Density Functional Study on the Mechanism of Amadori Rearrangement Reaction

The reaction mechanism of amadori rearrangement in the initial stage of Maillard reaction has been investigated by means of density functional theory calculations in the gaseous phase and aqueous solution. Cyclic ribose and glycine were taken as the model in the amadori rearrangement. Reaction mechanisms have been proposed, and possibility for the formation of different compounds has been evaluated through calculating the relative energy changes for different steps of the reaction by following the total mass balance. The calculations reveal that the amadori rearrangement initialized via the intramolecular rearrangement, transferring one proton from N(3) to O(4) atom. In the next step, the second proton is also transferred from N(3) to O(4) atom, corresponding to the cleavage of C(4)-O(4) bond and the release of one water molecule. Then another proton is transferred from N(3) to C(5) atom via TS3 with the reaction barrier of 58.3 kcal.mol(-1) after tunneling the effect correction calculated at the B3LYP/6-31+G(d) level of theory, and this step is rate limiting for the whole catalytic cycle. Ultimately, the product is generated via keto-enolic tautomerization. Present calculation could provide insights into the reaction mechanism of Maillard reaction since experimental evaluation of the role of intermediates in the Maillard reaction is quite complicated.