Matrix-assisted laser desorption/ionization of amphiphilic fullerene derivatives

Matrix-assisted laser desorption/ionization (MALDI) coupled with reflectron time-of-flight mass spectrometry has been applied to the analysis of fulle rene derivatives. As a common structural feature, the derivatised fullerene s comprised a long chained, organic ligand connected via a methylene bridge to the [60]fullerene. Using a structurally similar model analyte, this inv estigation includes the screening of fourteen different compounds regarding their suitability as MALDI matrices. The appearance of positive- and negat ive-ion mass spectra has been detailed, and the analysis has been supported by post source decay experiments. It was found that the performance of 9-n itroanthracene, which is currently one of the most universally used matrice s for the analysis of fullerene derivatives, is exceeded by some of these m aterials. In the negative-ion mode, excellent performance has been achieved using the two structurally related beta -carboline alkaloids, harmane and nor-harmane, as matrices. However, the best results for the analytes invest igated here have been obtained employing 2-[(2 E)-3-(4-tert-butylphenyl)-2- methylprop-2-enylidene]malononitrile (DCTB), This matrix provides analyte s ignals in both ion modes at comparatively lower threshold laser fluences, l eading to mass spectra, which display a very low degree of unwanted dissoci ations of the analyte. The formation of molecular analyte ions prevails, ra ther than ionization occurring via protonation or deprotonation. DCTB also efficiently promotes metal ion attachment to suitably ligated fullerene der ivatives. (C) 2001 Elsevier Science B.V.