IsoStar stores knowledge about intermolecular interactions in the form of scatterplots. Each scatterplot (Fig. 1) shows the distribution of a contact group (for example an O-H donor group) around a specific central group (for example a charged carboxylate group).

IsoStar is a server-client package. The server can be installed locally or alternatively a public server is available at the following URL: http://isostar.ccdc.cam.ac.uk. Details about access are provided in the CSDS release and installation notes.

IsoStar contains knowledge obtained from:

• The Cambridge Structural Database (CSD) (22,161 scatterplots)
• The Protein Data Bank (from protein-ligand complexes at better than 2.5 Angstroms resolution - 7,459 scatterplots)
• Theoretical interaction energies obtained using ab initio intermolecular perturbation theory (IMPT) (1,550 potential energy minima) (Fig. 2).

The information is updated annually from new releases of the CSD and the PDB, with improved coverage of central and contact groups.

The IsoStar system:

• Utilises a standard web browser front end for selection of contact (48 choices) and central (around 300 choices) groups
• Displays scatterplots via an intuitive and easy to use visualiser
• Controls the contact distance limits to be displayed
• Displays overview statistics for the scatterplot, including frequency and cumultative distribution plots (Fig. 3)
• Contours scatterplots with user defined contour levels (Fig. 4)
• Hyperlinks scatterplots to original CSD or PDB entries
• Calculates specific contact geometries
• Includes the ancillary program IsoGen for generating scatterplots to user specifications

IsoStar is distributed as part of the CSD system, for further information contact CCDC.