Oligosaccharides from red seaweeds: comparison between ESI-MS and UV-MALDI-MS

MST. KANIZ FATEMA; YASUTO SATO; HIROSHI NONAMI; DIOGO R. B. DUCATTI .; ALAN G. GONCALVES; M. EUGENIA R. DUARTE; MIGUEL D. NOSEDA; MARÍA C. MATULEWICZ; ´ROSA ERRA-BALSELLS; ALBERTO S. CEREZO

Hiroshima, Japón

Conferencia; The 55th Annual Conference on Mass Spectrometry; 2007

The Mass Spectrometry Society of Japan (MSSJ)

Oligosaccharides from red seaweeds: comparison between ESI-MS and UV-MALDI-MS (1Plant Biophys./Biochem. Research Laboratory, College of Agriculture, Ehime University, Japan 2Departamento de Bioquimica e Biologia Molecular, Universidade Federal do Paraná, Curitiba, Paraná, Brazil  3CIHIDECAR-CONICET, Departamento de Quimica Organica, Facultad de Ciencias Exactas, Universidad de Buenos Aires, Argentina) Fatema MST. Kaniz,1 Yasuto Sato,1 Hiroshi Nonami,1 Diogo R. B. Ducatti,2 Alan G. Gonçalves,2 M. Eugenia R. Duarte,2 Miguel D. Noseda,2 María C. Matulewicz,3 Rosa Erra-Balsells3, A. S. Cerezo3 Short Abstract: Herein we report the comparative ESI-MS and UV-MALDI-TOF-MS analysis of the following oligosaccharides: G-LA (beta-D-galactopyranose - 3,6-anhydro-L-galactose), G4S-DA (beta-D-galactopyranose 4-sulfate - 3,6-anhydro-D-galactose), G-LA-G and G-LA-G-LA. Experiments were carried out in the linear and reflectron modes and, as routine, in both in the positive- and negative-ion-mode. 2,5-Dihydroxybenzoic acid (DHB) and nor-harmane (nHo) were used as matrices. For the sulfated oligosaccharide signals were only observed in the negative ion-mode with both matrices. In the linear spectrum of the sulfated oligosaccharide a small signal consistent with a glycosidic C-cleavage between 3,6-anhydrogalactose and the adjacent galactose 4-sulfate unit was found. This type of cleavage was previously reported in the UV-MALDI-TOF-MS analysis of a complex mixture of oligosaccharides obtained by autohydrolysis of a partially cyclized mu/nu-carrageenan. The PSD mode afforded the expected different fragmentations of the glycosidic bonds together with some fragmentations of the sugar rings. Keywords: Oligosaccharides from red seaweeds, UV-MALDI -MS, ESI-MS. Red algal galactans generally consist of an alternating structure of 3-linked beta-D-galactopyranose and 4-linked 3,6-anhydro-alpha-galactopyranose or alpha-galactopyranose. These galactans are classified as carrageenans if the 4-linked residue is in the D configuration ot agarans if it is in the L configuration. Herein we report the UV-MALDI-TOF-MS analysis of the following oligosaccharides: G-LA (beta-D-galactopyranose - 3,6-anhydro-L-galactose), G4S-DA (beta-D-galactopyranose 4-sulfate - 3,6-anhydro-D-galactose), G-LA-G and G-LA-G-LA. (Las fórmulas de los oligosacáridos se encuentran en el texto en formato pdf correspondiente al Libro de Resúmenes) Shimadzu Kratos, Kompact MALDI 4 laser desorption time-of-flight mass spectrometer (Shimadzu, Kyoto, Japan), equipped with pulsed nitrogen laser (lambda = 337 nm; pulse with = 3ns), PDE and PSD (MS/MS) devices was used for UV-MALDI-MS studies. Experiments were carried out in the linear and reflectron modes and, as routine, in both in the positive- and negative-ion-mode. 2,5-Dihydroxybenzoic acid (DHB) and nor-harmane (nHo) were used as matrices. Very good spectra of the non-sulfated oligosaccharides were obtained with DHB and nHo in the positive ion-mode. Spectra of higher quality and signal to noise (S/N) ratio were obtained with nHo. On the contrary when fragmentations were studied in PSD mode, the efficiency of fragmentation was higher when DHB was used as matrix. These results agree with the fact that DHB behaves as a “hoter” matrix than nHo, releasing to the medium as prompt heat with higher efficiency the energy of the electronic excited stated populated after the laser shot (1,2). Thus, vibrational excitation of the carbohydrate (analyte) is more efficient and the molecular ion (precursor ion) yields more efficiently the fragmentation. For the sulfated oligosaccharide signals were only observed in the negative ion-mode with both matrices. Again, nHo showed higher S/N ratio for the molecular ion and DHB yielded better fragmentation pattern. In the linear spectrum of the sulfated oligosaccharide a small signal consistent with glycosidic C-cleavage between 3,6-anhydrogalactose and the adjacent galactose 4-sulfate unit was found. This type of cleavage was previously reported in the UV-MALDI-TOF-MS analysis of a complex mixture of oligosaccharides obtained by autohydrolysis of a partially cyclized mu/nu-carrageenan (3). The PSD mode afforded the expected different fragmentations of the glycosidic bonds together with some fragmentations of the sugar rings. 1) O.I.Tarzi et al., Chem. Phys. Lett., 426, 334-340 (2006). 2) O.I.Tarzi, Termal and photochemical stability of photosensitizers currently used as matrices in UV-MALDI-MS. Photochemistry of -carboline deirvatives. Ph.D. Thesis, University of Buenos Aires, Argentina (2007). 3) 2005, M. Ciancia et al., ARKIVOC, XII, 319-331 (2005).