The water-catalyzed mechanism of the ring-opening reaction of glucose
The hexopyranose mutarotation is an important focus for carbohydrate chemistry for more than 150 years. The paper describes the results of advanced computational studies aimed at elucidating the ring-opening reaction of glucose. Molecular simulations based on the combination of the DFT method with the molecular dynamics formalism allowed for a detailed insight into the mechanism of the process accompanied by the information of the kinetic and dynamic nature. The results indicate that the process is initiated by deprotonation of the anomeric hydroxyl group by water molecules and the subsequent proton transfer to the ring oxygen atom. The latter event has been identified as a ‘bottleneck’ of the process triggering the ring cleavage. The most time-consuming steps of the ring-opening reaction are the orientational rearrangements of water molecule(s) participating in the proton transfer(s) and the final extension of the newly-formed aldehyde chain. The orientational preferences of the aldehyde group present in the acyclic form of D-hexopyranoses are responsible for the anomeric equilibrium characteristics.