The amine group need to be protonated for Chitosan to dissolve in water, why then at pH lower than say 4,5 does the chitosan drop out of solution?
Chitosan is soluble in acidic solutions with a pH below 6.5 due to the protonation of its amine groups. When the pH falls below 6.0, the amino groups become highly protonated, resulting in a positively charged surface and the formation of chitosan salts. This increased protonation disrupts the charge interactions and hydrogen bonding needed for solubility, causing chitosan to precipitate and become insoluble in water at lower pH levels.
Thank you for your reply. This makes a lot of sense. While the reason for insolubility at high pH is well documented, this is an explanation that I have not yet managed to find. My next question is then about chitosan salts, I am talking about chitosan hydrochloride, are noted for their increased solubility in water ? How is chitosan hydrochloride soluble in an aqueous media if the increases protonation disrupts hydrogen bonding? @AbdelhakMaghchiche