title: PubChem3D: Diversity of shape.
abstract: BACKGROUND
  The shape diversity of 16.4 million biologically relevant molecules from the PubChem Compound database and their 1.46 billion diverse conformers was explored as a function of molecular volume.
  
  
  RESULTS
  The diversity of shape space was investigated by determining the shape similarity threshold to achieve a maximum on the count of reference shapes per unit of conformer volume. The rate of growth in shape space, as represented by a decreasing shape similarity threshold, was found to be remarkably smooth as a function of volume. There was no apparent correlation between the count of conformers per unit volume and their diversity, meaning that a single reference shape can describe the shape space of many chemical structures. The ability of a volume to describe the shape space of lesser volumes was also examined. It was shown that a given volume was able to describe 40-70% of the shape diversity of lesser volumes, for the majority of the volume range considered in this study.
  
  
  CONCLUSIONS
  The relative growth of shape diversity as a function of volume and shape similarity is surprisingly uniform. Given the distribution of chemicals in PubChem versus what is theoretically synthetically possible, the results from this analysis should be considered a conservative estimate to the true diversity of shape space.
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda MD 20894, USA. bolton@ncbi.nlm.nih.gov.
authors.forename: Evan E
authors.initials: EE
authors.lastname: Bolton
authors.forename: Sunghwan
authors.initials: S
authors.lastname: Kim
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Bryant