Relaxed potential energy surfaces of maltose

Abstract

Experimentally observed solution conformations of carbohydrate molecules might correspond to a dynamical average of several interconverting conformers in solution. In order to understand and describe more precisely molecular flexibility and motions, new computational routes have to be envisaged. Compared to conventional approaches where sugar residues are treated as rigid, the optimization of all the internal parameters—i.e., bond angles, valence angles, and all torsional angles—is an important step toward more realistic information. Here we report the calculations of potential energy surfaces where all the internal coordinates of the molecules were “relaxed” and minimized through an extensive molecular mechanics scheme. For this work, a prototypical carbohydrate system, the disaccharide α‐maltose, was selected. The inclusion of the relaxed principle into conformational description of maltose does not generally alter the overall shape of the allowed low‐energy regions, or the position of the local minima. However, flexibility within the ring plays a crucial role. Its principle effect is the lowering of energy barriers to conformational transitions about the glycosidic bonds, permitting pathways among the low‐energy minima. This occurs with retaining the overall ⁴C₁ conformation of the glucose residues. The torsional angles corresponding to the orientations of the hydroxyl groups, especially the primary hydroxyl ones, display stable arrangements separated by energy barriers. They create subpopulations of stable conformers and it has not been possible to take into consideration interconversion of one subpopulation to another one. A “synthetic” relaxed potential energy surface is proposed, which can provide a realistic starting base for further investigation of solution behavior of dynamic simulations.