Ab Initio Molecular Dynamics Simulations of Aqueous Glucosamine Solutions: Solvation Structure and Mechanism of Proton Transfer from Water to Amino Group.

Glucosamine is a component of many cellular glycoproteins that constitutes the cartilage, and it has several biological activities, such as anti-inflammatory, antioxidant, antifibrotic, and anticancer, and has been used in arthritis and dermatological treatments. Considering that the biological activities of glucosamine occur mainly in an aqueous environment, it is essential to understand the effects of an aqueous solvent on its geometric and electronic parameters using ab initio molecular dynamics. The Car-Parrinello molecular dynamics results show that the hydroxyl groups form stable hydrogen bonds with the water molecules with intensities ranging from weak (closed-shell interaction) to intermediate (partially covalent interactions). The H bonds formed between the amino group and the water molecule range from weak (closed-shell) to strong (covalent), and it shows an infinity residence time. The natural bonding orbital (NBO) approach was applied to analyze the effects of charge-transfer interactions on the behavior of the hydrogen bonds. The main contribution to stabilizing energies comes from n → σ* hyperconjugation and explains the stability of the H bonds. The energy barrier for the proton transfer from water to the amino group is 0.88 kcal/mol, and the van der Waals complex energy is 0.3 kcal/mol. The low protonation energy barrier shows that glucosamine can be protonated in an aqueous environment at room temperature, which helps to explain many of its biological activities.