Volume 2 Chapter 7 Numeric Sub-menu *MATFLAG

Function

*MATFLAG is used to test for entries having a specified connectivity matching status flag.

CSD Contents

In the course of database building the bond length analysis program derives,for each error-free entry , the crystal connectivity record ie. the description of which atom is bonded to which atom.

The matching program then seeks to superimpose the crystal connectivity record on the chemical connectivity record, residue-by-residue.

This process can result in :

perfect matching
partial matching ie. at least one but not all residues matched
no matching

Matching failures arise from a variety of sources :

numeric data errors undetected by the bond length analysis,
disordered structures
polymeric structures
for a few structural types the algorithm fails.

At the time of writing this User Manual, of the error-free entries in the CSD having atomic coordinates

86% are perfectly matched

10% are partially matched

4% are totally mismatched

The connectivity matching status flags are:

connectivity matching not yet attempted 0
connectivity records not matched        1
connectivity records partially matched  2
connectivity records perfectly matched  3
connectivity matching impossible        4

Note that connectivity matching is impossible in the following situations :

chemical connectivity is absent
crystal connectivity is absent
- either because atomic coordinates are absent
- or because the entry is an error set in bond length analysis.

Graphics QUEST3D Procedure

Select *MATFLAG from the NUMERIC sub-menu and respond to the standard numeric prompts.

Basic QUEST Procedure

Ex.

T1  *MATF .EQ. 3

This will register hits for all entries which are perfectly matched.

Remarks

If too few hits are generated as a result of the connectivity matching requirement then you might relax the matching criterion to 'partial' rather than 'perfect' since in a partially matched entry the residue of interest to you may, in fact, be matched.

Related Bit Screens

The corresponding database bit screens are:

connectivity matching not yet attempted 82
connectivity records not matched        83
connectivity records partially matched  84
connectivity records perfectly matched  85
connectivity matching impossible        86

Ex.

SCRE  85

This will register hits for all entries which are perfectly matched.

Related Keywords

*CCOMMENT

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Volume 2 Chapter 7 Numeric Sub-menu *MAXATOMICNO .