Structural data on the intra-crystalline swelling of beta-chitin.
The intra-crystalline swelling of the highly crystalline beta-chitin from Tevnia jerichonana was investigated by X-ray crystallography and Fourier transform infrared (FTIR) spectroscopy, using hydrogenated and deuterated hydrochloric acids as swelling agents. Three levels of swelling were identified that could be defined as inter- and intra-sheet swelling. A moderate and reversible swelling in water and methanol gave crystalline beta-chitin cystallosolvates, namely dihydrate and methanolate, respectively. In these, an inter-sheet swelling was observed, corresponding to an expansion of only the b parameter of the unit cell of beta-chitin. Under these swelling conditions, the use of deuterated reagents had no effect on the amide N&z.sbnd;H&ctdot;O&z.dbnd6;C hydrogen bonds that hold the structure of beta-chitin together, but only induced a partial and reversible deuteration of the chitin hydroxymethyl groups. A more severe swelling - but still reversible - occurred with 6 N HCl or DCl, which converted the crystals of beta-chitin into a paracrystalline gel-like product resulting from inter-sheet+intra-sheet swelling. With this acid strength, the deuteration pattern indicated that a fraction of the amide hydrogen bonds was broken and became susceptible to an irreversible deuteration. A very severe and irreversible swelling occurred with 8 N HCl or DCl. In that case, the inter- and intra-sheet swelling was extensive to the point where all memory of the parallel-chain beta-chitin was lost. In addition, this swelling was accompanied by a drastic and rapid depolymerization. The treatment with 8 N HCl led invariably to crystalline alpha-chitin when the samples were neutralized.
Saito
Y
Y
Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, 113-8657, Tokyo, Japan. putaux@cermav.cnrs.fr
Okano
T
T
Gaill
F
F
Chanzy
H
H
Putaux
J L
JL
D000818:Animals; D002686:Chitin / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003903:Deuterium; D046911:Macromolecular Substances; D008958:Models, Molecular; D011077:Polychaeta / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared
D046911:Macromolecular Substances; D002686:Chitin; D003903:Deuterium