JMSSJ On-line

JMSSJ On-line, Vol. 50 (2002) No. 2, pp. 52-57

Reduction in Desorption Mass Spectrometry: Multiple Protonation on Flavins without Charge Increment		>> Full Text PDF >> References
*Yoshiyuki ITOH,^a) Yoko OHASHI,^b) Toshimichi SHIBUE,^c) Akio HAYASHI,^{a), †}Shojiro MAKI,^a) Takashi HIRANO,^a) and Haruki NIWA^a)** ^a)Dept. of Applied Physics and Chemistry, The Univ. Electro-Communications (1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan) ^b)Center for Instrumental Analysis, The Univ. of Electro-Communications (1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan) ^c)Materials Characterization Central Laboratory, Waseda Univ. (3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan)^† Present address: Graduate School of Materials Science, Advanced Institute of Science and Technology, Hokuriku (Tatsunokuchi, Nomi, Ishikawa 923-1292, Japan)*

Three flavin-containing compounds, namely, riboflavin, riboflavin 5'-phosphate (flavin mononucleotide, FMN) and flavin-adenine dinucleotide (FAD, Scheme 1), were studied using matrix-assisted laser desorption ionization (MALDI), fast atom bombardment (FAB) and electrospray ionization (ESI) mass spectrometry. It was found that the isoalloxazine ring (flavin) was reduced in the positive-ion MALDI and FAB ionization processes producing unusual ions [M+2]^+· and [M+3]⁺ in addition to the anticipated [M+1]⁺, whereas ESI generated only [M+H]⁺ as the molecular-related ion. The reduction mechanism is hypothesized as the protonation from the matrix with a concomitant electron transfer,^*1 rather than the transfer of hydrogen atom(s), H^·_·ESI, in which matrix is not used, did not produce [M+2]^+· nor [M+3]⁺ more than the natural isotope abundance of ¹³C in the sample molecules. The reduction site expands to N(1)=C(10a)-C(4a)=N(5), a1,4-diaza-1,3-butadiene system, in the isoalloxazine ring, resembling the behavior of prosthetic groups of aerobic dehydrogenases.

Key words: Riboflavin, FMN, FAD, Matrix, Reduction

[ Full Text PDF ] [ References ]