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 fullerene derivatives. As a common structural feature, the derivatised fullerenes comprised a long chained, organic ligand connected via a methylene bridge to the [60]fullerene. Using a structurally similar model analyte, this investigation includes the screening of fourteen different compounds regarding their suitability as MALDI matrices. The appearance of positive- and negative-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-nitroanthracene, which is currently one of the most universally used matrices for the analysis of fullerene derivatives, is exceeded by some of these materials. 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 investigated here have been obtained employing 2-[(2 E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB), This matrix provides analyte signals in both ion modes at comparatively lower threshold laser fluences, leading to mass spectra, which display a very low degree of unwanted dissociations of the analyte. The formation of molecular analyte ions prevails, rather than ionization occurring via protonation or deprotonation. DCTB also efficiently promotes metal ion attachment to suitably ligated fullerene derivatives. (C) 2001 Elsevier Science B.V.