Searching the interaction of carbohydrates with Z- and E-sinapinic in solid MALDI samples

SALUM M LAURA; SCHMIDT DE LEÓN TOBIAS; PETROSELLI GABRIELA; KASUGA JUN; HIROSHI NONAMI; ERRA BALSELLS ROSA

Geneva

Congreso; 20th International Mass Spectrometry Conference; 2014

IMSC

Successful application of MALDI-MS started with the introduction of commercial cinnamic acids as matrices. Rational design and synthesis of new cinnamics have been described too. Because the presence of a rigid double bond in its structure cinnamics can exist as two different geometric isomers, the E- and Z-forms. Commercial available cinnamics used as matrices are the E-isomer. As a new rational design of matrices, Z-cinnamics were synthesized and their properties as matrices studied. Their performance was compared with that of the corresponding E-isomer and classical matrices (DHBA, THAP, norharmane) for the analysis of carbohydrates. We demonstrated the good performance for Z-SA. Furthermore molecular modeling (DFT) of the optimized geometry and stereochemistry of E- and Z-forms suggested some factors governing the analyte-matrix interaction. This complementary tool showed that as consequence of the geometry change in the alkene rigid bond moiety, the stereochemistry of the matrix molecule changes dramatically and at molecular level the analye-matrix interaction changes too. In the first part of this study MALDI mass spectra were obtained in experiments conducted with sample prepared using the mixture and the thin layer method. Thus, to better understand the quite different performance of each geometric isomer as matrix the physical and morphological properties as well as the photophysics in solid state were studied. In order to get additional information about analyte-matrix interaction at molecular level in solid state, fluorescence and phosphorescence microscopy for solid surface scanning, solid flash-photolysis and MALDI-MS imaging of the same solid sample surface were complementary used. For sample preparation the mixture and sandwich method were used together with the called picotapa method because a picoL of analyte solution was loaded on the air-dried matrix layer. The picoL volume was manipulated with the Pressure Probe under microscope. Both, E- and Z-SA did not show fluorescence emission. For our surprise, when carbohydrates such as β-cyclodextrin or maltoheptaose were used as analyte, and sample was prepared by mixture method, fluorescence emission of the solid sample was detected. The new fluorescence observed was not homogeneously distributed all over the surface. As a clear ring with quite intense emission in its border when Z-SA was used and as few tiny weak florescent spots distributed at random on the surface when E-SA was used. The shape and bright of fluorescent image obtained depends on the matrix, and for each matrix the final image depends on the analyte too. The fluorescent image matched with the highest intensity analyte signals in the MALDI MS image. Changes in the photophysics of cinnamic acids in solid state by carbohydrates correlate with cinnamics behavior as MALDI matrices.