1070-4272/02/7506-0985 $27.00 C 2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 6, 2002, pp. 985!988. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 6, 2002,
Original Russian Text Copyright + 2002 by Novikova, Tishchenko, Iozep, Passet.
AND POLYMERIC MATERIALS
Influence of Synthesis and Isolation Conditions
on Properties of Dextran Polyaldehyde
E. V. Novikova, E. V. Tishchenko, A. A. Iozep, and B. V. Passet
St. Petersburg State Academy of Pharmaceutical Chemistry, St. Petersburg, Russia
Received November 22, 2001; in final form, February 2002
Abstract-The content of aldehyde groups in dextran polyaldehyde was studied in relation to the pH of
the reaction mixture in dextran oxidation and isolation of polyaldehyde.
There are indications in the literature that dextran
polyaldehyde (DPA) samples prepared by oxidation
of dextran with sodium metaperiodate at 18320oC
for 1 day and then isolated at pH in the range from
3.2 to 8.0 differ in spectral characteristics . It
was suggested that this is due to keto3enol tautom-
erism of DPA. In acid solutions, approximately half
of aldehyde groups are in the free state and hydrated
form. The other half is involved in intermolecular
hemiacetal bonds. With increasing pH, the intermo-
lecular networks are broken, and hydrated aldehyde
groups form mainly hemiacetal rings with aldehyde
groups of the oxidized unit.
Since DPA is used for constructing polymeric
drugs, it is of prime importance to ensure the repro-
ducibility of its initial properties. Therefore, the goal
of this study was to elucidate the influence exerted
by conditions of DPA synthesis and isolation and
by the pH of the DPA solution on its characteristics.
To find how the pH of the reaction medium in ox-
idation of a-glycol groups of the polysaccharide af-
fects the properties of the polyaldehyde, the reaction
of dextran with sodium periodate (0.75 or 1 mol of
per monosaccharide unit) was performed in
aqueous solutions with pH from 1.9 to 5.6 at 638oC
for 4 h until the oxidant consumption ceased (moni-
tored spectrophotometrically at 222.5 nm ). The
required acidity was adjusted with 0.1 formate buffer
solution, or by adding solutions of HCl and NaOH;
pH was monitored with an I-160 laboratory pH meter.
The products were isolated as described in , ana-
lyzed by the oxime  and hydroxamic  methods,
and characterized by the degree of substitution, C
(number of aldehyde groups per monosaccharide unit).
The number of 2,4-oxidized monosaccharide frag-
ments in the polyaldehyde (moles per mole of DPA
monomeric unit) was determined from the amount of
formic acid formed in oxidation of dextran, which, in
turn, was determined by titration with 0.1 N NaOH.
The number of 2,3- and 2,4-oxidized fragments, x,
was calculated by the formula
where a is the number of moles of consumed NaIO
and b is the number of moles of released formic acid
per mole of dextran monosaccharide units.
Viscometric studies, performed with a VPZh-2
viscometer (glass capillary diameter 0.56 mm) in
water at 21oC showed that the intrinsic viscosity
of DPA samples prepared by oxidation of dextran
at different pH is approximately the same (0.92 +
0.04 l mol
) and equal to that of the initial dex-
tran (0.95 l mol
). This fact suggests that, under the
reaction conditions, cross-linking is improbable, or its
extent is equal in DPA samples prepared at different
pH. As expected, the solubility of DPA samples de-
creases as compared to the initial polysaccharide.
For example, whereas dextran dissolves at room tem-
perature, DPA dissolves only upon heating.
Fig. 1. Degree of substitution, C
, of DPA, calculated from
the results of periodate oxidation, vs. pH of dextran solu-
tion (1) in formate buffer solution and (2) in water (before