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TEMPO-mediated Oxidation of Cellulose Nanocrystals (CNCs)

Regular Linking of Cellulose nanocrystals via Click Chemistry: Synthesis and formation of Cellulose N anoplatelet Gels. O. H. H. O. O. C. H. O. O. C. O. H. O. O. H. O. H. O. O. O. O. H. O. H. O. H. O. O. H. O. O. H. O. O. C. O. H. O. H. H. O. O. C.

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TEMPO-mediated Oxidation of Cellulose Nanocrystals (CNCs)

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  1. Regular Linking of Cellulose nanocrystals via Click Chemistry: Synthesis and formation of Cellulose Nanoplatelet Gels

  2. O H H O O C H O O C O H O O H O H O O O O H O H O H O O H O O H O O C O H O H H O O C (n-2)/2 2,2,6,6-tetramethyl-1-piperidinyloxy-radical (TEMPO) pH 10 R.T. NaBr NaOCl N a O O C O H N a O O C O H O O H O H O O O O H O H O H O O H O O N a O O C O H O H N a O O C (n-2)/2 TEMPO-mediated Oxidation of Cellulose Nanocrystals (CNCs) TEMPO –mediated oxidation selectively oxidizes the primary hydroxyl groups while leaving unaffected the secondary hydroxyl groups Montanari et al. Macromolecules, 2005, 38, 1665-1671

  3. Fourier Transform Infrared Spectroscopy (FTIR) TEMPO-oxidized CNCs CNCs C=O band 1730 cm-1 New signal at 1730 cm-1 indicates successful oxidation reaction

  4. Degree of Oxidation (DO) • DO was determined by using acid-base titration and FTIR • Excellent correlation was found between these two methods • Results are in good agreement with the recent literature (Montanari et al., Macromolecules, 2005, 38, 1665-1671, Saito et al., Biomacromolecules, 2006, 7, 1687-1691)

  5. Strong Acid – Weak Acid Titration 162 x C x (V2-V1) w-36 x C x (V2-V1) = 0.19 DO= Weak acid region Where, C= NaOH conc. V1, V2= amount of NaOH (L) W= weight of the O.D. sample (g) Value 36 is the difference between the molecular weight of an AGU and that of the sodium salt of a glucuronic acid 50 mg of dry TEMPO-oxidized material was suspended in 15 ml of 0.01 M HCl. After 10 min of stirring the suspension was titrated with 0.01M NaOH. Da Silva Perez et al., Biomacromolecules, 2003, 4, 1417-1425

  6. FT-IR Cellulose backbone (1050) I1730 I1050 DO= ≈ 0.20 COOH (1730) Habibi, Y., Chanzy, H., and Vignon, M. R. Cellulose, 2006, 13(6), 679-687.

  7. Click Chemistry • In general, 1,3-dipolarcycloadditionreactions have long been popular in the generation of carbohydratemimetics in the homogeneousreactionenvironment.1 • The reaction has gainedincreasing attention afterdiscoveringthat the 1,3-dipolarcycloadditionbetweenazides and terminal alkynescanbecatalysed by Cu(I) salts.2,3 • Severalauthors have described the use of thisnovel click-chemistry concept for the generation of carbohydratemimetics and derivatives.4,5,6 1. Gallos, J. K. and Koumbis, A. E. Curr. Org. Chem., 2003, 7(5), 397–426. 2. Tornøe, C. W.; Christensen, C.; and Meldal, M. J. Org. Chem., 2002, 67(9), 3057–3064. 3. Rostovtsev, V. V.; Green, L. G.; Fokin V. V.; and Sharpless, K. B. Angew.Chem., Int. Ed., 2002, 41(14), 2596–2599. 4. Huisgen, R. Pure Appl. Chem., 1989, 61(4), 613−628. 5. Kolb, H. C; Finn, M. G; and Sharpless, K. B. Angew. Chem., Int. Ed., 2001, 40(11), 2004−2021. 6. Wu, P.; Feldman, A. K.; Nugent, A. K.; Hawker, C. J.; Scheel, A.; Voit, B.; Pyun, J.; Fréchet, J. M. J.; Sharpless, K. B.; and Fokin, V. V. Angew. Chem., Int. Ed., 2004, 43(30), 3928 −3932.

  8. HuisgenCycloaddition • Cellulose nanoplatelet gels (Click chemistry) • Grafting click precursors onto TEMPO-oxidized CNCs • Huisgen reaction (1,3-dipolar cycloaddition) The HuisgenCycloaddition is the reaction of a dipolarophile with a 1,3-dipolar compound that leads to 5-membered (hetero)cycles.

  9. The Creation of the Azido Functionality on the Nano Crystals N3 (2120 cm-1) C=O(1730 cm-1)

  10. The Creation of the Alkyne Precursor on the Crystals

  11. The Formation of CNC-Based Click-Gels N3 disappeared

  12. Click Reaction Gel formation: Elemental analysis: Precursors in H2O vigorous stirring (1 min) CuSO4 Ascorbic acid aO = 100 % - C (%) – H (%) – N (%) The grafting densities of CNC-PR and CNC-AZ were calculated by using the DO value of 0.20 for Tempo-oxidized CNCs and the elemental composition of CNC-PR and CNC-AZ ; grafting densities of CNC-PR and CNC-AZ were found to be ~50% and ~35%, respectively

  13. Transmission Electron Microscopy a b Individual CNC TEM images of TEMPO-oxidized cellulose nanocrystals (a) and cellulose nano-platelet gel (b). Scale bar 500 nm The average dimensions of the crystals were found to be approximately 10-20 nm width and 100-200 nm long.

  14. Thermogravimetric Analysis CNC-Click CNC-Click has different thermal properties than its precursors

  15. Benzoylation of Cellulose; Allowing the Visualization of Mol. Weight Distribution Cell-OH + Benzoyl-Cl Cell-Bz • Reaction is carried out in Ionic Liquid • UV – active benzoyl group • Benzoylated cellulose is completely soluble in THF (compatible with GPC)

  16. Gel Permeation Chromatography CNC-Click Solid line (CNC-Click); Dotted line (CNC-PR); Dashed line (CNC-AZ) CNC-click showed significantly higher molecular weight (cross-linking) Than its precursors (CNC-AZ and CNC-PR)

  17. Summary • The primaryhydroxyl groups in cellulose nanocrystalswere first selectivelyoxidized to carboxylicacidswhichwerefurtherused as reactive sites for the amidationreactions to provide the precursorsnecessary for the Click chemistryreaction. • Click-chemistry has been utilized for the preparation of new gel-like cellulose nanomaterials. • Benzoylation of CNCs allows complete dissolution of material into THF and makes GPC analysis possible

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