Journal
ACS MACRO LETTERS
Volume 8, Issue 12, Pages 1642-1647Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsmacrolett.9b00838
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- Academy of Finland [311255]
- Academy of Finland (AKA) [311255, 311255] Funding Source: Academy of Finland (AKA)
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Herein, we demonstrate an effective approach toward functionalization of cellulose nanocrystal (CNC) reducing ends by means of a Knoevenagel condensation reaction with a reactive beta-diketone (acetylacetone). The end-wise modification was elucidated by advanced NMR analysis, which was facilitated by dissolving the CNCs in ionic liquid electrolyte and by the concomitant assignment of a model compound derived from D-cellobiose. The diffusion-edited H-1 experiment afforded a simple method to identify the assigned model resonances in the reducing end-modified CNCs. The condensations can be carried out in aqueous bicarbonate solutions, avoiding the use of hazardous solvents. Under these preliminary aqueous conditions, end-group conversion of up to 12.5% could be confirmed. These results demonstrate the potential of beta-diketone chemistry and the Knoevenagel condensation for functionalizing cellulose reducing ends. Application of this liquid-state NMR method for confirming and quantifying reducing end conversion is also shown to be invaluable. Extension of this chemistry to other 1,3-dicarbonyl compounds and solvation conditions should allow for the topochemical and (axially) chirotopic installation of functional moieties to CNCs, paving the way to asymmetric cellulose-based nanomaterials with unique properties.
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