8.2 Chitosan-4-Thiol-Butylamidine [117]
To prepare chitosan-4-thiol-butylamine, chitosan was first selectively depolymerized
following the method developed by Huang et al. [118]. Then, the inclusion of thiol
groups in the different hydrolyzed chitosans was carried out following the method
developed by Bernkop-Schnu ¨rch et al. [119]. In brief, 1 g of chitosan was solubilized
in 100 mL of acetic acid solution (1%, w/v). The pH of the solution was adjusted to
6.5 with NaOH (1 N). Then, Traunt’s reagent (2-iminothiolane) was added in a
weight ratio of 5:2 for chitosan:2-iminothiolane. After an incubation period of 24 h at
room temperature under continuous stirring, the resulting thiolated polymer was
dialyzed using a Spectra/Por 3 membrane with a molecular weight cut-off of 3,500
against different aqueous media. Dialyzed products were freeze-dried and stored at
À20
C until use. The resulting polymer was chitosan-4-thiol-butylamidine.
8.3 mPEG-Grafted Phthaloyl Chitosan [120]
Chitosan with a degree of deacetylation of 85% was used for the preparation of
phthaloyl chitosan and it was designated as phCS 85. This phCS 85 was further used
for the preparation of mPEG-grafted phCS. In brief, phCS 85 (1.0 g) was stirred with
mPEG of M n 2000 (mPEG 2000) (3.04 g, 0.4 mol equivalent to phCS 85) in DMF
solution (20 mL). 1-Hydroxy-1H-bezotriazole, monohydrate (HOBt) (0.59 g, 3 mol
equivalent to mPEG 2000) was added and stirred at room temperature until the
solution became clear. 1-Ethyl-3-(3
0 -dimethylaminopropyl) carbodiimide, hydrochloride (EDC) (0.89 g, 3 mol equivalent to mPEG 2000) was added and stirred
overnight. The mixture was dialyzed using a dialysis tubing cellulose membrane with
a molecular weight cut-off of 12,400 against distilled water to obtain the product
phCS 85-mPEG 2000 in white colloidal solution form. The product was collected in
solid form by centrifuging, washing with ethanol, and drying under vacuum.
Fig. 7 Synthesis of chitosan-g-PEG copolymer [113]
104
J. Dutta
To prepare chitosan-4-thiol-butylamine, chitosan was first selectively depolymerized
following the method developed by Huang et al. [118]. Then, the inclusion of thiol
groups in the different hydrolyzed chitosans was carried out following the method
developed by Bernkop-Schnu ¨rch et al. [119]. In brief, 1 g of chitosan was solubilized
in 100 mL of acetic acid solution (1%, w/v). The pH of the solution was adjusted to
6.5 with NaOH (1 N). Then, Traunt’s reagent (2-iminothiolane) was added in a
weight ratio of 5:2 for chitosan:2-iminothiolane. After an incubation period of 24 h at
room temperature under continuous stirring, the resulting thiolated polymer was
dialyzed using a Spectra/Por 3 membrane with a molecular weight cut-off of 3,500
against different aqueous media. Dialyzed products were freeze-dried and stored at
À20
C until use. The resulting polymer was chitosan-4-thiol-butylamidine.
8.3 mPEG-Grafted Phthaloyl Chitosan [120]
Chitosan with a degree of deacetylation of 85% was used for the preparation of
phthaloyl chitosan and it was designated as phCS 85. This phCS 85 was further used
for the preparation of mPEG-grafted phCS. In brief, phCS 85 (1.0 g) was stirred with
mPEG of M n 2000 (mPEG 2000) (3.04 g, 0.4 mol equivalent to phCS 85) in DMF
solution (20 mL). 1-Hydroxy-1H-bezotriazole, monohydrate (HOBt) (0.59 g, 3 mol
equivalent to mPEG 2000) was added and stirred at room temperature until the
solution became clear. 1-Ethyl-3-(3
0 -dimethylaminopropyl) carbodiimide, hydrochloride (EDC) (0.89 g, 3 mol equivalent to mPEG 2000) was added and stirred
overnight. The mixture was dialyzed using a dialysis tubing cellulose membrane with
a molecular weight cut-off of 12,400 against distilled water to obtain the product
phCS 85-mPEG 2000 in white colloidal solution form. The product was collected in
solid form by centrifuging, washing with ethanol, and drying under vacuum.
Fig. 7 Synthesis of chitosan-g-PEG copolymer [113]
104
J. Dutta