Evaluation of quaternary ammonium chitosan derivatives differing in the length of alkyl side-chain: Synthesis and antifungal activity

Chemical modification is one of the prominent methods used to improve the water solubility and bioactivity of chitosan. In this paper, a series of quaternary ammonium chitosan derivatives based on 6-O-chloroacetylated chitosan (CAClC) were successfully designed and synthesized. Detailed structural characterization was carried out by means of FT-IR, H-1 NMR spectroscopy, and elemental analysis. Furthermore, the antifungal activity against Botrytis cinerea, Gibberella zeae, and Physalospora piricola Nose was estimated using in vitro hypha measurements. Most of the quaternary ammonium chitosan derivatives showed an inhibitory index of >90% at 1.0 mg/mL and exhibited enhanced antifungal activity when compared to chitosan. On one hand, the higher density of positive charge contributed to the antifungal action. In addition, the inhibitory activity decreased roughly in the order of TriM [(CH3)(3)] > TriE (CH2CH3)(3)] > TriP [(CH2CH2CH3)(3)] > TriB [(CH2CH2CH2CH3)(3)]; NNTE (CH3)(2)(CH2CH3)] > NNTB [(CH3)(2)(CH2CH2CH2CH3)] > NNTK RCH3)(2)((CH2)(9)CH3)] at 1.0 mg/mL. The antifungal properties of all the quaternary ammonium chitosan derivatives against the targeted fungi decreased upon increasing the alkyl chain length. (C) 2018 Published by Elsevier B.V.