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Discover the structural intricacies and versatile properties of chitin and xanthan polysaccharides in this capstone course. Uncover the biodegradability, antimicrobial activity, and hydrogel formation potential of these special polysaccharides.
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Biomass FundamentalsModule 15: Special Polysaccharides:Chitin & Xantham A capstone course for BioSUCCEED: BioproductsSustainability: a University Cooperative Center of Excellence in EDucation The USDA Higher Education Challenge Grants program gratefully acknowledged for support
This course would not be possible without support from: USDA Higher Education Challenge (HEC) Grants Program www.csrees.usda.gov/funding/rfas/hep_challenge.html
Chitosan (deacetylated chitin) • Usually not fully deacetylated. • Deactylation value has striking effect upon solubility and crystallinity • Can form cationic site (as ammonium salt) • Rare in nature
1,4- linked glucoses Chemical structures of (a) cellulose and (b) chitin and chitosan (chitin occurs as mostly N-acetyl form (m) and chitosan occurs as amino form (n))
Structure of Xanthan • β-1,4-D-glucose backbone • Every alternate glucose residue has 3 sugar side chain of 2 mannose residues • Nearest mannose can carry at C6 an acetyl group and farthest a pyruvate group with a glucuronic acid between th
Hydrogel Formation between Chitosan and Xanthan • Chitosan is a linear binary heteropolysaccharide obtained by alkaline deacetylation of chitin • Xanthan is an extracellular heteropolysaccharide produced by Xanthomonas campestris • A hydrogel can be formed via ionic bonding & van der Waals interactions
Polyionic Matrix Formation • Mixing • Modification of concentration of each polymer at end (due to pH changes) • Polyionic interactions between NH3+ (chitosan) and COO- (xanthan) • As a result of coacervation (partitioning), water molecules arrange themselves in layers
Polyionic Interaction Phenomenon • At surface, water is oriented via H-bonding, next layer is random resembling silica gel • In last step of formation, mixing causes structural modification by removing “random” water layer
Why is it Attractive? • Matrix for enzyme immobilization • Hydrophilic microenvironment – swelling! • Allows for inclusion & stabilization • Enhances activity • Promotes activity in organic solvents • Synergistic activity observed for enzyme combinations
Swelling Degree • How well does this material “swell?” • What are the properties that control it? • What can we do to control it? • Why is it useful?
What is going on with regard to swelling? Ionic effect • Diffusibility of molecular chains of polymers • Longer the time, the higher the intermixing with higher probability of interaction among the ionic groups
What is going on with regard to swelling? Molecular Weight Effect • Higher MW is more unstable at pH – precipitation can occur • Swelling degree is SMALLER • However, given time since the larger MW can diffuse much more slowly than the lower MW and thus have a smaller change in swelling degree
What is going on with regard to swelling? pH • It governs the number of amine groups as a salt • When the pH increases, the number of amine groups increase and the number of ammonium groups decrease • This results in a diminution in interaction between the chitosan and xanthan
Solubility • Chitin • semicrystalline polymer with extensive inter- and intra-molecular hydrogen bonds : difficult to dissolve in dilute acids or organic solvents under mild conditions • many solvents : toxic, corrosive, or mutagenic • Chitosan • more tractable form than chitin • readily dissolves in dilute mineral or organic acids by protonation of free amine groups at pH below about 6.5
Chemical Reactivity of Chitosan • Three reactive groups : primary (C-6) and secondary (C-3) hydroxyl groups, and amino (C-2) group • Etherification, esterification, N-alkylation, N-acylation, cross-linking, and graft copolymerization, etc.
Chitosan: biodegradability, biocompatibility, antimicrobial activity, nontoxicity, and versatile chemical and physical properties Leads to: pharmaceutical and medical applications, textiles, wastewater treatment, biotechnology, cosmetics, food processing, and agriculture.
ANTIMICOBIAL ACTIVITY OF CHITOSAN Mechanism • Interaction of the positively charged chitosan with the negatively charged residues at the cell surface of fungi and bacteria alterations of cell surface and permeability leakage of intracellular substances inhibition of normal metabolism of microorganisms • Small chitosan fragments, hydrolyzed by host hydrolytic enzyme penetrate into the cell of microorganisms interaction of chitosan with DNA inhibition of RNA and protein synthesis reduces cell viability
Degradation of chitosan • Chemical • Acid hydrolysis • Base catalyzed oxidation • Enzymatic • Chitinases • Chitosanases • Endo enzymes (random cleavage) • Exo enzymes (chain ends) • Lysozyme commonly used (found in tears)
Chitin chemistry • Purpose: to modify properties • Inorganic esters • Organic amides and esters • Ethers • Amines • Graft copolymers • Metal chelates • Schiff base
Inorganic esters • Nitrates • Sulfates (anticoagulant) • Phosphates (biological activity) • Xanthates (for solubility)
Organic amides and esters • Large number described • Changes solubility • Changes absorption affinities • Changes bioadhesion • Hydrophilic/hydrophobic • Biocompatibility