Molecular forces in protein structure and crystallography

The paper deals with the nature of the intermolecular forces and the laws governing these, which play an important part in the stability of molecular crystals and in the conformation of biological macromolecules. The method of contact criteria which give the disallowed ranges of conformations is briefly discussed and then the energy criteria are considered. Intermolecular potential functions for non-bonded interactions (both van der Waals and repulsive), electrostatic forces, hydrogen bonds, and hydrophobic interactions are discussed, followed by a treatment of intramolecular distortions of bond lengths, bond angles, and torsional angles. The last of these are important for the study of conformations. The possibility of non-planar distortion of peptide units is specially discussed. Application of these ideas to the calculation of the structures of molecular crystals is indicated