Three - Dimensional Aspects of the Sugar Code - The Sugar Code - page 20

Figure 2.3 Conformational energy maps of
Gal β 1,4Glc ( β - lactose) and Gal β 1,4GlcNAc ( β -
LacNAc). The fi rst two maps (A and B) also
showing the energy profi les originate from
www.glycosciences.de; the two additional maps
were obtained from 1-ns water simulations (see

Figure 2.5 for details) and illustrate the Φ , Ψ
sampling during the simulations. The confor-
mations, corresponding to energy minima lo-
cated on the map, are marked M1, M2 and
M3.

signifi cant reduction of the dimensionality to two, considering only the Φ , Ψ

dihedral angles for rotation around the glycosidic bond. Consequently, the quality
of these calculations was improved by expanding the energy terms and also by
using improved parameterization of energy functions. The energy contours were
drawn into the

maps, indicating the minima for the most probable conforma-
tions. Although simple potential energy functions were used in the fi rst calcula-
tions, these conformational maps were already instrumental to delineate the
molecular shape of the studied disaccharides.
Together with the progress in development of more sophisticated force fi eld
methods, signifi cant efforts were also devoted towards detailed energy calculation
using quantum mechanical (QM) methods. The fi rst - ever published semiempiri-
cal quantum chemical study of a disaccharide appeared in the early 1970s [7].

Φ , Ψ