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?

<p>Decreased water solubility (B)</p> Signup and view all the answers

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

<p>Removal of acetyl groups to enhance polymer properties (C)</p> Signup and view all the answers

What method was used to prepare Chit4?

<p>Homogeneous deacetylation (C)</p> Signup and view all the answers

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

<p>Acetic acid (A)</p> Signup and view all the answers

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

<p>High-field proton NMR spectroscopy (C)</p> Signup and view all the answers

What is the significance of measuring intrinsic viscosities in chitosans?

<p>To assess molecular weight and polymer properties (C)</p> Signup and view all the answers

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

<p>I = $D / DPn$ (B)</p> Signup and view all the answers

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

<p>Precipitation with ethanol (A)</p> Signup and view all the answers

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

<p>To exchange ions and purify the product (A)</p> Signup and view all the answers

What type of chitosan preparation involved the addition of NaOH?

<p>Fractionation of undegraded chitosans (C)</p> Signup and view all the answers

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

<p>Heterogeneous deacetylation (B)</p> Signup and view all the answers

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

<p>To achieve full neutrality and solubility (A)</p> Signup and view all the answers

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

<p>The number of acetylated units varies among the chitosans. (C)</p> Signup and view all the answers

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

<p>To analyze the distribution of monomers along the polymer chain. (B)</p> Signup and view all the answers

How were the precipitates during chitosan preparation handled?

<p>They were easily removed from the supernatant. (B)</p> Signup and view all the answers

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

<p>It helps to adjust the pH of the chitosan solution. (D)</p> Signup and view all the answers

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

<p>They were applied in studying TNF-α production. (B)</p> Signup and view all the answers

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

<p>Dissolving the chitosan in distilled water overnight. (C)</p> Signup and view all the answers

Flashcards

Binomial distribution of oligomers

The distribution of oligomers (short chains) in a randomly degraded binary copolymer follows a binomial pattern.

Mole fraction calculation (f)

The formula calculates the proportion of an n-mer (chain) containing x 'A' units and (n-x) 'D' units in a copolymer.

Chitosan-HCl solutions

Solutions made by dissolving chitosan in water, diluting with acetic acid, adding NaNO2 followed by sodium borohydride reduction and converting back to hydrochloride salt.

Hydrochloric acid degradation

Chitosan-HCl is degraded by adding HCl to a pH of 2.5, then heating for 100 hours to depolymerise.

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Water insolubility of Chitosan

Chitosans with neutral or basic pH are insoluble in water.

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Chitosan Solubility

Chitosan's ability to dissolve in water depends on factors like pH, ionic strength, and its chemical structure. It's generally insoluble at neutral pH but soluble in acidic conditions.

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Why is Chitosan Insolubility Useful?

Chitosan's insolubility at neutral pH makes it easy to remove from solutions just by adjusting the pH. This property is beneficial in certain applications.

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Neutral-Soluble Chitosan

A type of chitosan that remains dissolved in water even at neutral pH (pH 7.5). It's prepared by specific methods like controlled degradation and fractionation.

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Degradation of Chitosan

Breaking down chitosan molecules into smaller chains. This is achieved by using hydrochloric acid under specific conditions.

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Fractionation of Chitosan

Separating chitosan into different fractions based on their solubility. This process involves adjusting pH and isolating the soluble components from the insoluble ones.

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Chitosan-HCl Salt

A form of chitosan that is more stable and easier to handle. It's produced by converting chitosan into its hydrochloride form.

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TNF-α Production

A process where human monocytes (immune cells) produce a protein called Tumor Necrosis Factor-alpha (TNF-α) in response to certain stimuli.

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Applications of Neutral-Soluble Chitosan

Neutral-soluble chitosan has potential applications in various fields, such as biomedicine and drug delivery, due to its ability to interact with biological systems at physiological pH.

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Chitosan-HCl

A salt formed by reacting chitosan with hydrochloric acid (HCl). It is soluble in water and acetic acid.

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Deacetylation

The process of removing acetyl groups from chitosan, increasing its positive charge and water solubility.

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Heterogeneous Deacetylation

Deacetylation process where the chemical reaction occurs only on the surface of chitosan particles, creating a gradient of deacetylation.

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Homogeneous Deacetylation

Deacetylation process where the chemical reaction occurs uniformly throughout the chitosan particle, leading to consistent deacetylation.

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Intrinsic Viscosity

A property of a polymer solution that describes the resistance to flow caused by the shape and size of the polymer molecules.

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Number-average Molecular Weight (DPn)

The average molecular weight of a polymer, calculated by summing the molecular weights of all individual polymers and dividing by the total number of polymers.

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Degree of Scission

A measure of how much a polymer chain has been broken down into smaller chains, calculated as the ratio of the number of broken bonds to the initial number of polymer units.

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pH-solubility Experiments

Experiments used to determine the solubility of a substance at various pH values, revealing its charge and reactivity.

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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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Water-Solubility of Partially N-Acetylated Chitosans PDF

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.

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