|French, Alfred - Al|
Submitted to: American Society for Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2002
Publication Date: 6/1/2003
Citation: Mendonca, S., Cole, R.B., Zhu, J., Cai, Y., French, A.D., Johnson, G.P., Laine, R.A. 2003. Incremented alkyl derivatives enhance collision induced glycosidic bond cleavage in mass spectrometry of disaccharides. American Society for Mass Spectrometry. 14:63-78. Interpretive Summary: Understanding the composition of carbohydrate molecules is a prime requirement for understanding much of biology. For example, many carbohydrates are involved in cellular recognition processes that are inherent in diseases. Mass spectroscopy is used increasingly to chemically identify carbohydrate molecules, because it furnishes exact weights for the molecule and its fragments that occur from collision during the experiments. Generally, it is far less tedious to determine this information with mass spectroscopy than with other methods, even though the product of a run on this equipment can be a confusing array of lines that must be interpreted. The present project attempts to gain additional structural details from mass spectrometry on intermediate sized carbohydrate molecules. The tested hypothesis was that fragmentation that occurs during the experiment depends on the internal flexibility of the molecule. Molecules that are likely to have different degrees of flexibility were synthesized and their fragmentation was compared with their flexibility as determined by computer modeling studies. This work helps to improve the theoretical foundation for a tool that is widely used and could lead to further advances in the identification of molecules. Without further work, it is of interest mostly to scientists engaged in mass spectrometry of carbohydrates.
Technical Abstract: Electrospray ionization and collision induced dissociation on a triple quadrupole mass spectrometer were used to determine the effect of spatial crowding by peralkylation (methyl to pentyl) of two anomeric pairs of disaccharides (maltose/cellobiose and isomaltose/gentiobiose). Protonated molecules fragmented extensively under low energy conditions. At comparable collision energies the methyl derivative fragmented the least, followed by ethyl, propyl, butyl and pentyl. Collision energy is converted to rotational-vibrational modes in competition with bond cleavage, as represented by the slope of product/parent ion (D/P) ratio versus offset energy. Variable rotational freedom at the glycosidic linkage from the incremented alkyl groups is thought to be responsible for this effect. Discrimination of anomeric configuration was also assessed for these stereoisomeric disaccharides. A systematic study showed that an increasing discrimination was attained for the 1-6 isomeric pair. Parent and product ion scans confirmed the consistency of fragmentation pathways among derivatives. Chem-X and MM3 molecular modeling programs were used to obtain minimum energy structures and freedom of motion volumes for the permethylated disaccharides. The modeling indicated that the collision induced spectra are dependent on the freedom of rotational motion around the glycosidic bonds.