS) a set of compounds ranging from zinc-tetraphenylporphyrin (ZnTPP) to an array containing nine zincporphyrins and compared the results with laser desorption of neat porphyrin films. The mass accuracy (0. 1%) and resolution (100-200 FWHM) of MALDI-MS for multiporphyrin arrays are, while lower than those for peptides, sufficient to identify higher molecular weight impurities arising from side-reactions in the synthesis of the arrays. The amount of fragmentation was very extensive in the neat samples. The samples deposited on the matrix, on the other hand, gave a lower yield of ions, but the fraction of intact molecule ions was higher. This striking effect of the matrix, in reducing the extent of fragmentation raises questions concerning the mechanisms of MALDI. A paper describing these findings was published in porphyrins. We are currently engaged in an effort to improve the ionization yield of porphyrins through the addition of efficient electron transfer reagents to the samples used for both ESI and MALDI-MS analyses.