Synthesis, characteristic and antibacterial activity of N,N,N-trimethyl chitosan and its carboxymethyl derivatives

O-Methyl free N,N,N-trimethyl chitosan (TMC) was synthesized by treating chitosan with formic acid and formaldehyde firstly, followed by methylation with CH3I. TMC was further carboxymethylated by monochloroacetic acid to obtain N,N,N-trimethyl-O-carboxymethyl chitosan (TMCMC). The products were characterized by FTIR, 1H NMR, EA and TGA. Their antibacterial activity was investigated against Staphylococcus aureus and Escherichia coli. The antibacterial activity of TMC decreased as the degree of substitution increased at pH 5.5. But the structure activity relationship was reversed at pH 7.2. TMCMC acted weaker than TMC, and its activity decreased as the degree of carboxymethylation increased. The experimental results showed that the activity of N,N,N-trimethyl amino group was weaker than other non-quaternized amino groups, and carboxymethylation didnot enhance the antibacterial activity directly.