283
9 Polyphenol Glycosides as Potential Remedies in Kidney …
In the contrast, only small changes were observed in the solution of d-mannose,
d-glucose, d-xylose, d-arabinose, d-galactose, d-fucose, l-sorbose [17, 43]. These
sugars has no ax–eq–ax configuration in three subsequent hydroxyl groups. This
fact again supports the thesis that such arrangement in six membered cyclitols is
required for the complexation with calcium cations. However, some of these sugars
can form complexes in bidentate form.
Weak interactions between d-xylose and calcium ions were observed in NMR.
None of the forms of d-xylose possesses the required ax–eq–ax configuration needed for the strong bonding. Authors [43] attributed the NMR shift change to weak
interactions in the bidentate mode. α-anomer in the
4
C 1 conformation has ax–eq pair
and in the
1
C 4 conformation the cis ax–ax pair. Presented results indicate also that
from two β-anomers
4
C 1 and
1
C 4, only β-anomer in
1
C 4 conformation has two cis
axial OH groups. Since only the β4
C 1 structure dominates, the conclusion is that
none of β-anomers form complexes with calcium [44]. The final conclusion was
that the chemical shift change was due to the complex formation within the α4
C 1
conformation. The α4
C 1 possess an ax–eq pair which form stronger interaction that
ax–ax in the case of α1
C 4 conformer.
In the case of d-glucose [43], between all possible conformers which are able
to bind in the bidentate form, only the α4
C 1 conformer having ax–eq pair (O1,
O2 hydroxyl oxygen atoms) is responsible for a weak interaction with calcium. In
the absence of calcium the major conformer is constituted of β4
C 1 characterized
with all equatorial hydroxyl groups—allowing stronger interactions with water.
This conclusion is supported by the fact that 2-deoxyglucose does not bind to the
calcium ion.
d-Galactose can form only weak complexes in α4
C 1 and α1
C 4 pyranose conformations due to the presence of ax–eq hydroxyl groups and β4
C 1 due to the ax–eq
pair of the hydroxyl groups arrangement.
d-Fructose and l-sorbose are ketoses. The first one forms weak complexes in
the β-pyranose 1C4 conformation with ax–eq sites for binding of calcium and weak
complexes by α- and β-furanose isomers. l-Sorbose forms also very weak complexes. It is possible only in the β-4C1 conformer due to two sets of cis ax–ax.
9.3 Other Methods Used for Complex Formation Studies
in the Case of Polyphenol Glycosides
There are a number of other methods, spectroscopic as infra-red (IR), ultraviolet–
visible (UV–Vis), which allow the evaluation of the ability of the Ca
2 +
complex
formation. Not all of them are suitable in every case. We have decided to explore
the flame photometry and conductometric titration since the NMR changes were too
small to perform the correct analysis.
The flame photometry indicates the concentration of calcium in the solution.
It could be used for evaluation of dissolving power of the ligand or prevention of
crystallization of the solid calcium salts in solution.
9 Polyphenol Glycosides as Potential Remedies in Kidney …
In the contrast, only small changes were observed in the solution of d-mannose,
d-glucose, d-xylose, d-arabinose, d-galactose, d-fucose, l-sorbose [17, 43]. These
sugars has no ax–eq–ax configuration in three subsequent hydroxyl groups. This
fact again supports the thesis that such arrangement in six membered cyclitols is
required for the complexation with calcium cations. However, some of these sugars
can form complexes in bidentate form.
Weak interactions between d-xylose and calcium ions were observed in NMR.
None of the forms of d-xylose possesses the required ax–eq–ax configuration needed for the strong bonding. Authors [43] attributed the NMR shift change to weak
interactions in the bidentate mode. α-anomer in the
4
C 1 conformation has ax–eq pair
and in the
1
C 4 conformation the cis ax–ax pair. Presented results indicate also that
from two β-anomers
4
C 1 and
1
C 4, only β-anomer in
1
C 4 conformation has two cis
axial OH groups. Since only the β4
C 1 structure dominates, the conclusion is that
none of β-anomers form complexes with calcium [44]. The final conclusion was
that the chemical shift change was due to the complex formation within the α4
C 1
conformation. The α4
C 1 possess an ax–eq pair which form stronger interaction that
ax–ax in the case of α1
C 4 conformer.
In the case of d-glucose [43], between all possible conformers which are able
to bind in the bidentate form, only the α4
C 1 conformer having ax–eq pair (O1,
O2 hydroxyl oxygen atoms) is responsible for a weak interaction with calcium. In
the absence of calcium the major conformer is constituted of β4
C 1 characterized
with all equatorial hydroxyl groups—allowing stronger interactions with water.
This conclusion is supported by the fact that 2-deoxyglucose does not bind to the
calcium ion.
d-Galactose can form only weak complexes in α4
C 1 and α1
C 4 pyranose conformations due to the presence of ax–eq hydroxyl groups and β4
C 1 due to the ax–eq
pair of the hydroxyl groups arrangement.
d-Fructose and l-sorbose are ketoses. The first one forms weak complexes in
the β-pyranose 1C4 conformation with ax–eq sites for binding of calcium and weak
complexes by α- and β-furanose isomers. l-Sorbose forms also very weak complexes. It is possible only in the β-4C1 conformer due to two sets of cis ax–ax.
9.3 Other Methods Used for Complex Formation Studies
in the Case of Polyphenol Glycosides
There are a number of other methods, spectroscopic as infra-red (IR), ultraviolet–
visible (UV–Vis), which allow the evaluation of the ability of the Ca
2 +
complex
formation. Not all of them are suitable in every case. We have decided to explore
the flame photometry and conductometric titration since the NMR changes were too
small to perform the correct analysis.
The flame photometry indicates the concentration of calcium in the solution.
It could be used for evaluation of dissolving power of the ligand or prevention of
crystallization of the solid calcium salts in solution.