Building Up Key Segments of N-Glycans in the Gas Phase:  Intrinsic Structural Preferences of the α(1,3) and α(1,6) Dimannosides

The intrinsic conformer specific vibrational spectra of two important subunits of the core pentasaccharide of N-linked glycans, the α(1,3) and α(1,6) dimannosides, have been recorded in the gas phase. Coupling these measurements with a computational exploration of their conformational landscapes has enabled their conformational assignment and has identified characteristic vibrational signatures associated with particular conformational familiesincluding those that do or do not display inter-ring hydrogen bonding across the glycosidic linkage. In addition, the IR spectra of the monosaccharide moieties provide benchmarks, through which the conformational assignments can be refined. This introduces a general concept of modularity and secondary structure in oligosaccharidesessential for the success of similar studies on larger oligosaccharides in the future.