Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
TABLE 2.1
Free Energy of Nonbonding Interaction in the Pyranose Ring
Interaction Energy (kJ mole −1 )
Axial–Axial
H–O 1.88
O–O 3.76
O–(CH3, CH2OH) 6.27
Equatorial–Equatorial
O–O 10.45
O–(CH3, CH2OH) 1.46
Equatorial–Axial
O–O 1.88
O–(CH3, CH2OH) 1.46
Note: In aqueous solution at room temperature.
conformational analysis to monosaccharides. The relative stability of the α-(2.4) and
β-(2.5) anomers and the α to β ratio in the equilibrium can be predicted for this
equilibrium process.
HO
HO
CH2OH
O
CH2OH
O
HO
HO OH
OH
OH
OH
2.4 2.5
conf = 10.03 kJ/mol Econf = 8.57 kJ/mol
α : β =36 : 64 (experimented and calculated)
2.2 THE COMPLEX FORMATION OF CARBOHYDRATES
WITH CATIONS
The hydroxyl groups of carbohydrates can coordinate to metal cations. The ability
to form complexes and the stability of the relevant complexes of neutral carbohydrates
strongly depend on the conformational orientation of the neighboring hydroxyl
groups. Several carbohydrates with the axial–equatorial–axial sequence of hydroxyl
groups form stable complexes with the Na + , Mg 2+ , Zn 2+ , Ba 2+ , Sr 2+ , and Ca 2+ ions.
Thus, α-D-gulopyranose forms a tridentate complex (2.6) with calcium chloride in
solution (stability constant K = 3.7 M -1 ) whereas β-D-gulopyranose (2.7) cannot
form such complex.