Thirsty Sugars – Where does the Water go in their Structures?
Faculty Mentor Name
Andreas H. Franz
Research or Creativity Area
Natural Sciences
Abstract
Purpose: The goal of the research project was to answer the question how transient hydrogen bonding among sugar hydroxyl groups stabilizes and define the sugar’s solution geometry.
Results: Isotope effects1 (H-O-13C “beta” and H-O-C-13C “gamma”) and H/D exchange2 visible in NMR spectra allowed us to investigate the structures of maltose and maltotriose in DMSO with minimal water content. Using COSY, HSQC, and HMBC data, all carbon and hydrogen signals of maltose and maltotriose in dry DMSO were identified. In the ¹³C NMR spectra with H2O/D2O present, expected isotope effects were observed for most carbons. However, unexpected additional isotope shifts along the ɑ-1,4 linkage were observed. We designated the effects β* and attributed them to intermolecular hydrogen bonding. Whether the hydrogen bond was direct between the hydroxyl groups or mediated by bound water molecules could not completely be delineated. Computational analysis did not disprove the existence of a water molecule hydrogen bonding along the ɑ-1,4 glycosidic linkage. Future INTOXY experiments measuring the rate of H/D exchange are expected to provide insight into whether the β* effect comes from a hydrogen bond with a water molecule or simply between the OH groups.
Significance: Carbohydrates are among the most important macromolecules to life, serving as the preliminary source of energy for all living organisms. Formed by repeating units of monosaccharides linked by glycosidic bonds, carbohydrates exist in water-rich environments within living organisms. It is difficult to analyze the molecular structure of saccharides in water due to signal resolution and signal overlap, particularly in long polysaccharides. Techniques such as X-ray crystallography can be used to investigate the structure of polysaccharides in solid or crystal form. However, in living organisms, sugars exist in solution and are better characterized by Magnetic Resonance (NMR) spectroscopy. Our results provide evidence for significant hydrogen bonding across the a-1,4-linkage of glucose oligosaccharides with implications as far as the helical structure of amylose is concerned. Our results also provide the basis for future investigation of the role of water in structure stabilization of oligosaccharides in nature.
- P. E. Hansen, Journal of Labelled Compounds and Radiopharmaceuticals 2007, 50 (11-12), 967-981 https://doi.org/https://doi.org/10.1002/jlcr.1440.
- M. D. Battistel; H. F. Azurmendi; D. I. Freedberg, J. Phys. Chem. B 2017, 121 (4), 683-695 https://doi.org/10.1021/acs.jpcb.6b10594.
Thirsty Sugars – Where does the Water go in their Structures?
Purpose: The goal of the research project was to answer the question how transient hydrogen bonding among sugar hydroxyl groups stabilizes and define the sugar’s solution geometry.
Results: Isotope effects1 (H-O-13C “beta” and H-O-C-13C “gamma”) and H/D exchange2 visible in NMR spectra allowed us to investigate the structures of maltose and maltotriose in DMSO with minimal water content. Using COSY, HSQC, and HMBC data, all carbon and hydrogen signals of maltose and maltotriose in dry DMSO were identified. In the ¹³C NMR spectra with H2O/D2O present, expected isotope effects were observed for most carbons. However, unexpected additional isotope shifts along the ɑ-1,4 linkage were observed. We designated the effects β* and attributed them to intermolecular hydrogen bonding. Whether the hydrogen bond was direct between the hydroxyl groups or mediated by bound water molecules could not completely be delineated. Computational analysis did not disprove the existence of a water molecule hydrogen bonding along the ɑ-1,4 glycosidic linkage. Future INTOXY experiments measuring the rate of H/D exchange are expected to provide insight into whether the β* effect comes from a hydrogen bond with a water molecule or simply between the OH groups.
Significance: Carbohydrates are among the most important macromolecules to life, serving as the preliminary source of energy for all living organisms. Formed by repeating units of monosaccharides linked by glycosidic bonds, carbohydrates exist in water-rich environments within living organisms. It is difficult to analyze the molecular structure of saccharides in water due to signal resolution and signal overlap, particularly in long polysaccharides. Techniques such as X-ray crystallography can be used to investigate the structure of polysaccharides in solid or crystal form. However, in living organisms, sugars exist in solution and are better characterized by Magnetic Resonance (NMR) spectroscopy. Our results provide evidence for significant hydrogen bonding across the a-1,4-linkage of glucose oligosaccharides with implications as far as the helical structure of amylose is concerned. Our results also provide the basis for future investigation of the role of water in structure stabilization of oligosaccharides in nature.
- P. E. Hansen, Journal of Labelled Compounds and Radiopharmaceuticals 2007, 50 (11-12), 967-981 https://doi.org/https://doi.org/10.1002/jlcr.1440.
- M. D. Battistel; H. F. Azurmendi; D. I. Freedberg, J. Phys. Chem. B 2017, 121 (4), 683-695 https://doi.org/10.1021/acs.jpcb.6b10594.
