Searching the interaction of the analyte with Z- and E-sinapinic acid

J. KASUGA; M.L.SALUM; H. NONAMI, ; ROSA ERRA BALSELLS

Osaka

Conferencia; The 62nd Annual Conference on Mass Spectrometry,; 2014

The Mass Spectrometry Society of Japan

Searching the interaction of the analyte with Z- and E-sinapinic acid (Ehime University1, University of Buenos Aires2) J.Kasuga1, M.L.Salum2, ??R.Erra-Balsells2, H. Nonami1 Keywords: UV-MALDI MS, Z-Sinapinic acid, E-Sinapinic acid, Pressure Probe, Sample preparation   Successful application of matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) started with the introduction of efficient matrices such as cinnamic acid derivatives (i.e., 3,5-dimethoxy-4-hydroxycinnamic acid, SA; ?¿-cyano-4-hydroxycinnamic acid, CHCA). Since the empirical founding of these matrices other commercial available cinnamic acids with different nature and location of substituents at benzene ring were attempted. Rational design and synthesis of new cinnamic acids have been recently described too. Because the presence of a rigid double bond in its molecule structure cinnamic acids can exist as two different geometric isomers, the E- and Z-forms. Commercial available cinnamic acids currently used as matrices are the trans- or E- isomer (E-cinnamic acids or trans-cinnamic acids). As a new rational design of MALDI matrices, Z-cinnamic acids were synthesized and their properties as matrices studied.1 Their performance was compared with that of the corresponding E-isomer and classical crystalline matrices (3,5-dihydroxybenzoic acid; 9H-pirido(3,4b)indole, norharmane) in the analysis of neutral/sulfated carbohydrates. Thus, we demonstrated the outstanding performance for Z-SA. Sulfated oligosaccharides were detected in negative ion mode and the dissociation of sulfate groups was almost suppressed. The influence of the E-/Z- photoisomerization of the matrix during MALDI was evaluated and we concluded that E-/Z- photoisomerization does not play a key role during the MALDI event in the carbohydrate analysis. Furthermore molecular modeling (density functional theory study) of the optimized geometry and stereochemistry of E- and Z-cinnamic acids revealed some factors governing the analyte-matrix interaction. This complementary tool revealed that as consequence of the geometry change in the alkene rigid bond of the cinnamic moiety, the stereochemistry of the matrix molecule changes dramatically and at molecular level the analye-matrix interaction too. In the first part of this study MALDI mass spectra were obtained in experiments conducted with sample prepared using the classical mixture method and the thin layer or sandwich method, as it was described elsewhere.2 Thus, to better understand the quite different performance of each geometric isomer as matrix the physical and morphological properties as well as the photochemical stability and photophysics in solid state were studied.   In order to get additional information about analyte-matrix interaction at molecular level, in solid state, fluorescence microscopy for solid surface scanning and MALDI-MS imaging of the same solid sample surface were complementary used. For sample preparation the classical mixture and sandwich method were used together with a scale modification of the latter. We called this method picotapa method because a picoL of analyte solution was loaded on the air-dried matrix layer prepared with a 0.5 uL of stock matrix solution. The picoL volume was manipulated with the Pressure Probe,3,4 tip and the sample preparation was performed under microscope enhance field. Both cinnamic acids, E- and Z-SA, showed as a thin solid layer deposit a very weak fluorescence emission. For our surprise, when carbohydrates such as ?À-cyclodextrin or maltoheptaose were used as analyte, and sample was prepared by mixture method, increasing of fluorescence emission of the solid sample was observed. It is worth noting that 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.   References M.L.Salum et al., Org. Lett., 12, 4808-4811 (2010). M.L.Salum et al., J. Mass Spectrom., 48, 1150-1159 (2013). Y. Gholipour et al., J. Am. Soc. Mass Spectrom., 19, 1841-1848 (2008). Y. Gholipour et al., Anal. Biochem., 19, 1841-1848 (2013).