Quantification of disaccharides in solution using isomer-selective ultraviolet photodissociation of hydrogen-bonded clusters in the gas phase

Chemical properties of gas-phase hydrogen-bonded clusters were investigated as a model for interstellar mo-lecular clouds. Cold gas-phase hydrogen-bonded clusters of tryptophan (Trp) enantiomers and disaccharide isomers, including D-maltose and D-cellobiose, were generated by electrospray ionization and collisional cooling in an ion trap at 8 K. Product ion spectra in the 265-290 nm wavelength range were obtained using tandem mass spectrometry. NH2CHCOOH loss via the C alpha-C beta bond cleavage of Trp occurred frequently in homochiral H+(D- Trp)(D-maltose) compared with heterochiral H+(L-Trp)(D-maltose) at 278 nm, indicating that an enantiomeric excess of L-Trp was formed via the enantiomer-selective photodissociation. The photoreactivity differed between the enantiomers and isomers contained in the clusters at the photoexcitation of 278 nm. A calibration curve for the quantification of disaccharide isomers in solution was constructed by photoexcitation of the hydrogen-bonded clusters of disaccharide isomers with H+(L-Trp) at 278 nm. A linear relationship between the natural logarithm of the relative product ion abundance and the mole fraction of D-maltose to D-cellobiose ratio in the solution was obtained, indicating that the mole fraction could be determined from a single product ion spectrum. A calibration curve, for quantification of Trp enantiomers, was also obtained using D-maltose as a chiral auxiliary.

Automated summary

Chemical properties of gas-phase hydrogen-bonded clusters were studied as a model for interstellar molecular clouds. Cold gas-phase hydrogen-bonded clusters of tryptophan enantiomers and disaccharide isomers were generated and analyzed using tandem mass spectrometry. The photoreactivity and quantification methods of the clusters were investigated, providing important insights into their composition and behavior.