PRELIMINARY POTENTIAL-ENERGY CALCULATIONS OF CELLULOSE I-ALPHA CRYSTAL-STRUCTURE

Packing energy calculations were used to evaluate various models of Ia cellulose, based on unit cell dimensions proposed by Sugiyama et al. Both a rigid-ring method, PLMR, and a full-optimization molecular mechanics technique, MM3, were used. The model found to be best with both methods was packed ''up'' (the z coordinate of O5 is greater than that of C5); O6 atoms were in tg positions, forming sheets of hydrogen bonded chains. With the PLMR program, the energy of the best model was almost 3 kcal/mol lower than the second best model. The MM3 studies also showed substantially higher energies for the alternative models. Also, some alternative PLMR models had substantially higher atomic movement during MM3 optimization.