Why are chitosans called polycations?

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The term polycation indicates that chitosans carry multiple positive charges. This is the case when chitosans are dissolved in slightly acidic media which lead to protonation of the free amino groups of the glucosamine units within the chitosan chain. Polycationicity is a unique feature of chitosans, no other naturally occurring biopolymer is polycationic. In fact, most biological macromolecules and biopolymers such as proteins, nucleic acids or sulfated polysaccharides are negatively charged, and chitosans can thus easily bind to them and influence their biological activities. The polycationic nature of chitosans is thought to be at least partially responsible for some of their biological activities, most notably their antimicrobial activity and their gene-condensing capacity. It is noteworthy, however, that chitosans have biological activities also at neutral pH values, most notably biomedically relevant activities towards human cells grown under near-neutral conditions. Also, other (non-natural) polycationic polymers such as Poly-Lysin or DEAE-Dextran do not show the same bioactivities as chitosans.