Susceptibility of dibutyryl chitin and regenerated chitin fibres to deacylation and depolymerization by lipases

Abstract

Dibutyryl chitin obtained by esterification with butyric anhydride and regenerated chitin obtained from dibutyryl chitin by saponification, both in the form of wet-spun fibres and non-wovens, were examined by infrared spectrometry and X-ray diffraction spectrometry. Chitin fibres and chitosan fibres were also studied for comparison, and found to maintain the XRD spectral features of the parent chitin and chitosan. On the opposite, DBC fibres and non-woven exhibited depressed crystallinity, the peak at 0.46–0.47 nm, typical of chitin, being hardly detectable, while the one usually at ca. 1.00 nm was present at ca. 1.20 nm. Both DBC fibres and non-woven were highly oriented. When exposed to porcine pancreatic lipase or wheat germ lipase, the DBC fibres gained improved crystallinity with peaks at 1.14–1.18 and 0.41 nm, due to partial regain of chitin structure as a consequence of partial enzymatic removal of butyryl groups, as confirmed by ATR-FTIR. The RC fibres exhibited broad XRD peaks at 0.96 and 0.36 nm; sharper peaks at 0.34, 0.46–0.49 and 0.96 were observed after exposure to lipases, due to removal of a disordered polymer fraction susceptible to the unspecific enzymatic depolymerization. In fact the RC fibres were found to have 8% lower degree of acetylation compared to parent chitin, as a consequence of the alkaline regeneration treatment. In conclusion, these modified chitins are scarcely susceptible to degradation by lipases (besides to lysozyme, as already reported in the literature); therefore their biochemical significance in wound management seems limited. They, however, appear to be the ideal textile materials for providing mechanical support to freeze-dried chitosan sponges having amply documented activity in wound healing, and for the preparation of specialty textiles.