title: Vibrational Signatures of Isomeric Lithiated N-acetyl-D-hexosamines by Gas-Phase Infrared Multiple-Photon Dissociation (IRMPD) Spectroscopy.
abstract: Three lithiated N-acetyl-D-hexosamine (HexNAc) isomers, N-acetyl-D-glucosamine (GlcNAc), N-acetyl-D-galactosamine (GalNAc), and N-acetyl-D-mannosamine (ManNAc) are investigated as model monosaccharide derivatives by gas-phase infrared multiple-photon dissociation (IRMPD) spectroscopy. The hydrogen stretching region, which is attributed to OH and NH stretching modes, reveals some distinguishing spectral features of the lithium-adducted complexes that are useful in terms of differentiating these isomers. In order to understand the effect of lithium coordination on saccharide structure, and therefore anomericity, chair configuration, and hydrogen bonding networks, the conformational preferences of lithiated GlcNAc, GalNAc, and ManNAc are studied by comparing the experimental measurements with density functional theory (DFT) calculations. The experimental results of lithiated GlcNAc and GalNAc show a good match to the theoretical spectra of low-energy structures adopting a4C1chair conformation, consistent with this motif being the dominant conformation in condensed-phase monosaccharides. The epimerization effect upon going to lithiated ManNAc is significant, as in this case the1C4chair conformers give a more compelling match with the experimental results, consistent with their lower calculated energies. A contrasting computational study of these monosaccharides in their neutral form suggests that the lithium cation coordination with Lewis base oxygens can play a key role in favoring particular structural motifs (e.g., a4C1versus1C4) and disrupting hydrogen bond networks, thus exhibiting specific IR spectral features between these closely related lithium-chelated complexes. Graphical Abstract ᅟ.
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA.|Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200031, China.
authors.forename: Yanglan
authors.initials: Y
authors.lastname: Tan
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Precision Spectroscopy, Institute of Theoretical and Computational Science, East China Normal University, Shanghai, 200062, China.
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI, 48824, USA.
authors.forename: Pengfei
authors.initials: P
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA.
authors.forename: Corey N
authors.initials: CN
authors.lastname: Stedwell
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA.
authors.forename: Long
authors.initials: L
authors.lastname: Yu
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA. polfer@chem.ufl.edu.
authors.forename: Nicolas C
authors.initials: NC
authors.lastname: Polfer
keywords: Gas-phase conformations; IRMPD spectroscopy; Lithiated N-acetyl-D-hexosamine; Mass spectrometry; Vibrational signatures