Use of a General Purpose Force-Field (MM2) for the Conformational Analysis of the Disaccharide α-D-Galactopyranosyl-(1 → 3)-β-D-Galactopyranose

Conformational analysis for disaccharide α-D-Galp-(1 → 3)-β-D-Galp was carried out by molecular mechanics calculations with the general purpose force-field MM2. The adiabatic potential energy surfaces were obtained using a total force-field, and by substracting the effects of hydrogen bonding and electrostatic forces. The effect of modifying the dielectric constant was also studied. A complex conformational equilibrium was shown. The positions and energies of the minima were also calculated with the force field MM2CARB. Linkage rotations (A), NOS values and interatomic distances calculated for the preferred conformations were compared with those from experimental data; it is concluded that in aqueous solutions hydrogen bonding should be discarded, and that electrostatic interactions are of little significance.