Chitin: Structure and Properties
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Chitin: Structure and Properties

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Questions and Answers

What is the primary source of chitin in nature?

  • Mushrooms
  • Insects
  • Fungi
  • Crustaceans (correct)

    • Which of the following statements accurately describes chitosan?

  • It is a deacetylated form of cellulose.
  • It is a natural biopolymer abundant in plants.
  • It has less structural stability than chitin.
  • It is derived from chitin. (correct)

    • What percentage of dry weight chitin is typically found in the shells of crustaceans?

  • 15% - 30% (correct)
  • 1% - 11%
  • 30% - 50%
  • 10% - 30%

    • Which allomorph of chitin is the most abundant and has high thermodynamical stability?

    <p>Alpha-chitin</p> Signup and view all the answers

    How many allomorphs of chitin are recognized?

    <p>Three</p> Signup and view all the answers

    In which of the following structures is chitin NOT typically found?

    <p>Bird feathers</p> Signup and view all the answers

    What is the significance of the structural similarity between chitin and chitosan?

    <p>It affects their applications in environmental cleanup.</p> Signup and view all the answers

    From which language is the term 'chitin' derived, and what does it mean?

    <p>Greek; covering</p> Signup and view all the answers

    Which characteristic differentiates chitin allomorphs from one another?

    <p>Orientation of microfibrils</p> Signup and view all the answers

    In which component of organisms is chitin primarily found?

    <p>Exoskeleton</p> Signup and view all the answers

    Which of the following best describes the environmental significance of chitin?

    <p>It plays a role in the carbon cycle.</p> Signup and view all the answers

    What percentage of chitin is typically found in the dry weight of cockroaches?

    <p>38%</p> Signup and view all the answers

    Which scientist first identified chitin in insects?

    <p>Auguste Odier</p> Signup and view all the answers

    Chitin is primarily composed of which type of macromolecule?

    <p>Carbohydrates</p> Signup and view all the answers

    What distinguishes a-chitin from b- and g-chitin?

    <p>Thermodynamical stability</p> Signup and view all the answers

    What is the primary structural form of chitin found in nature?

    <p>Crystalline microfibrils</p> Signup and view all the answers

    What mathematical model is most commonly used to describe the kinetics of hydrogel swelling?

    <p>Fickian diffusion model</p> Signup and view all the answers

    Which of the following best characterizes the equilibrium swelling percentage of hydrogels?

    <p>It is affected by the polymer's molecular weight.</p> Signup and view all the answers

    In the context of hydrogels, what does the swelling ratio assess?

    <p>The proportionate increase in volume upon hydration.</p> Signup and view all the answers

    Which process can significantly affect the swelling behavior of chitosan-based hydrogels?

    <p>Nucleophilic attack on polymer side chains</p> Signup and view all the answers

    How is first order kinetics typically characterized in the context of hydrogel swelling?

    <p>Swelling rate is proportional to the remaining unabsorbed water.</p> Signup and view all the answers

    Which aspect could hinder the mechanical strength of chitosan hydrogels during applications?

    <p>High degree of acetylation</p> Signup and view all the answers

    What role do crosslinking agents like glutaraldehyde play in hydrogel preparation?

    <p>They promote chemical stability and mechanical strength.</p> Signup and view all the answers

    In second order kinetics, how is the swelling process typically characterized?

    <p>Rate depends on the square of the concentration of water.</p> Signup and view all the answers

    What does the symbol 'n' represent in relation to diffusion?

    <p>The slope of the ln F versus ln t graph</p> Signup and view all the answers

    In Fick's second law of diffusion, what is the role of the variable 'D'?

    <p>It represents the diffusion coefficient</p> Signup and view all the answers

    What is the purpose of plotting data until 60% solvent has entered the gel structure?

    <p>To calculate the diffusion coefficient 'D'</p> Signup and view all the answers

    Which temperature range is utilized for the Thermogravimetric Analysis?

    <p>30°C to 500°C</p> Signup and view all the answers

    What is the significance of the intercept value 'k' in diffusion studies?

    <p>It is derived from the ln F versus ln t graph</p> Signup and view all the answers

    What does Peleg's empirical equation involve in the context of hydrogel absorption?

    <p>Two parameters describing the absorption behavior</p> Signup and view all the answers

    In which type of analysis is the DSC unit Q-200 employed?

    <p>Thermal properties assessment of hydrogels</p> Signup and view all the answers

    What is likely the outcome of a nucleophilic attack in crosslinked CS hydrogels?

    <p>Increased water absorption rate</p> Signup and view all the answers

    What does the equation $dS/dt = k_{1r}(S_{eq} - S)$ represent?

    <p>A model of first-order kinetics for hydrogel swelling</p> Signup and view all the answers

    How is the swelling ratio (SR) in hydrogels mathematically defined in the context of second-order kinetics?

    <p>$dS/dt = k_{2r}(S_{eq} - S)^2$</p> Signup and view all the answers

    What indicates that the hydrogel is following first-order kinetics based on the graph of $ln(S_{eq}/(S_{eq} - S))$ versus time (t)?

    <p>The plot is a straight line with R2 values near 1.</p> Signup and view all the answers

    In the context of hydrogel synthesis, what role does the lone pair of electrons on nitrogen play?

    <p>It facilitates a nucleophilic attack on the carbonyl carbon.</p> Signup and view all the answers

    What is indicated by the equation $S = 1 + k_{2r}²t$ after integrating from S=0 to S and t=0 to t?

    <p>The solution showing second-order kinetics in swelling behavior.</p> Signup and view all the answers

    What characterization is essential for determining the absorption kinetics of a hydrogel?

