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

William Marcondes Facchinatto; Danilo Martins Dos Santos; Anderson Fiamingo; Rubens Bernardes-Filho; Sérgio Paulo Campana-Filho; Eduardo Ribeiro de Azevedo; Luiz Alberto Colnago

doi:10.1016/j.carbpol.2020.116891

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

Carbohydr Polym. 2020 Dec 15:250:116891. doi: 10.1016/j.carbpol.2020.116891. Epub 2020 Aug 13.

Authors

William Marcondes Facchinatto¹, Danilo Martins Dos Santos², Anderson Fiamingo³, Rubens Bernardes-Filho², Sérgio Paulo Campana-Filho⁴, Eduardo Ribeiro de Azevedo³, Luiz Alberto Colnago²

Affiliations

¹ São Carlos Institute of Chemistry, University of São Paulo, Av. Trabalhador Sao-Carlense 400, CEP 13566-590, Caixa Postal 780, São Carlos, São Paulo, Brazil. Electronic address: william.marcondes@gmail.com.
² Brazilian Corporation for Agricultural Research, Embrapa Instrumentation, Rua XV de Novembro 1452, CEP 13560-970, Caixa Postal 741, São Carlos, São Paulo, Brazil.
³ São Carlos Institute of Physics, University of São Paulo, Av. Trabalhador Sao-Carlense 400, CEP 13566-590, Caixa Postal 369, São Carlos, São Paulo, Brazil.
⁴ São Carlos Institute of Chemistry, University of São Paulo, Av. Trabalhador Sao-Carlense 400, CEP 13566-590, Caixa Postal 780, São Carlos, São Paulo, Brazil.

PMID: 33049828
DOI: 10.1016/j.carbpol.2020.116891

Abstract

We propose a novel approach relied on high-resolution solid-state ¹³C NMR spectroscopy to quantify the crystallinity index of chitosans (Ch) prepared with variable average degrees of acetylation (DA¯) from 5% to 60 % and average weight molecular weight (M¯_w) 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.

Keywords: Chitosan; Crystallinity; High-resolution SSNMR spectroscopy.