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 glucose [Gasse et al., J. Chem. Phys. 158, 145101 (2023)] demonstrating 2D-IR spectroscopy of carbohydrates using vibrational probes. Here, we build on that work and test azide groups as alternative for studies of carbohydrates to expand the available set of local probes. Many common carbohydrates with different azide labeling positions, such as galactose, glucose, or lactose, are readily available due to their application in click chemistry and hence do not require additional complex synthesis strategies. In this work, we have characterized azide-labeled glucose,, galactose, acetylglucosamine and lactose in water using IR and 2D-IR spectroscopy to test their potential for future applications in studies of carbohydrate-protein interactions. Our findings indicate that their absorption profiles and vibrational dynamics 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, highlighting their potential to probe more complex biological processes, i.e., enzymatic catalysis.