Details of glucose solution near-infrared band assignment revealed the anomer difference in the structure and the interaction with water molecules

Glucose is not only widely used as an energy source, glycosylation of protein, and drought tolerance in living organisms, but its polymerization and degradation are also important in the industrial and agricultural fields. Understanding the interaction between carbohydrate and water molecules is desirable because most of these reactions occur in an aqueous environment. In the field of near-infrared spectroscopy, the aqueous solution of carbohydrates is one of the featured targets, but few studies have clarified directly near-infrared band that captured the interaction between carbohydrates and the surrounding water molecules. For band assignment of glucose solution, we obtained near-infrared spectra of two glucose anomers in deuterium oxide as well as four types of glucose isotopes and applied a partial least squares regression analysis to these spectra with the specific rotation. Consequently, we found that different spectra of glucose anomers in the region of 1682–1823 nm contain two glucose bands and a solvent water band. It is considered that the two glucose bands originate from an exocyclic hydroxymethyl CH2 group and a CH group on the C1 carbon, on the other hand, the solvent water band at 1746 nm originate from water molecules that specifically interact with one of the glucose anomers. Taking advantage of the chemical characteristics of glucose, our detailed band assignment in the near-infrared spectrum of aqueous glucose solution revealed the difference of each anomer structure and interaction with water molecules.