Quantum Chemical Calculation of the Formation Mechanism of the Sugar Smoking Pigment 5-(α-D-Glucopyranosyl-(1-6)-α-D-glucopyranosyloxymenthyl)-2-furancarboxaldehyde

In order to explore the formation pathways of 5-(α-D-glucopyranosyl-(1-6)-α-D-glucopyranosyloxymenthyl)-2-furancarboxaldehyde (5-GGMF), a pigment formed during the process of sugar smoking, the thermal decomposition reaction site of sucrose, the dehydration reaction modes between glucose and 5-hydroxymethylfurfural (5-HMF) and between two molecules of glucose, and the formation pathways of 5-HMF and 5-GGMF were analyzed by quantum chemical calculation. The results showed that the initial position of thermal decomposition of sucrose was the cleavage of fructosyl-oxygen bond. van der Waals force played a leading role in the complexes formed by the interaction between glucose and 5-HMF and between two molecules of glucose, and the intermolecular dehydration reaction was promoted by strong hydrogen bonding. The formation of 5-HMF from the glucose moiety formed after the pyrolysis of sucrose needed more activation energy than from the fructose moiety formed with a lower reaction rate, indicating that the fructose moiety was more prone to form 5-HMF. Among the two formation pathways of 5-HMF from the fructose moiety, pathway 5 was more prone to occur than pathway 4, because pathway 5 showed obvious advantages in energy and reaction kinetics. In the formation pathways of 5-GGMF from sucrose, the energy barrier of the transglycosylation pathway was overall lower, which was more favorable than the disaccharide dehydration and trisaccharide dehydration pathways. Among them, pathway C2, including three steps: the pyrolysis of sucrose to produce fructose and glucose, the reaction of glucose with 5-HMF to form 5-glucosyloxymethylfurfural (5-GMF), and the reaction of 5-GMF with a molecule of free glucose to produce 5-GGMF, was most conducive to the generation of 5-GGMF from both an energy barrier and kinetic perspective. The results of this study can provide a theoretical basis and reference for controlling and intervening in the color of sugar smoked products in the future.