Data Item _chem_comp.formula


Item name
Category name
Attribute name
Required in PDB entries
Used in current PDB entries
Yes, in about 100.0 % of entries
Used in the Chemical Component dictionary

Item Description

The formula for the chemical component. Formulae are written according to the following rules: (1) Only recognized element symbols may be used. (2) Each element symbol is followed by a 'count' number. A count of '1' may be omitted. (3) A space or parenthesis must separate each cluster of (element symbol + count), but in general parentheses are not used. (4) The order of elements depends on whether carbon is present or not. If carbon is present, the order should be: C, then H, then the other elements in alphabetical order of their symbol. If carbon is not present, the elements are listed purely in alphabetic order of their symbol. This is the 'Hill' system used by Chemical Abstracts.

Item Example

 C18 H19 N7 O8 S

Data Type

Data type code
Data type detail
text item types / multi-line text ...
Primitive data type code
Regular expression
[][ \n\t()_,.;:"&<>/\{}'`~!@#$%?+=*A-Za-z0-9|^-]*