Photochemistry and Photophysics of several hydroxyacetophenones, potential UV-MALDI-MS matrices for carbohydrates

LUCIANO H. DI STEFANO; OLGA I. TARZI; ROSA ERRA-BALSELLS

Conferencia; 21era Conferencia de la Sociedad Inter-americana de Fotoquímica (I-APS); 2011

I-APS

One of the most succesful applications of organic photochemistry in solid state is UV-MALDI mass spectrometry. In this analytical technique, desorption/ionization of the analyte is induced by a UV laser and assisted by a photosensitizer (matrix). Although the standard compounds used as matrices in UV-MALDI-MS are commercial, most of their photochemical properties remain unknown and there is not yet a clear model for the photosensitized process that takes place from the matrix to the analyte, after the UV-laser shot. Besides, there are no rules when it comes to choosing the right matrix for a particular analyte. Knowing which properties photosensitizers should have to efficiently desorb the analyte, could help not only to simplify the UV-MALDI experiment but also to obtain new structures useful as matrices. It is well known that commercial 2,4,6-trihydroxyacetophenone (THA) and 2,5-dihydroxybenzoic acid (gentisic acid) are good matrices especially for carbohydrates. Previous results in our laboratory showed photochemical stability and low fluorescence quantum yields for both compounds.  Therefore, we decided to study several hydroxyacetophenones to see how their photochemical and photophysical behaviour relates to their performance as UV-MALDI matrices. UV-MALDI-MS experiments with different oligosaccharides showed that 2,5-dihydroxyacetophenone desorbed more efficiently the analyte than the other isomers tested. Electronic absorption, emission and excitation spectra of the compounds shown in the scheme were obtained and studies of their photochemical behaviour were performed in solution at different wavelengths and conditions. Thermal stability studies of these compounds in solid state were also conducted.