N-Reacetylated Oligochitosan: pH Dependence of Self-Assembly Properties and Antibacterial Activity

Abstract

Oligochitosan (short chain chitosan) is more soluble in acidic aqueous media than a high molecular weight (MW) chitosan, but its antimicrobial activity decreases with increase in degree of acetylation (DA) and increase in pH above a critical pH threshold point. In the present study, oligochitosans varying in MW were additionally N-acetylated and their self-assembly properties and antibacterial activity toward Staphylococcus aureus and Escherichia coli were investigated in a wide pH range as a function of MW and DA. Light scattering studies reveals that reacetyleted oligochitosan with M ≤ 11 kDa is completely soluble in alkaline media (up to pH 12.5), if its DA is not less than 16%. Reacetylated chitosans with DA ∼ 30% are solubile in the entire pH range up to 12.5, if their M is not higher than 25 kDa, but they aggregate and precipitate from the solution at pH ≥ 8 when their M is above 25 kDa. Considering the influence of DA and MW, the antibacterial activity of reacetylated oligochitosans is maximal in the short interval of DA 16-28% at pH 7.4. These results are promising for expanding practical application of oligochitosan in pharmaceutical, cosmetic, and food compositions.

Unusual Compatibility of N‐Reacetylated Oligochitosan with Sodium Dodecyl Sulfate in Aqueous Solution with a Wide Range of the Solution pH

“…Therefore, it seemed reasonable to investigate the interaction of SDS with RA‐oligoCHI that, as it was shown in our earlier publication, [ 34 ] was found soluble in aqueous solutions with a wide range of the solution pH from 2 to 12 in comparison with the parent oligoCHIs. [ 18 ]…”

“…In this research, solubility of RA‐oligoCHIs with M w ≤ 12 kDa and DA 24–31% in acid‐free aqueous media [ 34 ] and the visual transparency of some RA‐oligoCHI/SDS mixtures in both acidic and alkaline media moved us to investigate the compatibility of a series of RA‐CHI specimens differing in MW and DA values with 0.05–2.5% SDS in a solution by turbidity measurements. As it was shown earlier, the solubility and CMC of SDS were independent of the solution pH above pH 4 while the absorbance of SDS solution increased with the increase in SDS concentration.…”

Honeybee chitosan-melanin complex: isolation and investigation of antimicrobial activity

“…Studies of antimicrobial activity of CMC were performed at two values of pH 5.7 ± 0.1 and 7.0 ± 0.1, as it was shown that the pH value of the medium is of great importance for the antibacterial effect of chitosan [5,6,22]. This aspect is poorly investigated Note.…”

“…The efficiency of binding of the CMC with negatively charged cell surface, in turn, depends upon the value of chitosan's positive charge. The pKa value of chitosan of the marine crustaceans is in a range of 6.2-6.6 [6], in the medium at neutral pH 7 or higher its charge is minimal and its binding with cell surfaces 3.2 ± 0.9 Note: The number of CFU in the control at the start of incubation (control 0 h) was accepted as 100%. The difference in all experimental data compared to control 0 h value showed a high level of significance, P < 0.01, (n = 3).…”

“…This property of chitosan is widely used in dressing materials for healing wounds and burns [3], the comprehensive information up to 2011 year see in excellent review by Dai T. et al [2]. Further investigations were devoted to an enhancement of the antimicrobial activity of chitosan or its fragments by their complexation with different antimicrobial agents, including nanoparticles, and via an improvement of water solubility of their preparations in neutral or weak alkaline media [4][5][6][7][8].…”