Chemistry of N-acetylated Chitosans

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Questions and Answers

What is the primary method used to convert chitosan to its hydrochloride salt?

Heating in distilled water

Lyophilizing after reduction with sodium borohydride (correct)

Diluting with 4% acetic acid

Dissolving in hydrochloric acid

Which factor is primarily responsible for the insolubility of commercial chitosans at neutral and basic pH-values?

Presence of sodium nitrite

Chemical composition (correct)

High molecular weight

Acetic acid concentration

In the context of calculating mole fractions of oligomers, what does the variable FA represent?

Fraction of acetylated units in the undegraded chitosan (correct)

Total molecular weight of the chitosan

Rate of degradation of chitosan

Fraction of deacetylated units

What is a known chemical property of chitosans when subjected to hydrochloric acid at pH 2.5?

Decreased water solubility Signup and view all the answers

What process is indicated by 'deacetylation' in the context of chitosan preparation?

Removal of acetyl groups to enhance polymer properties Signup and view all the answers

What method was used to prepare Chit4?

Homogeneous deacetylation Signup and view all the answers

Which substance was used to convert commercial chitosan to chitosan-HCl salt?

Acetic acid Signup and view all the answers

What technique was utilized to determine the fraction of acetylated units in chitosan?

High-field proton NMR spectroscopy Signup and view all the answers

What is the significance of measuring intrinsic viscosities in chitosans?

To assess molecular weight and polymer properties Signup and view all the answers

The degree of scission in chitosan is calculated using which formula?

I = $D / DPn$ Signup and view all the answers

Which of the following was NOT mentioned as a step in the preparation of chitosan hydrochlorides?

Precipitation with ethanol Signup and view all the answers

Why were samples dialyzed against 0.2 M NaCl during the chitosan chloride preparation?

To exchange ions and purify the product Signup and view all the answers

What type of chitosan preparation involved the addition of NaOH?

Fractionation of undegraded chitosans Signup and view all the answers

What method was used to prepare the chitosans mentioned in the study?

Heterogeneous deacetylation Signup and view all the answers

What is the main reason for adjusting the pH in chitosan solutions?

To achieve full neutrality and solubility Signup and view all the answers

Which of the following best describes the composition of the chitosans used in the study?

The number of acetylated units varies among the chitosans. Signup and view all the answers

In what context is NMR spectroscopy potentially relevant to the analysis of chitosans?

To analyze the distribution of monomers along the polymer chain. Signup and view all the answers

How were the precipitates during chitosan preparation handled?

They were easily removed from the supernatant. Signup and view all the answers

What role does sodium hydroxide (NaOH) play in the preparation of chitosans?

It helps to adjust the pH of the chitosan solution. Signup and view all the answers

What was a significant result of the neutral-soluble fractions of chitosans?

They were applied in studying TNF-α production. Signup and view all the answers

What was the first step in preparing the degraded chitosan solutions?

Dissolving the chitosan in distilled water overnight. Signup and view all the answers

Study Notes

Water Solubility of Partially N-acetylated Chitosans

Chitosan is a family of unbranched binary hetero-polysaccharides, composed of β(1-4)-linked GlcNAc (A-unit) and 2-amino-2-deoxy-β-D-glucopyranose-GlcN (D-unit). A- and D-units are randomly distributed in water-soluble partially N-acetylated chitosans.
Commercial chitosans typically contain 0-0.2 of acetylated units. They are insoluble in water at neutral and basic pH.
They are soluble in acidic pH solutions. This insolubility at neutral pH can be both useful (easy removal from solutions) and problematic (limiting application in other cases, like biological effects at physiological pH).

Solubility as a Function of pH and Composition

Four partially N-acetylated chitosans with different acetylation fractions (FA: 0.01, 0.17, 0.37, 0.60) were investigated.
The chitosan with FA=0.60 was soluble at all pH between 4 and 9.
Other chitosans precipitated at pH 6-7.5, with increased solubility at higher pH values as FA increased.
This is important because solubility differences impact enzyme access and biological effects.

Depolymerization and Solubility

Three chitosans with the lowest FA values were depolymerized with nitrous acid.
The fully deacetylated chitosan was insoluble at pH 7.5.
The most acetylated chitosan (FA=0.60) remained fully soluble at all pH values observed.
Chitosans with FA=0.17 and 0.37 separated into neutral soluble and insoluble fractions.
The amount of soluble material increased with decreasing depolymerization.
The soluble fractions had a higher FA and lower degree of depolymerization than insoluble fractions, consistent with random degradation of chitosans.

Materials and Methods

Four chitosans were prepared by either heterogeneous or homogeneous N-deacetylation.
Different fractions in acetylated units (FA) were investigated.
Chitosans were converted into chloride salts by dissolving in acetic acid, dialysis, and lyophilization.
The amount of precipitated chitosan was determined at increasing pH values. This was achieved by mixing chitosan solution with dilute sodium hydroxide.
Nitrous acid depolymerization was used to degrade the chitosan chains.
Solutions were fractionated between soluble and insoluble fractions using different pH values (often to pH 7.5).
Fractionation of the degraded chitosans was conducted by adjusting the pH.
Chemical composition was determined by high-field proton NMR spectroscopy.
Intrinsic viscosities of chitosans were determined.
Molecular weights were estimated using the Mark-Houwink-Sakurada equation.

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Description

This quiz explores the water solubility characteristics of partially N-acetylated chitosans and how their composition affects solubility across different pH levels. It emphasizes the relationship between acetylation fractions and solubility, highlighting both the practical applications and limitations of chitosans in various pH environments.