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Figure 2
The α-chitin structure and X-ray diffraction model for a single chitin fibre and a fibre array at different tilt conditions. (a) (Left, top) the ortho­rhombic structure of α-chitin. The three directions are labelled a, b and c, with the c axis along the fibril axis. (a) (Left, bottom) Small variations in the unit-cell orientation lead to angular broadening wμ and radial broadening dq0. (a) (Right) A single chitin fibril (green cylinder) and the reciprocal-lattice reflections distributed as symmetric rings around the c axis due to fibre symmetry (red 002, blue 110, green 013); μ is the opening angle between reflection rings and the c axis. (b) An array of chitin fibrils (green cylinders) with the same orientation and the three generated prototypical reciprocal-lattice intensity bands. The same colours are used for the three reflection rings as in panel (a). (c) A chitin fibril array with different orientations and the diffraction distribution in reciprocal space. γ is the distribution angle of fibres in the x–y plane. (d) A single chitin fibre (green cylinder) with (left) a tilt angle of α and (right) tilt angles of (α, β). The translucent diffraction rings are from a single chitin fibre without tilt (α = 0°, β = 0°). (e) (Top row) Diffraction rings in the fibre frame coordinates, (middle row) 2D X-ray patterns in laboratory coordinates and (bottom row) 1D intensity distributions along the azimuthal direction (χ) at different tilt conditions. The chitin fibre distribution shown here is small, with Δγ0 = 1°. Column (i) no tilt, α = 0°, β = 0°; column (ii) small α tilt, α = 10°, β = 0°; column (iii) large tilt angles, α = 30°, β = 60°. The same colours are used in the 1D profiles of the three reflections as for the diffraction rings in reciprocal space [panel (a)].

IUCrJ
Volume 13| Part 1| January 2026| Pages 63-76
ISSN: 2052-2525
https://doi.org/10.1107/S2052252525009686