Section 22.4.5.1. van der Waals radii

The hard-sphere atomic model is central to chemistry and molecular biology and, to an approximation, atomic van der Waals radii can be regarded as transferable from one structure to another. They are heavily used in assessing the general correctness of all crystal-structure models from metals and alloys to proteins. Pauling (1939) was the first to provide a usable tabulation for a wide range of elements, but the values of Bondi (1964) remain the most highly cited compilation in the modern literature. His values, assembled from a variety of sources including crystal-structure information, were selected for the calculation of molecular volumes and, in his original paper, Bondi (1964) issues a caution about their general validity for the calculation of limiting contact distances in crystals. In view of the huge amount of non-bonded contact information available in the CSD, Rowland & Taylor (1996) recently tested Bondi's statement as it might apply to the common nonmetallic elements, i.e. H, C, N, O, F, P, S, Cl, Br and I. They found remarkable agreement (within 0.02 Å) between the crystal-structure data and the Bondi values for S and the halogens, and agreement within 0.05 Å for C, N and O (new values all larger). The only significant discrepancy was for H, where averaged neutron-normalized small-molecule data yield a van der Waals radius of 1.1 Å, 0.1 Å shorter than the Bondi (1964) value. In the specific area of amino-acid structure, Gould et al. (1985) have studied the crystal environments and geometries of leucines, isoleucines, valines and phenylalanines. Their work provides estimates of minimum non-bonded contact distances and indicates the preferred van der Waals interactions of these primary building blocks.