Simulation of X-ray diffractograms relevant to the purported polymorphs cellulose IV_I and IV_II

Diffractograms were simulated for model nanocrystals of cellulose I_β, using numerical summation of radiation scattered from all carbon and oxygen atoms in the nanocrystal. Diffractogram peaks were sometimes displaced by a few degrees from positions calculated by the Bragg equation, as predicted in a published study based on a different mathematical approach. Simulated diffractograms showed 2 or 3 peaks, depending on the cross-sectional size and shape of the model nanocrystal. Some of the 2-peak diffractograms resembled published results for the purported polymorph cellulose IV_I, or for cell-wall cellulose, supporting suggestions that cellulose IV_I is simply cellulose I fragmented into nanocrystals with relatively small cross-sectional dimensions. A published diffractogram for cellulose IV_II could not be simulated with acceptable precision, suggesting that this polymorph might have a crystal structure distinctly different from that of cellulose I_β.