Fibrous structures: Their character and the role of interatomic forces in their analysis

An introduction is given to the various types of spatial relationships that occur among molecules in fibrous materials and the concepts associated with their diffraction. Fibrous materials provide limited diffraction patterns that rarely contain enough information to completely determine the atomic arrangement in the fiber repeat unit. This information must be supplemented with chemical and physical information to uniquely characterize the structure. The analysis of the diffraction from the polysaccharide heparin is presented in detail to illustrate how calculations of the nonbonded interatomic potential energy were used as a criterion for developing a model of the structure. The model is sterically reasonable and is consistent with the diffraction pattern.