2.2.3. Optimized method – TMC 2
The optimized synthesis of TMC was carried out in two steps:
first by the Eschweiler–Clarke reaction, treating chitosan with
formaldehyde in the presence of formic acid using a protocol modi-
fied from Verheul et al. (2008) and second by treating the obtained
N-dimethyl-chitosan (DMC) with CH3I in order to obtain TMC 2,
using the best reaction time and precipitation solvent ratio determined
for TMC 1.
Briefly, 2 g of chitosan were added to 6 mL of formic acid, 8 mL
of formaldehyde and 36 mL of distilled water. This reaction was
carried out at 70 ◦C under reflux (Liebig condenser) for 118 h. Afterwards,
the volume was reduced with a Rotavapor and the pH was
subsequently adjusted to 12 using 1 M NaOH. The precipitate was
isolated by paper filtration, followed by washing with water in
order to remove any impurities and un-reacted formaldehyde. Filtrated
N-dimethyl-chitosan (DMC) was suspended in water at a
concentration of 2% (w/v) and the pH adjusted to 4 using 1 M HCl
and further stirred until complete DMC dissolution. The solution
was filtered and dialyzed for 3 days, with water changes twice daily.
Then the product was lyophilized for 2 days and analyzed.
1 g of dried DMC was solubilized in 160 mL of water under stirring
at room temperature. The pH was adjusted to 11 by drop-wise
addition of 1 M NaOH until gel formation occurred. This step was
followedby washing twice with water andthree times withacetone
through a filter. Then, dried precipitate was suspended in 50 mL
NMP and the dispersion was stirred at 70 ◦C under reflux conditions
until the complete dissolution of the chitosan derivative (DMC).
Next, CH3I was added at a ratio of 1:25 to the reaction medium and
left for 140 min to complete the reaction. Subsequently, precipitation
with ethanol:diethylether (4:1) and centrifugation at 3220 × g
for 15 min were performed. Dialysis was done for 3 days. In order
to obtain a better ion exchange, the first day of dialysis was done
against a 1% NaCl solution in water and the last 2 days against