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EDIT-REP

EDIT-REP allows you to alter the position of the brackets and value of the multiplier around a repeat unit in the structure.

Remarks

If your structure contains no repeat units then EDIT-REP is greyed in the EDIT menu so that you cannot select it.

Example

Suppose we have constructed the fragment (i) below

We wish to edit the repeat unit so that the O in the chain is included in the repeat unit.

EDIT-REP allows you to change the multiplier value associated with a repeat unit and then gives you the opportunity to move the corners of the brackets, to change the atoms that lie in the repeat unit.

• Select EDIT-REP

  When you select the command, if you have more than one repeat unit on the screen, you are prompted to select an atom in the required one, in exactly the same way as for DEL-LIG and DEL-REP.

• Please select any atom in the required REPEAT:
  

  Once you have selected one of the atoms in the required repeat unit, red crosses mark all the atoms which currently lie within that repeat unit. However, in the case of (i) we only have one repeat unit on the screen, so the program prompts:

• Please enter new multiplier:
  (Press <RETURN> to retain previous value.)
  

  If you do not wish to change the value of the multiplier:

• Press RETURN

  Green crosses are drawn at the corners of the brackets and the program prompts:

• If you want to move a bracket corner, please select it with the cursor.
  Select "CANCEL" if you don't want to move a corner.

• Select the top right-hand bracket corner

  The green crosses on the other three corners are turned off, and you are prompted:

• Please select a new position for this corner:

• Select position a

  

  The structure is redrawn with the O atom now included in the repeat unit.

  

  The program gives you an opportunity to move the repeat unit brackets again:

• If you want to move a bracket corner, please select it with the cursor.
  Select "CANCEL" if you don't want to move a corner.
  

  As the repeat unit is how we want it:

• Select CANCEL

In the EDIT menu, whenever you shift, scale or rotate part or all of a structure which contains a ligand or repeat unit, the brackets may not fit perfectly around the correct atoms afterwards. So, after every such operation, the program attempts to move the bracket corners to the correct position.

However, occasionally after an editing operation, one of the atoms in the structure which was not in a ligand or repeat comes too close to the ligand or repeat atoms, and so encroaches into the [] or (). The program will sound an alert and enable you to move the offending atom further from the [] or () by following the series of steps outlined for EDIT-LIG or EDIT- REP above.

For example, if the structure in (i) is rotated through 90deg. using the ROTATE command in the EDIT menu, the program will redraw the structure as shown in (ii), trying to incorporate the correct atoms in the repeat unit. In this case the program will sound and alert and produce the message:

• WARNING - Atom number 6 lies incorrectly within a LIGAND or
  REPEAT unit.
  Please use EDIT-LIG or EDIT-REP to fix this.
  

The structure can then be edited using EDIT-REP so that it appears as is shown in (iii).

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Volume 2 Chapter 5 Edit Menu ELEMENT TYPES.