2009_Book_FoodChemistry

4.3 Oligosaccharides 293
can be written as O-β-D-Fru f (2 → 1)α-D-Glcp
and O-α-D-Glcp(1 → 4)D-Glcp, respectively.
A calculation of conformational energy for all
conformers with allowed Φ,ψ pairs provides
a Φ,ψ diagram with lines corresponding to
iso-conformational energies. The low-energy
conformations calculated in this way agree with
data obtained experimentally (X-ray diffraction,
NMR, ORD) for oligo- and polysaccharides.
H-bonds fulfill a significant role in conformer stabilization.
Cellobiose and lactose conformations
are well stabilized by an H-bond formed between
the HO-group of C-3 in the glucose residue and
the ring oxygen of the glycosyl residue. Conformations
in aqueous solutions appear to be similar
to those in the crystalline state:
(4.114)
Branching also occurs in oligosaccharides. It
results when one monosaccharide is bound to
two glycosyl residues. The name of the second
glycosyl residue is inserted into square brackets.
A trisaccharide which represents a building block
of the branched chain polysaccharides amylopectin
and glycogen is given as an example:
(4.115)
(4.118)
In crystalline maltose and in nonaqueous solutions
of this sugar, a hydrogen bond is established
between the HO-groups on C-2 of the glucosyl
and on C-3 of the glucose residues (4.119). However,
in aqueous solution, a conformer partially
present is stabilized by H-bonds established
between the CH 2 OH-group of the glucosyl
residue and the HO-group of C-3 on the glucose
residue (4.120). Both conformers correspond to
the two energy minima in the Φ,ψ diagram.
The abbreviated formula for this trisaccharide is
as follows:
(4.116)
The conformations of oligo- and polysaccharides,
like peptides, can be described by providing the
angles Φ and ψ:
(4.117)
(4.119)
(4.120)
Two H-bonds are possible in saccharose, the first
between the HO-groups on the C-1 of the fruc-