Structure-Transport Relationships in Aqueous Fructose Solutions: A Combined Molecular Dynamics and NMR Diffusion...

Fructose is widely used in the food industry and is proposed as a sustainable biomass feedstock for chemical manufacturing. Upon dissolution in water, it undergoes mutarotation into different tautomers, primarily β-d-fructopyranose (68%) and β-d-fructofuranose (22%), as well as into the linear keto d-fructose structure. Although present only in small amounts, the linear tautomer may alter diffusion within aqueous media and porous catalytic materials. To elucidate the structure-transport properties of aqueous solutions containing fructose, molecular dynamics (MD) simulations are combined with nuclear magnetic resonance (NMR) diffusion experiments. Classic MD simulations are conducted at atomistic resolution using three different force fields. The NMR diffusion experiments are conducted in deuterated water to differentiate water from sugar peaks in the experimental signal. When the OPLS-AA force field is implemented, the MD simulated diffusion coefficients, as well as bulk system densities, are consistent with experiments, indicating the atomistic models are realistic. Interrogating the simulation trajectories confirms that fructose molecules aggregate into clusters, which lowers the diffusion coefficients of both fructose and water at high fructose concentration. Modest differences are observed in the mobility of the two cyclic tautomers, even in the presence of the linear counterpart. Such insight into the structure and mobility of fructose in bulk aqueous solutions across a range of concentrations is paramount to understanding several industrial processes, for example those involved in catalytic biomass upgrading technologies.