Chemical table file

ctab

Filename extension	.mol, .sd, .sdf
Type of format	chemical file format

Chemical table files are files that contain information about chemicals.

File formats

Chemical table files come in various formats. In addition to the formats discussed below, other formats include RGfiles, Rxnfiles, RDfiles, XDfiles and Clipboard.

Molfile

An MDL Molfile is a file format created by MDL (now Symyx who have merged with Accelrys), for holding information about the atoms, bonds, connectivity and coordinates of a molecule. The molfile consists of some header information, the Connection Table (CT) containing atom info, then bond connections and types, followed by sections for more complex information.

The molfile is sufficiently common that most, if not all, cheminformatics software systems/applications are able to read the format, though not always to the same degree. It is also supported by some computational software such as Mathematica.

The current de-facto standard version is molfile V2000; although, more recently, the V3000 format has been circulating widely enough to present a potential compatibility issue for those not yet V3000-capable.

MDL publishes a specification of their Connection-Table formats, which include Molfile and SD formats.^[1]

Following are the contents of a Molfile of benzene created in ChemSketch, as seen in a text editor:

 benzene
 ACD/Labs0812062058
 
  6  6  0  0  0  0  0  0  0  0  1 V2000
    1.9050   -0.7932    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
    1.9050   -2.1232    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
    0.7531   -0.1282    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
    0.7531   -2.7882    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
   -0.3987   -0.7932    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
   -0.3987   -2.1232    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
  2  1  1  0  0  0  0
  3  1  2  0  0  0  0
  4  2  2  0  0  0  0
  5  3  1  0  0  0  0
  6  4  1  0  0  0  0
  6  5  2  0  0  0  0
 M  END
 $$$$

Lines	Section	Description
1-3	Header
1		Molecule name ("benzene")
2		User/Program/Date/etc information
3		Comment (blank)
4-17	Connection table (Ctab)
4		Counts line: 6 atoms, 6 bonds, ..., V2000 standard
5-10		Atom block (1 line for each atom): x, y, z, element, etc
11-16		Bond block (1 line for each bond): 1st atom, 2nd atom, type, etc
17		Propeties block (empty)
18	$$$$	See note

Note: According to the official molfile specification,^[specify] the '$$$$' notation applied only to the SDF file – not to the molfile, so ChemSketch molfiles will not always function properly.

SDF

SDF is one of a family of chemical-data file formats developed by MDL; it is intended especially for structural information. "SDF" stands for structure-data file, and SDF files actually wrap the molfile (MDL_Molfile) format. Multiple compounds are delimited by lines consisting of four dollar signs ($$$$). A feature of the SDF format is its ability to include associated data.

Associated data items are denoted as follows:

>  <Unique_ID>
XCA3464366
 
>  <ClogP>
5.825

>  <Vendor>
Sigma

>  <Molecular Weight>
499.611

Some programs that can import SDF files (e.g. ISIS/Base) require that the first data field after the molecule data (in the example above, Unique_ID) be a unique identifier for each record.

Multiple data items are permitted on multiple lines.^{[clarification needed]} The MDL SDF-format specification requires that a hard-carriage-return character be inserted into any text field whose content exceeds 200 characters. This requirement is frequently violated in practice, as many SMILES and InChI strings exceed that length.

See also

• Chemical file format#Converting Between Formats

References

• Dalby, A.; Nourse, J. G.; Hounshell, W. D.; Gushurst, A. K. I.; Grier, D. L. et al. Description of several chemical structure file formats used by computer programs developed at Molecular Design Limited, Journal of Chemical Information and Computer Sciences, 1992, 32, 244-255.

1. ^ Symyx Solutions, Inc. (June 2010), CT File Formats, Symyx Solutions, Inc., http://accelrys.com/products/informatics/cheminformatics/ctfile-formats/no-fee.php . CTFile format definitions available on request (registration required).

External links

• SDF Toolkit free software to process SD files (SDF).
• NCI/CADD Chemical Identifier Resolver generates SD files (SDF) from chemical names, CAS Registry Numbers, SMILES, InChI, InChIKey, ....