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Influence of H-bonds on acidity of deoxy-hexose sugars

Mosapour Kotena, Z ; Sharif University of Technology | 2020

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  1. Type of Document: Article
  2. DOI: 10.1002/poc.4094
  3. Publisher: John Wiley and Sons Ltd , 2020
  4. Abstract:
  5. The unusual monosaccharaides such as deoxy-hexose sugars, including methyl-pentose and aldo-pentose, are promising and important sugars in life science. However, little research on H-bond interactions in these systems has been reported. The aldo-pentose has a proton instead of the CH2OH group on C5; conversely, methyl-pentose has a CH3 group on C5. The aim of the present study is to investigate the role and nature of intramolecular H-bonds on acidity of CH3-pentose sugars (L-fucose and L-rhamnose) and aldo-pentose sugars (D-xylose, L-lyxose, D-ribose, and L-arabinose) using B3LYP/6-311++G (d, p) level. The calculated acidity values (ΔHacid) of these Dexoy-hexose were found to be from 343 to 369 kcal.mol−1, indicating they are stronger acid than ethanol and 2-propanol with the acidity values of 378.3 and 375.1 kcal.mol−1, respectively. This is related to the stabilization of the conjugate bases of these sugar through intramolecular H-bonds, which were analyzed in this study using atoms in molecules (AIM) and natural bonding orbital (NBO) methods. AIM and NBO analyses indicate the presence of one bifurcated intramolecular H-bond in the conjugate bases of L-lyxose and L-arabinose and two bifurcated H-bonds in conjugate base of D-ribose, whereas the conjugate bases of L-fucose, L-rhamnose, and D-xylose present one normal intramolecular H-bond. According to the topological parameters and charge transfer data, existence of normal and bifurcated intramolecular H-bonds could greatly increase acidity of deoxy-hexose sugars. The H-bond strength in the conjugate bases of aldo-pentose sugars is higher than that in the conjugate bases of methyl-pentose sugars including CH3 group on C5, making aldo-pentose sugars stronger acid than methyl-pentose sugars. © 2020 John Wiley & Sons, Ltd
  6. Keywords:
  7. Acidity ; Deoxy-hexoes sugars ; Hydrogen bonding ; Charge transfer ; Complexation ; Atoms in Molecules ; B3LYP/6-311++G ; Conjugate basis ; H-bond strength ; Hexose sugars ; Natural bonding orbitals ; Pentose sugars ; Topological parameters ; Sugars
  8. Source: Journal of Physical Organic Chemistry ; Volume 33, Issue 10 , June , 2020
  9. URL: https://onlinelibrary.wiley.com/doi/abs/10.1002/poc.4094