Water-soluble N-carboxymethylchitosan derivatives: Preparation, characteristics and its application

In this work, only N-substituted chitosan derivatives (water-soluble N-carboxymethylchitosan derivatives: N-CMC) with different degrees of substitution were obtained by reaction of a fully deacetylated chitosan (derived from deacetylation of chitosan using decrystallized method) with monochloroacetic acid at pH 8 and temperature of 90 degrees C. The structure of N-carboxymethylchitosan and chitosan was characterized by IR, H-1, C-13 and H-1-C-13 NMR-HSQC spectra. In the IR spectrum of the N-carboxymethylchitosan, the appearance of peak at 1742 cm(-1) was assigned for CO group of -NH-CH2-COOH of substituted chitosan. In the H-1 NMR spectra, the peaks at about 3.81 divided by 4.06 ppm, assigned for -CH2- groups of -NH-CH2- and -N(CH2)(2)-, were the major feature, while in the H-1-C-13 NMR-HSQC spectra, signals of -CH2- confirmed the presence of these two different substituted -CH2- groups. The degree of substitution (DS) of N-monosubstitution (DSN-mono) decreased from 0.47 to 0.03 meanwhile that of N,N-disubstitution (DSN,N-di) increased from 0.52 to 0.96 since the mass ratio of chitosan/monochloroacetic acid changing from 1/1 to 1/4. The N-carboxymethylchitosan derivatives have been used for adsorption Cu(II) ion from aqueous solution. The results shown that the optimum conditions for adsorption Cu(II) ion in nitrate solution were pH 6.5, temperature of 30 degrees C, for 60-90 min and the substituted chitosan derivative having DSN-mono of 0.16 and DSN,N-di of 0.81 had maximum adsorption capacity of 192 mg Cu(II) per gram of N-CMC. (C) 2008 Elsevier Ltd. All rights reserved.