Evaluation of chitosan crystallinity: A high-resolution solid-state NMR spectroscopy approach


We propose a novel approach relied on high-resolution solid-state 13C NMR spectroscopy to quantify the crys- tallinity index of chitosans (Ch) prepared with variable average degrees of acetylation (DA) from 5% to 60 % and average weight molecular weight (Mw) ranged in 0.15 × 106 g mol−1–1.2 × 106 g mol−1. The Dipolar Chemical Shift Correlation (DIPSHIFT) curve of the C(6)OH segment revealed increased mobility dynamic, which induced different distribution from trans-to-gauche conformations in relation to C(4). Indeed, 1H-13C Heteronuclear Correlation (2D HETCOR) showed that distinguished C4 chemical shifts correlates with the same aliphatic protons. The short-range ordering can be assigned to C4/C6 signals on 13C CPMAS and, for our case, the deconvolution procedure between disordered and ordered phases revealed increasing crystallinity with DA, as confirmed by SVD multivariate analysis. This work extended the knowledge regarding the use of 13C CPMAS technique to predict the crystallinity of chitosans without the use of amorphous standards.


Facchinatto, William Marcondes; dos Santos, Danilo Martins; Fiamingo, Anderson; Bernardes-Filho, Rubens; Campana-Filho, Sérgio Paulo; deAzevedo, Eduardo Ribeiro; Colnago, Luiz Alberto

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