What Does Chitosan Contain? Exploring Its Chemical Composition and Properties

November 25, 2025 •

2 min read

As the second most abundant natural polymer after cellulose, chitosan is a derivative of chitin found in crustacean shells and fungi. This unique biopolymer is composed of two primary sugar derivatives, and understanding what chitosan contains is key to grasping its diverse applications and functionalities.

Quick Summary

Chitosan is a linear polysaccharide composed of randomly linked D-glucosamine and N-acetyl-D-glucosamine units. Its specific ratio of these two monomers, known as the degree of deacetylation, dictates its solubility and other physicochemical properties.

Key Points

Core Monomers: Chitosan is a copolymer of two randomly linked sugar units: D-glucosamine and N-acetyl-D-glucosamine.
Deacetylation is Key: The proportion of D-glucosamine units (free amino groups) is determined by the degree of deacetylation of chitin.
Reactive Amino Groups: Free amino groups ($–NH_2$) are responsible for chitosan becoming positively charged in acidic solutions, enabling binding with negatively charged substances.
Functional Hydroxyl Groups: Hydroxyl groups ($–OH$) on the sugar rings are involved in hydrogen bonding, affecting the polymer's strength and solubility.
Source and Processing Matter: The composition of chitosan, including molecular weight and deacetylation degree, is influenced by its origin (e.g., shellfish vs. fungi) and manufacturing method.
Chitin vs. Chitosan: Chitin consists solely of N-acetyl-D-glucosamine units and is insoluble, while chitosan contains a mix of monomers and is soluble in weak acids.

The Monomer Building Blocks of Chitosan

Chitosan is a natural polysaccharide, a large molecule made up of smaller, repeating sugar-based units called monomers. Chitosan is a copolymer consisting of two randomly distributed, $\beta$-(1→4)-linked monomer units: D-glucosamine and N-acetyl-D-glucosamine.

D-glucosamine (GlcN): These deacetylated units have a reactive amino group ($−NH_2$) at the C-2 position, which gives chitosan its positive charge in acidic solutions.
N-acetyl-D-glucosamine (GlcNAc): These acetylated units have an acetyl group ($–COCH_3$) at the C-2 position and are the same repeating units found in chitin.

The Role of Deacetylation

Chitosan is mainly produced from chitin through alkaline deacetylation, a process that removes acetyl groups to create free amino groups. The Degree of Deacetylation (DD) measures the proportion of D-glucosamine units to N-acetyl-D-glucosamine units. A higher DD indicates more free amino groups and is a key factor differentiating chitosan from chitin. Chitosan is generally defined as having a DD greater than 50%.

Key Functional Groups and Their Influence

The functional groups on the chitosan polymer are crucial for its properties:

Amino Groups ($−NH_2$): Located on D-glucosamine units, they become positively charged ($−NH_3^+$) in acidic water (pH < 6.5). This positive charge allows chitosan to interact with negatively charged molecules, contributing to its antimicrobial and wound-healing properties.
Hydroxyl Groups ($−OH$): These groups at the C-3 and C-6 positions influence hydrogen bonding within and between polymer chains, affecting solubility and mechanical strength.

Comparison: Chitin vs. Chitosan

Understanding what chitosan contains is clarified by comparing it to chitin, its precursor.


Feature	Chitin	Chitosan
Primary Monomer	N-acetyl-D-glucosamine only	D-glucosamine and N-acetyl-D-glucosamine
Degree of Deacetylation (DD)	Less than 50%	Typically greater than 50%
Functional Amino Groups	No free amine groups	Free amino ($−NH_2$) groups
Solubility	Insoluble in most solvents	Soluble in dilute acidic solutions
Electrical Charge	Neutral	Polycationic in acidic conditions

Factors Affecting Chitosan Composition

Chitosan's composition is variable, influenced by several factors:

Source: The origin of chitin (crustaceans, insects, or fungi) affects the final chitosan's characteristics.
Preparation Method: The deacetylation process parameters, like alkaline concentration, temperature, and time, control the DD and molecular weight.
Molecular Weight: Classified into low, medium, and high weights, molecular weight impacts solubility and biological activities like antimicrobial effects.

Conclusion

Chitosan's composition, a copolymer of D-glucosamine and N-acetyl-D-glucosamine formed by chitin deacetylation, gives it unique properties. The presence of amino and hydroxyl functional groups underpins its positive charge in acidic conditions, chelation abilities, and antimicrobial activity. The source material and production process further customize its composition, influencing its applications in fields such as biomedicine and agriculture. A thorough understanding of what chitosan contains is therefore fundamental to utilizing this versatile biomaterial effectively.

Learn more about chitosan's processing and properties at this comprehensive overview from the National Institutes of Health.

Frequently Asked Questions

The two monomers, D-glucosamine and N-acetyl-D-glucosamine, are randomly linked together through $\beta$-(1→4)-glycosidic bonds to form the linear polysaccharide chain of chitosan.

The degree of deacetylation is the percentage of D-glucosamine units (deacetylated units) relative to the total number of monomer units in the chitosan polymer. A higher DD indicates more free amino groups and a greater positive charge.

Chitosan is soluble in dilute acidic solutions because the free amino groups on its D-glucosamine units become protonated ($−NH_3^+$). This imparts a positive charge to the polymer, allowing it to dissolve. It is insoluble in neutral or alkaline water because the amino groups are uncharged.

The primary sources of chitin for industrial production are the exoskeletons of marine crustaceans, such as shrimp and crabs. Chitin is also found in the cell walls of fungi and the cuticles of insects.

The key functional groups are the primary amino group ($−NH_2$) at the C-2 position and hydroxyl groups ($−OH$) at the C-3 and C-6 positions. These groups are responsible for its reactivity, chelation, and antimicrobial activity.

Chitosan's composition can vary depending on its source. For example, fungal-derived chitosan may have a higher and more consistent degree of deacetylation than that from crustaceans. This can result in differences in molecular weight and overall properties.

Chitin is less soluble because it has no free amino groups. The presence of acetyl groups at all C-2 positions leads to extensive and strong hydrogen bonding, resulting in a more crystalline structure that is resistant to dissolving in most common solvents.