By dividing the total VDW volume of all atoms by the volume of the peptide as determined from the molecular surface one obtains the packing density of the molecule.
Typical Packing Densities
Close Packed Spheres: 0.74
Small Organic Molecule Crystals: 0.70 - 0.78
Proteins: 0.75
It is interesting to note that proteins pack as tightly as small organic molecules, in spite of their much higher number of conformers. It has been suggested that the need to pack tightly might be used to define the correct structure of a folded protein.
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