Biomass Fundamentals Module 15 : Special Polysaccharides: Chitin & Xantham

1. 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

2. 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

3. 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

4. 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))

5. Biosynthesis leads to parallel chain structures

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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?

13. Time of Coacervation and MW Effects on Swellability

14. 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

15. 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

16. What is going on with regard to swelling? pH

17. 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

18. 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

19. 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.

20. 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.

21. 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

22. 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)

23. Chitin chemistry • Purpose: to modify properties • Inorganic esters • Organic amides and esters • Ethers • Amines • Graft copolymers • Metal chelates • Schiff base

24. Inorganic esters • Nitrates • Sulfates (anticoagulant) • Phosphates (biological activity) • Xanthates (for solubility)

25. Organic amides and esters • Large number described • Changes solubility • Changes absorption affinities • Changes bioadhesion • Hydrophilic/hydrophobic • Biocompatibility

26. Ceric ion initiated grafting:Site specific