Chitosan hydrochloride, chitosan lactate, and chitosan quaternary are all derivatives of chitosan (produced by reacting chitosan with different acids or reagents). Their core differences stem from key properties such as substituent groups, charge characteristics, and solubility, which in turn lead to significant variations in their physicochemical properties and application scenarios. The following is a detailed comparison from multiple dimensions to help understand the core differences among the three:
I. Core Differences: Structure and Charge Properties
The essential distinction between the three lies in the “modification method” of the amino group (-NH₂) in the chitosan molecule, which directly determines their charge state and chemical characteristics:
Type
Core Substituent Group
Charge Property (in Aqueous Solution)
Key Features
Chitosan Hydrochloride
-NH₃⁺Cl⁻ (ammonium salt formed by the reaction of amino groups with hydrochloric acid)
Weak cationic
Stability depends on an acidic environment; low charge intensity
Chitosan Lactate
-NH₃⁺C₃H₅O₃⁻ (ammonium salt formed by the reaction of amino groups with lactic acid)
Weak cationic
Lactate is an organic acid radical, offering better biocompatibility
Chitosan Quaternary
-N⁺(CH₃)₃X⁻ (amino groups substituted with “trimethyl” to form quaternary ammonium cations)
Strong cationic
Charge is stable and intense, independent of pH; the only “strong cationic” derivative among the three
II. Comparison of Key Physicochemical Properties
1. Solubility (One of the Most Core Differences)
Solubility directly determines the application scenarios of the three (e.g., whether they can be used in neutral/alkaline environments):
Chitosan Hydrochloride: Only soluble in acidic aqueous solutions (e.g., water with pH < 6, dilute hydrochloric acid/acetic acid solutions). It precipitates in neutral/alkaline environments due to deprotonation of amino groups and cannot remain stably dissolved. Example: Soluble in 0.1% dilute hydrochloric acid, but becomes turbid when the pH is adjusted to 7 by adding NaOH.
Chitosan Lactate: Its solubility is slightly better than that of chitosan hydrochloride. It can dissolve in weakly acidic to near-neutral aqueous solutions (pH ≈ 5-7), but still precipitates in strongly alkaline environments (pH > 8). Additionally, solubility is affected by the degree of lactate substitution—the higher the substitution degree, the better the solubility. Advantage: No additional “strong inorganic acid” is required to adjust the pH; the lactate groups themselves can maintain a weakly acidic dissolution environment, making it more suitable for scenarios sensitive to “strong acids” (e.g., food, cosmetics).
Chitosan Quaternary: Soluble across the entire pH range (stable dissolution in water at pH = 2-12) with high solubility (some grades are soluble in polar organic solvents such as ethanol). It is the only derivative among the three that can be used in neutral/alkaline environments. Core Reason: Quaternary ammonium cations (-N⁺(CH₃)₃) do not rely on protonation (independent of pH), so their charge remains stable and will not precipitate due to changes in the environmental pH.
2. Stability
Chitosan Hydrochloride/Chitosan Lactate: Stability depends on an acidic environment; they are prone to precipitation when exposed to alkalis. During long-term storage, if the environmental humidity is high, solubility may decrease due to “desalination”.
Chitosan Quaternary: It exhibits extremely high stability, unaffected by pH and temperature (at conventional operating temperatures < 80°C). Its solution can be stored for a long time (light protection is required to prevent microbial contamination), and its physicochemical properties rarely change.
3. Biocompatibility and Safety
Chitosan Lactate: Lactic acid is a product of human metabolism (e.g., a product of glycolysis). After substitution with lactate groups, there is no residual toxicity, and it has the best biocompatibility among the three. It is commonly used in food additives, oral health products, and medical dressings (e.g., wound repair).
Chitosan Hydrochloride: Chloride is an inorganic acid radical, and it has good safety. However, attention should be paid to the irritation of the “acidic environment” to local tissues (e.g., direct application to broken skin may cause slight stinging). It is mostly used for industrial-grade bacteriostasis and water treatment.
Chitosan Quaternary: Quaternary ammonium groups have a certain degree of “cationic toxicity” (toxic to bacteria/fungi but also slightly irritating to human cells), so their biocompatibility is slightly lower than that of the first two. Its dosage needs to be controlled, and it is mostly used for external disinfection (e.g., skin and mucous membrane disinfection) and antibacterial coatings. Oral administration is not recommended
