Modificação química da superfície de nanocristais de celulose via reação click para a obtenção de bionanomateriais funcionais

Abstract

In this work we aimed at the preparation of surface functionalized cellulose nanocrystals (NCC) with two bioactive molecules with potential anticancer activity (alkyne-1,4-naftoquinone QA, and azide-1,4-naftoquinone QN3) and two fluorescent molecules (2,1,3-benzothiadiazole aminopiridine BTD, and fenazine-nor--N3 Fenazine) via click chemistry with the formation of 1,2,3-triazole covalent linkage. In order to render NCCs surface suitable for the appendage of the molecules, a first functionalization step was required to yield azide functionalized nanocrystals (NCC-N3) and alkyne functionalized nanocrystals (NCC-P). One batch of NCC-N3 was then clicked with the alkyne terminated QA (yielding NCC-QA) and the other with the alkyne terminated BTD (yielding NCC-BTD). Similarly, one batch NCC-P was clicked with the azide terminated QN3 (yielding NCC-QN3) and the other with the azide terminated Fenazine (yielding NCC-Fen). The pristine NCC, the precursors and the click products were characterized by FT-IR, XRD, CHN, TG, TEM, 13C CP/MAS NMR, and XPS. In addition, the fluorescently labelled NCC were characterized by means of UV-Vis and fluorescence spectroscopy to evaluate whether the click product was rendered fluorescent. Elemental analysis data provided an estimation of the degree of substitution (DS) of NCCs hydroxyl groups by the azide and alkyne groups and the clicked molecules. Values for DS were 13% and 30% for NCC-N3 and NCC-P, respectively; and 10% for NCC-Fen, 20% NCC-BTD and NCC-QN3 and 12% NCC-QA. All click products were thermally more stable than the pristine NCC, which also provided further evidence for surface modification. Despite the fact that the click products suffered a decrease in their crystallinity indexes (CI), which ranged between 51-56%, compared to pristine NCC (88%), TEM analysis proved that the nanocrystalline structures were well preserved even after 3 or 4 surface modification reactions.