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Fast-forward approach of time-domain NMR relaxometry for solid-state chemistry of chitosan
William Marcondes Facchinatto1, Rodrigo Henrique Dos Santos Garcia1, Danilo Martins Dos Santos2
1Sao Carlos Institute of Chemistry, University of Sao Paulo, Av. Trabalhador sao-carlense 400, CEP 13566-590, Caixa Postal 780, Sao Carlos, SP, Brazil.
Abstract:
Chitosans with different average degrees of acetylation and weight molecular weight were analyzed by time-domain NMR relaxometry using the recently proposed pulse sequence named Rhim and Kessemeier - Radiofrequency Optimized Solid-Echo (RK-ROSE) to acquire 1H NMR signal of solid-state materials. The NMR signal decay was composed of faster (tenths of μs) and longer components, where the mobile-part fraction exhibited an effective relaxation transverse time assigned to methyl hydrogens from N-acetyl-d-glucosamine (GlcNAc) units. The higher intrinsic mobility of methyl groups was confirmed via DIPSHIFT experiments by probing the 1H-13C dipolar interaction. RK-ROSE data were modeled by using Partial Least Square (PLS) multivariate regression, which showed a high coefficient of determination (R2 > 0.93) between RK-ROSE signal profile and average degrees of acetylation and crystallinity index, thus indicating that time-domain NMR consists in a promising tool for structural and morphological characterization of chitosan.
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