Synthesis and structural characterization of N,N,N-trimethyl chitosan

N,N,N-trimethyl chitosan (TMC) with molar mass 29 similar to 136 kg/mol and degree of quaternization 70% similar to 82% was synthesized from chitosan via N,N-dimethyl chitosan (DMC) by a two-step method. Size exclusion chromatography (SEC) coupled with multiangle laser light scattering was employed to characterize the molar mass and chain conformation of DMC and TMC. Nearly no degradation was found for DMC, but degradation by similar to 50% was observed from TMC. Apart from degradation, the shift of SEC peak toward higher elution volume for N-methylated chitosan was attributed to the increase in chain flexibility. It was shown that chitosan, DMC, and TMC took a random coil conformation in 200 mM acetate buffer, with persistence length decreased from 10 nm for chitosan, to 5.7 nm for DMC and 3.2 nm for TMC. The significant increase in chain flexibility upon N-methylation is most probably due to the breakage of intramolecular hydrogen bonds between chitosan repeating units.