STUDIES OF CRYSTALLINE NATIVE CELLULOSES USING POTENTIAL-ENERGY CALCULATIONS

Energies for various trial packing arrangements of unit cells for the I alpha and I beta phases of native cellulose discovered by Sugiyama et al. were evaluated. Both a rigid-ring method, PLMR, and the full-optimization, molecular mechanics program, MM3(90), were used, For both phases the models that had the lowest PLMR energy also had the lowest MM3 energy. Both calculated models have the chains packed 'up', O6s in fg positions, and the same sheets of hydrogen-bonded chains, The I beta structure model is essentially identical to that proposed previously for ramie cellulose by Woodcock and Sarko, It is also the same as the best parallel model previously proposed that was based on the X-ray data of Mann, Gonzalez and Wellard, once the various unit cell conventions are considered. Also, the energies from both methods for all three celluloses, I alpha, I beta and II, are in the order that rationalizes their relative stabilites.