2D-IR spectroscopy of azide-labeled carbohydrates in H2O

Carbohydrates constitute one of the key classes of biomacromolecules, yet vibrational spectroscopic studies involving carbohydrates remain scarce as spectra are highly congested and lack significant marker vibrations. Recently, we introduced and characterized a thiocyanate-labeled glucose1 demonstrating the use of vibrational reporter groups for 2D-IR spectroscopy of carbohydrates. Here, we expand upon those results and elucidate the performance of azide groups as vibrational reporter for carbohydrates. Originating from applications in click-chemistry, different azide-labeled carbohydrates are readily available. We have characterized azide-labeled glucose, galactose, acetylglucosamine and lactose in water using IR and 2D-IR spectroscopy. Our findings indicate that their absorption profiles are primarily determined by the labeling position on the ring. However, we also observe additional variations between samples with the same labeling position. Furthermore, we demonstrate that their usage remains feasible at biologically relevant concentrations.