273
9 Polyphenol Glycosides as Potential Remedies in Kidney …
densed aromatic polycarbon fragment, which exhibit complexation activity to calcium ions. Polyphenol glycosides constitute the group of such compounds, which
beside standard aromatic part substituted by many hydroxyl groups also possess
glycon part of the carbohydrate molecule. The number of potential binding sites in
these compounds increases due to additional oxygen atom contained in sugar part.
The carbohydrate part increases their solubility in water, which is of great advantage if such compounds are used in kidney stone therapy.
9.2 Carbohydrates as Ligands
In this section we try to bring the issue of Ca
2 +
complexation by sugars from the
structural point of view. Gyurcsik and Nagy [11] pointed out that although some
reviews regarding carbohydrates–metal complexes are available (e.g. “Complexes
of natural carbohydrates with metal cation” by Alekseev et al. [12]), no comprehensive monograph which treat carbohydrates as ligands can be found. We also do not
pretend to cover the whole topic of the area. Hence, we will mostly focus on the
general principles of forming complexes by carbohydrates with a special emphasis
to the cases in which calcium constitutes the metal ion and we present selected the
most typical structures.
At the beginning, it should be noted that interactions between carbohydrates and
metal ions are usually weak. Water strongly binds to hydroxyl groups of carbohydrates, and as a result complexes in water solution and in solid state can be structurally different. The formation of carbohydrate complexes in water requires replacement of water molecules by hydroxyl group from the first coordination sphere. To
form complex in water the interaction of the ligand must be stronger than that with
water molecules. Therefore there are some complexes which cannot exist in water
solution but they exist in crystalline form. Monosaccharides and oligosaccharides
as well as polysaccharides possess in their skeleton, as donors, hydroxyl oxygen
atoms which are relatively weak ligands. Some sugar derivatives can possess ionizable functional group, which might exhibit stronger interactions with metal ion.
Carbohydrates with carboxylic, sulphonic or phosphate groups as an anchoring sites
can form much stronger complexes with calcium ions [13–16]. They are not the
subject of consideration in this chapter.
In 1961 J.A. Mills studied the acidity of sugars by the paper electrophoresis.
He has found that some sugars, even at neutral pH, penetrated toward cathode. This indicated that they are positively charged probably by complexing
cations. The extent of migration was a measure of the complexing ability. The
only coordination centers in neutral sugars are constituted by oxygen atoms of
hydroxyl groups. Since water solvates cations much better, the question that
arises is regarding the number hydroxyl groups needed to form a stable complex. It is believed that at least two or three hydroxyl centers in the favorable
arrangement are required. There is another question related to their favorable
steric arrangements.
9 Polyphenol Glycosides as Potential Remedies in Kidney …
densed aromatic polycarbon fragment, which exhibit complexation activity to calcium ions. Polyphenol glycosides constitute the group of such compounds, which
beside standard aromatic part substituted by many hydroxyl groups also possess
glycon part of the carbohydrate molecule. The number of potential binding sites in
these compounds increases due to additional oxygen atom contained in sugar part.
The carbohydrate part increases their solubility in water, which is of great advantage if such compounds are used in kidney stone therapy.
9.2 Carbohydrates as Ligands
In this section we try to bring the issue of Ca
2 +
complexation by sugars from the
structural point of view. Gyurcsik and Nagy [11] pointed out that although some
reviews regarding carbohydrates–metal complexes are available (e.g. “Complexes
of natural carbohydrates with metal cation” by Alekseev et al. [12]), no comprehensive monograph which treat carbohydrates as ligands can be found. We also do not
pretend to cover the whole topic of the area. Hence, we will mostly focus on the
general principles of forming complexes by carbohydrates with a special emphasis
to the cases in which calcium constitutes the metal ion and we present selected the
most typical structures.
At the beginning, it should be noted that interactions between carbohydrates and
metal ions are usually weak. Water strongly binds to hydroxyl groups of carbohydrates, and as a result complexes in water solution and in solid state can be structurally different. The formation of carbohydrate complexes in water requires replacement of water molecules by hydroxyl group from the first coordination sphere. To
form complex in water the interaction of the ligand must be stronger than that with
water molecules. Therefore there are some complexes which cannot exist in water
solution but they exist in crystalline form. Monosaccharides and oligosaccharides
as well as polysaccharides possess in their skeleton, as donors, hydroxyl oxygen
atoms which are relatively weak ligands. Some sugar derivatives can possess ionizable functional group, which might exhibit stronger interactions with metal ion.
Carbohydrates with carboxylic, sulphonic or phosphate groups as an anchoring sites
can form much stronger complexes with calcium ions [13–16]. They are not the
subject of consideration in this chapter.
In 1961 J.A. Mills studied the acidity of sugars by the paper electrophoresis.
He has found that some sugars, even at neutral pH, penetrated toward cathode. This indicated that they are positively charged probably by complexing
cations. The extent of migration was a measure of the complexing ability. The
only coordination centers in neutral sugars are constituted by oxygen atoms of
hydroxyl groups. Since water solvates cations much better, the question that
arises is regarding the number hydroxyl groups needed to form a stable complex. It is believed that at least two or three hydroxyl centers in the favorable
arrangement are required. There is another question related to their favorable
steric arrangements.