SPIROOXAZINES AS A MOLECULAR PROBE FOR THE STUDY OF MATRIX-ASSISTED LASER-DESORPTION IONIZATION PROCESSES .1. STUDY OF THE INTERACTION EFFECT BETWEEN THE MOLECULAR PROBE AND THE MATRIX/

In a search for a better understanding of the desorption/ionization pr ocess in matrix-assisted laser desorption/ionization (MALDI), photochr omic systems such as spirooxazines have been studied by Fourier transf orm ion cyclotron resonance mass spectrometry coupled with a laser int erface, These compounds become intensely blue upon exposure to ultravi olet light and return to the original color if the radiation is stoppe d, The blue color is due to the opening of the carbon-oxygen bond, cre ating a delocalized pi-electron photomerocyanine structure which absor bs light in the 500-650 nm range, The spirooxazines appear to be an ex cellent probe for the study of MALDI processes because the opening of the spiro structure induces the typical formation of the triply proton ated molecules [M + 3H](+) simultaneously with the color change, The s ource of hydrogen in the matrix has been deduced by using nicotinic ac id, methyl nicotinate anal deuterated nicotinic acid as matrices, The differences between the direct laser desorption (LD) (detection of mol ecular ion, M+.) and the MALDI process are discussed. A detailed mecha nism of spiro-compound fragmentation is proposed. (C) 1997 by John Wil ey & Sons, Ltd.