Structural Aspects of the Swelling of β Chitin in HCl and its Conversion into α Chitin

The solid state transformation of chitin β into chitin α under the influence of aqueous HCl of increasing concentration was investigated in the case of highly crystalline β chitin microfibrils isolated from the vestimentiferan tube of Tevnia jerichonana . With acid strength below 6 N, the chitin microfibrils remained un-affected. With acid strength between 6 and 7 N a total decrystallization was observed when the samples were immersed in the acid solution. When the initial β chitin was washed, crystals or one of their hydrates was restored, but the initially large microfibrils of chitin became split into a series of parallel subfibrils of much smaller diameter. With acid strength from 7 N to 8 N, decrystallization was also observed but it was accompanied by a substantial cutting and dissolution of the chitin chains. These smaller chains recrystallized in epitaxy on the remaining β chitin microfibrils in a subsequent washing step. In this case, the recrystallization led to morphologies resembling those of shish kebab where the “kebab” overgrowths consisted of α chitin spindle-like crystals organized in epitaxy on the underlying β chitin microfibrillar remainder. When acid strengths of 8 N and above were used, the sample recrystallized exclusively as α chitin upon washing. As opposed to the case where lower acid concentration was used, a total loss of the fibrillar morphology was observed with HCl of 8 N and above.