The Electronic Nature of the 1,4-[beta]-Glycosidic Bond and Its Chemical Environment: DFT Insights into Cellulose Chemistry

The molecular understanding of the chemistry of 1,4-[beta]-glucans is essential for designing new approaches to the conversion of cellulose into platform chemicals and biofuels. In this endeavor, much attention has been paid to the role of hydrogen bonding occurring in the cellulose structure. So far, however, there has been little discussion about the implications of the electronic nature of the 1,4-[beta]-glycosidic bond and its chemical environment for the activation of 1,4-[beta]-glucans toward acid-catalyzed hydrolysis. This report sheds light on these central issues and addresses their influence on the acid hydrolysis of cellobiose and, by analogy, cellulose. The electronic structure of cellobiose was explored by DFT at the BB1K/6-31++G(d,p) level. Natural bond orbital (NBO) analysis was performed to grasp the key bonding concepts. Conformations, protonation sites, and hydrolysis mechanisms were examined. The results for cellobiose indicate that cellulose is protected against hydrolysis not only by its supramolecular structure, as currently accepted, but also by its electronic structure, in which the anomeric effect plays a key role. Strong nature: The electronic nature of the 1,4-[beta]-glycosidic bond and its chemical environment is examined by DFT calculations on cellobiose. The results reveal that cellulose is protected against hydrolysis not only by the hydrogen-bond network, as currently accepted, but also by the electronic structure, in which the anomeric effect plays a key role.