    <p>The swelling ratio at various time intervals.</p> Signup and view all the answers

    What does the variable $S_{eq}$ represent in the context of hydrogel swelling?

    <p>The final equilibrium swelling ratio.</p> Signup and view all the answers

    Which of the following factors impacts the rate constant $k_{1r}$ in first-order kinetic models of hydrogel swelling?

    <p>The temperature of the environment during hydration.</p> Signup and view all the answers

    Study Notes

    Chitin

    • Chitin is a natural mucopolysaccharide found in the cell walls of mushrooms and insects.
    • It was discovered by Henri Braconnot in 1811 who named it “fungine”, then by Auguste Odier, in 1823, who renamed it to “chitin”.
    • Chitin is the second most abundant natural biopolymer in the world, after cellulose.
    • It is found in the outer layers of organisms like crustaceans, insects, fungi, and fish.
    • Chitin is found in crystalline microfibrils.
    • It is the major constituent of the cell wall in fungi and yeast, in teeth of the radula, calcified layers of shells of mollusks, and gladii (pen) of squids.
    • Chitin is found in the exoskeleton of arthropods.
    • The amount of chitin in crustacean shells is between 15% to 30% of the dry weight.
    • It exists in three allomorphs: α, β, and γ.
    • These allomorphs differ in their hydration degree, size of the unit cell, number of chains per unit cell, and microfibrils orientation.
    • α-chitin is the most common allomorph and has high thermodynamical stability

    Chitosan

    • Chitosan is a derivative of chitin.
    • It is the N-deacetylated form of chitin.

    Chitin: Structure and Properties

    • Chitin is a natural mucopolysaccharide found in various organisms including insects, fungi, and crustaceans.

    • Henri Braconnot discovered chitin in 1811, calling it "fungine".

    • Auguste Odier further characterized chitin in 1823.

    • Chitin is the second most abundant natural biopolymer after cellulose.

    • Chitin forms crystalline microfibrils found in various structures:

      • Exoskeletons of arthropods
      • Cell walls of fungi and yeast
      • Teeth of radula (in mollusks)
      • Calcified layers of shells (in mollusks)
      • Gladii (pens) of squids

    • Chitin content varies by organism:

      • Crustacean shells: 15%-30%
      • Grasshoppers: 4%-11%
      • House crickets: 1%-2%
      • Cockroaches: > 38%
      • Filamentous fungal cell wall: 10%-30%
      • Yeast cell wall: 1%-2%

    • There are three chitin allomorphs: α, β, and γ.

    • Allomorphs are differentiated by:

      • Degree of Hydration
      • Size of the unit cell
      • Number of chains per unit cell
      • Orientation of microfibrils

    • α-chitin is the most abundant allomorph and has the highest thermodynamic stability.

    Hydrogels & Chitosan (CS)

    • Hydrogels are hydrophilic networks, they can be synthetic or natural polymer based.
    • Synthetic hydrogels use acrylic acid , acrylamide , polyurethane and poly(ethylene glycol)
    • Natural hydrogels use polysaccharides such as cellulose, dextran, starch, and chitosan (CS).
    • CS is often used as a base for natural hydrogels
    • CS challenges are lack of mechanical strength, swelling time, and biodegradability time
    • Blending CS with acrylamide or crosslinking with glutaraldehyde and genipin can increase mechanical strength
    • Equilibrium swelling is the maximum absorption capacity of the hydrogel
    • The time needed for a hydrogel to reach its equilibrium swelling is a key factor for applications like drug delivery and controlled release

    Crosslinked CS Hydrogels

    • CS molecular weight: 800,000 Da (1526.464 g/mol)
    • Degree of deacetylation 90-98%
    • CS is crosslinked with glutaraldehyde
    • The crosslinking process involves a nucleophilic attack reaction by the carbonyl carbon of glutaraldehyde due to the lone pair of electrons in the amino group
    • Glutaraldehyde concentration influences the rate of swelling and maximum swelling capacity

    Swelling of CS Hydrogels

    • Swelling ratio (SR) is a measure of hydrogel swelling
    • The SR is determined gravimetrically by measuring the weight of a dried pellet before and after immersion in distilled water
    • The SR value is correlated to the amount of water absorbed by the hydrogel

    Kinetic Models for Swelling

    • Three kinetic models for swelling are First Order kinetics, Second Order kinetics, and Fickian Diffusion
    • First Order kinetics is characterized by a linear relationship when plotting ln(Seq/(Seq-S)) against t
    • Second Order kinetics is characterized by a linear relationship when plotting S against 1/(1+k2rSeqt)
    • Fickian diffusion is a common model used to describe swelling
    • The diffusion coefficient (D) is calculated using the equation: 𝐷 = 𝑘1/(𝜋𝑟^2(4)).

    Applications of Hydrogels

    • Hydrogels are widely used in applications like diapers, drug delivery systems, contact lenses, and tissue engineering
    • Controlled release fertilizers are an important application of hydrogels, the rate of swelling is critical for effective nutrient release.
    • Hydrogels are also used in wound healing, bio-imaging, and biosensors

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    Related Documents

    Chitosan: Structure, Properties, and Importance in Environmental Cleanup PDF
    Kinetics, Absorption, and Diffusion of Crosslinked Chitosan Hydrogels PDF

    Description

    This quiz explores the intriguing world of chitin, a natural mucopolysaccharide found in fungi and arthropods. Delve into its discovery, abundant presence, allomorphs, and structural significance in various organisms. Test your knowledge on this essential biopolymer.

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