Silk fibroin-microcrystalline cellulose (cellulose whisker) composite films with varied compositions were prepared by casting mixed aqueous solution/suspensions of the two components. Silk fibroin was dissolved in 10M LiSCN followed by dialysis; a cellulose whisker suspension was prepared by sulfuric acid hydrolysis of tunicate cellulose. Macroscopically homogeneous films were obtained at all mixing ratios. While the Young's modulus of the composite films showed a linear, additive dependence on the mixing ratio, the tensile strength and ultimate strain showed a maximum at a 70 -80% cellulose content, reaching five times those of fibroin-alone or cellulose-alone films. At the same mixing ratio, infrared spectra of the composite films showed a shift of the amide I peak from 1654 to 1625 cm Ϫ1 , indicating the conformational change of fibroin from a random coil to a ␤ structure (silk II) at the whisker-matrix interface. This change seems to be induced by contact of fibroin molecules with a highly ordered surface of cellulose whisker.

The crystal structure of β-chitin, a homopolymer of N-acetylglucosamine, was determined using highly resolved X-ray fiber diffraction data obtained from uniaxially oriented specimen of diatom spines. The labile N-acetyl groups and hydroxymethyl groups were directly located in the Fourier omit maps constructed using the glycosyl backbone as phasing model. Using the 216 independent intensities extending to a resolution of 1 A ˚, we could refine the structure without any restraints on bond angles to obtain a reasonable model with high accuracy. The carbonyl oxygen of acetamide group formed intermolecular hydrogen bonding between the primary hydroxyl and amine groups forming a two-dimensional hydrogen bonding network in a plane perpendicular to the pyranosyl plane. The hydrogen bonding pattern explains why the conformation of the acetamide groups is slightly rotated from standard conformation.

Inclusion complexation of beta-chitin with linear aliphatic amines was studied by X-ray diffraction. All tested amines, C3 to C8 monoamines and C2 to C7 diamines with terminal amino groups, reversibly formed crystalline complexes with beta-chitin by immersion of dry chitin in pure liquid. Complex formation caused linear increase in the 010 sheet spacing of beta-chitin depending on the carbon number of amine. The complexes could be classified as type I and type II according to the increment of sheet spacing against carbon number. All monoamines formed type II complexes. In dry conditions, diamine formed a type I complex though the type of diamine complex differed for guest species in wet conditions. Based on the unit cell dimension and thermogravimetry, type II and type I are likely to correspond to guest-host (amine-chitobiose) ratios of 2:1 and 1:1, respectively. These differences seem to arise from varied interactions between functional groups of chitin and amines.

Crystal conversion of beta-chitin to alpha-chitin by aq. NaOH treatment was studied for a highly crystalline beta-chitin sample from diatom spine. The minimum NaOH concentration to cause swelling was between 25% and 30% w/w. The alkali-swollen material was poorly crystalline and was regenerated as alpha-chitin on washing with water. This conversion caused total collapse of the original microfibrillar morphology. These features are similar to those of 7 N-8 N HCl treatment reported earlier, but alkali treatment was free from depolymerization or deacetylation.

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