Quantification of anomeric structural changes of glucose solutions using near-infrared spectra.

Glucose is the most abundant carbohydrate found in living organisms. It exists as two anomers: α-D-glucose and β-D-glucose, which differ in how the hydroxyl group on the C1 carbon is directed. In solutions, the ratio between α- and β-D-glucose is typically 4:6 but can vary depending on the surrounding ions or temperature. In this study, we obtained near-infrared (NIR) spectra of the glucose anomers based on concentration, and analyzed the spectral difference between each anomer by spectra subtraction and principal component analysis, respectively. Moreover, by simultaneously measuring the optical rotation and NIR spectra from dissolution to equilibration, we showed that NIR spectra quantitatively estimated the specific rotations of glucose solutions using partial least-squares regression in the 1100-1800 nm wavelength range. All the analytical results indicated that the absorption at 1742 nm possess the potential to distinguish each glucose anomer quantitatively. Therefore, we addressed the prediction of the specific rotation by the absorption at 1742 nm, and demonstrated that the absorption normalized by line subtraction showed the high correlation with measured specific rotation. The absorption at 1742 nm reflects structural changes of the glucose anomers in solution. Our spectroscopy study not only provides spectral information about glucose anomers, which are the most fundamental chemical compounds in organisms, but also shows the possibility to detect the anomer ratio in vivo for the fields of agriculture and medicine by taking advantage of NIR.