mm3 Potential energy surfaces of α-3-linked l-fucobiose and fucotriose and their sulfated counterparts Original Research Article

The adiabatic potential energy surfaces (PES) of α-l-Fuc-(1 → 3)-α-l-Fuc and their counterparts disulfated at 2,2′ and 4,4′, and tetrasulfated at 2,2′,4,4′, which are representative of fucoidan structures, were obtained using the mm3 force field, and plotted as contour maps and as 2D graphs representing the energy versus the ψ angle. The surfaces of the corresponding trisaccharides were also obtained and represented by a single 3D contour map for which the energy is plotted against the two ψ glycosidic angles. For the nonsulfated disaccharide, similar populations of two minima occur. A substantial sulfate effect is observed. Whereas sulfation on both of the 2-positions shift the global minimum to positive ψH angles, sulfation on both of the 4-positions deepen the well at negative ψH values. A similar effect occurred in their galactose counterparts. Sulfation on the 2- and 4-positions carry the additive effect of both groups. The same trend was observed for both linkages present in the trisaccharides, with minor differences. For instance, the 4,4′,4″ trisulfated compound exhibits a trend by which the glycosidic linkage closer to the nonreducing end appears to be highly flexible, with similar energies in both conformers. Raising the dielectric constant on nonsulfated oligosaccharides was found to give a better agreement with experimental determinations.