279
9 Polyphenol Glycosides as Potential Remedies in Kidney …
carbohydrate molecules; O1 and O2 from the first, O3 and O4 from the second and
O6 from the third. The coordination shell is completed by three molecules of water
[13].
Takashi et al. [30] and Cook and Bugg [31] studied the complexes of trehalose
(disaccharide formed by an α,α-1,1-glucoside bond between two α-glucose units)
with calcium chloride and calcium bromide respectively. Both structures were very
similar. In each complex the calcium ion is coordinated to one molecule of water
and four molecules of trehalose (hydroxyl groups O2 and O3 from two molecules
and two O6 hydroxyl oxygen from other molecules. These seven oxygen atoms are
arranged in pseudo pentagonal bipyramid—similar to one discussed for the calcium
bromide—lactose complex.
Fructose exists in the complex with calcium surrounded by eight oxygen atoms
from four molecules of sugar and two molecules of water, which form a distorted
square antiprism. Two fructose molecule binds through their O2 and O1 oxygen
atoms in bidendate fashion and other two by their O6 oxygen atom in monodentate
fashion [32].
The open chain carbohydrate derivatives like alditols form complexes with
calcium but their formation strongly depends on their conformation. Angyal [17]
based on NMR studies, has proposed that three consecutive hydroxyl groups have
to be able to form conformation similar to ax–eq–ax. It is possible when they have
the threo–threo configuration. In the case of the erythro–erythro configuration side
chains are parallel to each other, thus making such a conformation of relatively
higher energy. When three consequitive hydroxyl groups are in threo–erythro configuration two side chains are in the gauche arrangement which makes this isomer
less stable than threo–threo but more stable than erythro–erythro. Angyal pointed
out, based on electrophoretic mobility, that the ratio of all-threo to all erythro is in
the range of 0.24–0.09. The above consideration relates to complexes when three
hydroxyl groups from one alditol is complexed to the same calcium atom. If it is not
possible the carbohydrate becames bidendate ligand. The situation is less complicated when one or even two side chains are small hydrogen atoms.
Yang et al. [33] have studied the coordination behaviour of neutral erythritol
with calcium and lanthanide ions. Erythritol is one of the simplest representative of
carbohydrates with four carbons each with the hydroxyl group on it. The hydroxyl
group are not in the threo–threo arrangement to form tridentate ligand. They have
identified three different metal complexes with the molar ratio of metal ion to erythritol as 2:1, 1:1, and 1:2. In all structures erythritol acts as the bidendate ligand.
The structures are shown on Fig. 9.6. In the first structure (Fig. 9.6a) the calcium is
surrounded by seven ligands: three chloride ions, two water molecules, and two hydroxyl groups from erithritol, which results in the pentagonal bipyramidal arrangement. In the second structure (Fig. 9.6b), calcium is coordinated to four hydrohyl
groups from two erythritol molecules and four molecules of water. Chloride ions do
not coordinate to calcium. Calcium is 8-fold coordinated in the bicapped trigonal
prism. In the third structure (Fig. 9.6c) the calcium is surrounded by eight hydroxyl
groups from four erythritol molecules.
9 Polyphenol Glycosides as Potential Remedies in Kidney …
carbohydrate molecules; O1 and O2 from the first, O3 and O4 from the second and
O6 from the third. The coordination shell is completed by three molecules of water
[13].
Takashi et al. [30] and Cook and Bugg [31] studied the complexes of trehalose
(disaccharide formed by an α,α-1,1-glucoside bond between two α-glucose units)
with calcium chloride and calcium bromide respectively. Both structures were very
similar. In each complex the calcium ion is coordinated to one molecule of water
and four molecules of trehalose (hydroxyl groups O2 and O3 from two molecules
and two O6 hydroxyl oxygen from other molecules. These seven oxygen atoms are
arranged in pseudo pentagonal bipyramid—similar to one discussed for the calcium
bromide—lactose complex.
Fructose exists in the complex with calcium surrounded by eight oxygen atoms
from four molecules of sugar and two molecules of water, which form a distorted
square antiprism. Two fructose molecule binds through their O2 and O1 oxygen
atoms in bidendate fashion and other two by their O6 oxygen atom in monodentate
fashion [32].
The open chain carbohydrate derivatives like alditols form complexes with
calcium but their formation strongly depends on their conformation. Angyal [17]
based on NMR studies, has proposed that three consecutive hydroxyl groups have
to be able to form conformation similar to ax–eq–ax. It is possible when they have
the threo–threo configuration. In the case of the erythro–erythro configuration side
chains are parallel to each other, thus making such a conformation of relatively
higher energy. When three consequitive hydroxyl groups are in threo–erythro configuration two side chains are in the gauche arrangement which makes this isomer
less stable than threo–threo but more stable than erythro–erythro. Angyal pointed
out, based on electrophoretic mobility, that the ratio of all-threo to all erythro is in
the range of 0.24–0.09. The above consideration relates to complexes when three
hydroxyl groups from one alditol is complexed to the same calcium atom. If it is not
possible the carbohydrate becames bidendate ligand. The situation is less complicated when one or even two side chains are small hydrogen atoms.
Yang et al. [33] have studied the coordination behaviour of neutral erythritol
with calcium and lanthanide ions. Erythritol is one of the simplest representative of
carbohydrates with four carbons each with the hydroxyl group on it. The hydroxyl
group are not in the threo–threo arrangement to form tridentate ligand. They have
identified three different metal complexes with the molar ratio of metal ion to erythritol as 2:1, 1:1, and 1:2. In all structures erythritol acts as the bidendate ligand.
The structures are shown on Fig. 9.6. In the first structure (Fig. 9.6a) the calcium is
surrounded by seven ligands: three chloride ions, two water molecules, and two hydroxyl groups from erithritol, which results in the pentagonal bipyramidal arrangement. In the second structure (Fig. 9.6b), calcium is coordinated to four hydrohyl
groups from two erythritol molecules and four molecules of water. Chloride ions do
not coordinate to calcium. Calcium is 8-fold coordinated in the bicapped trigonal
prism. In the third structure (Fig. 9.6c) the calcium is surrounded by eight hydroxyl
groups from four erythritol molecules.