The synthesis of water soluble N-acyl chitosan derivatives for characterization as antibacterial agents

Currently, natural polysaccharides are being utilized increasingly in the markets because they exhibit biodegradability, biocompatibility, versatility, and are found abundant in nature. The diversity of natural polysaccharides provides the chemist with a broad spectrum of raw materials that can be used in many biological applications. Chitosan is a natural polysaccharide that possesses excellent biological properties. It has been recognized for its antibacterial activity, in that it is destructive towards the bacterium Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The antibacterial property of chitosan can be enhanced by changing the hydrophobic/hydrophilic nature of the polysaccharide backbone. This research entails the chemical modification of chitosan with distinct linear aliphatic, cyclic, and novel hydrophilic anhydrides, followed by quaternization using 3-chloro-2-hydroxyl propyl trimethylammonium chloride (Quat-188) to enhance its antibacterial properties. It is believed that these types of hydrophobic/hydrophilic derivatives inhibit the growth of bacteria by initial electrostatic interactions with negatively charged groups of the bacterial cell surface. The antibacterial activities of the N-acyl chitosan Quat-188 derivatives were investigated using the minimum inhibitory concentration (MIC) method. In most cases, it was found that an increase in the percent extent of N-acyl substitution (% ES) led to a decrease in the percent extent of quaternization (% EQ), which resulted in an increase in the MIC of the derivative. For example, 2-glycerol glutamide chitosan Quat-188 with 5% ES and 61% EQ exhibited a MIC of 64 µg/mL against E. coli and 32 µg/mL against S. aureus. At 25% ES and 31% EQ, the derivative exhibited a MIC of 128 µg/mL against both E. coli and S. aureus. These results suggest that an increase in the extent of N-acylation results in a decrease in the amount of cationic charge that can placed on the polysaccharide backbone, which leads to a decline in the antibacterial activity