Cellulose nanofibrils (CNF) are renewable, biodegradable and biocompatible, which makes them ideal candidates as carriers in drug delivery applications. However, in-depth chemical and structural characterization of the CNF surface chemistry is often a challenge, especially for low weight percentage of functionalization compatible with drug delivery applications. Solid-state NMR spectroscopy is, in principle, a key technique to obtaining local structural information on this type of system and was indeed used in the past for studying CNF surface chemistry but either with a high level of grafting (5 to 10 %) or with the use of isotopically labeled molecules. Nevertheless, solid-state NMR fails to address application-driven systems that rely on a much lower level of grafting (~1 wt% or lower) and the use of non-isotopically enriched grafted molecules. This is notably the case for the system we have studied in this work, namely CNF functionalized with an anti-bacterial molecule (modified-metronidazole). This new CNF-based system is biologically active and represents an innovative drug carrier formulation with “on demand” release ability in the presence of esterase enzymes. There is thus a need to probe and quantify the mode of fixation, whether through adsorption or covalent binding, since this will directly influence the delivery kinetics and the overall dosage of the drug. In this work, we will show how we use Dynamic Nuclear Polarization to overcome the sensitivity limitation of conventional solid-state NMR and gain insight into the surface chemistry of this biologically active material. Notably, we will show how the data can be used to differentiate unambiguously adsorption from covalent grafting (~1 wt% in our case), locate the position of functionalization and estimate the efficiency of a two-step functionalization reaction. In addition, we will also show that these results cannot be obtained using other characterization techniques, such as FT-IR and elemental analysis. The main reason is that these techniques cannot differentiate unambiguously grafting versus adsorption and fail to report the presence of residual coupling agents (used during the synthesis) at the surface of the CNF. The latter are clearly evidenced from our NMR data with a wt% similar to the functionalizing molecules. This has direct implications for drug delivery, especially the evaluation of efficiency.

Probing surface chemistry of functionalized cellulose nanofibrils enabled by dynamic nuclear polarization enhanced solid-state NMR

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.