Volume 2 Chapter 3 3D-Constrain Sub-menu ENANTIOMER NOINVERT

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When a torsion angle is being tested for a selected range of values, specified by the SELECT command, if the test fails and if the space group is centrosymmetric then the fragment is inverted and the value tested again to determine whether the fragment is declared a hit.

The corresponding command in the instruction document is: ENANT NORM


Consider the following fragment in which the torsion angle TA1 has been defined as:

TA1 5 4 1 X1

Six entries in the database which contain this fragment are listed below with the values of TA1 and the space groups of the structures:

REFCODE        TA1 (FRAG 1)     TA1 (FRAG 2)         SPACE GROUP
ACMEPT10      -176.205          176.188                 P21/c
ACOHKT         -75.168           21.613                 P-1
AIMCTY        -146.695                                  P212121
ALCHRB10       -20.191                                  P21
ARITOL         150.295                                  P32
BARTUS10       -10.475                                  P21
If TA1 has been selected to lie in the range -30 to -15 degrees then a search with NORMAL active

(ie. command ENANT NORM in the instruction document) will hit ACOHKT and ALCHRB10.

The same search with NOINVERT active would hit only ALCHRB10.

Note that when the fragment is inverted all parameters are recalculated. Torsion angles are the most common enantiomorph-sensitive parameters.

Related Commands


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Volume 2 Chapter 3 3D-Constrain Sub-menu EXHAUSTIVE.