Solid-State Spectroscopic Characterization of α-Chitins Deacetylated in Homogeneous Solutions

Synthesis and spectroscopic characterization of alpha-chitins exhibiting degrees of acetylation (DA) between 0.5 and 1 were reported. Crab shell alpha-chitin consisting of microfibrils with a width of less than 1 mu m was regenerated from or alkaline deacetylated in 30% aqueous NaOH solution. After the deacetylation in homogeneous solution, the DA of alpha-chitins decreased steadily with prolonged deacetylation times from 1 to 0.54. The native microfibrils of starting alpha-chitin were destroyed, while aggregates or sheets were formed depending on the DA of chitins. According to WAXD measurements, deacetylated chitins with DA lower than 0.76 have different crystalline structures than starting alpha-chitin. Furthermore, FT Raman spectroscopy demonstrated a novel rapid method to determine the DA of chitin with correlation coefficients greater than 0.99. On the basis of the FT Raman signals ascribed to the amide groups, the amount of hydrogen bonds linked to C=O groups decreased strongly with lower DA and the relationship between them was presented.