TEMPO-mediated Oxidation of Cellulose Nanocrystals (CNCs)

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