SGMS Meeting 2000

MALDI-FTMS of Cyclic and Star-shaped Arrays of Metalloporphyrins

Titus Jenny¹, Albert Gossauer¹, Olivier Mongin¹, Gokhan Baykut², and Matthias Witt2
1 Organic Chemistry, Fribourg University; Switzerland
2 Bruker Daltonik, Bremen; Germany

Large molecular porphyrin arrays with an integral acceptor chromophore, mimicking the light-harvesting complex of photosynthetic bacteria have been designed and investigated photophysically1). Attempts to measure the mass spectra of these compounds by various ionization methods including ESI failed due to metal loss at the porphyrins induced by sample preparation.

FTMS experiments were performed using Bruker APEX II FTMS instruments equipped with 4.7 T and 7 T magnets. The newly developed hexapole-MALDI system with pulsed in-source collision gas is used for ionizing the samples. Ions from multiple laser shots were accumulated in the linear hexapole trap prior to transfer into the ICR cell. Samples are prepared with 1,8,9-trihydroxyanthracene (dithranol) as matrix.

High quality mass spectra (resolution > 110,000) of more than 10 high molecular weight (up to 5700) covalently interconnected metalloporphyrin arrays (star shaped or arranged in hexagonal cycles) were obtained. Contrary to the data obtained with electrospray ionization, where the added acid induces loss of the metal ions from the porphyrins, MALDI conditions produce spectra on intact molecules. Since all the measured molecules lack functional groups prone to be protonated or ionized by the medium, it is difficult to form ions of these molecules. Additionally, very low concentrations of analyte in a neutral matrix have to be used in order to prevent aggregation of the chromophores. Using the sensitive MALDI technique with dithranol as matrix enables to study these porphyrin arrays mass spectrometrically.

O. Mongin, N. Hoyler, A. Gossauer, Eur. J. Org. Chem. 2000, 1193.

P. Brodard, S. Matzinger, E. Vauthey, O. Mongin, C. Papamicaël, A. Gossauer, J. Phys. Chem. A, 1999, 103, 5858