A combined solid-state NMR and quantum chemical calculation study of hydrogen bonding in two forms of α-d-glucose

Abstract

Hydrogen bonding plays an important role in the structure and function of a wide range of materials. Solid-state ¹H nuclear magnetic resonance (NMR) spectroscopy provides a very sensitive tool to investigate the local structure of hydrogen atoms involved in hydrogen bonding. While there is extensive ¹H solid-state NMR data on O-H - - O hydrogen bonding in solid carboxylic acids, there has been no systematic ¹H solid-state NMR studies of hydroxyl groups in carbohydrates (and hydroxyl groups in general). With a view to studying the hydrogen bonding in more complex materials such as cellulose polymorphs, we carried out a detailed solid-state ¹H NMR investigation of the model compounds α-d-glucose and α-d-glucose monohydrate. Through a combination of fast magic-angle spinning (MAS), combined rotation and multiple pulse spectroscopy (CRAMPS), and two-dimensional (2D) correlation experiments carried out at ultrahigh magnetic fields, it was possible to assign all of the aliphatic (CH), hydroxyl (OH), and water (H₂O) ¹H chemical shifts in both forms of α-d-glucose. Plane-wave DFT calculations were employed to improve the hydrogen atom positions for α-d-glucose monohydrate and to calculate ¹H chemical shifts, providing additional support for the experimentally determined peak assignments. Finally, the relationship between the hydroxyl ¹H chemical shifts and their hydrogen bonding geometry was investigated and compared to the well-established relationship for carboxylic acid protons.

Keywords: Carbohydrates; Chemical shifts; DFT calculations; Hydrogen bonding; Proton NMR; Solid-state NMR.